Geotechnical and Foundation Engineering Practice in Industrial Projects 9789819979059, 9789819979066

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Mihir Roy

Geotechnical and Foundation Engineering Practice in Industrial Projects

Geotechnical and Foundation Engineering Practice in Industrial Projects

Mihir Roy

Geotechnical and Foundation Engineering Practice in Industrial Projects

Mihir Roy Kolkata, West Bengal, India

ISBN 978-981-99-7905-9 ISBN 978-981-99-7906-6 (eBook) https://doi.org/10.1007/978-981-99-7906-6 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable.

To geotechnical and foundation engineers practicing in Industrial Projects

Foreword

It is often felt that major technical books in the civil engineering domain do not adequately fulfill the requirement of practicing engineers dealing with real-life problems in design, detailing and construction of civil engineering work. It is equally rare to see experienced professionals venture into writing such books. The present book, authored by Dr. Mihir Roy having more than forty-five years’ experience in various types of industrial projects is an exception in the domain of Geotechnical and Foundation Engineering practice. A direct student of Prof. G. A. Leonard and M. E. Harr at Purdue University (USA) and M. R. Madhav at IIT Kanpur drawing upon his consummate expertise and experience in industries like iron and steel, thermal power, mineral beneficiation and marine projects has put in a stupendous effort in explaining various geotechnical issues. Conversion of fundamental principles of geotechnical engineering into good foundation and construction practice is dealt with step by step by analyzing and interpreting data using mathematical and computational thinking which has finally led to good design and construction solutions. Cross-cutting concepts are achieved by engaging argument from evidence. Competent design and construction of various foundations in large industrial projects play a major role in the successful implementation of projects followed by smooth operation of the plants. Every industrial project has its own technological requirements on foundation for various types of equipment and structures, transmission of vibration, etc. Such projects involve extensive site development including need-based soil improvement, selection of foundation type for heavily loaded structures and equipment, deep excavation for equipment foundation, multi-level utility tunnels, etc. Foundation solutions for marine structures, tailing storage dams, ash pond, controlling groundwater seepage and handling of failure during constructions are also unique in nature. All of these topics have been addressed in this book in significant details to arrive at safe, construction-friendly and cost-effective solutions. The chapters are rarely dealt in academics and would go a long way to enrich reader’s knowledge-base for those engaged in design and construction of such facilities in the industry.

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Foreword

Following my experience of nearly five decades in providing consulting engineering services in the field of large industrial projects in India and abroad, I have a strong conviction that this book, with its comprehensive coverage of comparative studies on alternative solutions, settlement control and groundwater flow will be extremely useful not only for geotechnical engineers but also for all civil engineering professionals in the fields of design and construction. It will also guide the academicians, researchers and graduate students toward acquiring knowledge for meaningful application of principles of geotechnical and foundation engineering into professional practice. The book, I feel would act as a precious guideline and will be an excellent asset to be collected in one’s personal library. Dr. Abhijit Dasgupta Former Joint Managing Director M. N. Dastur & Co (P) Ltd. Consulting Engineers Kolkata, West Bengal, India

Preface

Success in professional practice is characterized by three attributes: knowledge in basic (theoretical) principles, clear vision on the project goals and strong conviction for accountable performance. Availability of books on theories of geotechnical and foundation engineering is plenty, but limited on engineering practice and almost rare on practice in industrial projects. Domain of industrial projects is vast and includes wide range of heavy industries, namely steel, thermal power and many more. In each project, raw materials are transported from different sources for processing and manufacturing finished products for marketing. In-coming bulk raw materials are unloaded and stored in storage yards adopting fully mechanized systems; processing is carried out through a series of sophisticated plants and machinery, finished products are manufactured in specific plants and stored in stockyard for dispatch. All plants and machinery are heavy, sophisticated technological equipment. Guidelines for design of equipment foundations for material handling, processing plants and finishing units supplied by equipment manufacturer are quite stringent and obligatory for guaranteed productivity. Capital expenditure (CAPEX) for industrial projects is high. Therefore, geotechnical and foundation engineers have a tightrope to walk in equipment and cost-intensive industrial projects. Land for industry is either newly acquired area (Green Field) or land developed within existing plant by dismantling old units or developing dumping grounds (Brown Field). But in both cases, lands are to be prepared, developed and improved for design and construction of safe and economic foundation system. For construction of deep foundation deep excavations with sheet pile protection, associated dewatering, etc., are necessary. For thermal power and mineral beneficiation plants, ash/tailing storage ponds are to be built within plant premises. Geotechnical design and construction guidelines for above are the responsibility of geotechnical engineers. Industrial projects are set up either by public sector or private enterprise with huge capital investment for manufacturing finished products and sale for earning decent returns on investments.

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Preface

Therefore, priorities of foundation engineering in industrial projects are: – Safe, economic and construction-friendly design of foundations adopting advanced design tools. – Accident-free and timely completion of construction using modern technology. – Taking care of predictable natural phenomena like storm, flood, earthquake, sealevel rise but at the same time avoiding costly over-design. – Design and construction should ensure handing over finished foundations for erection of structures and equipment as per project implantation schedule. To meet the above challenges of foundations for industries, the book has been compiled with the following objectives. The first objective is to provide geotechnical and foundation engineers with simplified analytical and practical approaches to solutions of foundation engineering problems. Engineers need to deal with increasingly advanced analytical methods on usefulness of concepts into practice. Effort has been made in arranging the text to introduce theoretical concepts with practical application to form firm design basis and construction methods. The second objective is to present the governing formulae in simple form for ready use. Engineers often find mathematical concepts to be particularly rewarding. However in keeping with a utilitarian philosophy, conscientious attempt has been made to reduce solutions to simple forms. It is assumed interested engineers are familiar with and have knowledge in basic soil mechanics and foundation engineering and their limitations to appreciate precision of solution. A volume of this type should present theoretical concepts considerably condensed. In case where alternative solutions may be applicable, procedures for comparison before selection of optimum solution are presented. The volume is not meant for survey of literatures, only basic relevant principles and formulae have been presented. A number of completely worked-out examples on practical application of text materials of varying degrees of difficulty have been included. To help visualize site conditions, a large numbers of photographs from executed project sites have been provided. In writing a volume of this type, there arise the inevitable problem of selection but the book aims mainly on professional practice. In large engineering house, engineering division is generally headed by a manager or team leader. He has a much bigger role in guiding the team in efficient and resultoriented motivation. As such certain qualities are expected of the leader. He/she needs not only be approachable, friendly personality should also be in position to answer technical queries and provide guidance toward finding practical solutions and alternative approaches. These qualities significantly add to acceptance and confidence building within an organization and the clientele. Capability to guide comes primarily on knowledge in the subject, database and examples. Providing guidance can be easy if relevant references, formulae, appropriate methods are readily accessible.

Preface

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Large projects often face several problems during progress. How to mitigate them quickly is equally important. For that, one has to have wide exposure on various phases of projects. But the engineer may not afford time for knowledge up-gradation. In that case, if he has access to handy guidance and at the same time can foresee probable hurdles/risks and strategy to overcome them, he can steer a project team with confidence. The book is very helpful in carrying out pre-bid design engineering for preparation of competitive ‘techno-commercial’ proposal on major industrial projects in limited man-hours. At proposal stage, the management needs a lucid but data-based ‘concept note’ covering key technical and constructional issues relating foundation. At this stage, detailed or specialized analysis is not practicable unless specifically called for. Therefore, preliminary design including alternative solutions and construction methodology needs to be finalized in short time. The book includes chapters on almost all stages of foundation engineering subsequent to site selection, construction of foundations upto handing over. The book covers chapters on-site preparation, ground improvement, pile foundation, seepage and erosion control, marine projects including procedure for selection of ‘finished formation level’ (FFL), simplified liquefaction potential assessment, tailing storage management at mines. Chapters on ‘Failure during Construction’ with forensic studies on failures and unexpected ‘Site Hazards’ along with indigenous remedies adopted at site, should be of interest. A few newly developed analytical tools and techniques for early assessment of pile capacity, mix-design for soils, liquefaction which in author’s opinion have merit are also presented in Appendix. A number of desktop programs have been developed, tested and verified at project sites (programs not included in this edition). The concluding chapter is a candid look on professional practice in geotechnical and foundation engineering as seen by the author in over 45 years of professional practice in different categories of companies from pure consulting engineering to construction to EPC and independent consultant on major projects. The author is fortunate to have active participation in several major projects on steel, thermal power, mines and marine facilities upto successful completion. Always endeavor was to explore possibilities of alternative approaches to select better method commensurate with technical guidelines and site conditions. In doing so, non-availability of guidance on search for alternative solutions on variety of foundation engineering topics was felt strongly. In order to overcome the initial hurdles and to encourage calculation based on theory, the topics have been planned and organized for clear understanding and application. Confidence and comfort come when a project is clearly understood and concept plan is defined. Then the engineer has the freedom to act according to his/her decision-making ability. As mentioned in the beginning, the book attempts to address three attributes of success in professional practice.

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Preface

The author wishes to express hearty gratitude to large number of colleagues, friends and senior management of national, international consulting and construction houses. The author is particularly indebted to the senior executives of corporate and public sector enterprises for their interest and encouragement on new developments, including financial supports for carrying out laboratory, field and proof tests. The author wishes to dedicate the book to the loving memories of his beloved wife who left for heaven in 2020. Thereafter, I spent the time to compile the volume hoping it would be of great help to practicing geotechnical and foundation engineers interested in Industrial Projects. Kolkata, India

Mihir Roy

Contents

1

Introduction to Chapters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . This Chapter: Introduction to Chapters . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 2: Engineering Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 3: Geotechnical Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 4: Site Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 5: Ground Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 6: Foundation on Soft and Filled-Up Soil . . . . . . . . . . . . . . . . . . . Chapter 7: Pile Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 8: Seepage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 9: Erosion Control and Retaining Wall . . . . . . . . . . . . . . . . . . . . . Chapter 10: Marine Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 11: Simplified Liquefaction Potential Assessment . . . . . . . . . . . Chapter 12: Tailing Storage Management at Mines . . . . . . . . . . . . . . . . . . Chapter 13: Failure During Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 14: Site Hazard and Remedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 15: Geotechnical and Foundation Engineering Practice . . . . . . . Appendix 1: Units and Conversion Tables . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix 2: Standard and Correlations . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix 3: Desktop Excel Programs for Preliminary Design . . . . . . . .

1 3 4 4 4 5 6 6 7 8 8 9 10 10 11 11 11 12 12

2

Engineering Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Importance of Regional Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regional Geology of Bengal Delta Basin . . . . . . . . . . . . . . . . . . . . . . . . . . Observations Made from Geological Study . . . . . . . . . . . . . . . . . . . . . . Regional Geology of Asansol Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observations from Geological Study . . . . . . . . . . . . . . . . . . . . . . . . . . . Brief Definition of Primary Rock Parameters . . . . . . . . . . . . . . . . . . . . . . . Core Recovery (CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rock Quality Designation (RQD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 13 14 15 16 16 17 18 18 18

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3

4

Contents

Rock Mass Quality (RMQ) and Rock Mass Factor (j) . . . . . . . . . . . . . Rock Mass Rating (RMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geotechnical Investigation in Rock Strata . . . . . . . . . . . . . . . . . . . . . . . . . . Laboratory Tests on Rock for Classification and Engineering Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grades of Weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Average Range of Engineering Properties for Various Rock Types . . . . . Presumptive Bearing Capacity of Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for Design of Piles Terminating (Socketed) in Rock Strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 19 21

Geotechnical Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimization of Investigation at Large Green/Brown-Field Project Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boring in Shallow Water Body, Pond and Marshy Field . . . . . . . . . . . . . . Investigation in Shallow Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil Investigation Near River Bank and Bed Using Twin-Boat Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil Investigation in River Bed Using Twin-Boat Assembly . . . . . . . . Investigation at Sea from Jack-Up Barge . . . . . . . . . . . . . . . . . . . . . . . . . . . Truck/Tractor-Mounted Rotary Boring/Drilling Equipment . . . . . . . . . . . Geophysical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seismic Refraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seismic Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrical Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advanced Methods for Soil Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . Electric Cone Penetration Test (ECPT) . . . . . . . . . . . . . . . . . . . . . . . . . Seismo-Cone, Piezo-Cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hard/Old Filled-Up Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geotechnical Investigation in Slag Dump . . . . . . . . . . . . . . . . . . . . . . . . . . DCP–CBR Test for Road Sub-base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment and Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Format for Recording Field Data (Typ.) . . . . . . . . . . . . . . . . . . . . . . . . . Formula for Evaluation of DCP-CBR Value . . . . . . . . . . . . . . . . . . . . .

25 25

Site Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Site Development by Filling and Compaction . . . . . . . . . . . . . . . . . . . . . . Filling in Pond and Water Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing Bed Mud by ‘Mud Wave’ Technique . . . . . . . . . . . . . . . . . . Removing Water from Marshy Land . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Fill Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

41 41 42 43 44 45 46

21 22 22 23 23 23

26 28 28 29 29 30 31 31 32 32 32 33 33 34 34 35 36 37 38 38

Contents

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Mechanical Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vibratory (Dynamic) Roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheep’s Foot Roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamic Compaction/Consolidation (DC) . . . . . . . . . . . . . . . . . . . . . . Vibratory (Vibro) Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rapid Impact Compactor (RIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Land Development by Dredging and Reclamation . . . . . . . . . . . . . . . . . . . Strategy for Land Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Finished Grade/Formation Level (FGL/FFL) . . . . . . . . . . . . . . . . . . . . Criteria for Fill Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methodology for Dredging and Reclamation . . . . . . . . . . . . . . . . . . . . . . . Major Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methodology for Dredging and Reclamation . . . . . . . . . . . . . . . . . . . . . Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Filling with ‘Design-Mixed’ Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basis for Mix Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steps for Mix Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction with Design-Mixed Earth . . . . . . . . . . . . . . . . . . . . . . . . . Benefits of Design-Mixed Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

48 48 49 49 50 50 51 51 52 53 53 54 55 55 57 57 58 58 62

Ground Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground Improvements Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stone Column in Cohesive Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deep Soil Mixing (DSM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction to Deep Soil Mixing (DSM) . . . . . . . . . . . . . . . . . . . . . . . Governing Formulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation of L-C Column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steps for Mixing L-C and Installation of Column . . . . . . . . . . . . . . . . . Worked-Out Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technological Requirements for Battery Raft . . . . . . . . . . . . . . . . . . . . Technological Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preconsolidation with Prefabricated Vertical Drain (PVD) . . . . . . . . . . . . Basic Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Governing Formulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Geotechnical Design Parameters . . . . . . . . . . . . . . . . . . . . Worked-Out Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Design with PVD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stage-I Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stage-II Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact of Vertical Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

63 63 64 65 67 67 69 71 71 72 73 76 78 78 78 80 83 84 84 85 85 86 86 87

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Comparison of Results of Ground Improvement . . . . . . . . . . . . . . . . . . . . Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Arrangement Drawing for PVD . . . . . . . . . . . . . . . . . . . . . . . . . . . Deep Vibro-compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

88 88 89 89

6

Foundation on Soft and Filled-Up Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Construction of Foundation in Soft Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Excavation in Soft Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Mud Mat on Soft Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Foundation on Heterogeneous Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Hardstand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Hardstand for Heavy Crane Foundation . . . . . . . . . . . . . . . . . . . . . . . . . 97 Hardstand for Heavy Storage Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Sub-soil Data and Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . 98 Compaction Grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

7

Pile Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimation of Load Carrying Capacity of Pile . . . . . . . . . . . . . . . . . . . . . . Geotechnical Design of Pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deflection and Moments in Long Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural Design of Pile Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement Detailing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pile with Permanent Steel Liner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pile with Permanent Steel Liner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Permanent Steel Casing on Skin Friction . . . . . . . . . . . . . . . . Skin Friction for Pile with Permanent Steel Liner (Casing) . . . . . . . . Precast Segmental-Driven Pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steps for Precast Piling Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Capacity of Driven Pile Based on Energy Correlation . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Capacity of Driven Pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamic Pile Driving Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Correlations Based on Energy Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . Quasi-dynamic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Test Pile Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

105 105 107 108 112 114 119 119 120 121 121 122 126 127 128 128 131 131 132 135 136 140

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Seepage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seepage Through Homogeneous Earth Dam on Impervious Base . . . . . . Seepage Analysis Through Homogeneous Dams . . . . . . . . . . . . . . . . . Impervious Liner at Reservoir Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In-Situ Improvement of ‘Dead and Abandoned’ Flyash/Tailing Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Well Point Dewatering System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scheme for Well Point Dewatering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Number of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-Check (Approximate Method) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation and Operation of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Importance of Well Point Dewatering System . . . . . . . . . . . . . . . . . . . . . . Hazards Due to Failure of Groundwater Control . . . . . . . . . . . . . . . . . . . .

141 141 143 144 158

Erosion Control and Retaining Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Important Points for Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slope Protection with Gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gabions for Erosion Control and Slope Protection . . . . . . . . . . . . . . . . Gabion Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slope Protection with Gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gabion Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vertical Gabion Retaining Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multi-stage Gabion Retaining Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Block Gravity Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheet Pile Protection for Deep Excavation . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Braced Sheet Pile Protection for Deep Excavation in Soft Soil . . . . . . Estimation of Lateral Pressure on Sheet Pile . . . . . . . . . . . . . . . . . . . . . Estimation Strut Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimization on Number of Struts and Design Loads . . . . . . . . . . . . . Salient Features of 4th Trial (Fig. 9.12) . . . . . . . . . . . . . . . . . . . . . . . . . Importance of Full-Cycle Design (from Start of Excavation to Backfilling) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

177 177 178 179 179 180 180 181 181 182 183 185 186 187 188 189 191 191

10 Marine Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strategy for Land Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Finished Ground Level (FGL) . . . . . . . . . . . . . . . . . . . . . . Tidal Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rainfall Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Steps For Marine Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Berthing and Mooring Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Computation of Berthing Force and Fender Spacing for Ship . . . . . . .

195 195 196 196 196 197 197 198 199 200

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160 161 164 170 170 171 173 173

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Contents

Design And Construction Of Marine Piles . . . . . . . . . . . . . . . . . . . . . . . . . Piling for River Terminal (Jetty) on River Ganga . . . . . . . . . . . . . . . . . Construction of Marine Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction of Pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On-Shore Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Offshore Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quay Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction to Quay Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dredging For Shipping Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

203 203 204 205 206 206 208 208 210

11 Simplified Liquefaction Potential Assessment . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simplified Liquefaction Potential Assessment (LPA) . . . . . . . . . . . . . . . . Geotechnical Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods for Simplified Liquefaction Potential Assessment (LPA) . . . . .

215 215 217 217 217

12 Tailing Storage Management at Mines . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction to Mineral Beneficiation at Mines . . . . . . . . . . . . . . . . . . . . . Tailing Storage Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raising Height of Existing Tailing Dam . . . . . . . . . . . . . . . . . . . . . . . . . Design Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimation of Free Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety Against Slip on Inclined Base . . . . . . . . . . . . . . . . . . . . . . . . . . . New Technology on Filtration of Tailing for Storage Management . . . . . Software Generated Views of Multi-layered Storage Stacks Up to Full Height Showing Different Layers . . . . . . . . . . . . . . . . . . . . . . . . Key Points on Filtration Technology and Stacking Dry Tailing . . . . . . . .

247 247 250 250 251 255 256 258 259

13 Failure During Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 1: ‘Sliding’ of RCC Base Raft on Sloping Base (1981) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 2: Restoration of Pile Foundation (1983) . . . . . . . . . . . . Case History 3: Settlement of Building Due to ‘Buried Water Channel’ (1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 4: Differential Settlement Due to ‘Swelling Soil’ (1985) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 5: Influence of Underground Connectivity of River—Experience During Construction of Calcutta N–S Metro Rail (1980’s to 1990’s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 6: Liquefaction Due to ‘Blow-Out’ of Natural Gas Well (1997) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 7: Settlement of Ground Storage Tanks (2003) . . . . . . . Case History 8: Failure of Sheet Piles During Deep Excavation (2006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

265 265

262 263

265 266 269 269

270 271 273 274

Contents

Case History 9: Failure at Deep Excavation Due to Poor Maintenance of Well Points (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 10: Failure of ‘Contiguous Pile’ Retaining Wall (2014) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case History 11: Failure of Flyover Over Canal (2013) . . . . . . . . . . . . Case History 12: Ground Subsidence During Tunnel Boring with TBM (2019) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Map of 1660s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The ‘Ghost’ of Creek in Bowbazar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common Cause of Failure During Construction . . . . . . . . . . . . . . . . . . . .

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275 277 279 280 281 281 285

14 Site Hazards and Remedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dangers from Wild Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil Investigation Work at Iron Ore Mine in Orissa (1982) . . . . . . . . . Damages by Tornado at Construction Site (1983) . . . . . . . . . . . . . . . . . Failure of Driven Piling Rigs at Construction Sites (2006 and 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unfortunate Incident at Bored Piling Site (2010) . . . . . . . . . . . . . . . . . Safety Belts Caused Fatal Accident (1985) . . . . . . . . . . . . . . . . . . . . . .

287 287 287 287 290

15 Practice in Geotechnical and Foundation Engineering . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Professional Practice in Geotechnical and Foundation Engineering . . . . Education . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On-Job Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Personal Initiative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Job Prospect and Career Opportunity . . . . . . . . . . . . . . . . . . . . . . . . . . . Knowledge in Associated Branches of Engineering . . . . . . . . . . . . . . . Internal Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems Faced by Small and Medium Investigating Agencies . . . . . . . . ‘E-Classes’ Leading to ‘Learning Gap’ in Higher Education . . . . . . . . . . Guidance for Improving Engineering Skills . . . . . . . . . . . . . . . . . . . . . .

295 295 295 296 296 296 297 297 297 297 297 298 300 301

290 291 293

Appendix A: Units and Conversion Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Appendix B: Standard Correlations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Appendix C: Desktop Design Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 CV of Author and List of Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

About the Author

Dr. Mihir Roy, B.E. Civil (B.E. College, Now IIEST Shibpur), M.Tech. (IIT– Kanpur), Ph.D. (Purdue University, USA), worked as geotechnical and industrial foundation engineer for steel plants, thermal power plants, ash and tailing storage ponds, material handling systems, marine projects—port/jetty and storage terminal, liquefaction assessment, forensic engineering and urban infrastructure projects for over 45 years. He was employed at McClelland Engineers Inc. Houston, Texas (USA); Gammon India Ltd; M. N. Dastur & Co. Ltd.; FUGRO-KND Geotech Ltd [(JV with FUGRO, NV of The Netherlands] ; Shapoorji-Pallonji—EPC Division; Tata Consulting Engineers (TCE); Consulting Engineering Services (I) Pvt. Ltd. (CES)/JACOBS. He has also worked as consultant to many design and construction companies of industrial projects.

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Chapter 1

Introduction to Chapters

Selection of a site and getting formal possession of land for setting up an industry is a long process. Thereafter, a series of preconstruction activities have to be completed at site before starting civil works. Construction activities continue up to completion of foundations and handing over for erection of steel or civil structures and equipments. Involvement of foundation engineer is essential in every step like that of a ‘matchmaker’. Their role is to ensure compatibility between foundations for technological structures, sophisticated processing equipment and competent, stable founding media. If the foundations meet technological requirements of equipment suppliers, the plant can operate smoothly. But in case of ‘mismatch’ rated productivity may suffer. Role of geotechnical and foundation engineering in planning, design and safe construction of competent foundations for industrial projects is highlighted in the following paragraphs. In the beginning, it is necessary to conduct geological studies of the region and project site to understand formation mechanism, ground characteristics and risks if any on stability of foundations after setting up the industry and during operation. This is to be followed by detailed geotechnical investigation to explore stratification and soil/rock parameters for use in design and construction of foundation. The site whether a green or brown-field exists in ‘as is’ condition. The site needs to be made ready (prepared) by cutting high grounds, filling (engineered fill) of low areas with excavated or borrowed earth or dredged sand from river/sea bed and deposition. The site has to be leveled as per plant general layout and compacted mechanically. Effects of mechanical compaction carried out at ground surface are confined mainly in upper layers. Weak or soft layers down below may need to be improved adopting ground improvement techniques.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_1

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1 Introduction to Chapters

Design of foundations is then carried out based on geotechnical data fulfilling technological requirements specified by equipment suppliers. Both open/shallow and deep/pile foundations are adopted. In general, time spend in construction of foundations varies from 20 to 30% of total time taken for civil construction. This can be shortened by careful planning, design and execution methodology. In heavy industries, equipments are heavy requiring pile foundation. Selections of pile suitable for a site require detailed study on various aspects and types of piles. There are wide range of pile types depending on methods of design and construction. Movement of groundwater is a basic part of soil mechanics. Its influence can be found in almost every part of geotechnical engineering. Seepage analysis through water-retaining earth structures is necessary for stability analysis. Deep excavation by open-cut method covers wide area, and volume of excavation is high which can be greatly minimized by protecting sides of excavation with braced or anchored sheet pile walls. For deep excavation in high ground water level areas, construction areas must be dewatered up to required depth and maintained throughout construction period. River banks and seashore are prone to erosion and failures which should be protected with erosion control measures and/or retaining wall. For import/export of raw materials/finished products, transportation by sea/river is the most convenient mode of transportation followed globally. For loading–unloading of bulk goods from ship/barge, water-front structures jetty, berth, etc. are constructed on river bank or seashore. Criteria for design and construction of water-front structure are considerably different from those of structures on land. Impact of mooring and berthing of ships and tidal variation in marine structures need to consider additional loads based on ship data and marine environment. Incidents of earthquake can happen almost anywhere and anytime. Therefore, for safety of costly plants and machinery, risk factors from possible earthquake hazards need to be assessed. Earthquake can cause ground liquefaction, and remedial measures must be taken in design and construction. Earthquake assessment is considered specialized field and generally carried out by experts. But preliminary assessment of liquefaction potential can be carried out easily based on results of soil investigation and earthquake zone factors following simplified analytical approach. The results are helpful in design of earthquake-safe foundation system. In thermal power and mineral beneficiation plants, storage of ash and slime is integral part of plant operation. Ash and slime ponds are built by enclosing low area with earthen dams. When a pond reaches full storage capacity, additional capacity can be created by raising height of existing dam. Selection of method for raising height of existing dam and storage management of ash/tailing pond adopting modern technology are challenging tasks. Methods of height rising and aspects of storage management following filtration technology have been included. Even after careful design and construction, failures may occur during construction even due to simple reasons. Studies on failures (forensic engineering) are important and challenging. More often, failures are caused by not following design considerations and construction guidelines. Sometime, short-cut approach or over-confidence

This Chapter: Introduction to Chapters

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can lead to failure. Good engineering practice requires safety guidelines given in design/construction documents are to be followed at site. For example, performance of well points in deep dewatering system should be monitored periodically. Studies on case histories on failures help enrich knowledge to foresee possible risks. Survey and geotechnical investigation teams are the first entrains to remote project sites. They often face unknown and unthinkable hazardous situations from wild animals. Being far away and all by themselves, they feel helpless. Team members sometime devise interesting and innovative solutions to overcome risks. Few such interesting instances can throw light on avoiding/solving similar site dangers. Theme of the book is professional practice in industrial projects. Therefore, purposes of the book remain unfulfilled without introspection on different aspects of professional practice in the field. Scope and limitations, difficulties faced and suggestions to improve professional practice have been discussed rather candidly in the last chapter. The reader is at liberty to agree or disagree with some but may not be all of them. The chapters have been compiled and organized in sequence of activities starting from site preparation/development, design, construction of foundations and testing up to handing over. The effort of the author was to motivate the geotechnical and foundation engineers into successful practice particularly in industrial projects.

This Chapter: Introduction to Chapters The book on practice in geotechnical and foundation engineering has been compiled in fifteen (15) chapters. The chapters include wide range of engineering fields: geology, geotechnical investigation, site preparation, ground improvement, open and pile foundation, seepage and erosion control, retaining wall, deep dewatering, marine structures, liquefaction assessment, tailing and ash storage pond management. It has been assumed; readers are familiar with and have knowledge in basic soil mechanics, seepage and foundation engineering. The main objectives of the compilation are summarized below: (a) Provide practicing engineers with simplified analytical and practical approaches to foundation solutions (b) Make available governing formulae in compact tabulated format for everyday use (c) Normal range of values of geotechnical parameters for ready reference (d) Introduce theoretical concepts with practical application (e) Motivate engineers on self-assessment rather than depending fully on software solutions (f) Preparation of design and working drawing with detailing for use in construction (g) Fully (step-by-step) worked-out examples on application of text materials in design and construction

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1 Introduction to Chapters

(h) To expose reader with activities at project sites, large number of photographs of site works are included (i) The book is not meant for survey of literature; only basic relevant principles have been covered (j) Engineer can write concept note, project report and be able to take informed decision on foundation aspects. Instances of failure during construction or after commissioning have been brought out in Chap. 13. Failures occurred due to lack of knowledge or experience that could and should have been avoided during engineering and construction stages.

Chapter 2: Engineering Geology The chapter includes brief definitions of primary rock types, classification, tests on rock, range of values for common engineering parameters, significance of regional geology in planning site investigation and testing for geotechnical design and construction of foundation. Aim is to impress upon engineers on importance of geology and familiarity with preliminary geologic terms in connection with engineering geology.

Chapter 3: Geotechnical Investigation The chapter covers methods for improving speed of site exploration and quality of data combining conventional and geophysical methods adopting modern hightech equipment and tools, electronic data collection and transmission. Advantage of simultaneous back-end data analysis by experienced technician at field or home office can greatly speed up work with less manpower and inventory of machines. Investigation in water bodies like pond, canal, river and sea coast can be carried by assembling country boats. Also, method of exploration at sea using jack-up barge has been highlighted. Geotechnical investigation in deep hard old debris-filled areas of steel plant slag dumps poses great hurdle for advancing boring/drilling tools. Approach for puncturing hard slag or debris dump is included. A few simple methods for investigation in difficult situations have been included.

Chapter 4: Site Preparation Industrial projects require ‘good’ land which in general is not available. A site available in ‘as is’ condition needs to be ‘prepared’ by cutting/filling and developing as required. Selection of method of filling, source of borrowed material, deposition,

Chapter 5: Ground Improvement

5

compaction and leveling are based on several technological and economic factors. Simplified and practical approaches for filling pond and water bodies after removing bed mud by forming ‘mud wave’; extracting water in marshy land by series of dug wells/trenches can be useful. Fresh fill should be compacted by static or dynamic, vibratory/sheep’s foot roller, rapid impact and dynamic compaction methods. The methods have been discussed. Development of low land on river/sea banks for construction of port facilities requires large volume of fill material. Dredging sand from river/sea bed and reclamation is the only way to collect huge quantity of fill material. In old power plant plants and mines, large areas occupied by dead and closed ash/tailing ponds, and dumps of mine overburden are ‘waste’ materials. These waste materials can be used for construction of earth structures by ‘design mix’ of ‘good soil’ and ‘waste’ materials to improve engineering properties of the mix. Brief introduction to ‘capital dredging/reclamation’ and detailed discussion on ‘design mix’ of soils have been covered along with worked-out examples. These can be useful in preparation of Project Report chapters.

Chapter 5: Ground Improvement Methods for site preparation (Chap. 4) are ‘surface’ treatment by imparting kinetic energy to reduce voids along with partial expulsion of pore water. As impacts are applies on or near surface, depth of improvement is somewhat limited in upper levels depending upon input energy. Improvement of soft soil at greater depths is necessary for economic design and construction of open foundation avoiding costly, time-consuming piles. The chapter has been planned to cover common and modern methods of ‘in-ground’ improvement. The methods are based on principles of both ‘compaction’ and ‘consolidation’ and combination of both. Ground improvements by sand pile, sand drain, stone column and lime/cement injection are used successfully. Method of ‘deep soil mixing’ (DSM) is promising on several counts. Design steps for stone column and deep soil mixing have been covered in detail. A few case studies from project sites and comparisons of the methods have been included. Preconsolidation by preloading aided by prefabricated vertical pervious drains (PVD) is very effective and efficient technique for improvement of soft ground. Stepby-step approach for design of PVD has been presented with worked-out example. Geotechnical engineer can carry out preliminary designs considering stone column, PVD or DSM for selecting the optimum option for ground improvement work. Vibro compaction is efficient and faster technique for in-ground improvement of soft soils up to great depths. The technology is based on transmission of downhole 3D vibration through a specially designed probe to impart circular oscillatory vibration. The equipment is specially designed with stone feeder pipe through which stone is discharged to fill cavity created by vibration. The vibro technique works in dual mode: (a) compaction of granular soil particles into denser configuration

6

1 Introduction to Chapters

and (b) vibro-replacement technique builds series of load-bearing columns which act as ‘reinforcement’ in soil. Combination of these effects results in considerable improvement up to great depth. Above-mentioned topics have been covered in great detail.

Chapter 6: Foundation on Soft and Filled-Up Soil Extensive coverage on design and construction of all types of shallow foundations is available, and there is no need for repeating them. Instead, purpose of this chapter is to highlight practical approaches for construction of open foundation at difficult sites. Laying mud mat for large raft on soft spongy ground below GWL is very difficult. Simple method of laying mud mat in segments or precast PCC slabs which have been used successfully is presented. Other methods like compaction grouting, construction of ‘hardstand’ for heavy-duty storage floor and compacted granular base are not commonly available. These have been covered in some details. Construction of open foundation in heterogeneous filled-up sites, dump yards is challenging for foundation engineers. Methods and steps for construction of open foundation on such fills have been dealt with.

Chapter 7: Pile Foundation In general for large industrial projects, time taken for civil construction is about 30% of total construction time. Out of that about 12–15% time is needed for piling works. Therefore, saving time on piling work can result in overall time-saving up to 5% in civil works. Piling having a large number of options and methods is considered specialized field in geotechnical and construction engineering. Piles are (RCC, precast/prestressed concrete (PSC), steel joist, pipe/tube) inserted in ground to transmit (a) vertical compressive and tensile, (b) horizontal loads and (c) moments from structures either individually or in group to competent strata below ground. Piling requires knowledge in different engineering disciplines, namely geotechnical, civil design, soil-structure interaction, construction technology, execution methods, monitoring, load testing and safety during installation. Aim of this chapter is not to repeat what is available in books, codes and literatures but is an attempt to compile different aspects of piling relating to design and construction. This chapter highlights a few easy but practical solutions to pile installation which in general is not easily locatable. Standard methods of pile design have been represented in systematic manner for easy reference. Steps and procedures outlined here have been used successfully at various project sites.

Chapter 8: Seepage Control

7

Keeping above objectives in view, the chapter has been planned to include the following topics: • Pile design and construction. • Design of RCC piles: (a) Geotechnical design as per IS published by Bureau of Indian Standards, (b) structural design, (c) reinforcement design, (d) design drawing of pile. Design aspects of piles with permanent steel liner especially in marine environment may pose uncertainty in selection of skin friction component of pile capacity. Excerpts from published standards, codes and charts have been summarized for easy reference and used with judgment. Precast segmental-driven piles are advantageous over bored cast-in-situ piles on several counts. Steps for design, joint/splice details, manufacturing in casting yard, storage, handling and driving of precast segmental piles have been covered in great detail. Early assessment of safe capacity of driven piles based on preliminary soil investigation data, bore log, results of Standard Penetration Test (SPT) or Static Cone Penetration Test (CPT) following principle of energy correlation has been presented in detail along with results of field verification.

Chapter 8: Seepage Control Movement of groundwater is a basic part of soil mechanics. Its influence can be found in almost every part of geotechnical engineering. One common reason for slope failure of reservoir, ash/tailing (slime) ponds is seepage through downstream (D/S) face or toe region loosening compactness of soil and eventually leading to cracks, local slip, cavity, piping/‘sand boiling’ and in worst case collapse at weakest section. Seepage flow through earth dam can be analyzed easily following classical approach like Dupuit’s principles, and flow limes including phreatic surface (top-most flow path) can be determined following Kozney’s basic parabola. The phreatic surface depends primarily on geometry of dam and water levels at up and downstream (U/S and D/S) sides and interestingly not on coefficient of permeability (k) of earth in dam. For overall safety, it is necessary to confine seepage surface well within dam body with provision of berms on both sides, designing rock toe and providing horizontal or inclined sand chimney filter. Seepage analyses through earth dams with rock toe, horizontal and inclined chimney filters have been demonstrated in detail in this chapter. Construction of deep foundation requires deep excavation. At sites of soft soil with high groundwater table (GWT), deep excavation is risky unless seepage of groundwater is controlled and maintained throughout construction period. For deep excavation (10–15 m or more) and construction continuing for months, ‘multi-stage well point dewatering’ system is very effective. Designs of well point dewatering system are based on classical approach of ‘gravity flow to partially penetrating

8

1 Introduction to Chapters

wells’ and design of drainage wells is based on principles of flow midway between and parallel to ‘two line sources’. Spacing of wells is evaluated following principle of flow to ‘infinite line of partially penetrating wells from an infinite line source of seepage’. Design of well point system, location and spacing of wells; levels, diameter and depth of strainer pipes; lowered phreatic line should be based on results of geotechnical and field pumping tests. Fully worked-out example of ‘two-stage well point dewatering system’ including preparation of design drawing has been presented.

Chapter 9: Erosion Control and Retaining Wall Hill slopes, river bank and seashore often fail due to multiple reasons. Predominant causes of slope failure are erosion due to rain, high/low tide and seasonal floods. Earthquake also induces slope failure. Technology for slope protection has advanced greatly with new technology, products and application. Generally, failure of slope can be controlled by (a) preventing erosion of soil and (b) ensuring stability of slope by constructing flexible retaining wall made with natural materials. Methods for slope protection using Gabions are simple, cost effective and stable solution. Methods for manufacture and placement of gabions have been covered in this chapter. For deep excavation, sides of excavation need to be protected by enclosing the area with temporary steel sheet pile wall. Design of sheet pile retaining wall can be carried out following basic principles of earth pressure in soil mechanics. A geotechnical engineer can carry out design by ‘hand calculation’. Main advantages of hand calculation are it gives ‘feel’ for the numbers during design steps, and calculations are transparent for rechecking. Keeping the above objectives in view, step-by-step analysis of multi-level braced retaining wall executed successfully in a power plant site has been presented in detail. Moreover, importance of ‘full-cycle’ analysis starting from start of excavation to completion of construction and removal of topmost strut has been demonstrated.

Chapter 10: Marine Projects Traditionally, intercontinental movement of cargo is carried out through sea and river routes. For loading–unloading of goods, water-front facilities are built on river bank and seashore. Geotechnical and foundation engineer plays significant role in design and construction of safe foundation system for supporting sea-front structures and on-shore facilities.

Chapter 11: Simplified Liquefaction Potential Assessment

9

Focus of this chapter is on introduction to foundations for near-shore marine structures. Contents are aimed to highlight main aspects in planning and design of foundation for water-front structures which are not commonly found at one place. For instance, selection of ‘safe’ finished formation level (FFL/FGL) of a site considering marine factors, basis for selection of design loads on structures from ship movement, civil design criteria of port and jetty, construction of pile in shallow water and similar topics have been included. This chapter includes design basis for marine piles which are somewhat different from design of piles on land. Design loads from ship movement, e.g. berthing and mooring loads on jetty, design of fenders are discussed. The chapter also covers other aspects of marine projects, namely design basis of piles for berths, construction of marine piles from (a) temporary platform and (b) jack-up barge, introduction to Quay Wall and slope stability of shipping channel.

Chapter 11: Simplified Liquefaction Potential Assessment Earthquake is a natural phenomenon causing extensive damage and destruction in many parts of the globe. Its place, time and intensity of occurrence are not predictable with precision. Design of foundation and superstructure takes guard against anticipated intensity of earthquake considering certain factors as per provisions of codes. Liquefaction potential assessment (LPA) should be carried out for sites located in seismic zones. But detailed LPA is a vast subject and mostly carried out by specialists. Analysis of preliminary LPA can be carried out easily provided the governing equations and steps of calculations are available. The analysis needs data mainly on (a) seismicity for the zone and (b) results of soil tests from field and laboratory. Analysis can be carried out following several methods. Steps for simplified LPA following methods developed by (a) IIT-Kanpur and Gujrat State Disaster Management Authority and (b) Seed and Idriss or both (including influence of fines content) in soil have been covered as mentioned below. • Seven steps for Simplified LPA following two methods (1) Indian Institute of Technology, Kanpur (IITK) and National Center for Earthquake Engineering Research (NCEER), USA and (2) Seed and Idriss presented in simplified tabular format. • Evaluation of liquefaction potential index (LPI) which quantifies severity of liquefaction and predicts liquefaction damage/failure potential for a site has also been included. Spread-sheet programs with graphical display of results have been developed. Engineers can easily assess LPA for a site based on results of preliminary geotechnical investigation with the help of the programs. Examples on application of LPA on effects of partial liquefaction on single pile analyzed using above methods and program have been presented in Appendix 3 for demonstration.

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1 Introduction to Chapters

Chapter 12: Tailing Storage Management at Mines Normally, civil and geotechnical engineers may not be familiar with vast activities at ore and coal mines. Raw ore is crushed and screened. High-grade fractions are shipped to plant and poorer/finer fractions are beneficiated in clarifiers to extract better-grade ores and left-over (tailing/slime) is disposed in tailing/slime ponds built with earthen dam/dike/embankment. After years of use, ponds reach full storage capacity. Commonly dam height is raised to create additional storage capacity. When further rising is not feasible technically or economically, the pond is abandoned for good. However, vast areas covered by ‘dead ponds’ are wasted. But closed ponds can be improved adopting new technology and used for expansion project. Alternately, fresh slime can be dehydrating in filtration plant to extract water and convert fines to behave like ‘soil’ which can be handled and deposited over ‘dead pond’. In this process, storage of dehydrated tailing is possible without raising dam height. Geotechnical engineer plays major role in raising height of dam and storage of treated slime on dead pond. There are several approaches for raising height of existing dam for example: (a) upstream, (b) downstream, (c) central raising methods and (d) with retaining walls. Logical selection of height of freeboard depending on design wave height due to wind and also stability of ‘new’ dike built on existing slope should be checked. Methods for assessment of freeboard and stability of ‘slope on slope’ have been presented.

Chapter 13: Failure During Construction Even after careful planning and design, failure can and do occur during construction due to several reasons. Causes of failure can be known only after post-failure study is conducted by experienced engineers. It may so appear that actual situation had not been envisaged at planning or execution stage, side-lining design guidelines, negligence or even over-confidence. In some instance, it may remain as unpleasant surprise but failures do not occur without reasons known or unknown. Case histories of failure during construction at industrial and urban infrastructure project sites with varying degree of severity have been presented along with probable causes. Twelve (12) selected case histories from 1981 to 2019 at industrial and urban development project sites which were caused mostly due to inexperience or negligence are presented. Lessons learned from the events should be of interest and might be helpful in avoiding failure in future projects.

Appendix 1: Units and Conversion Tables

11

Chapter 14: Site Hazard and Remedy In most green or some brown-field industrial projects, survey and soil investigation teams are the first entrants to site. They often have to face variety of unknown and unexpected problems which need to be overcome/solved by themselves before starting field work. Even during progress of construction, situation sometime can change drastically leading to accident. Under the circumstance, site personnel feel helpless. Hazardous situations faced at some project sites and how they were overcome adopting interesting and innovative ideas have been presented. Different types of hazards from wild animals, equipment failure or even unpleasant situation have been presented. The chapter is expected to be of great interest for site engineers and supervisory personnel.

Chapter 15: Geotechnical and Foundation Engineering Practice Professional practice in geotechnical and foundation engineering in industrial projects needs to balance between technology and economy in cost and time. Other factors like constructability, quality, stability, durability and trouble-free planned service life are major considerations. Instances of failure during construction or after commissioning have been brought out in Chap. 13. Failures are occurred generally due to lack knowledge or experience of engineers during engineering or construction stages. Can it be due to shortage of knowledgeable and experienced personnel in projects? It calls for introspection starting from college education to training to practice and need-based corrective steps. There can be other angles too, e.g. prospects of professional career growth, modern business models, statutory and non-technical interferences. These aspects as seen and felt by the author during his profession spanning over 45 years in several heavy industrial projects have been laid bare candidly without prejudice. Differing views and disagreement are always honored. But shortage of knowledgeable and experienced geotechnical and foundation engineers in projects is undeniable.

Appendix 1: Units and Conversion Tables While going through textbooks, literatures, reports, codes, etc. of previous, recent years and foreign publication, one may face difficulty in comprehending or comparing actual magnitude of data due to use of different measuring unit systems (e.g. FPS, CGS, SI, etc.). The reader may sometime face difficulty in identifying conventional symbol for a parameter and corresponding conversion factors from one

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1 Introduction to Chapters

to other systems. Conversion tables and charts are generally available in print form and online. Still, one may prefer to have them handy. Keeping above objectives in view, basic units, symbols and conversion factors for different entities are furnished in tabular forms.

Appendix 2: Standard and Correlations Some common but helpful correlations and formulae in soil mechanics may not be available when actually needed. The correlations are considered standard for different soil and rock types. A few often referred correlations and formulae are included for quick reference only. These may be helpful because, most of these are taken from available references.

Appendix 3: Desktop Excel Programs for Preliminary Design Geotechnical engineers need to develop concepts on foundation system and construction method. A site in soft soil may need improvement for resting competent foundation. Depending upon soil type, multiple options for improvement are available. But selection of a method should be based on preliminary design/analysis. Depending upon soil type, stone column or deep soil mixing or dynamic consolidation can be considered. In such cases, analysis can be carried out based on soil data in desktop program. A number of Excel programs have been developed for carrying out preliminary designs based on geotechnical and codal data. Output from the programs in tabular and graphical forms can be very handy for project planning purpose. Desktop Excel programs have been developed for stone column, deep soil mixing, block gravity wall and simplified liquefaction potential assessment. However, programs have not been included in this edition of the book. Geotechnical and Foundation Engineering Practice in Industrial Projects is neither a handbook nor a made-easy but can be considered as guide to practical approaches to some apparently difficult geotechnical and foundation engineering issues in simple form. Once guidance on course of action is available, further steps can be decided. Detailed planning, design, construction methodology and testing procedures can proceed thereafter. It is expected the book would be of great interest to new and practicing engineers who feel urge to carry out jobs with an element of improvement, pride and ownership.

Chapter 2

Engineering Geology

Introduction Knowledge in geology is important for geotechnical and foundation engineers. It is because geology is like the ‘DNA’ and ‘horoscope’ of a region. An astrologer prepares horoscope based on precise positions of celestial objects like stars and planets at the time of birth and represents them in characteristic circular or cross diagrams on longlasting paper. Applying astronomical assessment and judgment, he forecasts series of events good and bad likely to happen chronologically throughout the life-cycle of the person. Moreover, probable dates and times of occurrence of ‘turns’ and ‘events’ throughout the life are indicated. In the same line, outcome from geological studies is very helpful in knowing ‘characteristics’ of the region and predicting engineering behavior of subsurface following assessment by experienced geologist.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_2

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2 Engineering Geology

Engineering geology broadly means ‘study of earth’ up to the depth required for assessment and engineering purposes. All types of foundations are placed on earth, be it soil or rock in any form. Performance of foundation depends on geological features like formation mechanism, degree of weathering, constituents and characteristics and several others. Therefore, it is preferable that geotechnical and foundation engineers should have working knowledge on geology. In geotechnical engineering, behavior of founding material under stress (load–deformation characteristics) is important because bearing capacity basically is load vs. settlement phenomenon. Nature of founding material in terms of constituents, structure, etc. can be judged from geological studies. Moreover, geotechnical engineering is also science applied with ‘judgment’ because the earth is formed by natural process and not always follow laboratory-scale behavior. For better judgment on founding strata, study on geology of the site should be mandatory.

Importance of Regional Geology For geotechnical engineers, it is important to know regional geology of project site. Because study of regional geology reveals several vital data on types of soil/rock, its formation mechanism, stratification, faults, fold, dip, etc. Planning of site exploration, selection of types of foundation and precautions to be taken during deep excavation for industrial projects is based on results of detailed assessment on regional geology. Movement of groundwater is a basic part of soil mechanics. Its influence can be found in almost every part of geotechnical engineering. Therefore, it is important to know groundwater conditions and their seasonal variations at site. So the steps for site exploration can broadly be divided into three steps: (a) Study regional geology (b) Geotechnical investigation (c) Hydrological investigation. A site assessment report is prepared based on data gathered/collected from the above studies. The report is used in planning and design of methods for site development and types of foundations for the main plant and other units. In order to demonstrate importance of studying regional geology in understanding subsoil characteristics, expected behavior of different layers and selection of competent founding layer, two examples are cited below. (a) Bengal Delta Basin (b) Asansol Plateau.

Regional Geology of Bengal Delta Basin

15

Regional Geology of Bengal Delta Basin Geological assessment of Bengal Delta Basin (in West Bengal) followed by engineering observations made from geological studies are presented below for reference. The Bengal basin is part of the great Indian Shield, which approximately to the east of longitude 87 E disappears under alluvium. On the west side of it is a number of Gondwana basins along the Damodar River valley, a few exposures of early tertiary are found in Orissa and Durgapur in the west and the north-west, respectively, and the late Mesozoic volcanic in Rajmahal hills on the north-west. It is only in the Shillong plateau in the north that the Archaean and Pre-Cambrian shield crops out again. River Ganga flows southwards through the gap between the Rajmahal hills and the Garo hills in the Shillong plateau and eventually branches off to Bangladesh in the east keeping a southerly branch called Bhagirathi which is called Hooghly in the lowest reaches. This river along with other mighty rivers from Damodar system in the west flows into the Bay of Bengal along with its sediments which formed upon deposition in the Bengal basin, the land mass is crisscrossed by rivers. Haldia is an industrial township in West Bengal. It is located on the west bank of the Hooghly River about 40 kilometer (km) north of the bay and nearly at south western border of the basin containing recent alluvium. Bengal Delta owes its origin to the delta-building activity of the silt-laden Ganga/ Hooghly River and its numerous tributaries traversing the region. Part of the Bengal Delta falls under Bangladesh. In India, the delta has a sea front of about 97 km. River Ganga has abandoned the Bhagirathi–Hooghly course and has taken the Padma– Meghna course in Bangladesh. Sundarban area in Bangladesh is considered relatively younger compared to its western counterpart in India. Depth of bedrock in this portion of the basin can only be measured in kilometers. The depositions have been through marine transgression in the top 25–30 m and through marine regression at lower depth. The sediments are of late Pleistocene– Holocene time and are predominantly fine grained up to the explored depth. The tidal sediments represented by soft silty clay found in boreholes contain considerable quantity of decayed vegetation indicating abundant growth of plants on soft mud which gradually subsided along with flora. Close observation of the area reveals that the lithology is very soft to soft dark gray to gray clay with decayed vegetation and wood fragments, stiff bluish gray silty clay with carbonaceous materials, pests’ bivalves and yellowish-brown micaceous silty sand. Reported carbon dating of this deposit indicates its age to be about 15,000–20,000 years.

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2 Engineering Geology

Observations Made from Geological Study Based on the geological features, the following ground and groundwater condition and engineering behavior of the region are evident. It can be seen that the site comprises soft to stiff alluvial soils with intermediate sandy and clayey layers, organic intrusions and no trace of rock. It then leads to infer bearing capacity will be medium to moderate with appreciable settlement potential. Piles will derive capacity from both skin friction and tip bearing and to be designed as friction-cum-bearing piles with low to medium lateral capacity. The soil is suitable for both bored and driven cast-in-situ or precast piles. Due to high water table and soft nature of soil, precautions should be taken for prevention of collapse and dewatering during excavation.

Regional Geology of Asansol Area The regional geology and tectonics of Asansol coal belt in West Bengal along with Raniganj, Jharia, Ramgarh, North and South Karanpura, Amamga and Hatur belong to the southern parts of the Damodar Valley coal reserve of Gondwana which produce the major percentage of cocking coal in the country. The Gondwana sequences are developed in the tectonic trough with faulted boundaries arranged along linear zones. The Gondwana belt of Damodar Valley runs along east–west trending faults, and the regional dip (0°–10°) of strata is generally toward the more faulted southern boundaries. The Raniganj–Asansol Coalfields fall under the lower Gondwana Group of rocks. The lower Gondwana sequence starts above the Precambrian basement of granite gneiss with the Talcher Boulder Bed. The Talcher Boulder Bed contains bounder conglomerate with gravels of quartzite and gneissic rocks. This is successfully followed by Karharbari Formations of rocks comprising 60– 120 m of pebbly grit and sandstone intercalated with coal seams. The Barakar Formation follows the Karharbari Formations comprising mainly of sandstone, shale and intercalated coal seams. The Barren Measure Formation intervenes between Barakar and Raniganj Formations. The rock type of Barren Measure Formation is sandstone which is characteristically ferruginous and lack coal seams (a variable amount of carbonaceous matter sometimes comprised of sandstone, shale and coal seams). Typical plant remains in lower Gondwana Group are generally termed as Glossopteris Flora which consists of Glossopteris, Gangamopteris, Taeniopteris, etc. Lithological sequence of the area shows lithofacies variations both laterally and vertically. Sandstone, shale and coal are a general vertical sequence. The sediments show frequent parallel and cross laminations, slump structure, convolute laminations as well as sole marks. Sediment character indicates fluvial to fluvio-lacustrine environment of deposition. The sandstone is feldspathic in nature (Arkosic) whereas the shale is mainly carbonaceous.

Regional Geology of Asansol Area

17

Standard Stratigraphic Sequence Group

Age

Formation

Lower

Upper

Raniganj Formation

Gondwana

Carboniferous Barren

Measure Formation

Group

Premium

Barakar Formation Talcher Boulder Bed

Observations from Geological Study Based on the geological features, it is seen lithology of site will be variable both vertically and horizontally. The sediments show frequent parallel and cross laminations which indicate fluvial environment of deposition. Sandstone, shale and coal are a general vertical sequence. These characteristics indicate the subsurface comprising stiff to hard strata variable in both depth and sidewise implicating need for comprehensive geotechnical investigation program. As for foundations, bearing capacity is expected to be moderate to high with low settlement. Piles will have to be designed considering higher-end bearing component. Normally, bored or drilled piles will be reasonable. Lateral capacity would be higher. Due to hard nature of soil, excavation can be taken to greater depths with moderate side protection. The above examples demonstrate importance of geological data on geotechnical and foundation engineering practice. Geology is specialized subject on earth science and a specialist on the subject is justifiably called ‘geologist’. Geology is a vast field dealing with features of natural processes the earth has gone through over ages. But a geotechnical engineer needs to know mainly near-surface geological features having impact on foundation engineering. Accordingly, the chapter focuses on a few selected topics on classification/ identification, definitions, exploration and normative range of certain engineering parameters. Keeping the objectives in mind, the chapter has been planned to cover the following topics. • • • • •

Brief definition of commonly used rock parameters and classification Geotechnical and geophysical investigation in rock strata Laboratory tests on rock for classification and engineering parameters Normal range of engineering properties for various rock types Commonly referred BIS codes.

The above items are covered briefly, for further details books, codes should be referred.

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Brief Definition of Primary Rock Parameters Strength of intact rock mass is enormous and capable of carrying high load. However, in nature, intact rock bodies are rare. Strength of any rock mass is dependent on number and nature of weak zones (fracture, joints, cleavage, etc.) present within the rock body. Engineering rock parameters are basically measures of weak zones present in the rock. Definitions of some common rock parameters are presented below.

Core Recovery (CR) Core recovery = (Total length of rock cores recovered by drilling/Total length of core run) × 100. Core recovery (CR) is expressed in percentage and is general indicator of intactness of rock. CR =

LC × 100 LD

where CR = Core recovery (%), L C = Total length of core recovered, L D = Total length of core run.

Rock Quality Designation (RQD) Rock quality designation provides a quantitative estimate of rock mass quality from drill core logs. RQD is defined as the percentage of intact core pieces longer than 100 mm. RQD = (Total length of intact rock cores pieces > 10 cm length/Total length of core run) × 100 RQD =

LI × 100 LD

where RQD = Rock quality designation (%), L I = Total length of core length > 10 cm recovered, L D = Total length of core run.

Brief Definition of Primary Rock Parameters

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Table 2.1 Quality classification of rock based on RQD and mass factor Quality classification

RQD (%)

Mass factor (j)

Very poor

0–25

0.15

Poor

25–50

0.20

Fair

50–75

0.20–0.50

Good

75–90

0.50–0.80

Excellent

90–100

0.80–1.00

Rock Mass Quality (RMQ) and Rock Mass Factor ( j) Rock mass quality (RMQ) and rock mass factor ( j) are the two concepts with the help of which qualitative and quantitative assessment can be made by relating the numerical intensity of discontinuities to the quality of unweathered rock masses and to quantify their effect on deformability. Rock mass factor is defined as: j=

Deformability of rock mass Deformability of intact mass

Table 2.1 shows classification based on RQD and mass factor of rock.

Rock Mass Rating (RMR) Rock mass rating (RMR) is a combination of several physical and engineering parameters used for the overall identification and behavior of a rock formation. Bieniawski published details of a geomechanics classification of a rock mass called rock mass rating (RMR) system. This system is widely accepted as classification both for civil and mining engineering purposes. Classification of rock depends on several physical and engineering parameters summarized in Table 4.4 by Bieniawski is reproduced below for reference only. However, it is pointed out that assessment of rock parameters and properties should be carried out only by qualified and experienced geologist.

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Laboratory Tests on Rock for Classification and Engineering Parameters

21

Geotechnical Investigation in Rock Strata Geotechnical investigation primarily comprises of boring in soil and drilling in rock. Investigation in rocky strata including collection of core samples is carried out by core drilling. Core samples are inspected visually, and engineering properties are determined by carrying out laboratory tests. Core drilling produces continuous subsurface profile and samples. By studying drilled core sample, one can determine the ‘core recovery (CR)’ and ‘rock quality designation’ (RQD) of rock formation which are major physical parameters of rock deposit (like N-value in soil). Preliminary assessment of rock is done based on results of these and other specialized tests, namely in-situ permeability (Packer) test and cross-hole shear test.

Laboratory Tests on Rock for Classification and Engineering Parameters For identification, classification and assessing of engineering properties of rock, different types of tests are conducted in field and also in laboratory on collected rock samples. As procedures for different field and laboratory tests are available in textbooks, codes, standards, etc., these are not repeated. Plan for investigation in rocky areas is done by geologist. Loss of drilling water, discontinuities, weak zones, etc. if met during drilling are logged/recorded in drill logs. Several tests are done in laboratory on core samples. Depending upon the purpose, classification of rocks is done on the basis of several physical and engineering parameters, few of them along with standard units are listed below for reference (Table 2.2). For test procedures and interpretation of results, reference is to be made on relevant books, standards and codes. Table 2.2 Engineering parameters of rock Name, description

Unit

Name of parameter

Unit

Conditions of discontinuities

**

Water absorption

%

Spacing of discontinuities

m, cm

Slake durability

%

Orientations of discontinuities

**

Density

t/m3

Rock quality designation

RQD

Porosity

%

Specific gravity

NA

Void ratio

%

Point load index

MN/m2

Uniaxial compressive strength

MPa

** Detailed description of condition and orientation of discontinuities are to be recorded

22

2 Engineering Geology

Grades of Weathering Rock undergoes weathering when exposed to various natural agencies like sun, water, wind, etc. Degree of weathering designates grade of rock. Grade of weathering has direct bearing on strength parameters of rock. Various weathering grades are presented below. 1. 2. 3. 4. 5.

W 0 —Fresh rock (unweathered) W 1 —Slightly weathered W 2 —Moderately weathered W 3 —Completely weathered W 4 —Decomposed ( residual soil).

Average Range of Engineering Properties for Various Rock Types Presumptive net allowable bearing pressure based on RMR and classification (Ref. Table 2.3, IS: 12070-1987) is reproduced in Table 2.3 for quick reference only. Representative engineering parameters commonly associated for different rock types (as per Bowels book, P-278) are summarized in Table 2.4 for quick reference. Please note these are to be verified by laboratory tests. Table 2.3 Net allowable bearing pressure based on RMR and classification RMR

Rock mass classification

Description

Net allowable bearing pressure (t/ m2 )

81–100

Class I

Very good rock

600–448

61–80

Class II

Good rock

440–228

41- 60

Class III

Fair rock

280–151

21–40

Class IV

Poor rock

145–90–58

< 20

Class V

Very poor rock

55–45–40

Table 2.4 Representative engineering parameters for rock types Rock type

Unit weight (kN/m3 )

Modulus of elasticity (MPa × 103 )

Poisson’s ratio

Compressive strength (MPa)

Basalt

28

17–103

0.27–0.32

170–415

Granite

26.4

14–83

0.26–0.30

70–276

Schist

26

7–83

0.18–0.22

35–105

Limestone

26

21–103

0.24–0.45

35–170

Sandstone

22.8–23.6

3–42

0.20–0.45

28–138

Shale

15.7–22

3–21

0.25–0.45

7–40

Guidelines for Design of Piles Terminating (Socketed) in Rock Strata

23

Table 2.5 Net safe bearing pressure for different rock types Rock material

Bearing pressure (t/m2 )

Massive crystalline bedrock (granite/gneiss etc.)

1000

Foliated rocks (schist/slate etc.)

400

Limestone

400

Sedimentary rocks (sandstone/shale)

250

Soft broken bedrock

100

Table 2.6 Minimum length of rock socket for piles Rock type

Min. socket length

Sound and homogenous rock (granite, gneiss etc.)

1–2 D

Moderately weathered, closely jointed rock (schist, slate)

2–3 D

Soft sedimentary rock sandstone, mudstone etc

3–4 D

D Diameter of pile

Presumptive Bearing Capacity of Rocks For preliminary assumption of net safe bearing pressure for various types of rock as per (Table 2.2 of IS 12070-1987) are presented in Table 2.5 for quick reference only. It is recommended to verify actual bearing pressure before use.

Guidelines for Design of Piles Terminating (Socketed) in Rock Strata The suggested minimum length of socket in rock for piles as per (IS: 14593) is presented in Table 2.6.

General 1. Rock, in general, is good founding material provided it is reasonably intact. Presence of (a) weak planes (joints/fractures etc.) and (b) grade (degree) of weathering makes an intact rock considerably weak. 2. While considering pile through rock, one should remember minimum factor of safety should be 6 while in soil it generally varies from 2 to 3.

24

2 Engineering Geology

After knowing upper-surface geological features of the region, concept-planning on probable foundation types is selected. Planning of site exploration, foundation and precautions to be taken during deep excavation are based on results of detailed assessment on regional geology.

Chapter 3

Geotechnical Investigation

Introduction Geological data for a site is considered as ‘horoscope’ and geotechnical investigation report is ‘Medical or Health Audit Report’ of the site. When a public or private sector investor plans to venture into a new investment plan on a project, he certainly will prefer to ensure geological stability and constructability of foundations at the site. Planning type of foundation and designs is based on conclusions and recommendations of geotechnical investigation report on the projects site. Aspects of engineering geology have been discussed in Chap. 2, and geotechnical aspects are covered in this chapter. Basic objective of geotechnical investigation is to explore sub-surface condition of the site. Results of all field and laboratory tests are compiled in soil report which is a valuable and permanent document on the site for present and future reference. The designer ‘visualizes’ the sub-surface conditions through the ‘eyes’ (reports) of geotechnical engineers. Geotechnical and civil design of foundation are based on the report. Except for modern technological improvements, general practice for investigation was and still is ‘borehole-field and laboratory tests’ approach. Possibilities of disturbances during boring/drilling and sample collection cannot be ruled out. Quality of sample collection, storage, handling, transportation, delay, extraction, etc. can result in non-representative soil data. Interpretation especially identification of soil/rock types and its variation is very important for preparation of schedule for laboratory tests. Due to these factors (disturbances), civil designers often prefer liberal approach and over-design (uneconomic) foundation. Occasionally, important field observation can be missed posing risk during construction. Geotechnical engineering is considered a specialized field and demands attention, care, quality assurance in field work and laboratory test, data interpretation, evaluation of representative design parameters and foundation recommendations.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_3

25

26

3 Geotechnical Investigation

Primary purpose of soil exploration is to reveal sub-soil stratigraphy, their variations, consistency, engineering parameters, groundwater, etc. for use in design and construction. Conventional practice of soil investigation by soil boring/rock drilling is time consuming and costly. Moreover, under present socio-economic and political scenario, longer presence of workers and equipment in field may not be desirable for multiple reasons. In view of this, field activities are to be planned in such a manner that required data on ground can be collected following advanced technology with minimum presence in field. Methods for geotechnical exploration, sample collection, field and laboratory tests are extensively covered in textbooks, codes, journals and not repeated here. Purpose of the chapter is to highlight possibility of optimization by combination of conventional and geophysical methods of investigation. The chapter includes (a) methods for boring in shallow water using country boats, (b) twin-boat assembly and jack-up barge for deep waters, (c) boring/drilling in very hard old slag/debris dump and (d) use of hydraulic rotary rig with flight-augers. The methods have been presented for ready reference as these may not be available at hand when required. The methods have been demonstrated through photographs collected by the author.

Optimization of Investigation at Large Green/Brown-Field Project Sites In conventional method of geotechnical investigation, requiring large number of boreholes needs to engage large fleet of equipment, manpower and takes long time to complete field activities. Field work comprises boring/drilling, field tests, sample collection, storage and transport to laboratory which all are time consuming activities. Also, possibilities of human error/negligence and disturbances to samples cannot be ruled out. Elaborate site establishment continuing for longer period can be costly and may invite uncalled for local and site problems. The aim should be on minimum site presence but without compromise on quality of field data and quantity of sample collection. Scheme for site investigation can be optimized by combination of ‘conventional’ and ‘geophysical’ methods. Analysis of data from geophysical tests like seismic refraction, electrical resistivity and cross-hole methods reveals stratigraphy, consistency, water table and dynamic properties. Main advantages of geophysical exploration are that it requires limited number of qualified and experienced personnel for collection of bulk data and facility for online transmission to site or home office for analysis. In this approach, the site is surveyed marking proposed plant areas based on plant general layout. The areas are then suitably divided longitudinally and transversely by setting lines for determination of subsurface profiles. Ground surface along profile alignments are cleared of bush, vegetation, etc. to facilitate conducting geophysical tests. Seismic refraction tests (SRT) are carried out along profile lines and data stored

Optimization of Investigation at Large Green/Brown-Field Project Sites

27

in soft form. Electrical resistivity tests (ERT) are carried out concurrently. Results of SRT are analyzed using software to develop continuous sub-surface profile along traversed lines. Profiles of groundwater developed from ERT data are superimposed on profile data. The results are plotted to develop continuous long and cross sections of entire site. Thereafter, locations of a limited number of boreholes are selected strategically to supplement and confirm data from geophysical tests and also to evaluate strata-wise engineering parameters of soil/rock. Boring and sample collection are to be done under strict supervision of geotechnical engineer. Laboratory test is conducted based on test schedule prepared by experienced geotechnical engineer who will study bore logs, examine samples and compare them with profile drawings developed from geophysical tests. Fine-tuning of profiles is carried out based on results of field and laboratory test. Based on data of geophysical and geotechnical test, sub-soil profiles along with design soil parameters are prepared for design purpose. Thereafter, some special tests like electrical cone penetration test (ECPT), seismic cone penetration test (SCPT) or cross-hole tests for dynamic parameters and pumping out tests for determining locations for deep tube well may be carried out if required for design. Introduction of modern technology and tools may appear somewhat unfamiliar but are needed to improve on data quality and save project time and cost. Advantage of combined approach is demonstrated by an example from oil refinery project site in west coast of India. Initially, geotechnical exploration for a large ‘green field’ petrochemical project in coastal areas of Gujrat state was planned considering 70–80 boreholes of 30–40 m depth requiring elaborate logistic support. Estimated time and cost for investigation could not be accommodated in overall project schedule. It was then decided to adopt combined approach. Revised investigation plan comprised of (a) seismic refraction profile (cumulative length ~ 14 km) covering length and breadth of the site, (b) electrical resistivity at selected points and (c) only 10 Nos. of 40–45 m deep bore/drill holes with field tests and sample collection at strategic locations. Additionally, a few special tests like cross-hole, block vibration and pumping out tests were conducted. Data from geophysical prospecting was processed progressively and simultaneously to establish stratigraphy and tentative properties. Results of field and laboratory test from confirmatory boreholes were utilized to fine-tune engineering parameters for each layer. The geotechnical report prepared incorporating all test results along with required design parameters, dynamic and permeability values. In this process, whole investigation could be completed in about half of originally estimated time and cost to the satisfaction of project authorities. In another ‘green field’ coke oven and captive power plant project site spread only over ~ 210 acres area in Haldia, West Bengal, combined methods were adopted successfully. As per agreement with foreign equipment (coke oven) supplier required soil investigation to be carried out as per their requirements requiring 16 Nos. 40 m deep boreholes for each coke oven. For four (4) such units plus coal unloading, crushing, screening, conveyor, storage yard, captive power plant and ancillary units total number of boreholes worked out to about 75 which was quite high for a

28

3 Geotechnical Investigation

small site and had to be rationalized. To satisfy the foreign consultants, few boreholes were carried out at one coke oven site along with few geophysical tests and results compared nicely. Based on that, soil investigation was planned with only ten boreholes of 40 m depth and geophysical tests.

Boring in Shallow Water Body, Pond and Marshy Field Common methods of soil tests on land are available and not repeated. But how to overcome certain difficult site conditions (marshy land, shallow pond or canal, river bank or bed) particularly in remote areas? To overcome such difficulties, simple, practical and cost-effective methods taking advantage of locally available resources adopted successfully at several sites are presented along with site photographs (source: author). Soil investigation in deep waters like canal, river or seashore is carried out from floating platform built on pontoons or empty drums or from common river/sea barge or from jack-up barge. But shallow water poses difficulties because available depth of water may not be justifiable for engaging floating platform cost of which would be high. Marsh buggy or all terrain vehicle (ATV) is available in foreign countries. In absence of such equipment, simple arrangement from locally available sources can solve the situation in cost-effective manner. In shallow water (depth about 1–2 m), approach and boring location can be made by earth/sand-filled bags. This often solves problem during rainy season. In shallow ponds, water depth can be reduced temporarily by pumping out part of water and similar procedure can be adopted. For water depth above 2 m, approach and platform can be supported on bamboo frame structure (as done by decorators). In that case, boring equipment needs to be dismantled and carried in parts to test location and reassembled. Utmost care should be exercised on stability and safety aspects of the temporary platform and approach ramps to avoid accident. Although the methods take some extra time, the job can be done locally without external mobilization.

Investigation in Shallow Water For large projects, boring in water is carried out from floating platform built by assembling pontoons or empty drums. For stability, pontoons/drums are joined structurally. Small barge used for ferrying goods can be modified to set up boring equipment. However, investigation in pond, small canal in remote areas, boring location can be reached by country boat fitted with boring equipment as shown in Fig. 3.1. The boat can be fixed in position by anchors in water and ropes tied to tree or pegs on bank. The boring equipment and accessories are mounted on boat beforehand. Thereafter, boring operation is similar to boring on land. Special care should be exercised against accident and boat sway or toppling.

Soil Investigation Near River Bank and Bed Using Twin-Boat Assembly

(a) Investigation from Country Boat Fitted With Rig

29

(b) Boat Fixed In Position by Anchors on Bank

Fig. 3.1 Soil investigation from country boat

Soil Investigation Near River Bank and Bed Using Twin-Boat Assembly For boring near river bank or bed, elaborate arrangement is necessary. Generally, two country boats are tied and fixed together keeping some gap in between for passage of boring rods, tools and erection of a temporary working platform. Boring rig is erected on platform built on twin-boat assembly and balanced for stability during operation. The assembly is then towed to borehole location and fixed in position with multiple anchors. Boring operation and sample collection are carried out as per normal practice. After completion of bore hole, the twin-boat assembly is shifted to next location. After completion of whole work, the assembly is dismantled. Twinboat assembly is shown in Fig. 3.2. The method can be adopted at river bank or in river bed but takes care for tidal variation during high or low tides.

Soil Investigation in River Bed Using Twin-Boat Assembly For investigation in river far from shore, similar arrangement as before but ensuring stronger assembly and secured firmly can be adopted. Motor boat can be engaged for ferrying between platform and shore. In river with high tidal variation, special

(a) Investigation from Twin-Boat Fitted With Rig

(b) Arrangement of Twin-Boat Assembly

Fig. 3.2 Soil investigation in river from platform built on twin-boat assembly

30

3 Geotechnical Investigation

(a) Investigation from Twin-Boat Anchored to Bed

(b) Boring in River Bed In-Progress

Fig. 3.3 Arrangement for investigation in river from platform built on twin-boat assembly

care must be exercised. Tide timings and water level variations are to be collected from local river authorities or nearby ports and timetable for investigation to be set avoiding high tide period. Investigation in river during monsoon can be hazardous and preferably be avoided. Figure 3.3 shows arrangement for investigation in river.

Investigation at Sea from Jack-Up Barge For investigation in sea, where wave, tidal variation, high wind are prime concerns, heavy boring-cum-drilling machines are necessary. In marine environment, investigation is normally carried out from jack-up barge. A structural platform supported on four hydraulically controlled legs rests firmly on sea bed. The platform is tugged to test location, floated and fixed at predetermined level above expected wave heights. Motor boat or ferry launch is used for transportation of personnel and supplies. Typical arrangement of boring/drilling from jack-up barge with on-board boring/ drilling rig is shown in Fig. 3.4.

(a) Investigation from Jack-up Barge

(b) Another view of Jack-up Barge

Fig. 3.4 Arrangement for investigation at sea from jack-up barge

Geophysical Methods

(a) Truck Mounted Boring/Drilling Equipment

31

(b) Tractor Mounted Boring/Drilling Equipment

Fig. 3.5 Truck/tractor-mounted rotary boring/drilling equipment

Truck/Tractor-Mounted Rotary Boring/Drilling Equipment Deep boring by tripod rig takes long time and possibilities of disturbances are high. For faster progress and better quality, deep boreholes are executed using mechanical boring/drilling rotary rig. Several varieties of mechanical boring/drilling equipment are available. As cost of procurement and maintenance of such equipment are high, only specialized companies engaged in large projects can afford them. Truck-mounted self-hoisting hydraulic boring-cum-drilling rig is shown in Fig. 3.5a. Such machines are capable of boring to great depth (~ 100 m) including field test and sample collection. For details of mechanical rig, accessories and operation, one needs to refer respective manufacturer’s product brochure. Innovative modification to mechanized rig has been done by companies with entrepreneurship. Figure 3.5b shows mechanical rig assembled on standard tractor. Similar modifications are done by several companies to suit their need and affordability.

Geophysical Methods Geophysical methods are widely used because they enjoy several advantages over conventional boring/drilling methods. It is fast, reliable, lesser field activities and safe. Continuous sub-soil profile can be generated by these methods instead of logging stratigraphy only at borehole locations which need to be joined judiciously by experienced geotechnical engineer. As data interpretation is done by qualified personnel using software, it can be done at site or home office. Under normal unobstructed environment, prospecting over 1.5–2.0 km can be completed in a day. Common geophysical methods, namely seismic refraction and reflection and electrical resistivity, are discussed briefly for information.

32

3 Geotechnical Investigation

Seismic Refraction The seismic refraction methods (also called sounding) are based on principles of wave propagation through soil and rock mass and through interfaces. Test equipment comprises of 5–10 kg impact hammer pounding on a steel plate firmly in contact with ground and a series of electronic sensing device called geophone fixed firmly on ground surface in predesigned pattern. Each impact generates series of waves. Primary waves, namely surface, body and shear waves, travel through soil body at different speed depending upon their properties. The waves reflect at interface between layers and travel back to surface. Reflected waves are picked-up by the series of geophones placed in predesigned configuration. The geophones are connected by wire to portable recording unit for digital recording. Velocity of different wave types depends upon in-situ characteristics (density, consistency, voids, etc.) of soil mass and water table. First arrival (minimum travel) time of each wave type is recorded at every geophone and analyzed using software to reveal stratigraphy at test location. On completion of sounding at one location, entire setup is removed and re-set at next location to repeat sounding. In this fashion, total length is traversed by progressive sounding advancing the test along alignment.

Seismic Reflection Seismic reflection methods are based on principles of wave reflections from interfaces of soil/rock strata. The site is traversed along longitudinal and transverse directions following procedures similar to refraction. Each traverse line will be surveyed first, test locations pegged, coordinates and RL recorded. Surface of test point is cleared of vegetation, roots, etc., and a steel plate is placed firmly on ground ensuring good contact. About 8–10 geophones are placed firmly on ground on both sides at predetermined pattern along the alignments. There are certain limitations, e.g. ground surface needs to be fairly dry. Field data should be analyzed only by experienced technician. The seismic reflection method has some limitations on coverage and used for specific purpose.

Electrical Resistivity Basis for electrical resistivity test is to measure resistance offered by ground on flow of electric current. In this method, two pairs of probes/electrodes (metal rods) wired to a portable instrument are operated by dry batteries. One pair (transmitter) is meant for transmitting low-voltage current. Other pair (receiver) measures current received. Normally, the test at a point is carried out in orthogonal directions. Data records are analyzed following principles of current flow through conducting media. Normally,

Advanced Methods for Soil Exploration

33

test is done at specified locations and rarely for traversing. Electrical resistivity test is used for evaluating earth resistivity essential for design of earthing to control panels of high voltage power supply. The test is also very useful for identification of groundwater-bearing strata. This method is commonly adopted for prospecting water table and selection of preferred location for setting up bore wells.

Advanced Methods for Soil Exploration Static and dynamic cone penetration tests (CPT, DCPT) are often used to determine lithology and engineering parameters based on standard correlations. The tests are carried out and results interpreted following codes and standards. Cone tests although have certain limitations are advantageous because tests are quick, data analysis can be done simultaneously and basic information can be generated quickly. Limitations are on capacity of CPT equipment (commonly 10, 20 T), shifting, firm anchoring with ground and depth of probing. However, judicious selection of number and locations of CPT and boreholes can be advantageous.

Electric Cone Penetration Test (ECPT) Considering advantages of cone penetration tests, phenomenal improvement has been achieved by use of electric cone (ECPT). The cone is specially designed and fabricated sophisticated electro-mechanical instrument which is attached with extension tubes through which data cables pass. The cone assembly is pushed by hydraulic power pack at predetermined constant (low) speed by 10/20 T capacity equipment. Tip resistance and side friction are electronically sensed continuously and transmitted to on-board computer for recording. Profile of resistance experienced by the probe is displayed on screen. Detailed analysis, overall interpretation and preparation of ground report are done at office by trained technician/engineer. Profile of cone and jacket friction at a location is interpreted to identify classification and preliminary strength parameter (cohesion: C and angle of internal friction: ϕ) following standard correlations. It normally takes about one to two hour to probe 40–50 m depth. For greater mobility and ease of access to different locations, ECPT equipment can be mounted on truck or on all terrain vehicle (ATV) for difficult terrain. Figure 3.6 shows that ECPT equipment mounted on ATV is loaded on trailer for transport to site.

34

3 Geotechnical Investigation

Fig. 3.6 20 T capacity ECPT equipment mounted on ATV—ready for transportation to site

Seismo-Cone, Piezo-Cone For assessment of in-situ seismic and piezometric properties, electric cone instrument has been developed and patented by international companies. The seismo-cone equipment although looks similar to electric cone has mechanism of imparting vibration of desired frequency and amplitude and also receiver sensors to pick-up reflected signals. Seismo-cone is also pushed into ground in the same fashion as the electric cone. The seismic and piezometric cone is commonly called ‘seismo-cone’ and ‘piezo-cone’, respectively. Cone instruments can be mounted on truck or ATV. It is pointed out that the specialized cone assembly is highly sophisticated in design and must be operated only by experienced company-certified operator. In the same manner, cross-hole tests can also be done. The advanced methods provide quick, continuous profiles of in-situ dynamic properties and piezometric data avoiding disturbances inherent with boring method. The methods being highly advanced, data analysis and interpretation must be done only by experienced engineer having good knowledge on geology of the region. Readers interested to learn details of geophysical tests need to consult related textbooks, literatures, company brochures, etc. and interact with geophysical experts.

Hard/Old Filled-Up Sites Setting up new plant facility for expansion project within existing steel, power plant and mines face major problems due to non-availability of suitable land. However, at some remote area within the plant, there may be large areas, previously used for dumping waste material for years may be lying as waste dump. These areas can be used for new projects by dressing and leveling dumps, dismantling old structures

Geotechnical Investigation in Slag Dump

35

and clearing debris. Methods for site investigation on land and water body have been discussed. But the scenario is entirely different for old hard compacted debris dump of steel plant slag; plant wastes as it poses great hindrance to boring/drilling through hardened highly heterogeneous deposits by conventional equipment. Geophysical prospecting is redundant due to high degree of heterogeneity and variations of dump. The project authorities must ascertain feasibilities of site development, design and construction of foundations for proposed expansion project. Difficulties in site exploration over old dumping grounds are best explained through a case study at Tata Iron and Steel Company (TISCO), presently TATA STEEL works in Jamshedpur. TISCO started production of iron and steel from this works for over a century. Out of his extraordinary vision for the future of steel industry in India, Jamshedji Nusserwanji Tata (J. N. Tata) acquired vast parcels of lands in and around Jamshedpur Township. With increasing demands on steel, production of iron and steel including finished structural products expanded rapidly. Consequently, slag generated from blast furnace (BF) and Steel Melt Shop (SMS) was dumped generally haphazardly over open areas within plant boundary. Dumping of slag along with other plant debris over long years formed huge hillock-like dumps (height 50–60 m or more) called ‘slag dump’. All kinds of plant wastes, debris, spoils, hardened/ dismantled concrete, frozen steel, iron skulls, ingot molds and even parts of broken rail wagon could be found in ‘slag dumps’. As a result, slag dumps are very hard, highly heterogeneous and completely unpredictable. The fact that large areas were wasted by dumps and further expansion project facing serious space constraint, only option left was to explore feasibility of developing the wastelands. Typical characters and complexities of slag dumps can be seen in the following photographs (Fig. 3.7). In early 2000, TATA STEEL initiated an ambitious Growth Plan Project inside the century-old Jamshedpur works. As fresh acquisition of land for expansion was almost ruled out, new plants had to be accommodated within existing plant premises. Thicknesses of dumps in proposed areas were assessed from old and new topographical survey maps and found to be about 30–35 m. In order to build new plants, conditions of dump: layering, variation, strength, weakness of parent ground are to be investigated for deciding method for site leveling, side protection, compaction, finally selection of foundation types and method of construction.

Geotechnical Investigation in Slag Dump Geotechnical investigation work in slag-filled area should start with collection of past history of the fill namely, type of slag (BF or SMS) which possess different characteristics; age and thickness; physical appearance, etc. Boring using conventional manual or mechanized equipment is ruled out. Use of rock drilling equipments is not feasible due to highly heterogeneous and friable nature. After several trials with various equipment and method, it was finally decided to deploy bored piling equipment of 550–600 mm diameter. Improvised heavy bailer and rock chisel operating by mechanically operated winch were mostly successful in penetrating slag layers

36

3 Geotechnical Investigation

(a) Profile of Slag Dump Exposed After Excavation

(c) Large Cavity within Slag Dump

(b) Solidified Liquid Steel after Cooling

(d) Arc-Shaped Solidified Slag

Fig. 3.7 Typical profiles and complex characteristics of steel plant slag dumps

with some exceptions. On reaching original ground, standard soil/rock investigation equipment lowered for investigation of virgin layers up to the depth required for design purpose.

DCP–CBR Test for Road Sub-base Different techniques and equipments for site investigation have been discussed in previous sections. Generally, designs of pavement, airstrips, etc. are based on field CBR values. Transportation and setting up of field CBR equipment, field test and data interpretation on regular basis on pavement sub-grade for QA/QC purpose are time consuming and costly. However, a simple test called DCP-CBR can determine equivalent field CBR value with a lightweight, compact and portable equipment in much less time and cost. The test is considered as an alternative to conventional field CBR test by highway departments. Considering fresh engineers may not be familiar with DCP-CBR test, description of equipment, test procedure, data collection and interpretation are presented in working detail.

DCP–CBR Test for Road Sub-base

37

Fig. 3.8 DCP-CBR equipment and guidelines for assembly

Results of dynamic cone penetration (DCP) tests are measure of inherent strength of base-soil used for design of road/pavement for desired strength. The DCP data is correlated to basic CBR value to evaluate design CBR of road sub-grade. It is possible to obtain an approximate CBR value from the DCP-CBR test results by applying simple formula. The test can also be used for checking in-situ compaction of finished fill. DCP-CBR equipment can be packed in a handy portable box and assembled easily at site as shown in Fig. 3.8.

Equipment and Test Procedure DCP-CBR equipment and typical details are shown in Fig. 3.8. A drop hammer of mass 8.0 kg is allowed to drop freely for height of 575 mm to drive a standard hardened steel cone tip (cone angle 60°) in soil bed. The equipment is held vertically on ground at test location or on prepared sub-base for proof test. The 8 kg hammer is lifted manually to a height of 575 mm and dropped freely repeatedly to penetrate the cone in soil. Depth of cone penetration per blow is recorded, and the cycle is repeated. Continuous measurements on number of drops are taken up to full depth of penetration of about maximum 850 mm or less in case of stiffer soil.

38

3 Geotechnical Investigation

Format for Recording Field Data (Typ.)

DCP-CBR : Cone Penetration Field Record Client : Job No. ….

Project :

Project /Site : Location : ----------------------------------------------------------------------------------------------------------------------Description of Soil : ---------------------------------------------------------------------------------------------------------Chainage

Date

Depth below GL (m)

Chainage

Date

Depth below GL (m)

Depth (m)

No. of Blows

Penetration (cm)

Depth (m)

No. of Blows

Penetration (cm)

Formula for Evaluation of DCP-CBR Value Values of DCP-CBR can be evaluated following empirical relationship developed by TRL (overseas road node—31) relationship (Ref. 1). ( ) [ ] P ; DCP − CBR = (10) A A = Log10 (CBR) = Y − X × Log10 N where Constants X and Y are related to cone of probe, For 60º cone: X = 1.057 and Y = 2.48. Steps for evaluating DCP-CBR value from field records are described below and shown in table next page. Steps: Col. (1): P = Penetration of DCP probe in (mm) Col. (2): N = Number of hammer blows for total penetration (P) Col. (3): DCP(60º) = Penetration (mm) per blow = P/N

DCP–CBR Test for Road Sub-base

39

Col. (4): Log10 [DCP(60º)] Col. (5): X × Log[DCP(60º)], where Factor depending on type of cone Col. (6): V = Y – X Log10 (P/N). For 60º cone, X = 1.057 and Y = 2.48. Estimation of DCP-CBR values from penetration test results (1)

(2)

(3)

(4)

(5)a

(6)b

(7)

Penetration (P)

No. of blows (N)

DCP(60º) = (P/N)

Log(P/N)

X . x(4)

V =Y − X Log(P/N)

DCP-CBR = 10^(V )

mm

Nos.

(1)/(2)

Log10 (3)

X.(4)

Y-(5)

10(6)

380

60

6.3333

0.8016

0.8473

1.6327

42.9

310

55

5.6364

0.7510

0.7938

1.6862

48.6

381

45

8.4667

0.9277

0.9806

1.4994

31.6

196

15

13.0667

1.1162

1.1798

1.3002

20.0

230

30

7.6667

0.8846

0.9350

1.5450

35.1

206

30

6.8667

0.8367

0.8844

1.5956

39.4

340

20

17.0000

1.2304

1.3006

1.1794

15.1

256

45

5.6889

0.7550

0.7981

1.6819

48.1

298

35

8.5143

0.9301

0.9832

1.4968

31.4

= Factor = 1.057 and b Value (V ) = (Y ) − [F × Log(P/N)], Y = 2.48 for 60º cone, Average DCP-CBR = 34.7 aX

Overall CBR evaluated from layer-wise DCP-CBR values using Japanese formula: [ Overall CBR =

1

∑(Layer . Thickness) × (DCP − CBR) 3 ∑ (Layer Thickness)

]3 .

Various other models for converting DCP penetration rate to in situ CBR are available these include the following (Table 3.1). Above relationships have been collected from references. It is hoped the chapter is informative and useful in planning geotechnical investigation for large project site.

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3 Geotechnical Investigation

Table 3.1 Penetration rate—CBR relationships Cone angle

Reference

Relationship

60°

TRL8

log10 (CBR) = 2.48 − 1.057 log10 (DN)

60°

Sampson9

60°

30° cone

loge (CBR) = 5.8 − 0.95 loge (DN)

Plastic materials only

loge (CBR) = 5.93 − 1.1 loge (DN)

PI > 6 materials

loge (CBR) = 6.15 − 1.248 loge (DN)

PI < 6 materials

loge (CBR) = 5.70 − 0.82 loge (DN)

PI = 0 materials

loge (CBR) = 5.86 − 0.69 loge (DN) log10 (CBR) = 2.81 − 1.32 log10 (DN)

Harison10 Clayey soils

log10 (CBR) = 2.56 − 1.16 log10 (DN)

Sand S-W

log10 (CBR) = 3.03 − 1.51 log10 (DN)

Gravel G-W

log10 (CBR) = 2.55 − 0.96 log10 (DN)

Combined data

log10 (CBR) = 2.81 − 1.32 log10 (DN)

Soaked samples

log10 (CBR) = 2.76 − 1.28 log10 (DN)

Unsoaked samples

log10 (CBR) = 2.83 − 1.33 log10 (DN)

Smith and

Pratt11

Log10 (CBR) = 2.555 − 1.145 Log10 (penetration rate)

Chapter 4

Site Development

Introduction Site selection for new project is a lengthy process of decision making involving studies and assessment on multi-disciplinary aspects. It has to focus on location, topography, project requirements, statutory regulations, infrastructures, source of water and power and many more depending upon the nature of industry. Site is selected only after detailed cost–benefit analysis. The site is finally acquired after long land acquisition formalities. As geotechnical and foundation engineers have limited role in site selection, the topic is not included in the book. Main engineering activities to be undertaken at the selected site are presented in sequence of application. Industrial projects generally require large area of ‘good land’ which in most case is not available. Therefore, the site available in ‘as is’ condition needs to be prepared and developed for construction. This chapter deals with different aspects of site preparation and development. In undulating sites, high ground is cut and low areas are filled to designed grade level/s. Cutting earth/rock is not difficult as several methods, technology and modern high power equipment are available. But occasionally work may get stuck due to unusual problem where common methods may not be of much help. Simple methods adopted to overcome such difficult situations have been presented. Areas prepared by cutting/filling need compaction. Search on methods of compaction leads to a wide range of options, and it may be difficult to study them to select an appropriate approach. To simplify time-taking search process, different compaction techniques and equipments have been summarized for reference.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_4

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4 Site Development

Common problems of natural land are undulation, bush, marsh, shallow or deep pond, water body, low area near river/sea front. All such area generally require site-specific development by cutting high ground, filling low areas or combination of both depending on topography and project requirements. Taking advantage of existing topography, plant general layout is prepared on multi-terraced formation levels. Ideally, volumes of cut and fill should be ‘balancing’. Although, development by cutting is relatively easy, filling is difficult and challenging as it require several pre and post development activities. Methods of land development and compaction in difficult subsoil condition are available in books. However, certain preactivities such as dewatering soft marshy land, removal of mud and muck from pond bed, selection of types and sources of fill materials, mechanism for placement, compaction, etc. may not be readily available. Guidelines on such situations adopting practical approaches have been presented. Broad guidelines on use of different types of fill materials and equipment are discussed briefly for reference. Bulk material handling (import–export) projects are built in coastal region. Coastal lands are low and need to be developed by filling several meters up to design grade level requiring huge volume of fill material. Demand of huge fill material can only be met by dredging sand from river bed, sea floor, shipping channel and reclamation at site followed by mechanized compaction. Dredging being highly specialized branch of engineering adopting modern technology and costly equipment, geotechnical engineers may normally not be familiar with. Therefore, steps for capital dredging and reclamation have been covered broadly to familiarize with the technology. It is pointed out dredging and reclamation are highly professional work involving hightech, heavy equipment and is cost-intensive. Therefore, each project has to be dealt with site-specific considerations. An innovative approach for improving properties of ‘poor’ soil or ‘waste’ materials by mixing with ‘good’ earth based on the concepts of ‘design mix’ has been developed. For example, mixing soil with flyash improves engineering properties useful for construction of earth structures like embankments, dikes, etc. The concept and steps for ‘soil mix design’ have been explained through two worked-out examples.

Site Development by Filling and Compaction Fresh filling should never be done on parent ground. The ground surface should be stripped removing weeds, roots etc. before placement of fill, Ponds and water bodies to be dewatered, weeds, muck/slush to be removed from bed, allowed for natural drying before placing select fill materials: earth, flyash, silver sand, dredged sand, etc. Depending on site condition and availability of fill materials, appropriate methodology needs to be adopted. For example, in areas where groundwater is close to ground surface, pumping water from temporary well or trench could be helpful.

Site Development by Filling and Compaction

43

Slush/muck from bottom of pond may be removed by adopting ‘mud wave’ technique. These methods adopted successfully at project sites are discussed in following paragraphs.

Filling in Pond and Water Body Initial condition of a portion of proposed site for coke oven battery project in Haldia, West Bengal is shown in Fig. 4.1. The pond was used for collection of rain water and supply to plants. Large area including the pond of 5–8 m water depth was earmarked for an important plant unit. The area including the pond needs to be filled up and compacted (engineered fill) for setting up plant units fulfilling stiff settlement criteria. After several option studies, scheme for pond filling and development were planned on following lines: • Pond is to be dewatered, weeds/plants, bush, vegetation, etc. up-rooted and removed • Procedure based on ‘gravity separation technique’ shall be adopted to remove slush/muck from pond bed by ‘pushing’ a sufficiently high heap of fill material to develop ‘mud wave’ • Slush ‘pushed’ toward sides/corners of pond for mechanical/manual removal • Selected fill materials to be placed in layers and mechanically compacted with static and vibratory roller.

Fig. 4.1 Original condition of the plant site

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4 Site Development

The steps for ‘mud wave’ technique and dewatering marshy land are discussed in following paragraphs.

Removing Bed Mud by ‘Mud Wave’ Technique After pumping out, water from pond next step is to remove thick deposits of soft mud/slush from pond bed. Commonly old mud (up to knee deep) exists in very soft to soft state. Lowering equipment can be risky. An incident during mechanized removal mud from pond bed at site explains potential dangers of soft mud. Several ponds of moderate to great depths existed within the site. One such pond with moderate water depth was dewatered and air dried before removal of bed mud. A Poclain was lowered to remove mud from bank areas. On a working day, heavy rain started from mid-day and continued till next morning. Work had to be abandoned. But an unpleasant surprise was waiting for next morning. The Poclain sunk into mud and only the raised bucket was visible. This shows how deceiving/treacherous soft mud can be. Thereafter, it was decided to adopt indirect method for removal of soft bed mud. Steps for creation of mud wave are outlined below. The procedure based upon idea of ‘gravity separation’ is explained in a few simple steps: • Large volume of generally dry fill material is dumped near bank minimum up to 2 m height. • It then is pushed rapidly by dozers so as to fall in large volume and at great speed. • Energy of falling earth tries to reach pond bottom pushing soft mud in front. • After several ‘push’ in short interval, soft mud moves forward forming ‘wave’ in front of fill. • The process is repeated until major portion of the pond is filled up to predetermined level. • After sufficient area is filled by the method, it is compacted by lightweight equipment. • Next layer of fill material dumped near edge of freshly filled area. • The filling and compaction process are repeated until the pond is more-or-less filled up. • Filling to be planned to ‘push’ mud toward side/corner for ease of mechanical/ manual removal. Although the procedure appears simple, good planning, collection of sufficient fill material, inventory of earth moving and compaction machinery and above all strict safety and supervision have to be followed during entire operation including site clearing after completion of work. Procedure for ‘mud wave’ is shown schematically in Fig. 4.2 which is self-explanatory.

Site Development by Filling and Compaction

45

Fill material Pond (Dewatered)

Push by Dozer >2m

“Mud wave” mud/slush

Fig. 4.2 ‘Mud wave’ technique for removal of soft bed mud

Removing Water from Marshy Land Normally, marshy lands with shallow groundwater are soft to very soft and spongy. Movement of man and machinery is difficult and risky. Movement of earth moving vehicles, spreader, leveling equipments (grader/JCB/dozer/Poclain) and mechanical compactors is not possible. But if surface water can be pumped out and trapped water up to certain depth can be extracted, the area can be filled and compacted rather easily. Although surface water can be pumped out from a few pits dug along bank and pumping water out, extraction of trapped water below surface is not effective. In order to overcome the difficulty, two simple but practical approaches can be adopted. Few percolation wells of about 800–1000 mm diameter and 2–3 m deep dug manually. Sides protected with burnt clay rings and brick bats dropped at bottom to allow percolation of water from side and bottom. A few wells to be connected by pipe and water pumped out as required. In this process, groundwater up to certain depth can be lowered. Alternately, a few trenches of about 1½ m wide and 1½–2 m deep can be dug along/ across the area. Water accumulated in trenches will be pumped out periodically. In case of side collapse, trenches may be filled with coarse sand and brick chips. Water can be pumped out from some convenient spots. In these methods, ingress of water into well or trench will be more at initial stage and gradually slow down. After few days, the land can be approachable by man and light machines. A few taping points are to be maintained till completion of filling. Success of the schemes depends on careful and workable planning based on site conditions. Safety during excavation of dug well/trench in sequence, pumping arrangement, monitoring and other works must ensured. Schematic representation of dewatering from dug wells and trenches is shown in Fig. 4.3.

4 Site Development

Dug Wells in grid pattern

46

Trench Trench Open Trenches

Fig. 4.3 Dewatering from soft marshy land by dug well/trench method

Selection of Fill Materials Selection of type, source and quantity of fill materials poses great challenge because, required quantity of fill materials was not available locally. (a) Flyash is available from ash ponds of a thermal power plant located at about 80 km away. (b) Sand dredged from shipping channels in nearby port can be available. (c) Silver sand in small quantity is also available. Considering possibility of using all three types of fill materials, it was necessary to review technical and economic feasibilities of the fill materials. Outcome from the studies are summarized. (a) Filling with Flyash Method for collection of flyash from ash ponds and using at site is outlined briefly. Surface layer in ash pond is contaminated with vegetation, grass, shrubs, roots and organic matters which are to be discarded. Therefore, 500–600 mm thick flyash from surface will be excavated and disposed of. Any objectionable material found within flyash deposit shall be discarded. Clean flyash will be excavated and transported to site. To prevent dust nuisance, it must be covered with tarpaulin/plastic sheet during transportation and water sprayed on unloading. Filling using material other than earth to be done up to 500–1000 mm below finish formation level (FFL) and balance thickness to be covered with earth blanket to prevent dust pollution and for growth of vegetation. Flyash shall be placed in near-uniform thickness and allowed to dry to optimum moisture content. In case it is dry, water will be sprayed before compaction. Flyash is generally placed in layers of 300–400 mm thickness, spread by grader/dozer, adequately watered (about 2–3% below optimum moisture content) and mechanically compacted with vibratory roller

Site Development by Filling and Compaction

47

so that compacted thickness will be about 250–300 mm. For proper bonding between layers, surface of previously compacted layer is to be scarified and watered before placing new layer. Dredged or silver sand can be used in similar manner maintaining compaction moisture content slightly (3–5%) higher than optimum. Compaction is to be done to about 95% of maximum dry density. Field tests on moisture content and compaction control must be carried out simultaneously. Recommended tests on flyash: At source: Grain size distribution, unit weight, specific gravity, moisture content At placement: Placement moisture content, Proctor’s test. In order to achieve 95–97% compaction, vibratory roller is suitable. Typical data of vibratory roller for compaction control is presented in Table 4.1 for information. Compaction specification should be modified depending upon properties of fill materials and equipment used. The plant site including the pond (Fig. 4.1) was filled, compacted and finished as above and shown in Fig. 4.4. Table 4.1 Typical data of vibro roller Description

Range (Typ.)

Description

Range (Typ.)

Roller width

1.5–2.25 m

Roller weight

10–15 T

Amplitude of vibration

1.0–2.0 mm

Frequency of vibration

20–30 Hz

Roller speed

3–5 km/h

Number of passes

6 (min) to 8–10

Compaction moisture

30–39%

Fig. 4.4 View of the site after completion of site leveling

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4 Site Development

Mechanical Compaction Filled-up ground must be compacted to required density. Methods for compaction depend on properties of fill and technical requirements. Geotechnical engineer prepares specification and methodology for compaction based on results of laboratory tests. It is common practice to verify actual compaction by conducting field trials. If needed, the specification may be modified before start of work at site. As compaction criteria depend on several factors, specification should be prepared considering properties of fill material and technical requirements. Compaction of ground is achieved by impact, vibration or combination of both using mechanical equipments. Commonly used methods and equipments for compaction are briefly discussed below for information.

Vibratory (Dynamic) Roller Common practice for compaction of fill is by several passes of (8–12 T) capacity static roller. Static rolling has limitations. As compaction is imparted by self-weight of roller, depth and degree of compaction are limited in upper few meters and travel speed is slow. Static roller is commonly used for compaction of road sub-base. Some of the limitations of static roller have been overcome in vibratory roller. The front wheel/drum of roller can be vibrated at desired frequency and amplitude by the operator. Vibration imparted help in re-orientation of soil particles to denser configuration resulting in higher degree compaction. Moreover, roller speed can be much faster than static roller. Depth of improvement by vibratory roller is several meters and is also effective for finishing of surface layer. Soft ground or fresh fill can be compacted effectively by several passes (in perpendicular directions) of vibratory roller at moderate speed with varying frequency and amplitude as required. Medium and heavy-duty vibro rollers are shown in Fig. 4.5a, b for reference.

(a) Medium Vibro Roller (2-3 T)

Fig. 4.5 Vibratory roller in operation

(b) Heavy Duty Vibro Roller (5-7 T)

Mechanical Compaction

49

(a) Mechanical Compaction by Sheep-Foot Roller (b) Road Constructed on Compacted Embankment

Fig. 4.6 Compaction by vibratory sheep foot roller and road built on compacted embankment

Sheep’s Foot Roller Roller drum of Sheep’s foot roller is designed for imparting additional compaction. The drum is studded with specially designed metal sheep’s foot-like studs arranged in staggered manner. Normally, square studs of different size are used. The studs penetrate into loose soil up to their full depth to impart extra compactive effort. The roller is used for higher degree of compaction near surface which is beneficial for road construction. Sheep’s foot rollers are used in construction of highway and railway embankment, dyke where long stretch needs to be compacted. Figure 4.6a, b shows Sheep’s foot roller used in road construction and finished road. Roller drum of Sheep’s foot roller is designed for imparting additional compaction. The drum is studded with specially designed metal sheep’s foot-like studs arranged in staggered manner. Normally square studs of different size are used. The studs penetrate into loose soil up to their full depth to impart extra compactive effort. The roller is used for higher degree of compaction near surface which is beneficial for road construction. Sheep’s foot rollers are used in construction of highway and railway embankment, dyke where long stretch needs to be compacted. Figure 4.6a, b show Sheep’s foot roller used in road construction and finished road.

Dynamic Compaction/Consolidation (DC) In this method, improvement is achieved by repeated pounding of ground by heavy weight. A square or circular-shaped heavy hammer (10–15 MT) is lifted by crane to great height (5–15 m) and dropped freely on ground a number of times. Heavy weight falling freely from great height imparts high kinetic energy to underlying soil mass up to great depth. High energy of impact achieves compaction by reduction of voids and escape of water trapped in voids. Craters formed by impounding are filled with good earth or granular material. The work is carried out in grid pattern covering the entire area. Finally, the ground is carpeted with soil, leveled and compacted with

50

4 Site Development

vibratory roller. DC is noisy, causes considerable ground vibration, dust pollution and could damage nearby construction and installations. As cost for movement of a fleet of heavy equipment, crane and accessories are high, this technique is used only for very large project.

Vibratory (Vibro) Technique Deep vibro technique presents flexible solutions for improvement of soil by rearranging soil particles to very dense state. It works similar to concrete vibrator. Vibro compactor probe (mostly proprietary) of about 3 m long, 400 mm dia. weighing about 2400–4200 kg rotates at 25–30 cycles per second at 30–50 mm rotational amplitude. Both frequency and amplitude can be controlled depending upon soil type. This method is very effective in improving in-situ consistency and modulus of sub-soil up to great depth (several meters). The technique is economic, environmental-friendly and relatively quiet. The probe is lowered from a light mobile vehicle. For improvement of ground to greater depth, deep vibro technique (Ref. Chapter 5 on Ground Improvement) is adopted.

Rapid Impact Compactor (RIC) Soft ground can be compacted by imparting repeated impact energy by dropping weight from known height. RIC imparts energy by dropping 5–9 T weight (foot print up to 1.5 m dia.) through relatively small height (1.2–1.5 m) at 40–60 drops per minute. Energy of impact and frequency of drops can be varied depending upon nature of soil. Energy from impacts causes underlying soil particles to reorient and reach stable configuration to denser state. Crates formed by impacts are filled with granular materials, leveled and compacted by vibratory roller. RIC equipment operating at a site is shown in Fig. 4.7 and technical specification shown in Table 4.2.

(a) Rapid Impact Compactor (RIC)

Fig. 4.7 Rapid impact compaction

(b) RIC in Operation at Project Site

Land Development by Dredging and Reclamation

51

Table 4.2 Technical specification of rapid impact compactor equipment (Typ.) Manufacturer

BSP International Foundations Ltd., England

Height of equipment: 7.5 m

Width of rig: 3.55 m

Length of rig: 9.4 m

Working weight: 57.6 T (App)

Ram weight: 5, 7 or 9 T

Max. drop height: 1.2 m

Energy/impact: 6.0, 8.4 or 10.8 TM

Blows per minute: 40/60

Foot diameter: 1.5 m

Land Development by Dredging and Reclamation Land development by dredging sand from sea or river bed and deposition over land is practiced all over the world. Ports and harbors at Paradeep, Chennai, Goa and Mumbai were developed by dredging. Salt Lake City in Kolkata, West Bengal, was developed by dredging sand from Hooghly River. Sand dredged from river was pumped through pipelines and deposited over vast water-filled marshy lands generally up to 2 m above projected flood level. Now Salt Lake City is a modern planned township with highrise government, private office and residential complex, technology hub for IT and ITES services, manufacturing and infrastructures like Metro Rail and flyovers. Dredging and reclamation comprise of five basic activities namely: (a) collection of sand from river or sea bed by mechanical dredging, (b) transportation of sand in the form of slurry and pumping through network of pipelines, (c) deposition of sand slurry on land to be developed, (d) allowing water to escape after deposition of sand finally (e) dressing and mechanical compaction to desired degree. A large number of material handling projects are planned along coast lines. Development of such vast, soft and low areas requires huge quantity of fill material which can only be sourced by dredging from nearby river bed, shipping channel, sea floor and reclamation on low land. This being a relatively uncommon discipline, main steps for dredging and reclamation have been described in some detail for general information. It is cautioned, dredging and reclamation which are highly specialized disciplines of geotechnical engineering based on modern technology requiring large fleet of heavy and costly equipment and cost-intensive. Therefore, each project needs to be planned on merits of project and site-specific considerations. However, it is hoped the section will throw some insight on major aspects of land development by dredging and reclamation.

Strategy for Land Development For construction of port facilities like jetty, storage yard, etc. large area near sea/river bank needs to be filled and developed as per technological requirements. Planning should start from finalizing control parameters and end with completion of land preparation. Main steps for dredging and reclamation work and brief discussion on them are presented under following heads.

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4 Site Development

(a) (b) (c) (d) (e)

Finalization of finished grade/formation level (FGL/FFL) Criteria for fill material Selection of locations in river/sea suitable for dredging Methodology for dredging Transmission of sand-slurry through network of pipelines and booster pumping stations (f) On-site placement of slurry allowing excess water to escape (g) Selection of method to achieve required degree of compaction. Due to high cost of each activity, over-design is not permissible. Each activity should be planned carefully.

Finished Grade/Formation Level (FGL/FFL) Selection of finished ground/formation level (FGL/FFL) of site is to be taken based on judicious approach. It is important because even half-a-meter difference in fill level translates into big difference in quantity of fill material. Main objectives for selection of FGL are positive and permanent protection from (a) risks of flooding due to high tide, (b) heavy monsoon rain (c) wind-induced high wave, (d) natural drainage of rain water from filled-up land, (e) sea level rise due to global warming, etc. Detailed procedure for selection of FGL is presented in Chapter 10; results are summarized below for reference. Existing average ground level: + 5.3 m CD (Chart Datum—water level serving as origin on nautical chart) Highest high water level (HHWL) of sea: + 7.26 m CD Maximum wave height: 1.5 m + 0.75 m provision for future sea level rise due to ‘global warming’ Safe grade level works out as + 9.51 m CD, i.e. 6.69 m above mean sea level (MSL) Provision for estimated virgin ground settlement due surcharge from fresh fill. Based on the above, it emerges minimum grade level free from risks of flooding and natural drainage of rain water should be + 9.5 m CD. As existing average ground level is + 5.3 m CD, average thickness of fill up to. + 9.5 m CD will be 4.2 m. In case provision for ground settlement is considered (say 300 mm): Average safe grade level should be + 9.8 m CD, i.e. average 4.5 m of fresh fill.

Methodology for Dredging and Reclamation

53

Once FGL has been finalized, quantity of fill material is estimated. Then identification of locations in river/sea bed for dredging, methodology for extraction and transportation, deposition and compaction mechanism are to be finalized keeping cost and time factors into consideration. Strategy for land development is to be based on topographic, geotechnical, flood, rain, wind and wave pattern data.

Criteria for Fill Materials Probable locations for dredging are to be identified. Detailed underwater geotechnical investigation is to be carried out to assess depth of occurrence and thickness of materials adequate for suitable fill and their geotechnical properties. Underwater soil test is to be carried out from floating platform/Jack-up barge presented in Chap. 3. Fill material should be granular, non-cohesive, naturally occurring with minimum organic and deleterious matter contents. Following physical and engineering parameters are to be collected during soil tests. Preferred soil type: Medium dense brownish gray to gray silty fine sand with mica flakes. Typical physical soil parameters and preferred ranges are given below in Table 4.3 for guidance.

Methodology for Dredging and Reclamation Technology and methodology for reclamation of vast land by dredging are multidisciplinary and specialized field of engineering. Major equipments and accessories, steps for slurry transport, reclamation, compaction and testing are briefly discussed in following paragraphs for general information. Table 4.3 Preferred range of physical soil parameters

Geotechnical parameter

Range

Particle size: passing 63 μm sieve

10% maximum

Particle size: 63 μm to 100 mm

75% minimum

Maximum particles size 200 mm

10% maximum

Liquid limit

35% maximum

Plasticity index

6% maximum

Sulfate content

2.0% maximum

Chloride content

3.3% maximum

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4 Site Development

Major Equipment Large-scale dredging in sand bed commonly called ‘capital dredging’ is carried out following various dredging technology depending upon nature of dredging area and project. Dredging sand bed can be done by different methods, namely (a) heavy-duty suction, (b) hopper, (c) backhoe and (d) cutter-suction. For transportation, dredged sand is to be mixed with water to form slurry [(soil): (water) = (30–25%): (70–75%)] and pumped to reclamation site through floating and on-shore pipelines. This might call for permission from port and civic authorities. A heavy-duty suction dredger is shown in Fig. 4.8, and technical specification is presented in Table 4.4 for information only. Dredging agency shall arrange for (a) adequate inventory of plant and machinery like barges, floating cranes, tugs, launches, boats, etc. for use in water body; (b) dozer, pay loader, Poclain, JCB, hydra, static and dynamic rollers, etc. for laying, spreading and grading dredged materials; (c) construction and maintenance of temporary bunds/

Fig. 4.8 Heavy-duty suction dredger

Table 4.4 Technical specification of heavy suction dredger (Typ.) Typical sizes

Range

Typical sizes

Range

Overall length

84 m

Molded depth

4.25 m

Length and breadth of hull

67.5 and 15 m

Pumping distance

6 km (app)

Maximum draft with full bunkers

3.0 m

Power of pumps

2 × 3600 KW

Maximum depth of dredging

25 m

Power on cutter

1200 KW

Dia. of suction and discharge 800 and 750 mm Total installed power 11,400 KW pipes Power of submerged dredge pump

1000 KW

Productivity

≈ 0.8 mm3 per month

Methodology for Dredging and Reclamation

55

dykes on site. Dedicated positioning and survey instruments like electronic positioning system: (EPS) and geographical positioning system: (GPS) equipments are to be deployed.

Methodology for Dredging and Reclamation Land reclamation by dredging involves large fleet of heavy equipments both in water and on land. Deployment of specialized tools and techniques matching site condition and variations thereof are key to success of dredging operation. The work needs thorough planning, detailed survey, investigation, logistics, supply of spares, quality control and monitoring at every stage and coordination among all activities. The work should be carried out under strict supervision of qualified and experienced personnel and safety team. It is to be noted, dredging operation requires a number of statutory clearances/permission from local, state and central authorities before start of field work. Capital dredging and reclamation is a capital-intensive and time-consuming job. Primary activities in connection with capital dredging, reclamation and compaction are outlined below: (a) Survey: Topographic survey of fill areas, pipeline corridor; bathymetric survey at prospective dredging locations (b) Investigation: Geotechnical investigation including laboratory testing in areas of fill and at probable dredging locations in river channel, sea bed (c) Environmental impact and pollution study report are prerequisite statutory regulations (d) Development of detailed scheme for dredging, reclamation and compaction (e) Quality planning and monitoring by actual field and laboratory tests (f) Documentation: List of equipment, progress and results of quality control tests (g) Flexibility for modification arising out of site and weather condition. Fill area is to be divided into suitable compartments by building earthen dikes/ bunds up to required height where dredged materials in the form of slurry will be discharged; solids will settle and water allowed to escape through properly made and maintained drainage channels. Different stages of dredging, reclamation, compaction, shore protection and quality control field tests are illustrated in Fig. 4.9a–h.

Safety Capital dredging is huge operation involving fleet of heavy and modern equipment, accessories support vessels and experienced technical manpower and labor. The work being confined mainly in shallow and deep water body and muddy environment is

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4 Site Development

(a) Dredger in Operation at Sea

(c) Reclamation Process

(e) Leveling of Dredged Materials

(g) Edge Protection with Stone Pitching

(b) Floating Slurry Pipeline

(d) Channelizing Flow of Dredged Material

(f) Mechanical Compaction

(h) Field Compaction Test

Fig. 4.9 Different steps in dredging, reclamation, compaction

highly risky and hazardous. Therefore, strict safety and vigilance are required to avoid any untoward incident. The executing agency shall follow all safety precautions for prevention of injury or accidents and safeguarding lives, equipment and property. Dock safety and river safety regulations shall be observed strictly and safety officers will routinely inspect the works, plant, equipment, etc. First aid measures, rescue and lifesaving equipment must be available in proper condition readily available in case

Filling with ‘Design-Mixed’ Earth

57

of emergency. There should not be any compromise on safety aspect in all fronts and at all times.

Filling with ‘Design-Mixed’ Earth Methods of mixing earth with other materials (e.g. lime, cement, bentonite, chemicals) to improve properties for specific purpose are not uncommon. But systematic approach for mixing ‘good’ earth with ‘waste’ materials to render desired properties is not readily available. This section presents step-by-step approach for mixing waste materials with soil to develop composite earth good for construction of structured like embankment, dyke, etc. A simple mixing process to improve geotechnical properties of mixed earth and other materials termed ‘design mix for soils’ is outlined in this section. Step-by-step approach for design mix has been illustrated through two case studies for raising height of tailing dam and back-filling below coke oven battery floor. The methodology of mix design can be used with other materials as well, e.g. flyash, industrial wastes, slime with earth, sand, etc. for use in filling and construction.

Basis for Mix Design Basis for mix design is to fill majority of voids in coarse materials with fines to create compact configuration of grains to help improve important physical and geotechnical properties of the mix. For example, mixing fines with coarse materials increases cohesion with reduction in permeability to modify the mix to possess both cohesion (C) and friction (φ) [i.e. (C − φ) soil] suitable for use in filling and building various types of earth structures. Aim of the process is to develop ‘well-graded’ grain size distribution pattern characterized by ‘flatter’ slope of gradation curves of the mix over full ranges from fines to gravel/pebbles. A three-phased program for testing, simulation and confirmation is planned. In Phase-I, basic geotechnical parameters (grain size, strength, permeability, etc.) for all ‘good’ and ‘waste’ materials are to be determined separately and results studied to develop range of preliminary mixes to represent ‘well-graded’ pattern. Engineering properties of design-mixed materials are determined in PhaseII. This helps to ‘refine’ and finalize mix proportions. In Phase-III, confirmatory and special tests are performed on materials mixed in designed proportion. The steps are illustrated through two case studies on tailing dam and coke oven project.

58

4 Site Development

Steps for Mix Design Mine overburdens (OB) consisting primarily of sand, gravel, pebble, boulder and small fraction of silt and clay possess good friction angle (φ) but low cohesion (C) with high permeability (k). Slime comprising of coarse to fine silt sized particles with large clay fractions possess moderate friction (φ), high cohesion (C) and low permeability (k). Basis for mix design is to develop proportions of (φ) and (C − φ) components so that large voids in OB are filled with fines of slime to develop a dense compact conglomerate with reduced porosity. The mix is expected to possess better shear strengths (C and φ), reduced permeability and good compatibility which are essential for use in dam construction. A flow chart on testing program was prepared (Ref. Figure 4.10a). Case Study-1: Design-Mixed Earth for Raising Height of Tailing Dam In Phase-I study, total nine samples from selected sources were collected and tested in laboratory. Average grain size distribution patterns for coarse and fine materials were plotted in Fig. 4.10b. In Phase-II, preliminary mixing of average grain data carried out ‘numerically’ on desktop using results of Phase-I tests. Average patterns of both ‘coarse’ and ‘fines’ are mixed numerically in different proportions to best simulate ‘well-graded’ pattern and corresponding grain distribution patterns displayed interactively. Three mix proportions of coarse (E) and fines (S), namely M1 (60E: 40S), M2 (50E: 50S) and M3 (40E: 60S) were selected for further study. Three sets of samples were prepared in laboratory by mixing them in above proportions. Grain size pattern of each mix was determined in laboratory and shown in Fig. 4.11. Laboratory tests were conducted to evaluate engineering parameters of designmixed samples and average results of three sets of tests are summarized in Table 4.5. In Phase-III, desired mix proportion of course and fines to match design requirements was determined after several trials and laboratory tests. In order to re-confirm properties of final design-mixed soil, large shear box (30 × 30 cm) test was conducted. Based on results of all tests, ranges of design soil parameters were selected.

Construction with Design-Mixed Earth During initial stage of construction, difficulty may be faced on how to mix huge volumes of ‘good’ and ‘waste’ or coarse and fine materials in design-mixed proportion at construction site. Several options may be tried. Normally, number of dumperloads of ‘coarse’ and ‘fine’ materials based on designed mix proportion are stacked in adjacent heaps. Mixing is done by dozer, grader and JCB. This could be a satisfactory option. The mixed materials are then spread in layers, watered and compacted with static and vibratory rollers to specified degree of compaction and finish as shown in Fig. 4.12a, b.

Filling with ‘Design-Mixed’ Earth

59

PHASE-I

FINE MATERIALS

COARSE MATERIALS

Source

OVERBURDEN DUMP

Samples Number

OB-1

Average

OB-2

OB

HILL SLOPE

H-1

H-3

H

EMBANKMENT

OLD SLIME DUMP

E-1

OSD-1

E-2

E

OSD-3

ACTIVE POND

S-2

OSD

OBH FINES

COARSE

PHASE-II

M-1

Trial Mix : Mixing of coarse and fine materials

M-2 M-3

DESIGN MIX

(a)

(b) Fig. 4.10 a Flow chart for lab test on borrow. b Average grain size distribution curves for all samples

60

4 Site Development

Fig. 4.11 Grain size patterns after preliminary design mix Table 4.5 Soil parameters of laboratory mixed samples Parameter γ

Fines

Coarse

M1 (60:40)

M2 (50:50)

M3 (40:60)

Average

(kN/m3 )

22.5

22.67

23.44

22.38

22.81

22.87

OMC (%)

12.0

16.4

14.7

12.0

16.6

14.46

C (kPa)

9.0–13.5

~ 14.0

19.5

21.0

21.0

20.5

φ (°)

10–12

33–43

31

28

25

28

k × 10–6 (cm/s)

1.43

–

73.3

60.9

2.38

45.5

(a) Dumps of OB & Slime Stacked in Designed Proportion (b) Mixed by Dozer at Site & Compacted

Fig. 4.12 Construction with design-mixed earth

Filling with ‘Design-Mixed’ Earth

61

Case Study-2: Design-Mixed Granular Backfill Below Coke Oven Battery Floor The mix design method was used successfully in another project in selecting sands for controlled compacted granular backfill below coke oven battery floor which will be subject to sustained high temperature (~ 700 °C). The backfill is required to achieve safe bearing capacity of 12 T/m2 with only marginal settlement and remain stable under permanently hot environment. The difficult selection process involved 12 mostly natural materials (granitic stone dust, high silica sand, concrete grade sands from several sources) and granulated blast furnace slag. The grain size distribution patterns of the samples are shown in Fig. 4.13. Method of mix design presented above has been applied. Only three out of twelve samples tested were selected for use. The controlled compacted backfill below RCC coke oven floor was designed in two layers, each divided into sub-layers compacted mechanically to specified degree. The backfill work was checked regularly by conducting penetration tests and finally verified by conducting plate load tests. Compacted backfill is shown in Fig. 4.14. It was observed that the compacted bed built with design-mixed sands attained in-situ modulus of over 5000 T/m2 and estimated settlement under design load was 1.53 mm only.

0.05

0.5

Particle Size (mm)

5

50

100.0

90.0

80.0

% Passing

70.0

60.0

1. Gran Slag 2. Stone Dust Bakira-1 Bakura-2 Bakura-3 Bakura-4

50.0

Bakura-5 40.0

30.0

20.0

Bakura-6 BakuraAvg. 4. Used Sand

10.0

0.0

CLAY

SILT FINE

MEDIUM

SAND COARSE

FINE

MEDIUM

GRAVEL - PEBBLE - BOULDER COARSE

Grain Size Distribution Curves

Fig. 4.13 Grain size curves for selected materials

FINE

COARSE

COBBLE BOULDER

62

4 Site Development

Fig. 4.14 Backfill after compaction

Benefits of Design-Mixed Earth In many old thermal power plants and mines, large areas are kept occupied by ‘dead and closed’ ash and tailing ponds. Also, dumps of overburden are seen in mines. Both flyash and dry tailing are ‘waste’ materials but cannot be disposed of for want of space and environmental hazards like dust pollution, contamination of groundwater and as such vast valuable lands are wasted. In case flyash or mine wastes can be utilized in construction after improvement, it will solve environmental and groundwater problems. Most important, vast lands kept occupied by dumps and ash/ tailing ponds can be vacated for future expansion project. Drainage and environmental problem associated with the dumps are avoided. Method of ‘design mix’ can be used for other materials, e.g. flyash, furnace and other industrial wastes, tailings with earth, sand, etc. for use in construction of embankment, road sub-base, landfill, flood protection bund, etc.

Chapter 5

Ground Improvement

Introduction Aspects of ground preparation, development and compaction have been covered in Chap. 4. The fact that compaction is done on ground surface, improvement by ‘on ground’ methods are effective primarily in upper levels depending upon soil type and input energy. The methods are not effective for improvement at greater depths. But improvement of soft ground at greater depths is necessary for economic design and construction of foundation avoiding piles. This chapter has been planned on methods of ‘in-ground’ improvement up to desired depths. The methods are based on principles of both ‘compaction’ (escape of air from void associated with re-orientation of soil particles) and ‘consolidation’ (escape of pore water) and/or combination of both. Improvement to great depth can also be achieved by adopting advanced technology by imparting vertical and radial vibrations of controlled frequency and amplitude into ground up to great depth. Ground improvement is a vast specialized field of geotechnical engineering and is widely covered in books, codes, publications and internet. Purpose of this chapter is mostly practice-oriented. It starts with basic concept, model of soil-structure interaction for improvement, governing formulae, main steps for design calculation, safety factor, working details, study alternative methods of ground improvement and ends with ‘cost and time’ analysis for the alternative methods to help in decision-making process. In general, sub-soil in coastal and river basins consist primarily of very soft to soft to medium alluvial deposits underlain by stiff clay and overlain by silty sand. Upper soft layers can be improved adopting ground improvement techniques. Methods commonly used for ground improvement have been covered in this chapter.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_5

63

64

5 Ground Improvement

Ground Improvements Techniques Soft soils with poor strength and high settlement potential are generally considered unsuitable for construction but the ground can be improved by adopting improvement technique. Different methods are adopted for improvement. But selection of suitable method depends on ‘cost–benefit’ study on applicable methods. The methods are commonly used for large loaded areas e.g. material stockpile, tank farm, embankment, etc. Common methods for improvement of soft ground: Sand Drain:

These are drainage paths artificially installed in soft cohesive layers to achieve accelerated consolidation under influence of surcharge to improve consistency and shear strength. Sand Piles: Closed-end steel casing tubes are driven in soft soils, filled with graded sand, gravel and compacted while lifting the casing tube in stages. This is also known as ‘compaction piles’. Lime Injection: Injecting small quantity (2–4%) of lime into soil is known to improve consistency, CBR, swelling properties. Proper injection at deeper strata being uncertain, such treatment is generally limited only to near-surface layer. Stone Column: Stone column is well-known ground improvement technique and widely used in projects. A hole is made either by driving closed-end steel casing tube or conventional soil boring tool, filling with graded stone and compaction in stages from bottom to top. Deep Soil Mixing: In this technique cement, lime and additives are mechanically mixed with soft soil. When solidified, cement-lime-soil forms ‘soft column’ of predetermined diameter and depth which acts as ‘reinforcement’ to soil. The technique is also known as ‘soft treatment’. The technique has advantage over other methods and is capable of achieving higher degree of improvement. Ground improvement plan needs to consider method of execution, availability of equipment and executing agency. If the engineer has access to basic concepts of improvement techniques, governing formulae in simplified form and desktop program for preliminary analysis, for estimating time and costs (based on given rates), he can study alternative methods along with time and cost benefits for comparison. Having all pertinent data on ground improvement in hand, he can prepare welldocumented comprehensive report on ground improvement work for taking informed decision. In this chapter, three commonly used methods of ground improvement, namely (1) stone column (SC), (2) deep soil mix (DSM) and (3) preconsolidation using prefabricated vertical drain (PVD) have been presented in detail along with workedout examples.

Stone Column in Cohesive Soil

65

Stone Column in Cohesive Soil Objective of stone column is to treat soft cohesive or alluvial ground having relatively low bearing capacity and high settlement potential by ‘compacting’ and ‘reinforcing’ up to required depth. Reinforcing in the form of ‘compacted granular column’ of designed diameter up to required depth constructed in grid pattern, spacing and configuration. Ground improvement treatments are required for widespread loaded areas such as coal/ore stock pile, tank farm, filled-up site, embankments, etc. Load carrying capacity of treated ground may be estimated by summing up contribution from each of the following components: (a) Capacity of stone column resulting from resistance offered by surrounding soil mass against its lateral deformation (bulging) under axial load (Ref. Fig. 5.1) (b) Capacity of stone column resulting from increase in resistance offered by surrounding soil due to surcharge. (c) Bearing support provided by the intervening soil between the columns. Design of stone column is based on IS 15248 (Part-1): 2003. This standard (Part l) covers the design methodology as well as the construction techniques for installation of stone columns. The scope is limited to the computation of allowable loads and settlements for wide loaded area. Capacity based on bulging mode of failure of stone column is shown in Fig. 5.1. q (Load Intensity)

Fig. 5.1 Stone column with firm or floating support—bulging failure mode

2D 4D

D

66

5 Ground Improvement

Governing formulae for design of stone column are summarized below for quick reference. 1. Area replacement ratio (as ): aS =

AS AS = A A S + Ag

where A = area of stone column, Ag = area of ground surrounding column, A = total area within unit cell. 2. Stress concentration factor (n): n=

σS σg

where σs = average stress in stone column, σg = average stress in soil within unit cell. 3. Limiting stress on column bulging: ( ) φcol σv = (σr 0 + 4Cu ) . K col K pcol = tan2 45◦ + 2 where σv = limiting axial stress in column when it approaches failure due to bulging; σr L = limiting radial stress = (σr 0 +4Cu ); σr 0 = initial effective radial stress = K 0 . σv0 ; σv0 = average initial effective stress considering average bulge depth of 2 times diameter of column = 2γ D; K 0 = average coefficient of lateral earth pressure (1 − Sinφ) where φ = effective angle of internal friction. 4. Safe load due to column bulging: Q 1 = 0.5(π D 2 σv /4) where σv (yield load) defined above. 5. Mean radial stress due to surcharge: Δσr 0 =

qsafe (1 + 2K 0 ) 3

where Δσr 0 = increase in mean radial stress due to surcharge ‘q’; qsafe = C u . N c / 2.5 6. Safe load due to surcharge: Q 2 = 0.5(K pcol Δσr 0 A S )

Deep Soil Mixing (DSM)

67

7. Safe load from soil bearing: Q 3 = qsafe . A g A g = A − As 8. Overall safe load: Q = Q1 + Q2 + Q3 9. Sharing of load on soil and column: σg =

σ = μg σ 1 + (n − 1)as

where σg = vertical stress in surrounding ground and σs = vertical stress in compacted column. 10. Consolidation settlement of treated soil (S t ): σS =

n.σ μS σ 1 + (n − 1)as

St = m v . σg . H or m v . μs. σg . σ . H , mv = modulus of volume compressibility of soil St =

1 xS = βS 1 + (n − 1)a S

where S = consolidation settlement of untreated ground computed from onedimensional consolidation theory = m v σ . H where H = thickness of treated soil and β = settlement reduction ratio: β=

1 St = S 1 + (n − 1)as

where S t = settlement of treated soil and S = settlement of untreated soil.

Deep Soil Mixing (DSM) Introduction to Deep Soil Mixing (DSM) Soil mixing technique is primarily used for increasing shear strength, bearing capacity and reducing settlement potential of poor soils. This can also be used advantageously for vibration cut-off barrier, seepage control and other advantageous applications.

68

5 Ground Improvement

In deep soil mixing, lime and cement are mixed with soft soil to form ‘soft column’ (L-C column). The technology was developed by Kjeld Paus in the 1980s. It is a form of soil improvement involving introduction of cementitious compound (cement, lime or combination of both in different proportions) often referred to as ‘binder’ and mechanically mixing within soft soil from bottom to top. Dry binder is injected into soil up to required depth in a grid pattern. The columns serve dual purpose: (i) water from surrounding soil mass is drawn by binders for hardening resulting in increase of strength and lower compressibility of soft (L-C) columns and (ii) removal of moisture strengthens surrounding soft soil. DSM can be economic for improvement of soft ground for medium to moderately loaded foundation spread over large area, e.g. tank farm, raw material stockpile, embankment, stabilization of slope and deep excavation in soft cohesive soils, expansive clays, loose granular soils, pulverized ash, etc. Steps involved for DSM are briefly described below. The process requires penetration and mixing equipment specially manufactured for the purpose. The field works for forming stabilized columns involve four steps: • • • •

Penetration (not boring) by probe in grid pattern Completion of penetration to required depth Feeding binder, mixing with soil by rotary injector from bottom to top Completion of L-C column and withdrawal of probe.

Approximately, 100–150 kg of binder is commonly mixed per m3 of soft soil (silty clay or clayey silt). Development in strength of lime-cement column with time depends on soil type, quantity AND proportion of binder used. In most cases, strength starts to develop within a few hours and increases rapidly during first week, and about 90% strength is reached in about three (3) weeks. The soft columns should extend at least one row outside foundation area. Achieved improvement should be verified by conducting field tests. The design philosophy behind DSM is to produce a stabilized soil mass that mechanically interacts with surrounding natural soil. The intention is not to produce rigid pile-like elements which will attract major fraction of load. This method of ‘semi-rigid’ stabilization is often referred to as ‘soft treatment’ that can be achieved by designing with low binder content. This can achieve improvement of overall shear strength and modulus of soil. The applied load is partly carried by the L-C columns and partly by soil in between columns. Therefore, rigid column is not desirable since such treatment will prevent effectiveness of load distribution mechanism between soil and soft columns. Design philosophy of DSM is based on matching settlements of column and surrounding soil as schematically illustrated in Fig. 5.2a, b. The set of governing formulae for DSM are summarized for reference only. For further details need to refer book and literature. Standard nomenclatures in geotechnical engineering have been used and not re-defined here.

Deep Soil Mixing (DSM)

69

Fig. 5.2 Typical stress–strain behavior of soil and L-C column and pattern of L-C column

Governing Formulae Stress and Load on Stabilized Column 1. Column failure stress: σcol = 2Ccol + 3(σh + 5Csoil ) where σcol = stress in L-C column, C soil = cohesion in surrounding soil, σh = lateral earth pressure in soil 2. Creep stress in column: σcreep = m c . σcol where σcreep = creep stress in column, mc = standard constant depending upon soil type. 3. Young’s modulus of column E col = m E . σcreep Standard values of mc and mE depending upon soil type: Soil description

mc

mE

Clayey silt

0.80–0.9

150–200

Silty clay

0.8

150–200

Clay

0.7–0.8

150 (continued)

70

5 Ground Improvement (continued) Soil description

mc

mE

Organic clay

0.6–0.7

100

Peat

0.6

50–75

Silty, clayey sand

0.9

200–250

4. Allowable stress on column: σall = 0.7σcreep 5. Allowable load on column: Pall = σall Acol 6. Area of influence per column: ( Ai =

Pall q

)

Shear strength of column. 7. Undrained shear strength: τu = Ccol Composite soil parameters. 8. Area replacement ratio: ( a=

Acol A

)

9. Undrained cohesion: Cu = a . Ccol + (1 − a) . Csoil 10. Undrained friction angle: φu = Tan−1 [a . tan(φcol ) + (1 − a) . tan(φsoil )] 11. Composite modulus: E = a . E col + (1 − a) . E soil

Installation of L-C Column

71

12. Drained cohesion: Cd = a . Cd col + (1 − a) . Cd soil 13. Drained friction angle: φd = Tan−1 [a . tan(φd col ) + (1 − a) . tan(φd soil )] Above formulations are based on following considerations: (a) Settlements of soil and stabilized columns will be of the same order to ensure compatibility. (b) Resultant settlement of treated ground is less than 0.5% of treated depth. (c) Allowable stress on column to be 70% of creep stress.

Installation of L-C Column Normally, diameter of L-C column ranges between 600 and 800 mm and spacing varies from 1.0 to 1.5 m in square or triangular grid. The columns should terminate into hard or competent layer. About, 90% of final strength of L-C column is reached within three weeks. The DSM technique is capable of attaining safe bearing capacity up to 250 kPa or more where upper layers are soft but followed by stiff to hard strata.

Steps for Mixing L-C and Installation of Column Scheme for mixing and injection inside ground is shown in Fig. 5.3a. Step-1: Completion of bore up to bottom level by penetrating with the ejector probe. Step-2: Dry cement and lime discharged in tank in designed proportion and mixed well mechanically. Step-3: Cement-lime mix is supplied to ejector machine by feeder pipe. Step-4: Ejection of L-C mix into ground is done by specially designed tool attached to Kelley-mounted crawler vehicle (Fig. 5.3b). The ejector is pushed down into ground up to design depth. Dry L-C mix is injected under pressure and rotated for all-round mixing with soil to develop L-C column bulb. Step-5: The ejector is then lifted up to top of last bulb and the process is repeated. Step-6: Steps-4 and 5 are repeated till completion of one L-C column from bottom to GL. The equipment is then shifted to next location. The entire area is to be improved in this process.

72

(a) Mixing Arrangement of Cement & Lime Binder

5 Ground Improvement

(b) Ejection of Binder from Ejector Machine

Fig. 5.3 Scheme for mixing binders and ejection by ejector machine

Fig. 5.4 Steps for installation of L-C column shown schematically

Sequences for installation of L-C column mentioned above are shown schematically in Fig. 5.4. A 500–600-mm-thick compacted blanket of sand or granular material is necessary for even distribution of imposed load on improved ground. The blanket is to be laid covering entire improvement area and foundation to be constructed on compacted blanket.

Worked-Out Examples Techno-economic studies on improvement of ground achieved using (a) stone column (SC) and (b) lime-cement (L-C) column (DSM) have been studied for two sites. For this purpose, foundations of (a) coke oven battery raft (b) coke stockpile of thermal power plant have been selected for comparison.

Worked-Out Examples

73

Table 5.1 Generalized sub-soil profile of coke oven battery site (three layers) Soil parameter

Layer-I

Layer-II

Composite (I and II)

Layer-III

Soil type

Med stiff silty clay

Very soft silty clay

Med to stiff silty clay

Med. dense silty sand

Thickness (m)

3.0

7.0

10.0

8.2

N-value

5–8

2–3

–

25–40

Unit wt. (kN/m3 )

19.0

17.7

18.1

18.5

Cohesion (kPa)

37

20

25

0

Friction angle

0º

0º

0º

32º

Consolidation mv (m2 /kN)

3.0 × 10–4

3.7 × 10–4

3.49 × 10–4

–

Soil investigation data, technological requirements of foundation, control data for design with SC and DSM, results of analysis using simple desktop programs have been presented in this section. Additionally, for comparison and preparation of project implementation schedule, estimated cost and time for each raft adopting SC and DSM were worked out based on unit rates of raw materials and productivity at site. The input and results are summarized in following paragraphs which show great advantage of ground improvement over piles. Example 1: Raft Foundation for Coke Oven Battery (CO) Generalized sub-soil stratigraphy of the site is shown in Table 5.1. Soil at top 10 m was very soft with low bearing capacity and very high settlement. Each coke oven battery was designed to rest on (53 m × 14 m) raft resting at 1.5 m below FGL. Initially, it was planned to support raft on medium diameter bored piles. Estimated cost and time being high, alternative methods, namely: (a) stone column (SC) and (b) deep soil mixing (DSM) were explored. As PVD is advantageous mainly for large spread-out area and not for separated foundation blocks, PVD was not considered.

Technological Requirements for Battery Raft Technological requirements for (53 m × 14 m) CO battery raft resting at 1.5 m below GL, subjected to uniform load of 90 kPa for settlement limited within 50 mm. Estimated safe bearing capacity and settlement of the CO raft resting on virgin ground works out as 56 kPa and 186 mm, respectively, both of which far exceed design requirements. Therefore, ground improvement adopting SC and DSM was studied. Choices of materials for SC and DSM are described below.

74

5 Ground Improvement

(a) SC: Stones for column should be well-graded sound crushed stone/rock of size 75 mm down to 2 mm. (b) DSM: Cement and lime (in 75 and 25%) to be mixed well @ 150 kg /m3 of soil using special injector-cum-mixing equipment. Mixing can be done by wet or dry process depending on moisture content. Analysis was carried out using simple spreadsheet program wherein soil, site and design requirements were input. Different arrangements of column diameter, grid pattern and spacing, depth were tried and time and cost aspects of both options were worked out for overall comparison. Final results are summarized below.

Stone Column (SC) Design of ground improvement using stone columns was carried out following the set of formula given earlier using simple Excel program. Different options were tried, and the optimum design shows the following pattern. Stone column: Diameter = 800 mm, length = 10 m, spacing = 1.78 m in square or 2.7 m in triangular grid. In total, 350 Nos. of stone columns spaced @ 2.70 m c/c in triangular grid are required for each raft including one outer row of columns at periphery.

Deep Soil Mixing (DSM) Calculations for ground improvement by DSM were made using formulae presented earlier and following arrangement was found suitable. L-C columns: Diameter = 800 mm, length = 11 m, spacing = 1.94 m in square or 2.94 m in triangular grid. Total 335 Nos. of lime-cement columns spaced @ 3.0 m c/c in triangular grid are required for the raft including one additional outer row.

Cost and Time In order to compare estimated time and cost for each raft on stone columns and lime-cement columns, cost analysis was carried out considering following unit rates (Table 5.2) for material and workmanship. It is to be noted the study was conducted during (2006–2007) when rate were not as high as at present. Results of analytical study, improvement that can be achieved in soil parameters, bearing capacity, settlement, cost (including provision of 500 thick sand blankets) and time study are summarized in Table 5.3. Example 2: Stacker-Reclaimer Track Foundation for Thermal Power Plant The site is characterized by two soft layers of 2.0 and 5.0 m thickness at top. Soil profile

Worked-Out Examples

75

Table 5.2 Unit rates considered for cost analysis in Example 1 (2006–2007) Stone column

Lime-cement column

Description

Unit rate (Rs.)

Description

Unit rate (Rs.)

Graded stone

1200/m3

Cement

200/bag

Labor charges

250/m of column

Lime

150/bag

Productivity

4 Col per rig-day

Installation

400/m of L-C Col

Productivity

5 Col per equipment/day

Notes for L-C Col (1) Cement: Lime @ 75%: 25%; (2) L-C mixing with soil @ 150 kg/m3

Table 5.3 Results of ground improvement analysis for Example 1 Design considerations, soil data, results of analysis

Untreated ground

Diameter of column (mm) Length of column (m)

Ground improvement by Stone column

L-C column

–

800

800

–

10

11

Grid spacing (m)

–

1.78 □ (square) 2.70 Δ (triangular)

1.80 (square) 2.75 (triangular)

Cohesion: C (kPa)

25

–

30

Friction angle: φ (°)

–

–

6º

–

7.74 × 10–5

Consolidation: mv

3.49 ×

(m2 /kN)

10–4

Total no. of columns

–

350

335

Safe bearing capacity (kPa)

56

90

104

Estimated settlement (mm)

186

122

42

Estimated cost (Rs. Million)

–

3.5

2.9

Time frame (Rig—days)

–

87

67

of stacker-reclaimer site is presented in Table 5.4. Soil at top 7 m was very soft with low bearing capacity and very high settlement. Tracks for stacker-reclaimer were to be laid on (350 m × 10 m) rafts resting at 1.5 m below FGL.

Table 5.4 Generalized sub-soil profile (2 layers) Soil parameter

Layer-I

Layer-II

Composite

Thickness (m)

2.0

5.0

7.0

Gama

(kN/m3 )

19.1

18.0

18.1

C (kPa)

40

23

28

φ (°)

0

0

0

4.20E−04

2.80E−04

3.20E−04

mv

(m2 /kN)

76

5 Ground Improvement

Technological Requirements The foundation shall be designed for uniform load intensity of 150 kPa for settlement restricted within 25 mm. However, estimated safe bearing capacity and settlement of parent ground worked out to 62 kPa and 207 mm, respectively, both of which were unacceptable. Therefore, ground improvement methods were explored. Analysis was carried out considering specification and proportions of materials considered in Example 1.

Stone Column (SC) Design of ground improvement using stone columns was carried out as before. Different options were tried, and the optimum design yields the following pattern. Stone columns: Diameter = 800 mm, length 8.0 m, spacing = 1.15 m in square or 1.75 m in triangular grid. In total, 3300 Nos. of stone columns spaced @ 1.15 m c/c in square grid are required for the raft including one outer row of columns at periphery.

Deep Soil Mixing (DSM) Calculations for ground improvement by DSM were made and following arrangement was found suitable. L-C columns: Diameter = 800 mm, Length = 8.0 m, Spacing = 1.36 m in square or 2.07 m in triangular grid. Total 2650 Nos. of lime-cement columns spaced @ 1.36 m c/c in square grid are required for the raft including one additional outer row.

Cost and Time Study In order to compare estimated time and cost for each strip on stone columns and limecement columns have been worked out considering following unit rates as shown in Table 5.5. It is pointed out the rate considered were old (2008–2009) when the study was conducted and rates were much lower than present. Results of analysis and improvement that can be achieved in soil parameters, bearing capacity, settlement, cost (including provision of 350 thick sand blankets) and time study are presented in Table 5.6.

Worked-Out Examples

77

Table 5.5 Unit rates considered for cost analysis in Example 2 (2008–2009) Stone column

L-C column

Description

Unit rate (Rs.)

Description

Unit rate (Rs.)

Graded stone

900/m3

Cement

290/bag

Labor charges

500/m of column

Lime

170/bag

Productivity

4 Col per rig-day

Installation

250/m of L-C Col

Productivity

12 Col per equipment/day

Notes for L-C Col (1) Cement: Lime @ 100%:0%; (2) L-C mixing with soil @ 350 kg/m3

Table 5.6 Results of ground improvement analysis for Example 2 Parameter

Untreated ground

Ground improvement by Stone column

L-C column

C (kPa)

28

–

50

φ (°)

Nil

–

9

mv (m2 /kN)

3.20 × 10–4

–

3.85 × 10–5

Column dia

800 mm

800 mm

Spacing(SQR)

–

1.15 m

1.36 m

Spacing(TRG)

–

1.75 m

2.07 m

No. of cols

–

3500 (sqr)

2650 (sqr)

Column length

–

8.0 m

8.0 m

SBC (kPa)

62

150

163

Settl. (mm)

207

100

24

Cost (Rs. lakhs)

–

300

325

4

12

875

225

Progress/day Time. rig-days

–

The track foundation originally was designed considering 450 mm diameter piles requiring about 750 piles costing about double the costs of ground improvement. Above case studies show significant merits of DSM over SC for improvement of soft cohesive soils. It however is to be kept in mind that success of both methods depends exclusively on quality assurance (QA) and control (QC) starting from soil investigation, material selection (stone, cement, lime), proper mixing, execution and workmanship. Boring and prevention of bore collapse, pouring stone material or mixing L-C, stage-wise compaction, workmanship, etc. should be monitored strictly by skilled personnel. It is advised that field verification tests are conducted routinely up to completion of work.

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5 Ground Improvement

Preconsolidation with Prefabricated Vertical Drain (PVD) Method of improvement of soft ground by ‘preconsolidation’ is based on ‘dissipating pore water’ from soil mass through designated drainage paths under surcharge from temporary preloading in stages. The mechanism of extracting water is based on principles of three-dimensional (3D) consolidation. Mathematical formulation of 3D consolidation is somewhat complex and not necessary for design of improvement with PVD. Instead, basic concepts, governing formula, tables on time factors for various degrees of consolidation have been presented. Ground improvement adopting PVD is used successfully at industrial project sites. Concept of PVD is based on accelerating consolidation with prefabricated vertical drains under surcharge to ensure completion of maximum settlement associated with increase in shear strength during preloading process. It enjoys several advantages over other methods of improvement especially for large areas like ore/coal stockpile, container/truck terminal, tank farm, etc. Although PVD is a specialized field of geotechnical engineering, attempt has been made to introduce theory to practice of ground improvement adopting PVD in simplified form under following sub-heads: (i) (ii) (iii) (iv) (v)

Basic concept and theoretical formulation of 3D consolidation Governing formulae Selection of geotechnical and design parameters Worked-out example Execution and monitoring.

Lastly, comparison of benefits of ground improvement by above three methods, namely stone column (SC), deep soil mixing (DSM) and PVD at project sites have been presented. Basic concept and theoretical formulation of 3D consolidation are briefly discussed below for reference. For detailed theoretical development on the subject, the reader needs to refer textbooks, codes and literature.

Basic Concept Schematic arrangement and boundary conditions for accelerating 3D consolidation with permeable vertical drains are shown in Fig. 5.5 which is self-explanatory.

Governing Formulae The general differential equation governing 3D flow of water in consolidation process has two components vertical and radial flow: (1 − U ) = (1 − Uz ) × (1 − Ur )

Preconsolidation with Prefabricated Vertical Drain (PVD)

(a) General Arrangement

(b) Plan of Drainage Well Pattern

79

(c) Radial Flow to Drain

Fig. 5.5 Scheme for PVD: arrangement and theoretical model

U, U Z and U r are degree of consolidation for combined 3D, vertical U z and horizontal/radial flow. U z and U r are defined as: Uz = 1 −

m=α ∑ m=0

2 −M 2 Tz (2m + 1)π , m = 0, 1, 2, . . . . e where M = M2 2

8Tr n2 3n 2 − 1 ) x ln(n) − Ur = 1 − e− F(n) where Fn = ( 2 4n 2 n −1 R s where n = and r = . rw 2

r w is equivalent radius of PVD and R is equivalent radius of area of influence of PVD. Time factors for vertical and radial flow are given by: Tv =

Cv t Cr t and Tr = 2 H 2R 2

where T v and T r are time factors for vertical and radial consolidation C v and C r are coefficient of vertical and radial consolidation H = length of drainage path in vertical direction, i.e. total thickness of soft layers. Degree of consolidation can be obtained solving the general differential equation: (1 − U) = (1 − U z ) × (1 − U r ). Values of U z are available in textbooks and values of U r can be determined by solving radial flow equation and radial time factor (T r ) is presented in Table 5.7.

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5 Ground Improvement

Table 5.7 Time factors for vertical consolidation due to radial drainage Degree of Time factor T r consolidation R 10 15 rw = Ur % 5

20

25

30

40

50

60

80

100

5

0.006 0.010 0.013 0.014 0.016 0.017 0.019 0.020 0.021 0.023 0.025

10

0.012 0.021 0.260 0.030 0.032 0.035 0.039 0.042 0.044 0.048 0.051

15

0.019 0.032 0.040 0.046 0.050 0.054 0.060 0.064 0.068 0.074 0.079

20

0.026 0.044 0.055 0.063 0.069 0.074 0.082 0.088 0.692 0.101 0.107

25

0.034 0.057 0.071 0.081 0.089 0.096 0.106 0.114 0.120 0.131 0.139

30

0.042 0.070 0.088 0.101 0.110 0.118 0.131 0.141 0.149 0.162 0.172

35

0.050 0.085 0.106 0.121 0.133 0.143 0.158 0.170 0.180 0.190 0.208

40

0.060 0.101 0.125 0.144 0.158 0.170 0.188 0.202 0.214 0.232 0.246

45

0.070 0.118 0.147 0.169 0.185 0.198 0.220 0.236 0.250 0.291 0.288

50

0.081 0.137 0.170 0.195 0.214 0.230 0.255 0.274 0.290 0.315 0.334

55

0.094 0.157 0.197 0.225 0.247 0.265 0.294 0.316 0.334 0.363 0.385

60

0.107 0.180 0.226 0.258 0.283 0.304 0.337 0.362 0.383 0.416 0.441

65

0.123 0.207 0.259 0.296 0.325 0.348 0.386 0.415 0.439 0.477 0.506

70

0.137 0.231 0.289 0.330 0.362 0.389 0.431 0.463 0.490 0.532 0.564

75

0.162 0.273 0.342 0.391 0.429 0.460 0.510 0.548 0.579 0.629 0.668

80

0.188 0.317 0.397 0.453 0.498 0.534 0.592 0.636 0.673 0.730 0.775

85

0.222 0.373 0.467 0.534 0.587 0.629 0.397 0.750 0.793 0.861 0.914

90

0.270 0.455 0.567 0.649 0.712 0.764 0.847 0.911 0.963 1.046 1.110

95

0.351 0.590 0.738 0.844 0.926 0.994 1.102 1.185 1.253 1.360 1.444

99

0.539 0.907 1.135 1.298 1.423 1.528 1.693 1.821 1.925 2.091 2.219

KELLMAN after substituting all components in relationships for F n and neglecting (− 1/4n2 ), simplified the time required for consolidation with PVD as below: ( ) ) ( 1 D2 R t= x ln − 0.75 x ln 8C vr 1 − Ur rw

Selection of Geotechnical Design Parameters Success of ground improvement using PVD depends primarily on evaluation and selection of design soil parameters representative for the site. Detailed geotechnical

Preconsolidation with Prefabricated Vertical Drain (PVD)

81

investigation work covering the development area is to be carried out including sufficient number of laboratory tests for (i) undrained shear strength (C u ), (ii) coefficient of consolidation (C v ) and (iii) permeability (k). For design of PVD three soil parameters are important: (i) gain in shear strength with increased percent of consolidation (C u /p' 0 ), (ii) coefficient of radial consolidation (C vr ) and (iii) coefficient of permeability (k). (a) Gain in Shear Strength Gain in shear strength with progressive consolidation is to be evaluated at various stages of improvement using PVD. (C u /p' 0 ) value is commonly adopted for evaluating total shear strength during and after improvement. Commonly used relationships of (C u /p' 0 ) are reproduced below for reference. (i) Empirical approach after Skempton (1957) and Henkel (1960): ( ) ΔCu = 0.11 + 0.0037 I p Δp0' where I p = Plasticity index, ΔC u and Δp0' are increase in shear strength and effective overburden pressure. Total shear strength after improvement C u = C u0 + ∑(ΔC ui × U i ) where U i is percentage of consolidation. (ii) Empirical approach following Bjerrum and Simson (1960): ( ) Cu / p0' = 0.45(I p )0.5 for I p > 0.5 ± 25% (iii) Empirical approach following Karlsson and Viberg (1967): ( ) Cu / p0' = 0.50 Wi, for Wi > 0.2 ± 30% Wi = water content ( ) (iv) In absence of dependable Cu / p0' data, values around 0.3 are often considered. ( ) (v) However, a simple but logical approach for evaluating representative Cu / p0' value based on laboratory test results for a site is outlined. For every (strength ) effective overburden pressure p0' are test, value of C u and corresponding ( ) ' calculated ( )to determine Cu / p0 values and are tabulated depth-wise. Profiles ' (of Cu /' )p0 versus depth for all boreholes are plotted. Representative value of Cu /(p0 for)compressible layer can be selected from the plots using judgment. The Cu / p0' value can be adopted in design of PVD. (b) Coefficient of Radial Consolidation (C vr ) Determination of representative coefficient of radial consolidation is complex. Therefore, common practice is to use correlations between radial (C vr ) to vertical (C vv ) coefficients of consolidation. As such evaluation of representative value of (C vv ) for the layer is important. Consolidation tests are conducted on maximum number of samples. Values of (C vv ) for anticipated pressure range are tabulated depth-wise.

82

5 Ground Improvement

Doubtful results are discarded. Representative value of (C vv ) for the strata is selected from normalized average value of (C vv ). It is pointed out, appropriate value of (C vr ) is important for evaluating real time for given degree of consolidation. Based on analysis of results of several well monitoring tests and experience, Sven Hansbo (1981) stated that ratio of (C vr ) to (C vv ) can vary widely between 1 and 5 depending on soil type. However, range of values between 1.5 and 3.5 is commonly used in practice. (c) Coefficient of Permeability (k) Because value of coefficient of radial consolidation (C vr ) is dependent on correlation , it is between vertical and radial coefficients of consolidation and as cv = k((1+e) a v γw important to determine representative value of coefficient of permeability (k) for the site. In preliminary design stage, ‘k’ based on laboratory test results can be considered. However, it is recommended to verify (k) value by conducting field permeability or pumping-out test before start of field work. Design Steps Steps for planning and design of ground improvement work adopting PVD: Step-1: Soil bearing capacity (SBC) of natural ground is to be evaluated following bearing capacity formula and results of laboratory tests. Maximum depth of surcharge backfill at the beginning will be guided by initial SBC. Also settlement of ground under load intensity equivalent to SBC is to be calculated. Step-2: Based on technological requirements of bearing capacity and settlement after improvement, determine the order of improvement in SBC to be achieved during improvement. Step-3: Assess time required for 90–95% consolidation with PVD matching project implementation schedule. Step-4: Design size, spacing and grid pattern and depth of PVD. Estimate thickness of surcharge required to achieve target consolidation within given time. Also, check if SBC is adequate to sustain full height of surcharge in one step or to be applied in stages depending upon gain in strength on completion of consolidation at each stage. This exercise is to be preceded before placing next stage of surcharge. Step-5: Check improvement achieved after maintaining final surcharge up to designed period by field tests. Step-6: Piezometers and settlement gauges are to be installed for monitoring progressive improvements and verification with design considerations.

Worked-Out Examples

83

Sequence of Work (a) Detailed geotechnical investigation works, field and laboratory testing covering entire site (b) Finalize general soil profile and design soil parameters with emphasis on consolidation and strength (c) Development of concept model of improvement work (d) Geotechnical designs using PVD to meet required improvements in soil parameters (e) Preparation of detailed work plan for procurement and execution (f) Execution of field work with continuous monitoring and periodical field tests. For better understanding, the steps are explained through two fully worked-out examples.

Worked-Out Examples Example 3 Stacker-Reclaimer Track Foundation Selection and estimation/ simulation of design soil parameters and steps for design adopting PVD technique is explained through an example of stacker-reclaimer track foundation at a thermal power plant in Haldia. Generalized soil profile and design soil parameters of the site are presented in Table 5.8. Based on analysis of results of shear strength and consolidation tests, following design parameters are selected. Table 5.8 Generalized sub-soil profile of stacker-reclaimer site (3 layers) Layer no.

Description of soil

I

Soft silty clay

II

Soft clayey silt

Thickness (m)

φ (deg)

mv (cm2 /kg)

N-value

Unit wt. (kN/m3 )

C (kPa)

2.0

3

19.1

40

0

4.2 × 10–4

5.0

2

18.2

23

0

2.8 × 10–4

IIIA

Loose sandy 12.5 silt

8

18.0

0

28

IIIB

Med. Silty sand

22

19.0

0

30

3.0

Soft Layers (I, II) are to be improved to achieve design safe bearing capacity (SBC) = 125 kPa Equivalent parameters of combined Layers I and II work out as given below I and II

Soft silty clay/clayey silt

7.0

2–3

18.0

28

0

3.2 × 10–4

84

5 Ground Improvement

(a) Cohesion: C = 28 kPa, Unit weight: γ = 18 kN/m3 (b) Relationship between Cu and corresponding effective overburden pressure (p' 0 ): (C u /p' 0 ) = 0.264 (c) Coefficient of consolidation in vertical mode: C vv = 1.67 × 10–3 cm2 /s, Say C vv = 5.3 m2 /year (d) Based on literature survey and strata description, coefficient of consolidation in radial mode (C vr ) has been estimated considering C vr = 2.7 × C vv = (2.7 × 5.3) = 14.31 i.e. C vr = 14.31 m2 /year.

Design Requirements Design SBC for (400 m × 10 m) Track foundation: SBC = 125 kPa. Layer Nos. (I and II) of 7 m thickness are soft and need to be improved to achieve SBC ≥ 125 kPa. For soft layers: SBC considering factor of safety (FoS) = 2.5, estimated SBC = 57.57 Say 57 kPa. Improvement in SBC required: (125 − 57) = 68 kPa. For SBC of 125 kPa (FoS = 2.5), C reqd = 60.8 kPa Say 60 kPa. Improvement in C required: ΔC reqd = (60–28) = 32 kPa. Improvement in corresponding p’0 required: Δp' 0 = 32/0.264 = 121 Say 120 kPa. Considering 95% consolidation during period of preloading, required Δp' 0 = 126.3 Say 125 kPa. Considering unit weight of surcharge backfill γfill = 18 kN/m3 , height of backfill = 6.9 m Say 7 m. Because allowable SBC (ABC) of original ground for C = 28 kPa and FoS = 2.0: ABC = 72 kPa. Considering unit weight of surcharge = 18 kN/m3 , height of Stage-I backfill = 4 m i.e. HI = 4.0 m. Therefore, backfill surcharge is to be placed in two stages: Sage-I: HI = 4 m and Stage-II: HII = 3 m.

Preliminary Design with PVD Prefabricated vertical drain size and shape: 100 mm wide × 5 mm thick strip ∼ = (b = 0.1 m x t = 0.005 m). Equivalent diameter d w = [2 x (b + t)]/π = 0.067 m, i.e. radius rw = 0.033 m. Arrangement of PVD and grid spacing: S = 1.5 m in □ square grid. Diameter of equivalent circle of influence of PVD: D = 1.128 S = 1.695 m or Radius: R = 0.847 m. n = (R/rw ) = 25.67 Say n = 25.

Worked-Out Examples

85

Stage-I Improvement Considering 90% consolidation in Stage-I under 4 m surcharge = (4 × 18) = 72 kPa. Referring Table 5.7 of U r for R/r w = 25, and 90% consolidation, T r = 0.712. For C vr = 14.31 m2 /year, time for 90% consolidation: t 90 = 0.1429 year ∼ = 52 days. Improvement in cohesion (ΔC) under surcharge of 4 m maintained for 52 days is to be evaluated. 90% consolidation due to 4 m surcharge Δq = 4 × 18 × 0.9 = 64.8 ∼ = 65 kPa. Improvement in cohesion (ΔC) = 0.264 × 65 = 17.16 ∼ = 17 kPa. C u |Stage-I = 28 + 17 = 45 kPa and correspond SBC considering Short term FoS of 1.75 = 132 kPa, i.e. improved ground can sustain backfill height of 7.3 m. Therefore, Stage-II surcharge of additional 3 m backfill can be placed for further consolidation.

Stage-II Improvement Considering 95% consolidation in Stage-II of additional surcharge of 3 m: (3 × 18) = 54 kPa. As before referring Table 5.7, for R/r w = 25 and 95% consolidation, T r = 0.926. For C vr = 14.31 m2 /year, time for 95% consolidation: t95 = 0.186 year ∼ = 68 days. So total duration of improvement in Stage-I and II = 52 + 68 = 120 days. Improvement in cohesion (ΔC) under surcharge of 3 m maintained for 68 days is to be evaluated. 95% consolidation due to 3 m surcharge Δq = 3 × 18 × 0.95 = 51.3 ∼ = 51 kPa. Improvement in cohesion (ΔC) = 0.264 × 51 = 13.46 ∼ = 13 kPa. C u |Stage-II = 28 + 17 + 13 = 58 kPa and correspond SBC with Short term FoS of 2.0) = 149 kPa > 125 kPa. However, Stage-I surcharge of 4 m will continue consolidation during Stage-II period of 68 day. T = 68 days ∼ = 0.1863 years. tCvr Corresponding ΔT r : ΔTr = (D) 2 = 0.928 which corresponds to nearly 95% consolidation. Δq = (4 + 3) × 18 × 0.95 = 119.7 ∼ = 119 kPa and (ΔC) = 0.264 × 119 = 31.4 ∼ = 30 kPa. Total C u |Stage-II = 28 + 30 + 13 = 71 kPa. Design cohesion after Stage-I and II consolidation C = 70 kPa. Correspond SBC considering FoS = 2.5 = 143.9 kPa Say 140 kPa ≫ 125 kPa.

86

5 Ground Improvement

Impact of Vertical Consolidation So far, influence of radial consolidation has only been considered. But vertical consolidation of soft layers will also occur simultaneously during the preloading period. Although contribution of vertical consolidation on overall consolidation will be small, let us look into it mainly for academic interest. Overall degree of consolidation (U) is given by: (1 − U ) = (1 − Uz ) × (1 − Ur ), where Ur = 95%. Uz is evaluated below. Time factor T v is expressed as: Tv =

Cv t H2

where C v = 5.3 m2 /year, time t = 120 days ∼ = 0.328 year, H = 7.0 m. Substituting above values, T v = 0.035 which corresponds to about 20% consolidation i.e. U z = 20% ∴ (1 − U ) = (1 − 0.2) × (1 − 0.95) = 0.04. Therefore, overall consolidation of soft layers under combined consolidation is 96%, i.e. only 1% increases due to vertical consolidation. As before, improved C = 72.5 kPa, i.e. SBC after preloading = 149 kPa > 125 kPa. Above exercise shows nominal contribution of vertical consolidation in improvement process using PVD. It however is pointed out, this may not be true because it depends on (i) values of k r and k v and (ii) values of T v and T r which vary based on PVD design consideration.

Design Summary Results of ground improvement adopting PVD are summarized below for ready reference. SBC of virgin ground = 57 kPa to be improved to 125 kPa. PVD: (100 mm × 5 mm) strip, arrangement @ 1.5 m c/c square grid up to 8–9 m below EGL. Design backfill surcharge of 7 m height placed in two stages of 4 and 3 m. Stage-I Improvement: Surcharge height: H I = 4, maintained for 52 days to achieve 90% consolidation. Improved C = 45 kPa. Stage-II Improvement: Additional surcharge H II = 3 m, maintained for 68 days to achieve 95% consolidation.

Worked-Out Examples

87

Total duration of preloading = (52 + 68) = 120 days say 4 months. Improved C = 70 kPa corresponding SBC = 140 kPa > 125 kPa required for design. Influence of vertical consolidation is nominal.

Field Strategy Steps for site preparation and execution of PVD are briefly outlined below for general guidance. Step-1: Step-2:

Stripping, excavation for site leveling covering entire improvement area. Covering dressed ground surface with geotextile to separate sand blanket from parent soil. Step-3: Laying 300–500-mm-thick compacted medium sand blanket to act as drainage layer. Step-4: Over the compacted sand layer, PVD is installed mechanically as per design spacing and depth. Step-5: After installation of PVD, the area is covered with polythene sheet to prevent surcharge backfill getting mixed with sandy drainage blanket. Step-6: Place surcharge backfill up to height of Stage-I preloading and maintain for design time period. Step-7: After end of Stage-I loading, place backfill for Stage-II preloading and maintain for specified time. Step-8: Remove all surcharge backfill materials in steps after elapse of total period of surcharge. Step-9: Instrumentation: Execution of ground improvement adopting PVD should be monitored regularly. Continuity and quantity of flow (visual observation) of water from sand blanket are to be monitored routinely. Installation of piezometers and settlement gauges is recommended for verification with design estimates. The results are meant for confirmation of improvement work. Step-10: After removal of backfill, carry out geotechnical proof tests at several locations over improved area. Following tests are suggested: boring with SPT and collection of UDS, laboratory strength and consolidation test, any other test required by the designer. It is recommended to carry out plate load tests to ensure safe bearing capacity (SBC) actually achieved over improvement area. Above steps complete ground improvement work adopting preloading with prefabricated band drain. Band drain strips are dispatched in rolls. Figure 5.6a, b shows rolls of PVD stored at site and pore water coming out of ground after installation of PVD.

88

(a) Reels of PVD stored at site

5 Ground Improvement

(b) After installation of PVD, Pore Water Comes out

Fig. 5.6 Strips of prefabricated vertical drain stored at site and water coming out through PVD

Comparison of Results of Ground Improvement In order to assess comparative advantages/disadvantages of different methods of in-ground improvement, namely stone column (SC), deep soil mixing (DSM) and preconsolidation with pervious vertical drain (PVD), results of a case study carried out during planning stage for a project have been summarized below. It is pointed out the rates considered were old (2009–2010) when the study was conducted and rates were much lower then. However, the results show overall cost–benefit effects of different improvement techniques.

Case Study Area of improvement: 350 m × 10 m (A = 3500 m2 ). Top layer of 7 m thickness comprised of soft silty clay/clayey silt. N-values: between 2 and 3; unit weight = 18 kN/m3 ; cohesion = 28 kPa; friction angle = 0º. Virgin ground: SBC = 62 kPa, Settlement = 207 mm. Post-treatment target: SBC = 150 kPa, Settlement = 25 mm. Original plan was to adopt 450 mm diameter RCC plies, cost of which being quite high, alternative methods of ground improvement, namely (a) stone column (SC), (b) deep soil mixing (DSM) and (c) preloading with prefabricated vertical drain (PVD) considered. Improvements of ground achieved by all three methods were analyzed to evaluate technical acceptability and cost–benefit viability. The results were compared with initial proposal of 450 mm diameter bored pile. The results are summarized in Table 5.9 which is self-explanatory.

Deep Vibro-compaction

89

Table 5.9 Comparison of results of ground improvement analysis adopting SC, DSM and PVD Method

450 mm dia. pile

SC

DSM

PVD

Diameter/size (mm)

450

800

800

(100 × 5) PVD strip

Length (M)

26

8

8

9

Grid spacing (M)

1.35 □

1.15 □

1.36 □

1.5 □

Reqd. no./length

750 Nos

3250 RM

2650 RM

25,000 RM

SBC (kPa)

NA

150

163

150

Settlement (mm)

NA

100

24

9

No. of rigs/eqpt

3

4

2

2

Rig-days (days)

125

203

104

170 for preloading

Time (month)

5

7.5

3.5

(6 + 1)

Improved parameters

Total and unit costs (Rs.) Cost (Rs. Lakh)

600

270

470

150

Unit cost (Rs./M 2 )

17,140

7714

9791

3125

It is seen in above table that PVD although requires more time technically is most efficient and cost-effective solution. However, the final decision can be taken by project authority based on results presented in above table. Results of time–cost–benefit studies for deep soil mixing (DSM) and stone column (SC) methods can be presented in pyramid diagrams (Fig. 5.7) for presentation in project management/review meeting/workshop. Such visual representations are helpful in decision-making process by the management.

General Arrangement Drawing for PVD General arrangement of ground improvement with PVD and pre-loading and typical arrangement of piezometer and settlement gauges are shown in Fig. 5.8 for guidance.

Deep Vibro-compaction Vibro-compaction is an advanced technique for efficient and faster improvement of soft/loose soils up to great depths. The technology is based on transmitting 3D vibration down the hole through specially designed rotary vibratory probe. Main equipment is a vibrator assembly specially designed for circular oscillatory vibration. Commonly, a cylindrical probe of 3–5 m long weighing about 2 T is used. Core element of vibrator is an electrically driven eccentric weight which induces radial oscillation to the probe. The vibratory probe is attached to extension tubes of required

90

5 Ground Improvement

(a) Total Nos. of DSM / SC Columns

(b) Total No. of Rig-days for DSM / SC columns

(c) Total Costs for Improvement by DSM & SC

Fig. 5.7 Pyramid diagrams showing comparison between deep soil mixing and stone column

depth of improvement with flexible coupling and suspended from a light crane or crawler vehicle. Both frequency and amplitude of vibration can be controlled externally from control panel. The equipment is specially designed with stone feeder pipe through which graded stone is discharged to fill cavity developed by vibration. The vibro-technique works in dual mode: (a) Vibro-compaction technique compacts granular soils (medium to coarse sand, gravel, cobble, etc.) with negligible fines content by rearrangement of soil particles into denser configuration and (b) vibro-replacement technique builds load-bearing columns with gravel, crushed stone formed in cohesive soils or granular soils with fine content. The process starts with penetration of vibro-compactor (also called depth vibrator) into ground up to required depth of improvement. The vibrator compacts surrounding soils at bottom and discharge granular materials to form granular column. The probe is then withdrawn to next depth stage and the process is repeated up to top. Compaction and filling granular materials start from bottom to top to build stone-filled columns. This method is superior to conventional stone column technique because densification with compaction is done with vibration which is more efficient and faster compared to impact of hammer. The vibro-compaction technique is a specialized field of ground improvement. It is most effective in loose granular sites and to be adopted judiciously for alluvial soils after thorough study. The method is slightly costly compared to other methods of in-ground improvement, but progress, efficiency of compaction and neatness of site far override the initial cost effects.

Deep Vibro-compaction

91

Fig. 5.8 General arrangement of ground improvement with PVD, settlement gauge and piezometer

Steps for deep vibro-technique are briefly outlined below for reference. Step-1: The vibrator supported from a crane is positioned at column location and the aggregate chamber is filled with select granular filling materials. Step-2: The vibrator is lowered to design depth by displacing soil by vibration of probe or injection of compressed air/hydraulic thrust from the Kelley. Step-3: The probe is operated under controlled amplitude and frequency of vibration for few minutes.

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5 Ground Improvement

Step-4: The vibrator is pulled up slightly and stone metal is charged in the cavity and re-penetration of the vibrator compacts surrounding soil mass. Step-5: The process is repeated to build the stone-filled column from bottom to top surface. Step-6: Finally, a blinding layer of coarse material is placed and compacted with vibratory roller.

Chapter 6

Foundation on Soft and Filled-Up Soil

Introduction Design and construction of all types of shallow and open foundations are widely covered in detail in textbooks, codes and publications, and there is no need for repetition. Construction of shallow foundation starts with laying mud mat which in soft ground with high water table area may pose great difficulty. Seepage of water at excavated (founding) level can wash out cement from fresh concrete at different locations which without elaborate dewatering arrangement is difficult to control. Guidelines to tackle such difficult situation may not be available when most needed. In this section, a few simple practical approaches which have been used successfully at project sites are presented. Construction of foundation in old dumping grounds of heterogeneous hard materials, preparation of founding layer can be difficult. A few preconstruction treatments for such sites might solve such problems. Methods for design and construction of ‘hardstand’ which are often used for supporting heavy equipment or floor for storage of heavy materials like steel ingots, steel sheet rolls (coils) have been presented. In order to improve bearing capacity and control settlement or compaction of soil or rock below foundation, compaction grouting is used. Grouting is a specialized subject and is tailor-made for specific site and objectives. General guidance and a few key points on compaction grouting have been discussed for reference. It is hoped, practical methods to overcome such problems will be of interest to practicing engineers.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_6

93

94

6 Foundation on Soft and Filled-Up Soil

Construction of Foundation in Soft Soil Large underground or partly underground/projecting tanks for storage of water, oil or chemicals are often build on soft soil with high groundwater table condition. One may wonder why such tank is to be built on soft soils. Because, petrochemicals and water supply plants need a series of tanks for storage of crude/raw and refined/processed liquid products. Common practice is to locate a number of tanks of different sizes and capacities at convenient location called ‘tank farm’. Normally, bearing pressure requirements for such tanks are moderate and are located away from core plant areas within plant premises. For example, for supply of water to plants or township, raw water is collected from river or intake well which after treatment is supplied to distribution network. A number of storage and distribution tanks are necessary for storage and treatment cycles. As water is collected from perennial rivers, water treatment plants are conveniently located near river basin. Subsoil at basin areas are generally soft with high water table. Construction of base slab for tank often faces problem of seepage from bottom of excavation which needs to be controlled for construction of mud mat and raft.

Excavation in Soft Ground Excavation for foundation in soft ground needs to be done carefully in planned manner. Depending upon area, depth and groundwater level, excavation needs to be done in stages both area and depth-wise. Excavation, civil construction and backfilling should proceed in tandem. Excavated earth should be stored at distance of at least 1½ times the final depth of excavation. Also, water should not be allowed to accumulate inside pit. Water can be removed by sump-pump method and properly drained away from excavation to avoid recirculation back to excavation. Deep excavation can be made in 2–3 steps generally maintaining side slope of 1:1.5 (V:H) and provision of about 1.0 m wide berm in each step. It should be remembered; soil loose strength if left exposed or allowed to remain even under shallow water. Safer practice is to stop bed excavation about 300–500 mm above design founding level and final excavation is to be done just before laying mud mat. Therefore, all arrangements for concrete etc. should be kept ready before excavation to final level.

Mud Mat on Soft Ground Bottom of excavation for foundation in soft silt/clay, loose sand strata in high groundwater level areas often becomes soft/spongy making it difficult for laying mud mat. Draining water out from pit may not be effective. Steps normally taken are: (1) spread

Foundation on Heterogeneous Ground

95

dry granular material (brick bats/chips, waste building materials, dry earth/sand, slag etc.), (2) increase thickness of mud mat. In case such methods are not satisfactory following procedure might be helpful. (a) Mud mat over boulder soling A layer of about 200-mm-thick stone or slag boulder soling placed uniformly and hand-packed nicely over excavated surface. Then PCC mud mat is laid as usual. (b) Mud mat for large raft in soft ground Large mud mat should be laid in panels. The area shall be divided into a number of panels of suitable size. Alternate panels are to be cast first. Balance panels shall be cast after initial setting of panels cast earlier. Casting of mud mat panels shall follow a pattern, e.g. from one side/end/corner to other, from outer to center or reverse. In case of higher ingress of groundwater into excavation, a few sump pits are to be dug at planned locations. Water collected in pits to be pumped out at regular interval. This will eliminate swelling tendency by hydrostatic pressure. The pits will be closed with PCC mixed with water-resisting additives just before laying foundation concrete. If necessary, small pieces of pipes can be inserted into pit before closing. The pipes can be sealed after raft casting completed. Such treatments can be helpful in construction of basement raft, fully/partly underground reservoir and clarifier. (c) Precast PCC mud mat In soft/loose ground and high groundwater level areas, above methods may not be satisfactory. One might question, why a soft area with low bearing capacity and prone to high settlement is selected for foundation? This situation may arise where soil bearing capacity is not prime consideration e.g. construction of pile cap. Under such circumstance, precast cement concrete (PCC) tiles can serve as mud mat. Steps for laying precast mud mat as shown in Fig. 6.1 are discussed below. i. Precast PCC tiles/slabs (600 × 400 × 37 ~ 40 mm thick) are cast and cured properly. ii. After excavation, precast PCC tiles are placed evenly filling joints with weak mortar. iii. Second layer of precast tiles to be laid over first layer in same pattern but covering joints of first layer similar to brick bonding. Undulations in first layer to be leveled with sand packing so that top of second layer is even. iv. Angular/curve-shaped tiles to be placed near pile cut-off level. v. It is recommended to complete pile chipping before laying precast mud mat.

Foundation on Heterogeneous Ground In view of space crunch for new or expansion projects, plant authority often need to utilize old dumping grounds lying idle for years for new construction. Such sites have intrinsic problems which need to be tackled before releasing for new construction.

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6 Foundation on Soft and Filled-Up Soil

Fig. 6.1 Details of mud mat with precast PCC tiles

As every dumping site is different, each site has to be dealt separately. Construction of open foundation at highly heterogeneous dumping ground of assorted hard materials for years face many uncertainties which can neither be assessed properly nor generalized procedures can be formulated. General guidelines for design and construction of open foundation in such areas are outlined for information. 1. Complete site leveling to desired formation level by cutting/filling as required. 2. Compact entire area by several passes of heavy static and vibratory roller moving in cross directions. 3. Mark footprint areas of isolated, mat or strip foundation. 4. Mechanical excavation to be carried out up to design founding level plus thickness of treatment. 5. In order to facilitate proper treatment of bed and compaction, extent of excavation to be planned properly. For a series of isolated foundations in a row or long foundation like track, trench excavation to be carried out over full length. For shop floor or stackyard, the entire area to be excavated. After excavation, the area to be leveled and compacted mechanically. 6. Founding bed is to be prepared by filling select graded granular materials in designed layer thickness and each layer to be compacted mechanically to desired level. 7. For foundation of important equipment, it is advised to conduct footing load tests on prepared bed. 8. The work should be supervised by experienced field engineers.

Hardstand

97

Hardstand Hardstand commonly refers to localized ‘hardening’ of ground to sustain high load with limiting settlement. Hardstand is required say for erecting heavy-duty crane or hoist for erection of heavy equipment parts. It is also required for permanent storage of heavy finished products (e.g. iron ingots, rolled steel beams/joists, steel coil etc.) in steel plant. Design and construction of hardstand require expertise and experience. Basic idea behind hardstand is to improve in-situ modulus of sub-base which in turn improves bearing capacity and controls settlement. In this method loose weak bed materials are excavated and replaced with materials of known composition and properties to ensure adequate bearing capacity and settlement within permissible limit. This is achieved by improving low strain modulus of sub-base. Hardstand can be advantageous in areas for raw material storage, raft or long strip footing, rail track, road for heavy-duty vehicle like high-capacity dumper in soft soil. Salient features of hardstand can be explained through case studies from selected projects.

Hardstand for Heavy Crane Foundation For erection of heavy process equipment of coal dust injection plant at a steel plant, a revolving heavy-duty crane is to be erected. The crane will assist in lifting heavy equipment parts and assemble in stages while kept hanging for days together. General ground condition was not competent for setting up foundation for the crane as required bearing capacity was of the order of 20 t/m2 and settlement restricted within 25 mm. Estimated bearing capacity and settlement of site were 10–12 t/m2 and 80 mm, respectively. Problem of foundation for the crane was solved by constructing a designed hardstand to the satisfaction of crane supplier. After required study and design, scheme of hardstand with following design parameters was finalized. • Soil improvement: 1500-mm-thick hardstand with hard granular materials placed in four layers and each layer compacted at least to 95% of maximum dry density to achieve N > 50 and ϕ ∼ = 40° • Settlement after hardstand (E = 60 MPa): ∼ = 30 mm. Normally, top 2.0–3.0 m soil is to be excavated and replaced with graded granular materials, placed and compacted in specified manner. The non-cohesive materials shall be clean sand, stone dust, stone chips of building-grade quality. In order to ensure ‘minimum void’ and ‘design compaction’, gradation and proportions of granular materials selected after a few trials are given below for reference. Grain size (mm)

Percent by volume (%)

19.0–9.5

10

9.5–4.75

20 (continued)

98

6 Foundation on Soft and Filled-Up Soil

(continued) Grain size (mm)

Percent by volume (%)

4.75–2.00

30

2.00–1.18

30

Fines 600–75 μm

10

Note Variation limited within 5%

The graded granular materials should be dry-mixed, placed in layers of about 250–300 mm in thickness with sufficient watering and be compacted by multiple passes of vibratory roller to achieve 95% relative density. The compacted hard bed is expected to have angle of internal friction φ > 35° and low strain modulus of 450 kg/cm2 (4500 T/m2 ) to ensure bearing capacity of 20–30 T/m2 and reduced settlement (mostly immediate in nature). The work should be carried under strict supervision and quality control on granular materials, mixing, placement and rolling. Also, conducting laboratory and field test on relative density achieved at site is recommended. Surface treatment of hardstand can be done as required for crane movement.

Hardstand for Heavy Storage Floors Floor constructed on soft ground for stockpile of heavy materials (say iron ore, limestone, coal etc.) often suffer high total and differential settlements, depression, upheaval, crack, etc. seriously affecting movement of material handling equipment (stacker-reclaimer) and wastage due to ‘dead storage’. Repair of damages in operating floor is difficult as it needs partial shut-down. Common practice is to design heavily reinforced concrete floor of considerable thickness at high cost. Economic design and construction of such floor on soft ground is difficult because of weak sub-base, varying consistency, variation in constituent materials etc. Problems of sub-base are low in-situ modulus which if taken care, the problem can be solved. In case of higher imposed load (say 12–15 t/m2 ) in soft/loose soil, provision of cross-ribs can be helpful. The scheme is discussed with an example of a heavy material storage floor.

Sub-soil Data and Design Requirements i. Sub-soil at site has been identified in five layers. Soil profiles along with engineering parameters have been presented in Table 6.1. ii. Storage arrangement: Two-layer stacking of steel coil rolls (Wt. 25 T), resulting UDL (uniformly distributed load) ∼ = 11 t/m2

Hardstand

99

Table 6.1 Sub-soil stratigraphy at heavy material storage site Strata

Description

Thickness

N-value

Modulus (MPa)

I

Compacted fill

4.0 m

8

8

II

Loose flyash

5.75 m

1–2

2

III

Stiff sandy clay

3.0 m

20

35

IV

Disintegrated rock

3.0 m

> 100

30

V

Weathered rock

Cont.

Core 20%

> 40

The site can be prepared for storage floor adopting one or combination of following methods • RCC floor to be constructed not on soil but over a prepared hardstand • Design of hardstand modified with provision of compacted granular ‘grade beams’ below hardstand • Design hardstand meeting requirements of sub-base for the floor • Design RCC slab considering improved sub-base modulus Steps • • • • • • • • • •

Overall excavation up to 2 m below design floor level Introduction of compacted granular strips in grid pattern below hardstand Floor area to be divided in rectangular panels (say 3–4 m × 10–12 m) Compaction with drop hammer (diameter = 500–800 mm, W = 2–3 T, drop = 2 m) @ 1.2–1.5 m c/c Craters developed by hammer blows to be filled with hard granular material/slag, stone boulder Compaction with hammer to continue till penetration becomes negligible Total floor area will be covered with such compacted strips/grids, dressed and rolled The hardstand will be built over compacted grid system to improve effective modulus of sub-base RCC floor to be designed and constructed over hardstand Estimated long-term settlement of floor was around 30 mm.

The designed hardstand with granular grade beams below hardstand is shown in Fig. 6.2. Dimensions and spacing of granular grade beams have to be designed based on results of geotechnical test on sub-base in line with design of beams on elastic foundation in grid pattern. However sizes of hard materials for granular beam should be between 100–75 and 12 mm well graded. The grade beams are to be constructed in stages of about 500 mm thickness and each layer compacted well. The hardstand designed in three-four layers of 300–250 mm thickness and constructed as above. It is emphasized that success of hardstand is highly dependent on quality of material, workmanship and supervision.

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6 Foundation on Soft and Filled-Up Soil

Fig. 6.2 Details of compacted granular grade beams below hardstand

The RCC floor will be constructed over hardstand. Construction of hardstand may take little longer but overall economy and performance of storage floor will offset cost for construction of heavily reinforced thick RCC raft.

Compaction Grout Grouting as a whole is a specialized engineering field depending upon a number of factors: geotechnical tests, selection of grout material and equipment, injection plan and above all monitoring with proof tests. Grouting is commonly adopted for multiple purposes, e.g. stabilization of soft soil/fill, improvement of bearing capacity, controlling settlement, arrest seepage, stabilization of slope, filling joints/cracks and other purposes. Grouting is commonly done by injecting grouting agent namely cement slurry with chemical additives into soft soil, rock, fill, etc. under pressure. Grouts fill voids, joints/cracks to increase overall strength of the mass. Grouting pressure depends upon the medium to be grouted and grouting agent. Initially injection is done with varying pressure stages from low to medium to design pressure or refusal to ensure uniform flow of grout for total coverage. Based on the purpose, grouting is done in stages of depth, pressure, spacing which are decided during planning. It is important to verify performance of grout scheme by conducting test grout prior to implementation at site. Purpose of this section is not to deal extensively on grouting but to provide preliminary idea on compaction grouting to fresh engineers. It once again is cautioned grouting requires expertise to plan, preparation

Compaction Grout

101

of scheme, selection of grout materials and equipment, injection strategy and overall monitoring. Once the grouting work is completed successfully, the improvements can often be astounding.

Methodology Grouting scheme should be designed, planned, prepare specification and sketches to reveal the scope of work. A typical example is presented below for reference only. Commonly, grout mix consists of cement-bentonite in ratio 1:2 (by weight). Slurry of proper consistency to be prepared by adding adequate quantity of water thoroughly stirred and injected, initially under low pressure and gradually increased up to about 2.0 kg/cm2 or refusal or spillover, whichever is earlier. a. Grout points will be marked on ground at alignment and spacing shown in design sketch. b. Initially, a rod is driven/pushed into ground up to desired depth for insertion of grout pipe. c. Grout is injected in alternate at points and depth (levels) in first stage. Grouting of remaining holes and depths is done in subsequent stages ensuring setting of previous grout. d. Fresh cement-bentonite grout to be prepared in mixing drums. Requisite quantity of water will be added to prepare workable slurry and injected immediately. Grout in mixing drums shall be kept continuously stirred and set grout must be discarded. Record of grouting work, e.g. materials, mix proportions, depth, pressure, intake, time, mix consistency shall be maintained for checking and billing purpose. It is to be kept in mind, grouting operation may need to be modified depending upon site condition and performance. It is advisable to verify grouting scheme, mix and equipment on a ‘test grout’ program before starting actual grouting work. Grouting work should preferably be completed maintaining continuity. Example 1 Pressure Grout for Controlling Settlement Rail Supporting Structure Rail supporting structure for coke oven plant was supported on four RCC columns resting on 3.2 m square footing founded at 2.5 m below FGL. GA of column footings is shown in Fig. 6.3. At the time of rail fixing, it was noticed the columns suffered excessive settlements ranging from 41 to 126 mm. Amount of total and differential settlements of (~ 70–80 mm) was alarming. During site inspection, it was revealed deep excavation (up to 12 m) was done for construction of near-by Junction House. Rail supporting columns were supported on foundations at 2.5 m below FGL on freshly filled soil, compacted with hand-held plate vibrator.

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6 Foundation on Soft and Filled-Up Soil

Fig. 6.3 GA showing isolated footings and grout points (vertical and inclined)

Such mode of backfilling and compaction is not expected to be competent to sustain design-bearing pressure from rail support beams. In order to assess in-situ consistency and its variation with depth, Standard Penetration Tests (SPT) were carried out near each column base.

Treatment Ground treatment comprised of pressure grout with cement slurry and admixtures to improve general consistency of backfilled soil, imparting higher overall modulus, bearing capacity with reduction in settlement. Cased grout holes of nominal 100 mm diameter and up to rock (~ 12 m below) are to be bored. Grout injected in two depth stages: Stage 1: 1.0–2.0 m above rock and (ii) Stage 2: at 2.5–3.50 m below FGL.

Compaction Grout

103

Normally, cement slurry of 1 (cement): 3 (water) with admixtures to be injected under low to medium pressure gradually increasing to about 2.5 kg/cm2 . In order to achieve compaction immediately beneath footing, inclined boring to reach middle of raft bottom was done and grout injected at medium to high pressure till refusal. Detailed records of grout intake and maximum pressure at each stage and in each grout hole were maintained. In total, 26 grout points (22 vertical + 4 inclined) have been envisaged for all four columns. Number and location of grout points modified based on site conditions. The treatment arrested further settlement and stabilized the four-column frame. Rail supports were realigned and leveled for further erection.

Chapter 7

Pile Foundation

Introduction In areas where soil bearing capacity is low, foundations for heavy structures cannot be supported on shallow/open foundation. In such cases, heavily loaded foundations are supported on pile foundation to transmit loads and moments to competent strata at depths. Piles are long slender, one-dimensional with high l/r (length vs. radius) ratio structural member made of timber, reinforced cement concrete (RCC), precast/ prestressed concrete (PSC), rolled steel joist, pipe/tube inserted in ground to transmit (a) vertical compressive/tensile (b) horizontal loads and (c) moments from structures either individually or collectively in group to competent strata. Normally RCC piles can be of various cross sections (circular, square, hexagonal), diameter may range from 300/400 mm to 2500 mm or more, but piles are not generally designed to withstand torsion. Generally, piles are not connected directly to structure. A pile cap is constructed on a group of piles to serve as foundation for the civil/structural member and equipment. As such, loads and moments from structure are transmitted through pile cap to piles and finally to ground.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_7

105

106

7 Pile Foundation

‘Piling’ is a specialized interactive, interdisciplinary field of engineering combining geotechnical, civil design, soil-structure interaction, construction technology, quality controls, load testing and overall safety. Large number of textbooks, literature, standards and technical publication are available on design and construction of pile foundations. Purpose of this chapter is not to repeat what is available but is an attempt to compile the main aspects of pile design and construction. In design or site office, it may not be possible to have access to necessary books, codes, literature for relevant method, formula, charts. Keeping this in view, this chapter has been compiled on presenting approaches on piling practice comprehensively. Standard methods of pile design have been presented in simple step-by-step format starting from the selection of design soil parameters to geotechnical and structural design of reinforcement and detailing and finally representing in design drawing for use at site. Steps and procedures outlined here have been used successfully at various project sites. Pile foundation is very important for industrial and infrastructure projects. It is emphasized that successful completion of piling work depends on proper planning, design and construction involving modern technology, monitoring and testing. Pile construction requires inventory of conventional and modern equipment and accessories with active involvement of experienced personnel and skilled machine operators. Moreover, safety at work site, equipment and environmental concerns are equally important. It is to be noted that each project site is different and needs to be approached on site-specific manner rather than following routine practice. Keeping the above objectives in view, the chapter has been organized to include following topics: • Brief description on various types of RCC piles: bored, driven (cast-in-situ, precast), steel lined • Pile design and construction: – Design of RCC Piles (a) Geotechnical Design Steps: Methods of Design (as per BIS Code of Practice) (b) Structural Design Steps – Reinforcement Design – Preparation of working drawing for construction – Liner Pile: Pile with permanent Steel Liner – Precast Segmental-Driven Pile. • Assessment of preliminary capacity of driven pile based on energy correlation method RCC piles are broadly classified based upon the method of installation. Two primary methods are (a) board cast-in-situ and (b) driven cast-in-situ or precast piles. Salient features of both types are highlighted below.

Estimation of Load Carrying Capacity of Pile

107

Estimation of Load Carrying Capacity of Pile A wide range of commercial and in-house developed software programs are available which are used by feeding required soil and pile data. With the help of programs, various alternative solutions can be worked-out in short time. But based on my personal experience, I have seen several software-based design calculations with incorrect application of input parameters or design options. Therefore, I strongly recommend software solutions should be cross-checked with alternative method. There is no alternative to methodical and ‘steep-by-step’ hand calculation which is transparent. Moreover, hand calculation although requires some patience and time is very helpful in getting ‘feel for the numbers’ and overall confidence of the designer. Therefore, step-by-step calculations of piles starting from the selection of design soil parameters (based on soil report) to geotechnical and structural design for pile shaft capacity along with reinforcement detailing which generally are not covered comprehensively at one place, are compiled and presented in simple steps for guidance and use. Safe load carrying capacity (safe load) of pile depends on two factors (a) Geotechnical Capacity from side friction and tip bearing in soil/rock and (b) Structural Capacity of pile shaft itself. Accordingly, complete design of pile should consider both. Method of estimation of safe capacity of bored cast-in-situ RCC pile is covered in IS: 2911 (Part 1/Sec 2) published by Bureau of Indian Standards (BIS). For convenience, commonly required formulae, parameters needed during design are summarized below for ready reference.

108

7 Pile Foundation

Geotechnical Design of Pile Ultimate Load Carrying Capacity of Pile [as per IS; 2911 (Part 1/Sec 2): 2010] Pile Design for (C-φ) Soils Vertical Capacity Vertical capacity of pile is derived from two components (1) side friction and (2) tip bearing. As per Cl. B1 piles in cohesionless and Cl. B2 cohesive soils, ultimate load carrying capacity (Qu ) in (a) granular and in (b) cohesive soils and is given by the following formula: (1) Side friction component (Q u )1 =

n ∑

K i PDi tan δi Asi +

i=1

n ∑

αi ci Asi

i=1

(2) Tip bearing component (Q u )2 = A p (1/2Dγ Nγ + PD Nq ) + A p Nc c p Note: Contribution of (½Dγ N γ ) being comparatively small is neglected (conservative). Q u = (Q u )1 + (Q u )2 , where (Qu)1 and (Qu)2 are contributions from granular and cohesive soils, respectively. Following IS: 2911 (Part 1/ Sec2): 2010, general equation for ultimate pile capacity is given by: [ Qu =

n ∑ i=1

(

K i PDi tan δi Asi + A p PD Nq

] )

[ +

n ∑

] αi ci Asi + A p Nc c p ,

i=1

where Qu = Ultimate vertical load carrying capacity of bored RCC pile K i = Co-efficient of earth pressure in i-th layer, i = Layer No PDi = Mean effective overburden pressure of i-th layer δ i = Angle of wall friction between pile and soil for the i-th layer

Geotechnical Design of Pile

109

Asi = Surface area of pile shaft in i-th layer = π × D × Li L i = Length of pile in respective stratum Ap = Cross-sectional area of pile tip. = π/4 × (D)2 D = Diameter of pile PD = Effective overburden pressure at pile tip N q = Bearing capacity factor for bored pile depending on F F = Angle of internal friction of soil α i = Adhesion factor for i-th layer ci = Average cohesion for i-th layer N c = Bearing capacity factor, usually taken as 9 cp = Average cohesion at pile tip. Note: Values of (α i ) and (K i ) can be read from Figs. 7.1 and 7.2. Depending upon type of soil (cohesive or cohesionless) met in a layer, appropriate formula as per Cl. B1 or B2 above is adopted. Lateral Capacity Classical approach for the estimation of lateral capacity is by ‘p-y’ method. Lateral resistance for granular soils and normally consolidated clays is modeled according to the equation

Fig. 7.1 Values of α versus C

110

7 Pile Foundation

Fig. 7.2 Values of K versus φ

p = ηb z, y where p = lateral soil reaction per unit length at depth ‘z’ below ground level y = lateral pile deflection ïb = modulus of sub-grade reaction, recommended values are given in tables below. ‘p-y’ Curves Representative ‘p-y’ curves can be generated from the results of laboratory tests for different pile diameters as shown in Fig. 7.3. The ‘p-y’ concept is commonly used in design where both vertical and lateral capacities are important. Offshore piles generally fall in this category because unsupported length of pile shaft above sea bed is high and lateral deflection at cap level is important consideration in design of near- and offshore structures. Common practice for land piles is to follow provisions of sub-grade modulus concept as per BIS code which are reproduced below for quick reference.

Geotechnical Design of Pile

111

'p' Soil Resistance (kN/M)

'p' Soil Resistance (kN/M)

100

75

50

150

150

125

125

100

100

'p' Soil Resistance (kN/M)

125

75

50

75

50

25 25

25

0

0

0

0

0.05

0.1

x=0.5 m x=3.0 m

0.15 0.2 'y' Deflection (M) x=1.0 m

x=1.5 m

x=4.0 m

x=6.0 m

0.25

0.3

0.35

0

x=2.0 m

0.05

0.1

x=0.5 m x=3.0 m

0.15 0.2 'y' Deflection (M) x=1.0 m

x=1.5 m

x=4.0 m

x=6.0 m

0.25

0.3

0.35

x=2.0 m

0.1

0.15 0.2 0.25 'y' Deflection (M)

x=0.5 m

x=1.0 m

x=1.5 m

x=4.0 m

x=6.0 m

0.3

0.35

0.4

x=2.0 m

Where x= Depth

'p - y' CURVE FOR STATIC LOADING PILE DIA : 550 mm

'p - y' CURVE FOR STATIC LOADING PILE DIA : 500 mm

(a)

0.05

x=3.0 m

Where x = Depth

where x = Depth (m)

'p - y' CURVE FOR STATIC LOADING PILE DIA : 450 mm

0

(b)

(c)

Fig. 7.3 Typical ‘p-y’ curves for a 450 mm, b 500 mm and c 550 mm diameter piles

Modulus of sub-grade reaction Ref. IS: 2911 (Part-1/Sec 2):Table 3. Granular Soils, ïb (kN/m3 ) Soil Type

N-value

Very loose sand

0–4

Range of ïb (kN/m3 × 103 ) Dry

Submerged

< 0.4

< 0.2

Loose sand

4–10

0.4–2.5

0.2–1.4

Medium sand

10–35

2.5–7.5

1.4–5.0

Dense sand

> 35

7.5–20

5.0–12.0

Preloaded Clays with constant soil modulus are modeled according to the equation: p = K, y k1 0.3 where K = 1.5 x B , where k 1 is Terzaghi’s modulus of sub-grade reaction. Recommended values of k 1 are given in the following table.

Ref. IS: 2911 (Part-1/Sec 2):Table 4. Preloaded clays with constant soil modulus Soil consistency UCC qu (kN/M2 ) Range of ki (kN/ Design cohesion c Range of k i = 3.6 m3 × 103 ) (kg/cm2 ) c (kg/cm3 ) Soft

25–50

4.5–9.0

0.125–0.25

0.45–0.9

Medium stiff

50–100

9.0–18.0

0.25–0.50

0.9–1.8

Stiff

100–200

18.0–36.0

0.50–1.0

1.8–3.6 (continued)

112

7 Pile Foundation

(continued) Soil consistency UCC qu (kN/M2 ) Range of ki (kN/ Design cohesion c Range of k i = 3.6 m3 × 103 ) (kg/cm2 ) c (kg/cm3 ) Very stiff

200–400

36.0–72.0

1.0–2.0

3.6–7.2

Hard

> 400

> 72.0

> 2.0

> 7.2

Stiffness Factors For piles in sand and normally loaded clays: / Stiffness factor : T =

5

EI , ηh

where I = Modulus of pile material I = Moment of inertia of pile cross section ηh = Modulus of sub-grade reaction. For piles in preloaded clays: / Stiffness factor : R =

4

EI , KD

where E = Modulus of pile material I = Moment of inertia of pile cross section K =

k1 0.3 x 1.5 D

D = Diameter of pile.

Deflection and Moments in Long Piles Depth of virtual fixity (zf ): For piles in sands and normally loaded clays (without overhang): (i) Free head: zf = 1.9xR or 1.9xT; (ii) For fixed head: zf = 2.2xR or 2.2xT

Deflection and Moments in Long Piles

113

For piles in preloaded clays (without overhang): (i) Free head: zf = 1.62xR or 1.9xT; (ii) For fixed head: zf = 1.97xR or 1.9xT Pile head deflection (y): For free head pile: ( )3 H zf EI y= or H = 3 3 y 3E I Lf For fixed head pile: ( )3 H zf EI or H = 12 3 y, y= 12E I Lf where H is lateral load on pile head. Fixed end moment (M F ): For free head pile: M F = H.z f For fixed head pile: MF =

H.z f 2

Actual maximum moment: M = m(M F ), where m is reducing factor: Free head piles (without overhang): (i) For preloaded clay and sands: m = 0.30; (ii) For normally loaded clays: m = 0.42 Fixed head piles (without overhang): (i) For preloaded clay and sands: m = 0.70; (ii) For normally loaded clays: m = 0.82 In the previous section, first part of pile design, i.e. capacity based on geotechnical design, has been discussed. As pointed out earlier, second part is Structural design of pile shaft to sustain design loads and moments on pile shaft depending upon combination of vertical comprehensive or tensile (V or T) loads and shaft moment (M). Different load combinations are broadly been classified into three categories.

114

7 Pile Foundation

Case-1 Pure bending (M), no compression (V = 0) or tension (T = 0) Case-2 Compression (V) and bending (M) Case-3 Tension (T) and bending (M). Structural design including reinforcement detailing of piles for above cases has been demonstrated with worked-out examples and presented in tabular form for free and fixed head piles.

Structural Design of Pile Shaft For demonstration on method of structural design, a model pile was selected and geotechnical design was carried out the following BIS code of practice. Pile designs are common practice, and design steps are not repeated. Results of Geotechnical Design of a model 600 mm dia. 24.5 m long RCC Bored Pile summarized below. Pile Type: Bored Cast-in-situ RCC Pile

Concrete Grade: M25

Pile Diameter: 600 mm

Shaft length: 24.5 m from COL (cut-off level)

Vertical capacity: V = 125 T

Tensile capacity: T = 25 T

Lateral capacity: H = Free Head: 6.0 T

Fixed Head: 16.0 T

Example–Structural Design of Pile Shaft Codes and Reference: a. b. c. d. e.

BIS Codes of Practice Nos. IS: 2911 (Part-1/Sec-2) & IS: 2911 (Part-IV) BIS Code of Practice No. IS: 456-2000 BIS Design Aids for Reinforced Concrete to IS: 456: SP 16 ‘Torsteel Design Handbook’ by K. T. S. Iyengar & C. S. Viswanatha ‘Handbook for Limit State Design of Reinforced Concrete Members’ by V. K. Ghanekar & J. P. Jain, Structural Engineering Department, University of Roorkee, Tata McGraw Hill, New Delhi.

Structural Capacity Safe lateral (horizontal) capacity of pile depends on soil-structure interaction generally in upper layers. Therefore, lateral capacity has to be estimated based not only on geotechnical lines but also on structural (concrete) design. Design steps are illustrated through a worked-out example. Design Parameters: Pile Diameter D = 600 mm, Cut-off level = 2.0 m, Lateral deflection: Y = 5 mm (Test condition)

Structural Design of Pile Shaft

115

Reinforcements: Main bar: For Free Head: 20 mm, for Fixed Head: 25 mm Diameter Lateral Binder: 8 mm Diameter, Clear Cover = 50 mm. [Please refer Fig. 7.4] d ' = 50 + I =

25 + 8 = 70.5 mm 2

∴

d' 70.5 = = 0.1175 say 0.1 D 600

π D4 π(60)4 = = 636172 cm4 , 64 64

A pile =

π D2 = 2827.4 cm2 4

2 Concrete grade √ : M25 (2 f ck = 25 N/mm ) 2 E = 5000 f ck N/mm = 250,000 kg/ cm EI = 1.59 × 1011 kg cm2

/ T =

5

EI k1

Fig. 7.4 Working drawing of pile showing reinforcement details, design capacities and notes

116

7 Pile Foundation (0.525+1.245) 2

Table 1, IS 2911 (Part-1, Section-2): k1 = coarse sand). / ∴T =

5

= k1 = 0.885 (dry medium

1.59 × 1011 = 178 cm T = 178 cm. 0.885

Pile shaft length: L e = 24.5 m ≥ 4T (4 × 1.78) = 7.12 m. Therefore, the pile behaves as long column. Case-1: Pure Bending (V = 0 & H) Reference

Free head pile

Fixed head pile

Figure 2, Appendix-B IS:2911(Pt-1/Sec-2)

Depth of fixity: L f /T = 1.91 L f /T = 2.18 ∴ L f = 1.91 × 178 = 339.98 ≃ ∴ L f = 2.18 × 178 = 388.04 ≃ 340 cm 388 cm Deflection: Y = Q=

Figure 3, Appendix-B IS:2911(Pt-1/Sec-2) Structural Capacity of pile shaft Design Aids for Reinforced Concrete to IS: 456: SP 16

3E I L 3f

Y =

Q L 3f 3E I

3x1.5911 3403

Deflection: Y = × 0.5 = Q =

12E I L 3f

Q L 3f 12E I

Y =

6068 kg or Q = H free = 6000 kg say 6.0 T Hfree = 6.0 T

× 0.5 = 16,332 kg or Q = H fixed = 16,332 kg say 16.0 T Hfixed = 16.0 T

Fixed end moment: M F = Q. Lf Actual moment: M = m(M F ) m = 0.4 ∴ M = 0.4 × 6000 × 340 = 816,000 kg cm = 8.16 TM M u = 1.5 × 8.16 = 12.24 TM

Fixed end moment: M F = 0.5 × Q. L f Actual moment: M = m(M F ), m = 0.82 ∴ M = 0.5 × 0.82 × 16,332 × 388 = 2,598,094 kg cm = 25.98 TM Try H fixed = 10.0 T M = 0.82 × 10 × 3.88/2 = 15.908 TM M u = 1.5 × 15.908 = 23.862 TM Mu = 23.862x10000000 = f D3 25x D 3

Mu f ck D 3

=

12.24x10000000 25x D 3

0.0227 For d' D = 0.1,

Pu f ck D 2

=

=0

Mu = 0.0227 f ck D 3 p f ck = 0.022, p = 0.55% Ast = 15.55 cm2 Say 5 @

φT bars

12x1.5911 3883

ck

20

0.044 For d' D = 0.1,

Pu f ck D 2

=0

Mu = 0.044 f ck D 3 p f ck = 0.045, p = 1.125% Ast = 31.8 cm2 Say 7 @ 25

bars

φT

Structural Design of Pile Shaft

117

Case-2: Compression and Bending (V + H) Reference

Free head pile

Fixed head pile

Design loads Ultimate load Design Curve No C18 of Ref. (b)

V = 125 T & H = 6 T Pu = 1.5 × 125 = 187.5 T

V = 125 T & H = 16 T Pu = 1.5 × 125 = 187.5 T

Pu f ck D 2

=

Mu f ck D 3

=

187.5x10000 25x6002

= 0.208

M u = 1.5 × 8.16 = 12.24 TM

For

d' D

Mu f ck D 3

12.24x10000000 25x D 3

= 0.1,

Pu f ck D 2

= 0.0227,

p f ck

= 0.0227

= 0.208 and =0

Pu f ck D 2

=

Mu f ck D 3

=

= 0.208

187.5x10000 25x6002

M u = 1.5 × 25.98 = 38.97 TM

For

38.97x10000000 25x D 3

= 0.1,

d' D

Mu f ck D 3

Pu f ck D 2

= 0.072,

p f ck

= 0.072

= 0.208 and = 0.07

Provide nominal reinforcement @ p = 0.07 × 25 = 1.75% 0.8% Ast = 49.5 cm2 or 10 @ 25 φT bars (High) Ast = 22.6 cm2 Say 7 @ 20 φT bars As H = 6 T for 600 mm diameter pile was very uneconomic for foundation design, it was decided to increase H from 6 to 10 T with increase in number of main bars

As 10 Nos. 25 mm bars (for H = 16 T) for 600 diameter pile is both difficult to arrange and uneconomic, it was decided to revise H from 16 to about 10 - 12 T with reduction in number of main bars

Design capacities of both free and fixed head pile were considered uneconomic. For free head, lateral capacity of 6 T for 600 mm diameter pile is quite low. For fixed head condition, placement of 10 Nos. of 25 mm diameter bars will be difficult and also obstructs free flow of concrete to cover zone of pile shaft. Moreover, cost per pile will increase unnecessarily To resolve the issues, geotechnical and civil engineers revised design loads both for free and fixed head piles as presented below. The design was repeated considering revised horizontal loads Design With Revised Loads

Free head pile

Fixed head pile

V = 125 T & H = 10 T

V = 125 T & H ∼ = 10–12 T

Free Head: Alternative Design Try V = 125 T & H = 10 T Pu = 1.5 × 125 = 187.5 T

Fixed Head: Alternative Design Try 6 @ 25 φT bars, Ast = 29.45 cm 2

Pu f ck D 2

=

187.5×10000 25×6002

= 0.208

M F = (10 × 3.88)/2 = 19.4 TM M = m(M F ) = 0.82 × 19.4 = 15.908 TM M u = 1.5 × 15.907 = 23.862 TM Mu f ck D 3

For

d' D

Mu f ck D 3

=

23.862×10000000 25×D 3

= 0.1,

Pu f ck D 2

= 0.044,

p f ck

= 0.044

= 0.208 and = 0.018

p f ck

=

For

d' D

p f ck

29.45×4 25×π ×602

= 0.1,

= 0.04,

× 100 = 0.04

Pu f ck D 2

Mu f ck D 3

= 0.208 and

= 0.055

M u = 0.055 × 25 × 10 × (60)3 = 2.97 × 106 kg cm M=

Mu 1.5

MF =

M m

= =

2.97x106 1.5 1.98x106 0.82

= 1.98 × 106 kg cm = 2.414 × 106 kg cm 6

2x2.414x10 F H Fi xed = 2M = 12,443 kg LF = 388 Ast = 12.7 cm2 ≃ 12.44 T Say H fixed = 12.5 T Provide 0.8% reinforcement 7 @ 20 φT bars H = 10 T (for deflection of 8 mm)

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7 Pile Foundation

Case-3: Tension and Bending (T + H) Reference

Free head

Fixed head

Design tension Ultimate tension Design Curve No. 2.1-F2 of Ref. (c) ( γc ) N u . f c Ac ν = 1.5 ( γc ) M u μ = 1.5 . fc Ac h ( γc ) Ast . f y ω = 1.5 . fck Ac where

T = 25 T & H = 10 T T u = 1.5 × 25 = 37.5 T ≡ −Nu M F = T × L f = 10 × 3.4 = 34 TM M = m × M u = 0.4 × 34 = 13.6 TM Mu = 1.5 × 13.6 M = 20.4TM ( ) −37.5×1000 ν = 1.5 1.5 . 250×2827.4 =

T = 25 T & H = 10 T T u = 1.5 × 25 = 37.5 T ≡ −Nu M F = 0.5 × T × L f = 0.5 × 10 × 3.88 = 19.4 TM M = m × M u = 0.82 × 19.4 = 15.908 TM M u = 1.5 × 15.862 M = 23.862 TM ( ) −37.5×1000 ν = 1.5 1.5 . 250×2827.4 =

γ c = 1.5 f y = 415 N/mm2

−0.053 ( ) 20.4×100000 μ = 1.5 1.5 . 250×2827.4×60 = 0.048 ' For dD = 0.1, ν = −0.053 & μ = 0.048 ω = 0.20 Ast = ω fckf yAc = 25 0.20x 415 x2827.4 Ast = 34.06 cm2 or 7 @ 25 φT bars

−0.053 ( ) 23.862×100000 μ = 1.5 1.5 . 250×2827.4×60 = 0.056 ' For dD = 0.1, ν = −0.053 & μ = 0.056 ω = 0.23 Ast = ω fckf yAc = 25 0.23x 415 x2827.4 Ast = 39.17 cm2 or 8 @ 25 φT bars

Summary of Design Capacities Nominal Pile diameter: D = 600 mm, Bore depth: B = 26.5 m from FGL, Cut-off level = 2.0 m Bored cast-in-situ reinforced concrete pile terminated after 1.5 × D penetration in dense silty sand Safe Vertical capacity

V = 125 T

Safe Tensile capacity

T = 25 T

Safe Lateral capacity in

H - Free Head

H - Fixed Head

a) Bending only

6 T (with 5 @ 20 φT )

10 T (with 7 @ 25 φT )

b) Compression and Bending

10 T (with 7 @ 20 φT )

12.5 T (with 6 @ 25 φT )

c) Tension and Bending

10 T (with 7 @ 25 φT )

10 T (with 8 @ 25 φT )

Depth of Fixity from COL

3.40 m

3.88 m

Reinforcement Detailing

119

Design Capacities Because the foundations will be designed for various load conditions and combinations depending on structural design, following loading conditions have been considered for design. Vertical capacity V = 125 T Tensile capacity T = 25 T. Lateral capacity H = 12.5 T for compression and bending. Fixed Head H = 10.0 T for tension and bending.

Reinforcement Detailing Main Reinforcement It is pointed out that combination of vertical (compression and tension) and lateral loads and moment are governing factors for the selection of main bars. However considering depth of fixity, it is both unnecessary and uneconomic to continue the main bars of same diameter upto full length of pile. Common practice is to judiciously curtail main bars beyond depth of fixity by splicing with lower diameter bars continuing upto pile tip. Also to avoid wastage due to large numbers of cut pieces, curtailment is to be planned considering rolling length of bars (normally 12 m), cost and other considerations. Keeping the above in view, the following arrangements of reinforcing bars have been selected. Top rod φTop :

6 Nos. 25 φT for bending with compression 8 Nos. 25 φT for bending with tension Length of top rod: [(Provision for pile cap) + L f + Lap length] = 750 + 3880 + 800 (∼ = 40 × D) = 5430 mm ≃ 6 m Bottom rod φBot : 6 Nos. 20 φT for bending with compression (Bar diameter changed from 25 to 20 mm) 8 Nos. 20 φT for bending with tension (Bar diameter changed from 25 to 20 mm) Lateral Ties: Diameter of binder : φlateral > ( φmax / 4) , i.e. 6 mm Adopt φlateral = 8 mm Pitch of binder: D or 16φmin = 16 × 20 = 320 mm or 48φlateral = 48 × 8 = 384 mm > Adopt 300 mm Where φ = diameter of reinforcing bars and D = nominal diameter of pile

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7 Pile Foundation

Working Pile Drawing Working or design drawing for pile shall clearly shows the above details including dimensions (diameter, length, cut-off). Specimen ‘Working Drawing’ of pile should include reinforcement details, arrangement and spacing along with dimensions, design capacities and notes as shown in Fig. 7.4. The drawing prepared by geotechnical engineer is used for preparation of specification, bill of items and issued for construction and site supervision.

Pile with Permanent Steel Liner Water-front structures like port, harbor, and jetty are built on seashore or riverbank and extending into sea or river. Both bored and driven cast-in-situ piles are adopted in marine environment. Design and method of pile installation depend on several factors: (a) Soil type in river/sea bed, (b) distance from shore, (c) water depth, (d) tidal fluctuations, (e) approach to piling location by temporary platform, (f) boat, floating barge/jack-up barge, (g) road connectivity, etc. Marine piles (also called offshore pile) are designed based on mode of construction. (a) Land Mode Such piles are required for construction of foundation for near-shore structures, e.g. berth, jetty, etc., primarily for loading and unloading of bulk goods from ship/barge. As such pile points are not far from bank and installed basically following procedure for land piles. Piling areas are accessed by building temporary platform supported on timber or structural steel members. Pile boring/driving equipment is shifted and positioned on platform. After completion of work, the platform is dismantled. (b) Marine Mode Such piles are required for construction of foundation for offshore structures, e.g. deep-sea pipeline support, flyover, transmission line towers, bridge, etc. As the pile points are far from bank, piling operation is carried out from floating or jack-up barge. Pile boring/driving equipment and accessories are erected on barge. As shifting and positioning of barge takes long time, selection of positioning to be done judiciously so that multiple piles can be constructed from one position. Fabrication of reinforcement cage, steel liner and concrete batching plants are located on bank and transported to platform by tug boat or small barge. Motorized boat or ferry launch are used for transportation. Therefore, marine piling requires a fleet of support equipment and transport vessels.

Pile with Permanent Steel Liner

121

As mentioned earlier, both bored and driven cast-in-place RCC and steel piles are used in marine environment. Geotechnical and structural design of piles are commonly carried out following standards and codes applicable for the area. As top layers in river and sea beds are soft/loose, special care is necessary to ensure positioning and alignment of pile shaft through soft layers. Stability of pile point and pile bore is often maintained by providing extra-long temporary casing (withdrawn after concreting) or with permanent steel liner.

Pile with Permanent Steel Liner Permanent steel liners are used for (a) drivability and maintaining alignment in upper soft layers (requiring design modification of pile capacity) and (b) protective measures for durability of pile shaft. Corrosion of steel liner under seawater and various growths in marine environment must be controlled and protected by special treatment like protective coating, cathodic protection. Design and application of protective treatments are provided by specialized agency and are not covered. Steel liners are prefabricated temporary or permanent steel liner/casing. Inclusion of steel liner in marine piles is common practice. Design of steel liner, i.e. type of steel, thickness, stiffening if any and welding, depends on type of sub-soil, consistency, depth, method of installation, and others. The liner should be able to withstand impact from hammer blows without bending, buckling, deformation, and method of extraction during concreting in case of temporary liner. But an important factor for permanent liner is selection of representative ‘coefficient of friction’ between steel and soil as it differs considerably from those between concrete and soil. Design of lined piles need to consider this phenomenon. But there is no clear guideline for selection of friction coefficient between steel and different soil types. Literature search yields several design guidelines. Therefore, the designer needs to adopt friction coefficient representative for the soil type at site. For convenience, excerpts from selected published literatures and standards are reproduced for guidance. The designer needs to select representative value of friction coefficient based on informed and judicious discretion. The designer cannot afford to be over-safe by choosing conservative values of friction coefficient because unit costs of marine piles are quite high and conservative approach may prove uneconomic.

Effect of Permanent Steel Casing on Skin Friction It is known steel casing/liner causes reduction in skin friction at soil-casing interface. The degree of reduction however depends on several factors, namely type of steel used in liner, method of driving/installation of liner and pile construction. In case, steel casing is adopted for full depth in may result in drastic reduction in skin friction. Accordingly, the designer needs to exercise care and judgment for consideration

122

7 Pile Foundation

of skin friction component (δ) on pile capacity. Reduction in vertical capacity of lined pile has been studied based on publications and common practice in different industries. Excerpts from some of them are reproduced reference.

Skin Friction for Pile with Permanent Steel Liner (Casing) (A) Piles in Cohesionless Soil Reference–1 ‘Pile Load Capacity–Calculation Methods’–Bogumil Wrana Studia Geotechnica et Mechanica, Vol. 37, No. 4, 2015 It referred values of (δ) based on ‘NAVAL FACILITIES ENGINEEERING COMMAND PUBLICATION TRANSMITTAL DESIGN MANNUAL – Soil Mechanics, Foundations and Earth Structures, NAVFAC DM – 7.2 (1984)’. According to NAVFAC DM-7, values of angle of skin friction (δ) for different pile-soil interface has been suggested in Table 3. Lateral earth pressure coefficient (K) under compression and tension is presented in Table 4. Alternately, proposition value of (β) = [ tan δ(z) × K (z)] for different pile types can be selected from Table 4. Table 3 Pile skin friction angle (δ) Pile Type

Pile-soil interaction angle (δ)

Steel piles

20°

Timber piles

¾ φ'

Concrete piles

¾ φ'

Table 4 Lateral earth pressure coefficient (K) Pile type K (piles under compression)

K (piles under tension)

Driven H-piles

0.5–1.0

0.3–0.5

Driven displacement piles

1.0–1.5

0.6–1.0

Driven displacement tapered piles

1.5–2.0

1.0–1.3

Driven jetted piles

0.4–0.9

0.3–0.6

Bored piles (less than 60 cm dia.)

0.7

0.4

Pile with Permanent Steel Liner

123

(a) Piles in Cohesionless Soils Value of α is selected from Table 1, NAVFAC DM 7.2 depending upon undrained shear strength. β = μ(z) K(z) =tan δ(z) K(z), values from Tables 3 and 4. Value of β = μ(z) K(z) can be estimated according to the following propositions Author

Proposition of β value

McClelland (for driven piles)

β = 0.15 to 0.35 for compression β = 0.10 to 0.25 for tension (for uplift piles)

Meyerhof

β = 0.15, 0.75, 1.2 for φ’ = 28°, 35°, 37° for driven piles β = 0.10, 0.20, 0.35 for φ’ = 33°, 35°, 37° for bored piles

Kraft and Lyons

β = C tan(φ − 5) C = 0.7 for compression, C = 0.5 for tension (uplift piles)

Reference–2 ‘American Petroleum Institute : API Recommended Practice 2A-WSD’ (A) Table 6.4.3-1: Design Parameters for Cohesionless Soil

124

7 Pile Foundation

(B) Graphical interpretation of API recommendations: δ’ values in granular soils

For medium dense to dense sand/sandy silt, shaft friction factor (β) = 0.37 which is equivalent to friction angle: δ = 20.3°. Reference–3 ACE 12th International Congress on Advances on Civil Engineering 21–23 September, 2016, Istanbul, Turkey Skin Friction between Soil and Pile Materials ˙ H. S. Aksoy1, E. Inal2, M. Gör3 1

Department of Civil Engineering, Fırat University, Elazı˘g, Turkey, saksoy@firat. edu.tr 2

Department of Civil Engineering, Fırat University, Elazı˘g, Turkey, inal.esen@gmail. com 3

Department of Civil Engineering, Fırat University, Elazı˘g, Turkey, mesutgor@ gmail.com

Pile with Permanent Steel Liner

125

(B) Piles in Cohesive Soil Reference–4 Ref. ‘Pile Load Capacity–Calculation Methods’–Bogumil Wrana, Studia Geotechnica et Mechanica, Vol. 37, No. 4, 2015 Value of α is selected from Table 1, NAVFAC DM 7.2 depending upon undrained shear strength.

126

7 Pile Foundation

Above-cited references may be useful in selecting representative value for coefficient of friction between different pile types and soil.

Precast Segmental-Driven Pile As mentioned in the beginning driven piles if can be adopted in large project sites are advantageous on several counts. There are many varieties of driven piles which are widely covered in books, codes, publications. driven piles can broadly be classified into two categories, namely (a) ‘Driven cast-in-situ’ where pile shell fitted with shoe is driven by hammer blows or vibratory sinker and (b) ‘Driven precast Segmental piles’ where pile segments are cast in shop or casting yard and driven at site by impact (hammer blows) or vibratory sinkers. The advantages of precast over cast-in-situ piles are summarized below. Parameter

Cast-in-situ

Pre-Cast

Concrete Quality

Concrete not dense, has higher water-cement ratio required for flow

Dense concrete placed, vibrated & cured under controlled condition

Concrete pouring

Conc. dropped from shell mouth with chute / hopper

No need for supply of concrete at site

Quality of pile shaft

Non-uniform, chances of defect e.g. cold joint

Sound uniform pile shaft

Disturbance to concrete in adjacent pile

Driving of adjacent pile may damage green concrete

No chance of damage to pile shaft

Time for installation

Slow :Time for cage lowering and on-site concreting

Fast : No cage lowering & on-site concreting required

Readiness for civil work after installation

Curing time is required

No curing time –civil work can start forthwith

Cost aspect

Slightly cheaper

Slightly costlier but with significant saving on time

Average Productivity

2½ piles per rig day (two shifts)

6-7 piles per rig day (two shifts)

In view of the advantages of precast segmental (PSG) piles over cast-in-situ (CI) driven piles, technology for manufacturing different varieties of precast piles, namely (a) precast (PC), (b) precast prestressed (PSC), (c) hollow cylindrical/hexagonal piles of other shapes and sizes are used in industry. In this section, main aspects of precast segmental (PSG) piles, namely planning, manufacturing in casting yard at site, storage, handling, and installation methods including pile joint (splice) details and driving which are not comprehensively available at one place have been compiled for convenience. It is pointed out precast prestresses (PSC) concrete piles that are manufactured mainly in shops and have not been included in this section.

Precast Segmental-Driven Pile

127

Steps for Precast Piling Work Pile Design Geotechnical and structural design of PSG piles is carried out to finalize shape and lengths of piles of different capacities, reinforcement details and termination criteria (set). Structural design of shaft should be checked against stresses (bending) during lifting by two hooks, hanging and impacts of driving hammer. Planning Estimated total number of piles of various lengths and capacities need to be classified into a number based on segment lengths. It is important to rationalize segment lengths within two to three categories. Selection of pile joint should consider availability, speed and ease of joining at site. Mostly pile joints are proprietary/patented and procurement/manufacturing are to be completed at the earliest. Planning should finalize type of driving equipment (drop hammer, diesel hammer, vibratory sinker), number of equipment to match project implementation schedule and availability of piling fronts. Site Preparation for Fabrication Yard The site for fabrication yard should have road connectivity, facilities for power and water supply, steel, cement storage sheds, fabrication yard, hard concreted floor over casting yard, mini concrete batching plant, casting bays, space for stacking completed pile segments, a fleet of mobile equipment like hydra, JCB, crane, site office and first aid station. Procurement of Materials Contracts for regular supply of construction materials (steel, cement, sand) are to be finalized. However, supply of pile joints is very important because these are either patented and are supplied by authorized dealer or to be fabricated in workshops. It is advisable to build up stock of splice joints. Casting Pile Segments Series of casting bays made of steel formwork is built in casting yard. Prefabricated reinforcement cage fitted with steel driving head or tip for end segments and pair of joints (male–female joint) segments is to be placed properly in the formwork. Design-mixed concrete either from captive batching plant or from outside source is to be poured, compacted and finished smooth. After initial set, the segments are to be cured thoroughly before lifting and transportation to stacking yard. Driving of PSG Piles The piles are to be transported to piling site for installation. Mechanism for driving can be drop hammer of given weight and drop height, double-acting diesel hammer, vibratory sinker or other type. But in any case, segments are joined by a pair of ‘male–female’ coupler. After the first segment is almost driven, second segment is

128

7 Pile Foundation

placed maintaining correct orientation and alignment at top. Coupling is achieved by rotating the upper segment to locking position and finally locked permanently by inserting locking strip (key). As usual practice, care should be taken to avoid hard driving which may damage pile segment. Pile segments are to be driven sequentially and terminated after reaching termination strata and achieving target ‘set’ value. Selection of types and number of pile driving rigs is important at planning stage. Execution Different stages of manufacturing head/tip and pile joints, RCC segments, stacking and driving are shown sequentially in a series of photographs [Fig. 7.5 (a) to (n)] from a project site where more than 12,000 precast segmental square (350 × 350 mm) piles of 33 m and 18 m lengths have been constructed and installed successfully in 11 months time. The figures are self-explanatory by itself and don’t require elaboration.

Capacity of Driven Pile Based on Energy Correlation Introduction It is seen in the previous section, preactivities for precast segmental concrete (PSG) piles are quite elaborate. In order to take full advantage especially on installation details of PSG piles, it is necessary to plan for the preactivities well in advance. If pile design parameters can be settled at early stage, it will be welcome relief for planning and procurement to start driving of piles as per project implementation schedule. Pile parameters required for early start of preactivities are: (i) Assessment of safe vertical capacity, (ii) shaft lengths for medium and high capacity piles, (iii) estimated total number of piles and time required for driving pile, (iv) selection of driving method, equipment and productivity and most important (v) joint details. In cases, all above data are available at early stage, even before completion of geotechnical investigation including laboratory testing and preparation of soil report; this will be a ‘win–win’ situation. Preliminary capacity of driven pile can be evaluated using standard dynamic pile driving formula. Pile capacity can be estimated correlating energy during pile driving with those for conducting Standard Penetration Test (IS: 2131) or Static Cone Penetration Test (IS: 4968 - Part-III). The relationship has been developed and verified. The relations can also be used for studying drivability, hammer efficiency and time study.

Capacity of Driven Pile Based on Energy Correlation

(a) Fabricated Reinforcement Cage

129

(b) Pre-Fabricated Driving Head / Tip of Pile

(c) Matching Pair of ‘Male-Female’ Joint Segments

(e) Assembled Reinforcement Cage in Casting Bays

(d) Joints Fixed to Reinforcing Cage

(f) Casting with Design Mixed Concrete

Fig. 7.5 Different Stages of Manufacturing, Joint Details, Storage and Driving of PSG Piles

130

7 Pile Foundation

(g) Completed Pile Segments with Lifting Hooks

(h) Completed Segments Stored in Stack

(i) Bringing Matching Pair of Pile Segments

(j) Proper Placement of Pile Segments

(k) Top Segment Rotated to Lock & Keyed

Fig. 7.5 (continued)

(l) Welded Joints of Pile Segment (Not Recommended)

Capacity of Driven Pile Based on Energy Correlation

(m) Damage Head Due to Hard Driving

131

(n) Damage during Transportation & Handling

Fig. 7.5 (continued)

Preliminary Capacity of Driven Pile Mechanism behind driving pile and conducting SPT and/or pushing standard cone assembly during CPT in ground is basically similar. Values of SPT-N or CPT-q are measures of resistance to driving offered by sub-soil which in turn is related mainly to consistency and shear strength of surrounding soil. Logically, energy required for driving pile shaft or pushing SPT sampler or static cone into ground should be comparable. Based on this concept, energy during soil test and that during pile driving have been correlated to assess preliminary pile capacity using standard dynamic pile driving formula.

Dynamic Pile Driving Formula The so-called Simplex Formula used effectively in many driven piling sites has been adopted in the present development. As per the Simplex Formula safe capacity of pile is given by: In FPS Units: Wh M x U = 0.8 x L (1 + P) where

/

L , 50

132

7 Pile Foundation

U = Ultimate capacity (Ton) L = Driven length of pile (Ft) H = Height of free fall of hammer (Ft) M = Total number hammer blows W = Weight of drop hammer (Ton) P = Final set (Inch/blow) In MKS Units: ( R=

/ ) Np L WH , x x L 2.36 (2.54 + S)

where R = Ultimate capacity (kN) L = Driven length of pile (M) H = Height of free fall of hammer (M) N p = Total number hammer blows W = Weight of drop hammer (kN) P = Final set (cm/blow). It is seen from above, all parameters except value for ‘M’ or ‘Np ’ are not known and ‘set’ value is chosen for termination criteria. At site, M or Np is measured during actual driving. Therefore, if value of ‘M or Np ’ can be estimated from energy correlations, preliminary pile capacity can be estimated.

Correlations Based on Energy Principles Development of quasi-dynamic correlations between SPT, CPT and pile driving is explained through worked-out examples. Energy per unit area required for unit penetration of SPT sampler and CPT cone has been estimated. Similarly, energy per unit area required for unit penetration of (a) 350 mm square and (b) 550 mm diameter circular pile driven by 5 T drop hammer (80 cm fall) were also worked-out. Simple correlations between number of hammer blows per meter of pile penetration (M), N-values and cone resistance (q) have been developed. The correlation is used to estimate total number of hammer blows (M) for driving pile based on ‘N’ or ‘q’ values. A. Standard Penetration Test (SPT) Weight of monkey : W = 65 kg Height of free fall: h = 0.75 m. No. of blows for driving SPT sampler by 30 cm = N, i.e. N/30 blows per cm penetration.

Correlations Based on Energy Principles

133

Effective area at tip of split spoon : (a) Full cross-sectional area: A1 =

] π[ (5.08)2 − (3.5)2 = 10.647 cm2 4

Energy per unit area per cm penetration of split spoon sampler: E S P T1 =

65 × 75 N Wh N = × = 15.262 N kg/cm2 per cm penetration × AS P T 30 10.647 30

(b) 2 /3 of Cross-sectional area considering 35 mm diameter hole in split spoon for sample collection: A2 =

π 4

[(

] ) 5.08 − 3.5 x2 + 3.5 − 3.52 = 6.662 cm2 3

Energy per unit area per cm penetration of split spoon sampler: E S P T2 =

Wh N 65 × 75 N × = × = 24.390 N kg/cm2 per cm penetration AS P T 30 6.662 30

There is an uncertainty about how much tip area of SPT sampler is effective. Considering effective tip area is between (full) & (2/3), average of ESPT1 & ESPT2 : E avg = ½(15.262 + 24.390) × N = 19.826 N kg/cm2 per cm penetration B. Static Cone Penetration Test (CPT) q = cone resistance (kPa) a = area of cone = 10 cm2 Energy/cm of penetration = q × 10/100 = 0.1 q kg/cm2 per cm penetration C. Pile (a) Precast Square Pile (350 mm × 350 mm) Cross-sectional area of 350 mm square pile . Apile = 35 × 35 = 1225 cm2 Weight of pile driving hammer: W = 5 T = 5000 kg.

134

7 Pile Foundation

Average length of free fall : h = 80 cm No. of blows required for driving pile by 1 m: M, i.e. M/100 blows/cm

Pile

Wedge

Energy per unit area per cm of pile penetration: E pile =

5000 × 80 M Wh M = × = 3.265M × Apile 100 1225 100

= 3.265 M kg/cm2 per cm penetration Theoretically in all three cases, energy per unit area per unit penetration should be comparable. i.e. 3.265 M ≈ 19.826 N ≈ 0.1 q or M ≈ 6.07 N ≈ q/32.65 say M ≈ 6 N ≈ q/35 Similar study was done for the cast-in-situ circular pile. (b) Cast-in-Situ Circular Pile Behavior of driven cast-in-situ pile is somewhat different because diameter of pile shoe is kept slightly larger than diameter of pile shell to minimize resistance during driving. This phenomenon is different from the penetration of SPT sampler or CPT cone. In both cases, full friction between surrounding soil and side of split spoon or plunger remains active. Therefore, resistance for cast-in-situ driven pile should be looked somewhat differently. Cross-sectional area of 550 mm dia. pile: APile =

π × 552 = 2376 cm2 4

Quasi-dynamic Analysis

135

Pile Pile Shoe Wedge

As diameter of pile shoe is about 20 mm larger than the pile shell, side friction on pile shell will be much less and half of base area; i.e. 1188 cm2 can be considered effective. Weight of driving hammer: W = 5 T = 5000 kg. Average length of free fall: h = 0.8 m = 80 cm. No. of blow required for driving pile by 1 m = M, i.e. M/100 blows/cm. Energy per unit area per cm of pile penetration: E pile =

5000 × 80 M Wh M = × = 3.367M × A pile 100 1188 100

= 4.208 M kg/cm2 per cm penetration Therefore, 3.367 M ≈ 19.826 N ≈ 0.1 qor M ≈ 4.7 N ≈ q/42 say M≈ 5.0 N ≈ q/40 − − Energy correlations developed above have been used for assessing safe capacity of driven piles. The procedure is termed as quasi-dynamic analysis. Steps for analysis and results of three case studies are presented below. The method has also been used successfully in a few project sites followed by pre- and post-installation tests. Closeness of predicted versus measured results was encouraging.

Quasi-dynamic Analysis Steps to estimate preliminary capacity of driven pile following quasi-dynamic method are given below. 1. N-values from all boreholes are compiled to arrive at normalized profile of N-values versus depth representative for the site 2. Based on field bore log and N-value profile, pile termination level (L) can be selected by experienced geotechnical or piling engineer

136

7 Pile Foundation

3. Size and shape of pile, e.g. circular (diameter), square (side), are selected 4. Type of pile driving equipment, i.e. conventional-driven piling rig or crane mounted diesel hammer or other driver, is selected along with weight & drop height or hammer rating 5. Relationship between ‘M’ and ‘N’ is then derived following procedure outlined above. Profile of ‘M’ upto pile termination level will be developed from Nprofile using the relationships. M-profile to be integrated over full pile length to arrive at estimated total number of blows (∑M) 6. Pile capacity can be calculated following Simplex Formula for specified hammer, driven length (L) & total No. of blows (∑M) and ‘set’ (P) value 7. Driving time can be worked-out from number of blows (∑M) and average interval between strokes 8. Similar procedure can be adopted with CPT data. Normal rating of CPT equipment of about 200 kN capacity is recommended for long piles 9. Efficiency of different driving methods, drop or diesel hammer can be studied by this tool. Optimization of drivability, e.g. selection of weight and drop height of hammer, is also possible 10. It is pointed out quasi-dynamic approach is meant for early assessment of preliminary pile capacity and driving data. The tool can be used in cohesive, cohesionless and stratified areas also Quasi-dynamic method of energy correlation derived above was verified with driving records of piles, N-values and static cone test results from nearby locations. Values of (∑M) were estimated by multiplying N or q values with appropriate factors (derived above). The methods have been verified in three test piles (of different shapes and lengths) under a separate test pile program. Details of test pile work and outcome are presented in the following section.

Test Pile Program Detailed soil investigation comprising of boreholes, SPT, CPT and laboratory tests were conducted for a project site in Haldia, West Bengal. In order to thoroughly investigate and verify the energy correlations, a test pile program was undertaken. Three test piles were driven and load tested (cyclic tests). Description of test piles, estimated ∑M and safe capacity estimated using energy correlations (derived above), were evaluated. The results were compared with results following static and dynamic formulas.

Test Pile Program

137

Description of test piles, estimated profile of M-values following energy relations for full depth, comparison with actual driving records are presented below. Comparison of pile capacities based on conventional geotechnical (static) design and dynamic formula following quasi-dynamic approach has been presented. The results compared very well with results of load tests. Evaluation of other parameters related to driving equipment and that for time study have been presented in following paragraphs. Description of test piles 1. 350 mm square 33 m long precast RCC pile (DP-L) 2. 350 mm square 18 m long precast RCC pile (DP-S) 3. 550 mm diameter 32 m long cast-in-situ RCC pile (DCIS) Depth-wise profile of number of blows (M) estimated based on average SPT and CPT values following energy correlations are compared with actual number of blows for driving the test piles as shown in Fig. 7.6 for Test piles (a) DP-L, (b) DP-S and (c) DCIS. It is observed in all cases that profiles of ‘M’ evaluated from ‘N’ or ‘q’ values based on energy correlations developed earlier match very well with actual pile driving records. Several pile driving parameters namely (a) selecting of type and number of driving equipment, (b) time study and other data can be evaluated by use of quasi-dynamic approach. Match between estimated numbers of blows based on Energy Correlation and actual numbers are presented in Table 7.1. The table also shows number of blows required for driving using Diesel Hammer of 7 T-m rating. It shows considerable reduction in number of blows compared to conventional drop hammer. The tool can be used for studying efficiency of other hammer types. Time required for driving a pile with selected hammer can be determined from time per blow and total number of blows for driving pile. Safe pile capacities were determined using static formula based on (a) shear strengths (C & φ) and (b) cone resistance (q) from CPT following IS: 2911 (Part-I) and dynamic (Simplex) formula. Static and cyclic load tests were carried out on the test piles. The results are summarized in Table 7.2. It is observed results of geotechnical designs are quite close to capacities based on energy correlation for all three test piles. Results of static and dynamic capacities using conventional winch and diesel hammer were also studied. The results are presented in Table 7.3. It is observed test results compared very well with predicted capacity. It is observed, piling parameters estimated based on energy formula compared very well with driving records, estimated pile capacities and load test results. Closeness of the results between estimated and load tests for all three cases is encouraging.

138

7 Pile Foundation No. of Hammer Blows/m , Cone Resistance / 35, N-value x 6

No. of Hammer Blows/m , Cone Resistance / 35, N-value x 6 0

50

100

150

200

250

0

300

50

100

150

200

250

300

350

10.00

10

9.00 8.00

FGL + 6.5

7.00

5 Layer-I : Medium stiff silty clay

FGL + 6.5

6.00 5.00

0

-5

4.00

Test Pile : DP-L Cone Penetration: CPT-4 STP : SS-3 STP : SS-2 STP : BH-10

3.00

Test Pile : DP-S Cone Penetration: CPT-6 STP : SS-5 STP : BH-7

2.00

Layer-II : Very soft to soft silty clay

1.00 0.00

Layer-III : Loose to medium dense silty fine sand

RL (m)

-1.00

RL (m)

-10

-2.00 -3.00 -4.00

-15

-5.00 -6.00 -7.00

-20

Layer-IV : Medium stiff silty clay with decayed wood, veg etc.

-8.00 -9.00 -10.00

-25

-11.00

Layer-V : Stiff silty clay with calcareous nodules

-12.00

-30

Termination of Test Pie DP-S

-13.00

Termination of Test Pile DP-L

-14.00 Layer-VI : Dense to highly dense medium coarse sand

-15.00

-35

Pre-Cast Pile (DP-S) : Comparison of Hammer Blow, N-v alue & CPT

Pre-Cast Pile (DP-L): Comparison of Hammer Blow , N-value & CPT

(a) 350 mm square, 33 m Pre-cast pile (DP-L)

(b) 350 mm square 18 m Pre-cast pile (DP-S)

No. of Hammer Blows/m , Cone Resistance / 40, N-value x 4.5 0

50

100

150

200

250

300

10 FGL + 6.5

5

0

-5

Layer-I : Medium stiff silty clay

Test Pile : DCIS Cone Penetration: CPT-4 STP : SS-9 STP : SS-11 STP : BH-8 Layer-II : Very soft to soft silty clay Layer-III : Loose to medium dense silty fine sand

RL (m)

-10

-15

-20

Layer-IV : Medium stiff silty clay with decayed wood, veg etc.

-25 Layer-V : Stiff silty clay with calcareous nodules

-30

Termination of Test Pile DP-L Layer-VI : Dense to highly dense medium coarse sand

-35

Cast-in-situ Pile : Comparison of Hammer Blows,. N-value & CPT

(c) 550 mm circular 32 m cast-in-situ pile (DCIS)

Fig. 7.6 Comparison between ‘M’ values (based on energy correlation) and Pile Driving Records

Test Pile Program

139

Table 7.1 Estimated Number of Blows (drop and diesel hammers) and Actual data from Test Pile Test Pile Mkd

Pile Size Length

Ref. Soil Data BH, CPT

Type of Rig

DP-L

350 sqr L= 33 m

SS-3 CPT-4

Winch

350 sqr L= 18 m 550 dia L= 32 m

DP-S

DCIS

Relationship

Estimated No. of Blows based on SPT (MBH )

CPT (MCPT )

Avg. (MAVG )

Actual No. of Blows (MACT )

M≃6N≃q/35

2371

2535

2453

2140

Diesel

M ~ 3.5N≃q/ 60

1383

1478

1480

–

BH-7 CPT-6

Winch

M≃6N≃q/35

1252

1251

1251

1372

Diesel

M ~ 3.5N≃q/ 60

730

730

730

–

BH-8 CPT-4

Winch

M ~ 5.0N≃q/ 40

2300

1610

1955

2515a

Diesel

M ~ 3.5N≃q/ 60

1166

1444

1271

–

Note For winch: weight of hammer = 5.0 T, height of free fall = 80 cm For diesel hammer : rated energy = 7.0 Tm a Drop height of hammer was somewhat restricted due to malfunctioning of winch and engine Table 7.2 Comparison of pile capacity based on static and dynamic formula and load test Test Pile Mkd

Pile size and type

Shaft length (m)

Pile capacity (in Ton) based on Static cone

Borehole lab test

Average CPT and BH

Simplex formula

Load test

DP-L

350 Sqr. Precast

33

112

105

108

112

110

DP-S

350 Sqr. Precast

18

68

72

70

70

68

DCIS

550 dia. cast-in-situ

32

114

111

112

96

94

Table 7.3 Comparison of safe pile capacity based on quasi-dynamic approach and load test Test Pile Mkd

Pile size length

Type of rig

DP-L

350 sqr L = 33 m

DP-S DCIS

Safe capacity based on SPT (V BH ) (T)

CPT (V CPT ) (T)

Avg. (V AVG ) (T)

Load test result (PLoad Test ) (T)

Accuracy (%)

Winch

106

113

109

110

95–96

Diesel

108

115

112

350 sqr L = 18 m

Winch

78

78

78

68

85

Diesel

80

80

80

550 dia L = 32 m

Winch

105

99

102

94

88–95

Diesel

93

115

104

140

7 Pile Foundation

Concluding Remarks Importance of quasi-dynamic approach in early assessment of safe capacity and operational aspects of driven piling work has been demonstrated in previous sections. Calculation of estimated total number blows ‘M’ required for driving a pile upto full depth based on SPT or ‘q’ values is simple. An Excel program has been developed for assessing ‘M’-values directly from preliminary field data. Normally considerable time is required between completion of field work, laboratory testing and preparation of final geotechnical report. The time can be utilized advantageously in planning important preactivities for piling work, namely finalization of pile parameters (type and geometry), geotechnical and structural designs, preparation of bid documents, selection of construction agencies, site preparation and procurement of construction materials, setting up site office and supervisory team and so on. The approach has been adopted advantageously in a few projects with great success in saving time and cost of the projects. It is hoped the chapter will be of interest for practicing geotechnical and piling engineers engaged in planning, designs and preparation of design drawings, technical specification and construction management. Design and construction of piles in river and sea (marine piles) have been covered separately in Chap. 10.

Chapter 8

Seepage Control

Introduction Movement of groundwater is a basic part of soil mechanics. Its influence can be found in almost every part of geotechnical engineering. In addition, the elegance of its theory renders it of interest to engineers. Seepage of water through dam and water retaining structures pose serious safety concerns. Water reservoir, ash and tailing (slime) ponds are built with earth dams. Seepages through dam and pond bed are harmful in several ways. If seepage lines meet downstream (D/S) slope face, it causes ‘wet’ surface which is an early warning sign of probable failure as shown below. A dual-compartment ash pond with a partition dyke: left pond full and right pond emptied is shown below. Damages due to seepage through dam body are shown in Fig. 8.1a–f. Prolonged seepage (with high exit gradient) ‘scoop’ out soil particles from toe region adversely affecting stability. Seepage / percolation of water through bed cause not only water loss but contaminate groundwater. Therefore for safety and environmental protection, seepage control is prerequisite in the design of earth dams. Commonly commercial and in-house software packages for slope stability analysis are available, where seepage lines, phreatic / free surface (height of water head in dam body) having impact on stability; profile of seepage line / free surface need to be defined as input data for stability analysis. Profiles of seepage lines and quantity of flow can be determined easily following classical principles of seepage through dam. This chapter covers simplistic approaches to seepage analysis through dam body along with worked-out examples.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_8

141

142

8 Seepage Control

(a) Ash Pond with Partition Dyke : Left – Full, Right - Empty (b) Wet Surface due to Seeepage

(c) Damages to PCC Slope Protection Blocks

(d) Loss of Soil by Seepage below PCC Blocks

(e) ‘Sand Boiling / Piping’ at D/S Pond Bed

(f) Seepage water flow through Relief Pipes

Fig. 8.1 Damages on slope face due to seepage in two-compartment Ash Pond

In power plants and mines, ash and tailing ponds are built for permanent disposal of ash / tailing covering large areas. When the ponds are filled-up, they are abandoned and the space occupied by ‘dead’ ponds are wasted for good. If the deposits in closed ponds can be ‘improved’, developed areas can be used advantageously for building new storage or setting up plant units. Deposited ash and slime contain considerable amount of water as ‘pore water’. If major fraction of which can be extracted, consistency and strength of deposited ash / slime improve considerably resulting in higher bearing capacity with reduction in settlement. Principles of ‘horizontal seepage to well’ can be applied to extract trapped/pore water from deposited ash or slime.

Seepage Through Homogeneous Earth Dam on Impervious Base

143

Risk-free and economic design of deep excavation using braced sheet piles in high groundwater-level areas should start with lowering and maintaining groundwater at safe level which is very important but difficult. Lowering water level can be achieved by controlling seepage in the vicinity of construction sites. Principles of ‘seepage to wells’ are used in the design of dewatering scheme by ‘well point system’. Keeping the above objectives in view, this chapter has been organized to demonstrate the application of basic principles of seepage through homogeneous media to determine seepage through earth dams, improvement of deposits in dead ponds by provision of ‘drainage paths’/‘drainage point’ and ‘well point dewatering’ system. Methods for seepage analysis and control are presented through a number of worked-out examples from real projects. In order to draw attention on possibility of disastrous consequences due to inadequate planning and maintenance of groundwater seepage control systems, few cases histories of failures have been included.

Seepage Through Homogeneous Earth Dam on Impervious Base Seepage pattern through homogeneous dam is shown in Fig. 8.2. Seepage path is determined following Dupuit’s principles. Determination of free surface of seepage and quantity of discharge through homogeneous vertical dam based on Dupuit’s assumption are represented by: q = −ky

dy dx

Fig. 8.2 Seepage path through homogeneous earth dam on impervious base

144

8 Seepage Control

Integrating and substituting boundary conditions: x = 0, y = h1 and x = L and y = h2 in Dupuit’s formula, quantity of seepage is given by: ) ( k h 21 − h 22 q= 2L The equation specifies parabolic surface known as Dupuit’s parabola. In the absence of tailwater (h2 = 0), the line of seepage is seen to intersect impervious base. Also, it should be noted both the discharge and locus of the free surface are independent of dam slopes. Moreover, the free surface is dependent only on geometry and boundary conditions of dam and interestingly not on coefficient of permeability (k) which is required only for estimating quantity of seepage flow. Seepage through earth dam is generally analyzed as two-dimensional phenomenon. The flow domain modeled with a parabolic upstream face and horizontal toe drain (under filter) located at downstream to control/collect seepage water through dam was developed by Kozeny, and the free surface of water is represented by a parabola known as ‘Kozeny’s basic parabola’. Kozeny’s method is simple for determination of seepage surface and estimating quantity of seepage flow from reservoir. Steps for seepage analysis for 20 m and 30 m high ‘homogeneous’ earth dams are presented through a few worked-out examples for demonstration.

Seepage Analysis Through Homogeneous Dams Examples 1 and 2 20 m and 30 m high ‘Homogeneous’ dam are shown in Figs. 8.3 and 8.4, and design parameters are shown in Table 8.1. Method for developing phreatic surface for both dams is demonstrated in the following paragraphs. Surface of seepage through homogeneous dam closely resembles a parabola with corrections at ‘entry’ and ‘exit’ points. The parabolic surface represented by Kozeny’s basic parabola is defined by following equation: y2 − y20 + 2y0 x = 0 or y =

/

2x y0 + y02

Fig. 8.3 Seepage analysis for 20 m high homogeneous dam with rock toe

Seepage Through Homogeneous Earth Dam on Impervious Base

145

Fig. 8.4 Seepage analysis for 30 m high homogeneous dam with horizontal filter

Table 8.1 Design parameters of 20 m and 30 m high dams Description

20 m High Dam

30 m High Dam

Earth Dam Height of dam Crest width Side Slope (H: V) Free Board Design water head: hw

Fig. 8.3 20.0 m 10.0 m 2.0: 1.0 1.5 m 18.5 m

Fig. 8.4 30.0 10.0 2.0: 1.0 1.5 m 28.5 m

Permeability of dyke: k

1.00 × 10–5 cm/s

1.00 × 10–5 cm/s

Filter Zone Permeability of filter: k

Trapezoidal Rock Toe Horizontal Under Filter 2 m high, 6 m base width 1 m thick, 20 m long 1.00 × 10–2 cm/s 1.00 × 10–3 cm/s

where ‘x’ is horizontal distance from the focus, ‘y’ is offset of the parabolic phreatic surface from baseline and ‘y0 ’ is distance from focus to intercept of parabola with vertical line from focus. (Ref. Figs. 8.5 and 8.6). 20 M High Dam Referring (Fig. 8.5) and considering ‘F’ as focus of the parabola and also origin of co-ordinate system (0, 0) co-ordinates of the first point of the parabola estimated

Fig. 8.5 Seepage analysis for 20 m high ‘homogeneous’ dam

146

8 Seepage Control

Fig. 8.6 Seepage analysis for 30 m high ‘homogeneous’ dam with horizontal filter

from geometry of dam and water levels on both sides x = d = 58.1 m and y : (i.e. h) = 18.5 m y0 =

(/ (

h2

+

d2

) )

−d =

/( ) 18.52 + 58.12 − 58.1 = 2.874 m

Co-ordinates of the parabolic phreatic surface for 20 m high dam determined using the above equation are: X (m)

Y (m)

X (m)

Y (m)

2.874

0.00

− 28.0

13.008

0.00

2.874

− 33.0

14.069

− 3.0

5.050

− 38.0

15.056

− 8.0

7.365

− 43.0

15.982

− 13.0

9.110

− 48.0

16.857

− 18.0

10.570

− 53.0

17.689

− 23.0

11.852

− 58.1

18.500

Plotted seepage surface with correction at entry point following A. Casagrande is shown in Fig. 8.5. It is noted the free surface meets rock toe after touching downstream (D/S) slope surface and is not acceptable in design. To prevent this situation, flatter slope is needed which will involve more earthwork in dam building. Flow per unit length of dyke section is given by: q = k·y0, i.e. q = 2.874 × k For k: 1.00 × 10–5 cm/s ∼ = 8.64 × 10–3 m/day Quantity of seepage through homogeneous dyke section: q = 2.874 × 8.64 × 10−3 = 0.0248 M3 /M/Day.

Seepage Through Homogeneous Earth Dam on Impervious Base

147

Estimated quantity of seepage through 20 m high dyke: 0.025 M3 /M/Day 30 M High Dam For 30 m high dam (Fig. 8.6) and considering ‘F’ as focus of the parabola and also origin of co-ordinate system (0, 0) co-ordinates of the first point of parabola estimated from geometry of dam and water levels on both sides: x = d = 53.0 m and y : (i.e. h) = 28.5 m y0 =

(/ (

h2 + d 2

) )

−d =

/( ) 28.52 + 53.02 − 53.0 = 7.177 m

Co-ordinates of the parabolic phreatic line are tabulated below and plotted in Fig. 8.6. X (m)

Y (m)

X (m)

Y (m)

3.588

0.00

− 23.0

19.536

0.00

7.177

− 28.0

21.294

− 3.0

9.725

− 33.0

22.917

− 8.0

12.897

− 38.0

24.433

− 13.0

15.431

− 43.0

25.860

− 18.0

17.603

− 48.0

27.212

− 53.0

28.500

It is noticed even with long horizontal filter, the free surface although did not touch the slope face it passes close to it which is not desirable. This situation can be solved by designing the rock toe which is covered in next section. Flow per unit length of dyke section is given by: q = k·y0, i.e. q = 7.177 × k k: 1.00 × 10–5 cm/s = 8.64 × 10–3 m/day Quantity of seepage through homogeneous dyke section: q = 7.177 × k = 7.177 × 8.64 × 10−3 = 0.062 M3 /M/Day. Estimated quantity of seepage through 30 m high dyke: 0.062 M3 /M/Day Quantities of seepage per unit length for both dykes are shown in Table 8.2. It is observed, estimated seepage is negligible and horizontal filter, and rock toe can cater to the seepage. Example 3 Estimation of Seepage through Homogeneous Dyke with Rock Toe 9 m high homogeneous dyke with rock toe is shown in Fig. 8.7, and control parameters are given in Table 8.3.

148

8 Seepage Control

Table 8.2 Results of seepage analysis Sl. No

Height of Dam (m)

Seepage (M3 /M/Day)

1

20

0.025

2

30

0.062

A. Phreatic Line Method Kozeny’s basic parabola is represented by the following equation: y 2 − y02 + 2y0 x = 0 or y0 = x ±

/(

x 2 + y2

)

where y0 is the distance from focus to intercept of parabola with vertical line from focus. The homogeneous dyke section is shown in Fig. 8.7.

5m

11.25 m

D0 = 3.375

Directrix D 1.5

h = 7.5 m

1.0

G

F S/2 12.75 m 2.25 m

S=3.25

Fig. 8.7 Seepage analysis for 9 m high dam with ‘rock toe’

Table 8.3 Control parameters of 9 m high dyke with rock toe Description

Description

Dyke Section

Rock Toe

Width at top of dyke: 5.0 M

Top width of rock toe: 1.5 M

Height of dyke: 9.0 M

Height: 1.0 M

Slope (H: V): 1.5: 1.0

Slope (H: V): 1.0: 1.0

Base width of dyke: 32.0 M

Base width: 3.5 M Permeability ‘k’: 1.0 × 10–4 M/s

Depth of water: 7.5 M Permeability of dyke ‘k’: 1.0 ×

10–6

M/s

Seepage Through Homogeneous Earth Dam on Impervious Base

149

Considering ‘F’ as focus of the parabola and origin of co-ordinate system (0, 0) L = 11.25 M and 0.3L = 3.375 M Co-ordinates of the first point of parabola (D0 ): x (i.e. ‘d’) = 20.875 m and y (i.e. h) = 7.5 M Let the distance of directrix be at ‘y0 ’ from the focus Or y0 =

√(

) ) √( 2 7.5 + 20.8752 −20.875 = 1.3064 M h 2 + d 2 −d =

The last point of the parabola ‘G’ lies at S/2 from ‘F’ Co-ordinates of the parabola following the above equation are given below: X (M)

Y (M)

X (M)

Y (M)

X (M)

Y (M)

0.00

1.3064

6.75

4.3981

13.75

6.1346

0.75

1.9148

7.75

4.6857

14.75

6.3440

1.75

2.5058

8.75

4.9567

15.75

6.5467

2.75

2.9819

9.75

5.2136

16.75

6.7433

3.75

3.3919

10.75

5.4585

17.75

6.9343

4.75

3.7574

11.75

5.6928

18.75

7.1202

5.75

4.0903

12.75

5.9178

19.75

7.3014

20.75

7.4782

Flow per unit length of dyke section is given by: q = k·y0 , i.e. q = 1.3064 × 10–6 M3 /M/s. B. Graphical Flow Net Method ‘Flow net’ method of seepage analysis can be used effectively for quick verification of quantity of flow through dam. This has been done in following example. Kozeny’s parabola was developed as before for horizontal toe drain. A. Casagrande modified the parabola at entry point at face of rock toe by incorporating a correction factor ‘α’ based on angle of inclination with base. In this method, the phreatic line drawn following Kozeny’s basic parabola is modified at entry and exit points and is known as Casagrange’s extended Kozeny’s solution. Flow nets (i.e. flow lines and equipotential lines) are drawn graphically between phreatic line and dam base and upstream face of dam and upstream face of rock toe following principle of flow net construction.

150

8 Seepage Control

Fig. 8.8 Flow net for 9 m high dam with rock toe

A. Casagrande extended Kozney’s parabola to include dam with trapezoidal rock toe. Distance between basic parabola and seepage line at face at entry of rock toe, (Δa) can be drawn with a fair degree of approximation using chart after Casagrande. For instance, for (1:1) inclination at face of rock toe, ∠α = (90 + 45) = 135°, from chart [(Δa)/(a + Δa)] = 0.14. From the flow net: (Δa + a) = 0.73 M and Δa works out as 0.102 M. This being insignificant and having no influence on estimated seepage flow is not discussed further. The above corrections at entry and exit points made in the flow net for homogeneous dyke section are shown in Fig. 8.8. From the flow net: Number of flow channels (Nf ) = 2. Number of equipotential drops (Nd ) = 11.5 Quantity

of seepage per Nf −6 3 q = k.h · 1.30435 × 10 M /M/s Nd q = 1.30435 × 10−6 M3 /M/s

meter

length

Summary of seepage through homogeneous dyke: Phreatic line method = 1.30642 × 10–6 M3 /M/s Flow net method = 1.30435 × 10–6 M3 /M/s Closeness of both results is encouraging for confidence building. Average flow = 1.30538 × 10–6 M3 /s/M Say 0.113 M3 /M/Day

of

dyke:

Seepage Through Homogeneous Earth Dam on Impervious Base

151

Example 4 Dam with ‘Chimney’ and ‘Horizontal Filter’ A different type of dam section where seepage through dam can be controlled by collecting seepage water through highly permeable ‘chimney filter’ and transmit to toe drain through a long ‘horizontal filter’. The dam is safe because the free surface is cut-off way behind downstream face of dam. Scheme drawing of a dam with chimney and horizontal filters is shown in Fig. 8.9, and control parameters are given in Table 8.4. It may be noted; the vertical filter cuts off flow paths near midway and prevents flow lines reaching D/S face ensuring greater safety (stability) even with ‘stepper’ side slopes. A. Casagrande extended Kozney’s solution to include dams with slope drain and trapezoidal toe drain which has been followed for seepage analysis through dam by two methods: (A) phreatic line and (B) graphical flow net method. A. Phreatic Line Method The homogeneous dyke section with filter is shown in Fig. 8.9

5.0

11.25

1.5

2.25

D0 = 3.375

D 1.5

h = 7.5

1.0

Directrix G

F 16.0m S=6.459

Fig. 8.9 Section through a dam with ‘chimney’ and ‘horizontal’ filters

Table 8.4 Control parameters of 9 m high dam with chimney and horizontal filter Dyke section

Rock Toe

Width at top of dyke: 5.0 M

Top width of rock toe: 1.5 M

Height of dyke: 9.0 M

Height: 1.0 M

Slope: (H: V): 1.5: 1.0

Slope: (H: V): 1.0: 1.0

Water Level from top: 1.5 M

Chimney and Horizontal Filter

Depth of water: 7.5 M

Width/thickness of sand filter: 1.0 M

Chimney filter start from middle of crest

Slope: (H: V): 0.75: 1.0

Permeability of dyke ‘k’: 1.0 × 10−6 M/s

Permeability of filter ‘k’: 1.0 × 10−4 M/s

152

8 Seepage Control

Distance of ‘F’ from center line = (8 × 0.75 + 1.0) = 7 M Distance of D0 from center line = (2.5 + 2.25 + 3.375) = 8.125 M Distance of D0 from D = (8.125 − 7.00) = 1.125 M L = 11.25 M and 0.3 L = 3.375 M Considering ‘F’ as focus of the parabola and origin of co-ordinate system (0, 0) Co-ordinate of the first point of parabola (D0 ): x (i.e. ‘d’) = 1.125 M and y (i.e. h) = 7.5 M Let the distance of directrix be at ‘S’ from the focus. Hence, S = 6.4589 M. The last point of the parabola ‘G’ lies at S/2 from ‘F’. Please refer to Fig. 8.10 for clarification. Co-ordinates of the parabola: X (M)

Y (M)

X (M)

Y (M)

0.00

6.4589

− 1.00

5.3665

0.50

6.9409

− 1.50

4.7266

1.00

7.3916

− 2.00

3.9852

− 0.50

5.9379

− 3.00

1.7216

Quantity of seepage per q = (S · k) = 6.4589 × 10−6 M3 /s/M

meter

length

of

q = 6.4589 × 10−6 M3 /M/s

Horizontal Filter

Rock Toe

Fig. 8.10 Flow nets through dam with ‘chimney’ and ‘horizontal’ filters

dyke:

Seepage Through Homogeneous Earth Dam on Impervious Base

153

B. Graphical Flow Net Method The flow net for homogeneous dyke section (Fig. 8.9) is drawn and shown in Fig. 8.10. Distance between basic parabola and seepage line at rock toe, (Δa) determined as in Example-3 works out as Δa = 0.6079 M. The corrections are made in the flow net (Fig. 8.10). From graphical flow net: Number of flow channels (N f ) = 1.2 Number of equipotential drops (N d ) = 1.4 Quantity

of seepage per Nf −6 3 q =k·h· = 6.4286 × 10 M /M/s Nd q = 6.4286 × 10−6 M3 /M/s

meter

length

of

dyke:

Summary of seepage through dyke with chimney and horizontal filter From phreatic line method = 6.4589 × 10−6 M3 /M/s From flow net method = 6.4286 × 10−6 M3 /M/s Average =

6.44375 × 10−6 M3 /M/s Say 0.557 M3 /M/Day

Quantity of Seepage for Different Types of Filter and Rock Toe Methods for estimating quantity of seepage through dam with different filter and rock toe arrangements have been presented above. But the examples are for different dam height and water depths. Question may arise which system will be most effective for a dam of given control parameters. To resolve the issue, studies were conducted on a model dam with same control parameters (height, side slopes, water depth) but with different exit systems. Results are summarized below. Phreatic line method has been adopted to determine seepage through the 15 m high dam (water depth = 13 m, free board = 2 m) under full reservoir conditions. Three different exit arrangements have been considered: (i) Rock toe (without sand filter) (ii) Horizontal filter and rock toe (iii) Chimney with horizontal filters and rock toe. A 15 m high dam (water depth = 13 m) with the above three types of seepage water collection systems has been selected for study. The phreatic surfaces have been determined following Kozneys’ basic parabola method. Resulting phreatic lines are shown in Figs. 8.11, 8.12 and 8.13 with (a) rock toe, (b) horizontal filter and rock toe and (c) chimney with horizontal filter and rock toe, respectively. Quantities of seepage for all cases have been estimated for comparison.

154

8 Seepage Control

Fig. 8.11 Section through 15 high dam with rock toe (no sand filter)

Fig. 8.12 Section through 15 high dam with horizontal filter with rock toe

Fig. 8.13 Section through 15 high dam with chimney and horizontal filter with rock toe

It is seen above (Fig. 8.11), the phreatic line crosses lower portion of downstream face which means, surface of D/S slope is likely to be wet and is not permissible. Therefore, partial horizontal filter along with rock toe has been included to restrict the flow path well within the body of dam as shown in Fig. 8.12. To assess influence of chimney and horizontal filters, seepage analysis has also been carried out and resulting phreatic line is shown in Fig. 8.13. Estimated quantities of seepage through the 15 m high model homogeneous dam (water depth 13 m) and with different arrangements of rock toe and filters for collection of exit water under full reservoir condition are presented in Table 8.5 for comparison.

Seepage Through Homogeneous Earth Dam on Impervious Base

155

Table 8.5 Estimated seepage through dam with different exit system Figure No

Description

Seepage (M3 /M/Day)

Figure 8.11

Rock toe and no sand filter

0.075

Figure 8.12

Partial horizontal filter with rock toe

0.096

Figure 8.13

Chimney and horizontal filter with rock toe

0.381

Table 8.5 reveals effectiveness of different exit water collection systems through dam body. Higher quantity of seepage means the phreatic line will be further away from D/S slope face, and the dam is safer for long time. It is observed that estimated quantities of seepage are nominal and horizontal filter with rock toe is capable of safe discharge of seepage water. As such chimney filter may not be essential. ‘Core and Shell’ Type Dam In case, quantity of seepage was high, a ‘cut-off’ core comprising of impervious cohesive soil would have been provided in-between shell on both up and downstream sides. Typical model of ‘core and shell’ type dam is shown in Fig. 8.14. As construction of ‘core and shell’ type dam is difficult, this type of dam section is rarely used. Example 5 Design of Dam with Provision for Raising Height in Future As mentioned in the beginning, capacity addition of pond is possible by raising height of dam in future. Provision of wider crest will facilitate height raising say by another 5 m or so. Out of several methods, downstream raising appears suitable as construction can be carried out while the storage pond is in operation. Typical scheme for downstream raising is shown in Fig. 8.15. Seepage analysis through raised dam can be carried out as before following method of Kozeny’s basic parabola. Seepage Analysis Through D/S Raised Dam Seepage analysis through ‘raised dam’ is to be carried out. Model dam for future raising height of dike by 8 m adopting D/S raising methods is shown in Fig. 8.16a, and control parameters are presented in Table 8.6.

Fig. 8.14 A 20 m high ‘core and shell’ type dam

156

8 Seepage Control

Fig. 8.15 Increasing height of existing dam by ‘downstream raising’

(a) Details of Upstream Raised Dam

(b) Flow Net with Four Flow Channels

Fig. 8.16 a Details of upstream raised dam b Flow net with four flow channels Table 8.6 Control parameters of present dyke and planned raising by 8 M in future RL of Top of Masonry Dyke: + 540.0

Width at top of dyke: 5.0 M

RL of Top of Earthen Dyke: + 538.5

Side Slope (H: V): 1.5: 1.0

RL of Maximum Water Level: + 538.0

Free Board: 2.0 M

RL of Top of Present Dyke: + 534.0

Depth of filter to existing core: 2.0 M

RL of Top of Existing Core: + 532.0

Design water head (MWL to filter) H w : 8.0 M

RL of Horizontal Sand Filter: + 530.0

Permeability of dyke kAvg : 4.55 × 10–7 M/s k Max : 7.33 × 10–7 M/s

Seepage Through Homogeneous Earth Dam on Impervious Base

157

The Kozeny’s parabola method has been adopted for estimating seepage through raised dyke for new height and maximum water depth. Seepage analysis was carried out following phreatic line method. Phreatic Line Method Kozeny’s basic parabola is represented by the following equation: y2 − y20 + 2y0 x = 0 ) ( ¨ x2 + y2 ory0 = x ± O where y0 is the distance from focus to intercept of parabola with vertical line from focus. The raised dyke section is shown in Fig. 8.16a Considering ‘F’ as focus of the parabola and also origin of co-ordinate system (0, 0) D = 14.113 M, L = 12.00 M and 0.3 L = 4.00 M Co-ordinates of the first point of parabola (D0 ): x = D0 : (d + 0.3 L) = 14.113 + 4.0 = 18.1134 M and y: (i.e. H w ) = 8.0 M Let the distance of directrix be at ‘y0 ’ from the focus y0 =

/

HW2 + D02 − D

Substituting values of HW and D0 in above equation, y0 = 1.688 M Or y0 = 1.688 m and the parabola start ‘a0 ’ lies at y0 /2 from ‘F’, i.e. a0 = 1.688/2 = 0.844 m Start point of the parabola: (x = + 0.844, y = 0.0) Co-ordinates of the parabolic phreatic line following the above equation have been worked-out and tabulated. X (M)

Y (M)

X (M)

Y (M)

0.00

1.6880

− 10.0

6.0506

− 1.0

2.4951

− 11.0

6.3235

− 2.0

3.0986

− 12.0

6.5850 (continued)

158

8 Seepage Control

(continued) X (M)

Y (M)

X (M)

Y (M)

− 3.0

3.6024

− 13.0

6.8365

− 4.0

4.0440

− 14.0

7.0791

− 5.0

4.4418

− 15.0

7.3137

− 6.0

4.8058

− 16.0

7.5410

− 7.0

5.1461

− 17.0

7.7616

− 8.0

5.4642

− 18.0

7.9761

− 9.0

5.7649

− 18.113

8.0000

Flow per unit length of dyke section is given by:

q = k · y0

q = (1.688 × k) M3 /M/s Flow net with four flow channels for the same raised dam is shown in Fig. 8.16b. From the flow net method Fig. 12.8b: Number of flow channels (N f ) = 4; Number of equipotential drops (N d ) = 20, h = 8.0 m. Flow per unit length of dyke section is given by: q = k.h. NN−d f = (1.60 × k) M3 / M/s. Flow per unit length based on (a) phreatic line and (b) flow net methods are comparable. Summary of seepage per meter through raised dyke Results of permeability tests carried out on samples, average and maximum values of ‘k’ are: Average 4.55 × 10–7 cm/s = 0.393 M/Day. Maximum 7.33 × 10–7 cm/s = 0.633 m/Day. Quantity of maximum seepage through raised dyke: (a) Phreatic Line Method: 1.688 × 0.633 = 1.068 M3 /M/Day (b) Flow Net Method: 1.60 × 0.633 = 1.013 M3 /M/Day Estimate quantity of seepage through raised dyke about 1.0 M3 /M/Day.

Impervious Liner at Reservoir Bed Raw water reservoirs are generally constructed by excavating few meters below ground and constructing earth embankment of design height above ground. In-flow and out-flow of seepage water from reservoir bed needs to be prevented. Earlier practice was to provide ‘impervious clay blanket’ at reservoir bed and embankment with clay core. Presently impervious films (liner) of various specifications and make are available.

Impervious Liner at Reservoir Bed

159

The liners are delivered in rolls, which are spread on prepared bed and joined by hot air welding or adhesive. Edges of films are encased properly. The films made of inert materials are flexible, durable, stretchable and are effective in preventing seepage. But in few cases such liners are observed to fail after a few years of operation. Repair of damaged liner is very difficult process and is seen to fail after few years. The reason is not so much with quality of material but more on detailing and workmanship. It is observed that liners are often laid on hard PCC bed and/or the film is covered with PCC mat or precast PCC slabs joined with cement mortar. The problem lies with the hard bed or hard protective cover. It is to be noted a large water body of few meter of water depth impose immense load which induce ground settlement typically of saucer shape at pond bed under full reservoir condition. Under low water condition, the bed tries to rebound. Due to reversing settlement and rebound, the hard bed suffers multiple cracks which continue to progress area and depth-wise with time shattering the hard bed and/or hard protective cover. Sharp edges of concrete and stone chips cause multiple puncher/rupture of liner resulting in water loss through multiple leakages. Instead of hard bed or protective layer, flexible treatment will be logical. Flexible treatment will allow safety against settlement / rebound of bed due to variation in water depths. Simple steps outlined below might be helpful in preventing damage to impervious liner. Steps of flexible treatment below and on top of liner shown in Fig. 8.17 are outlined below for reference. Detailed scheme for liner placement is to be prepared for each case. (a) Bed and sides of excavation to be inspected for evenness / uniformity and compacted thoroughly. (b) A layer of sand (~100 to 150 mm) to be laid and levelled before laying liner. (c) Liner will be laid loosely and extra length to be left as provision for expansion. (d) Another layer of sand (~100 to 150 mm) will be placed on liner. (e) Sand and film to be protected with brick laid on edge or precast PCC slab but without mortar joint. (f) Special care should be taken at junction between bed and slope face and at top of reservoir.

Brick on edge / PCC slab 100 mm tk. sand

Fig. 8.17 Detail of placement and protection of impervious liner in reservoir

Film

160

8 Seepage Control

In-Situ Improvement of ‘Dead and Abandoned’ Flyash/ Tailing Ponds In thermal power plants and mines, ash/tailing ponds are built for permanent disposal of flyash/tailing. On reaching full capacity, the ponds are closed and abandoned for good. In this process, vast areas of land are wasted. It however is possible to utilize closed ponds for fresh slime/ash storage or expansion project. Ash and slime deposits in dead pond hold considerable amount of water trapped in voids and pore spaces. If major fraction of trapped water can be extracted, consistency and shear strength of deposited materials improve significantly resulting in higher bearing capacity with reduction in settlement which is prerequisites for new construction. Therefore, focus of improvement should be on accelerating trap water removal process. Pore or trapped water can be extracted following the principles of ‘horizontal seepage to well’ by constructing ‘Drainage Paths’. The drainage paths accelerate consolidation process under the surcharge from fresh fill. For faster consolidation of large areas of dead pond, water extraction process can be further accelerated by improving design of drainage path to ‘Drainage Point’. In this process, faster consolidation is achieved by installing drainage points and connecting them to common header to pump-out pore water. Drainage Path/Drainage Point System Simple steps for extraction of trapped/pore water by installing drainage system are briefly outlined below. Consistency, strength and depth-wise variation of filled pond are to be determined by carrying out soil test. Scheme for improvement adopting principle of horizontal seepage to wells is to be designed based on soil data. The treatment basically comprises of the following steps (Ref. Figure 8.18): Step-1: For faster improvement in upper layers, ‘drainage paths’ described below and shown in Fig. 8.18: (a) are installed. (a) Cased boring of 400–500 mm diameter 6–8 m deep holes at about @ 5–6 m c/c grid to be sunk (b) Inserting geotextile wrapped HDPE strainer pipe (bottom plugged) centrally inside borehole (c) Filling annular space with filter media (graded gravel and course to medium clean sand) packed loosely (d) Top of boreholes to be sealed with bentonite/clay plug for about 1.0 m length. The filter pipe is to be kept projecting for escape of water to facilitate drainage of trapped water from stored ash/tailing (e) After completion of wells, the area is to be covered with 1.0 m thick granular draining material like sand, gravel, granulated slag or mine overburden.

Well Point Dewatering System

(a) Detail of ‘Drainage Path’

161

(b) Detail of ‘Drainage Point System’

Fig. 8.18 Scheme for improvement of deposited flyash/slime in ‘dead’ pond a Detail of ‘drainage path’ b Detail of ‘drainage point system’

Step-2: Finished ground levels (FGL) of such area almost always need to be raised by a few meters by placing new fill-in layers and compacted mechanically. The fill acts as surcharge for consolidation process and the drainage paths greatly accelerate the process. Step-3: For faster improvement of larger areas, drainage well system is modified by connecting a number of wells to common header pipe and pump to extract water and discharge to proper outlet. This system is termed drainage point System and is shown in Fig. 8.18b. Step-4: It is recommended to verify actual improvements achieved by conducting soil tests after treatment. The methods have been used successfully for improving deposited flyash in active ash pond for setting up color coating of steel sheets in a steel plant and also in a filled-up tailing pond in a zinc beneficiation plant.

Well Point Dewatering System For deep excavation in alluvium soil with high groundwater level, controlling seepage water is essential but difficult. Seepage of groundwater can be controlled effectively by adopting properly designed well point dewatering system. For depths of excavation greater than 8 m, it is advisable to adopt temporary ‘well point dewatering’ system designed based on soil data, hydrological parameters and technical requirements.

162

8 Seepage Control

Design of well point dewatering system is based on principle of ‘gravity flow to wells’. The design procedure is simple and can be carried out in office using hand calculator. Depending on site considerations and technological requirements, single or multi-stage well point system may be required. In steel and thermal power plants (TPP), ore/coal transported by rail wagons are unloaded mechanically for returning rakes to railways urgently. Unloading is done mechanically in (a) Wagon Tippler (WT) where each wagon is literally toppled side-wise to drop entire load into underground hoppers and (b) track hopper (TH) where full rail rake enters long building for mechanically unloading contents from wagons into a series of underground hoppers or belt. Unloaded materials are conveyed to ore / coal stockyards through a network of underground and on-ground conveyor system connected through (c) junction houses (JH). For construction of foundations for WT, TH and JH deep excavation along with dewatering are essential. In such situation, there is no better alternative but to adopt single or multi-stage well point system depending on site conditions and technological requirements. Individual ‘well point’ is made by boring 300 to 500 mm diameter cased borehole upto 2–3 m below bottom of planned dewatering level, inserting strainer pipes (bottom closed) wrapped with non-woven geotextile and short piece of PVC or GI pipe attached at top for connection to header pipe. Assembled strainer pipe is inserted centrally in boreholes, annular space is filled with filter grade sand and mouth plugged with bentonite clay to seal air passage [Ref. Figure 8.17b]. A number of wells are connected to common header pipe to pump. Dewatering is to be done by regulated pumping from the wells and simultaneously monitoring GWL. Well point system for deep dewatering has been adopted successfully at several project sites. Theoretical basis for design and steps for calculation is presented. Coal transported by rail is unloaded in WT and TH is stored in coal yards. For construction of foundations for WT, TH, JH and conveyor tunnels, deep excavation with sheet pile protection needed. For economic design of braced sheet pile, slope profile of open excavation and safety during entire construction period, design and operation of proper dewatering system are essential. Technological requirements on depths of foundation and dewatering for main units are shown in Table 8.7. Table 8.7 Technological requirements for depth of dewatering Unit name

Max. Depth of foundation (m)

Depth of dewateringa (m)

Wagon Tippler (WT)

RL—13.0

11.5

Junction House (JH)

RL—10.0

8.5

Track Hopper (TH)

RL—8.5

7.0

a Depth

safety

of highest water level in excavation considering GWL @ − 2.5 m plus 1.0 m for additional

Well Point Dewatering System

163

Geotechnical Investigation Following geotechnical investigation was carried out over the construction areas (a) Soil investigation by carrying out boreholes, field and laboratory tests Geotechnical investigation revealed following stratigraphy: EGL to 2.0 m: Top layer: Silty clay 2.0–7.0 m: Second layer: Soft to very soft clayey silt with mica flakes (N = 2–4) 7.0–22.0 m: Followed by: Medium to dense fine sandy silt/silty sand with mica (N = 15–29) At the time of geotechnical investigation, groundwater encountered at 2.5 m below EGL (b) Results of in-situ permeability tests by falling head method are shown below. Depth

Strata

Permeability ‘k’ (cm/s)

5.0

Clayey silt

4.39 × 10−5

9.9

Clayey silt

2.71 × 10−5

12.5

Sandy silt

4.01 × 10−5

14.0

Sandy silt

4.56 × 10−5

(b) Full scale ‘pump-out test’ Test parameters and results of pump-out test: (a) (b) (c) (d) (e) (f) (g) (h) (i) (j)

Depth of Test: 23.50 m Submergible Pump: 16.0 m below EGL Capacity of Pump: 1 HP Static Water Level: 4.252 m Total Aquifer Tapped: 5.50 m Aquifer Thickness: 21.0 m Constant Discharge: 23.563 m3 /day Total Draw Down: 7.06 m (operated for 6 h) Specific Capacity: 3.338 m2 /day Hydraulic Conductivity (k): 1.1 × 10– 04 Cm/s.

Control Levels Depth from EGL of control levels selected for design profile of open excavation presented in Table 8.8.

164 Table 8.8 Control levels for design profile of open excavation

8 Seepage Control

Description

RL (M)

Depth from EGL

Reference Level

0.0

–

EGL /NGL

− 2.5

0.0

GWL (Pump test)

− 6.75

4.25 m

1st berm

− 4.72

2.22 m

2nd berm

− 7.22

4.72 m

3rd berm

− 8.72

6.22 m

Bot. of Exvn

− 11.72

9.22 m

Max. WL at pit bot

− 13.00

10.50 m

Scheme for Well Point Dewatering Design Considerations 1. Although groundwater was recorded at 4.25 m below GL during pump-out test, design water level considered at 2.5 m below GL considering rain during extended construction period. 2. Depths of excavation varied from 8.0 to 12.0 m. In order to ensure dry and safe working condition at bottom of excavation eliminating probability of the highest water level at pit bottom restricted to more than 1.0 m below the deepest excavation level. 3. Maintaining effective maximum level calls for lowering water level at edge of excavation to 11.5 m. 4. Considering geometry and hydraulic parameters, 11.5 m lowering of water level by single stage well points was not feasible. Therefore, it was decided to adopt two stage well point dewatering system, viz. Upper (1st) and Lower (2nd) stages. 5. After a number of trials, it was observed that well points in first (upper) and second (lower) stages can be located 500 mm above 1st and 2nd berm levels at 2.22 m and 4.72 m depths from EGL. A series of wells are to be connected by common header to pump. 6. Size, depth, spacing, discharge, etc., for the well point system have been workedout following ‘Method of Analysis’ and ‘Calculations’ described below. Method of Analysis Design of well point dewatering system is based on classical approach of ‘Gravity Flow to Partially Penetrating Wells’ midway between and parallel to ‘Two line Sources’ (Fig. 8.19). Spacing of wells is calculated following principle of flow to ‘infinite line of partially penetrating wells from an infinite line source of seepage’ (Fig. 8.19). Design of well point system to finalize location of wells, levels, diameter and depth of strainer, lowered phreatic line, etc., are based on results of field pumpingout test. Analytical model and formulae for evaluating seepage flow to wells are outlined in the following paragraphs.

Scheme for Well Point Dewatering

165

L

l

l

QP

L

QP

Line Source

hs h0 b

hD

H

b

Fig. 8.19 Gravity flow to two partially penetrating wells from two line sources

1. Gravity flow to partially penetrating wells midway between and parallel to two line sources of seepage (Fig. 8.19) is adopted for estimation purpose. Where l = distance from center line of excavation to well L = distance from well to line source of seepage b = diameter of well hD = head midway between wells H = distance from impervious layer to GWL Head hD midway between two slots can be estimated from the following equation: [ h D = h0

C1 C2 (H − h 0 ) + 1.0 L

]

Parameters are shown in the above figure. C 1 , C 2 depend on (l/h0 ) and (b/H) and read from curves. 2. Spacing of well points is based on principal of flow to infinite line of partially penetrating wells from an infinite line source of seepage. (Fig. 8.20). Line Source of Seepage QP

QP

a

QP

a

QP

a

QP

a

QP L

a

Infinite line of wells Spacing = a

Fig. 8.20 Flow to infinite line of wells from an infinite line source of seepage

166

8 Seepage Control

Spacing of well points (a) is given by the following expression: a h 2D − h 2w a ln = 2 2 2π L 2πrw H − hD 3. Estimate of flow per well is based on gravity flow to partially penetrating slot from a line source of seepage. Discharge per well is given by: ] [ ) H − h0 k ( 2 H − h 20 Q P = a 0.73 + 0.27 H L 4. Total number of wells (n) is determined by dividing length of berm by spacing ‘a’ and multiplied by 2 for both sides. Total discharge from wells is evaluated by multiplying with number of wells: = (QP × n). 5. Choice of pumps, header and outlet will depend on cumulative discharge from a number of wells. 6. For effective dewatering, it is necessary to operate pumps in both upper and lower stage wells. Operation of pumps could be regulated after achieving stable and satisfactory working condition at site. 7. Estimated gross volume of discharge determined following above procedure can be cross-checked with approximate method for computation of flow to dewater an excavation. q=

) ( π k H 2 − h 2w ( ) ln rRw

NOTE: nomenclatures used in above formulae, e.g. hw , rw, etc., have been defined in sketches and in detailed calculations. Detailed Calculations Analytical steps for two-stage well point dewatering system arrived after a number of trials following the above approach are presented in detail in the following paragraphs. General arrangement and details of two-stage well point system are shown schematically in Fig. 8.21. As mentioned earlier, lowering of water level by 11.0 m will be achieved in two 5.5 m stage intervals. Detailed calculations for stage-wise dewatering system are presented below. Stage-1 (Upper Level) Lowering of water level from RL—4.5 M to RL—10.0 M, i.e. 5.5 m H = (22.0 − 4.5) = 17.5 m

Scheme for Well Point Dewatering

167

Fig. 8.21 Profile of excavation with two-stage well points and phreatic surface

hD = (22.0 − 10.0) = 12.0 m l = (10.50 + 15.42) = 25.92 m Say 26 m Assume h0 = hD = 12.0 m H − hD = 17.5 − 12.0 = 5.5 m, b = 50 mm ∼ = 0.05 m Trial-1 l 26.0 b 0.05 = = 2.17 and = ≈ 0.0 hD 12.0 H 17.5 From Fig. 3.22 (‘Foundation Engineering’ by G. A. Leonards): C 1 = 1.0 and C 2 = 1.45. Based on layout, distance of line source assumed: L = 50 m (this parameter is not much sensitive) [

] C1 C2 + 1.0 = 13.9 − h (H 0) L i.e. hD |1 = 13.9 m h D = h0

Trial-2 H D − h0 = 13.9 − 12.0 = 1.9 m Assume h0 = 12.0 – 1.9 = 10.1 m b 0.05 l 26.6 = 2.57 and = ≈ 0.0 = hD 10.0 H 17.5

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8 Seepage Control

C 1 = 1.02 and C 2 = 1.45 Substituting values of C1 and C2 and (H − hD ) = (5.5 + 1.9) = 7.4 m hD |2 = 12.3 m which is reasonably close to required value of 12.0 m Therefore, hD = 12.0 m and h0 = 10.1 m (H – h0 ) = (17.5 – 10.1) = 7.4 m Assume (h0 – hw ) ≈ 0.01 H = 0.01 × 17.5 = 0.175 m hw = 12.0 − 0.175 = 11.825 m. Spacing of well points (a) is given by following equation: a h 2D − h 2w a ln = 2 2 2π L 2πr H − hD w Substituting values of and solving for ‘a’: hD = h0 = 12.0 m, hw = 11.825 m, L = 50.0 m, H = 17.5 m, For bore diameter of 150 mm, radius: rw = ½(150/1000) = 0.075 m Substituting above values in above equation: a = 3.845 m Adopt spacing of well points: a1 = 3.5 to 4.0 m c/c Discharge per well is given by: ] ) H − h0 k ( 2 H − h 20 Q P = a 0.73 + 0.27 H L [

Substituting a = 3.5 m, k = 0.095 m/day, H = 17.5 m, h0 = 10.1 m, H − h0 = 7.4 m QP = 1.15 m3 /day per well Increasing discharge by 30%: yield per well: Q = 1.3 × 1.15 ∼ = 1.5 m3 /day/well Stage-2 (Lower Level) In order to bring draw-down level to EL-13.0 which is more than 1.0 m below bottom-most level of excavation (EL-11.72 M), water level at well to be lowered from EL-10.0 M to EL-15.5 M, i.e. 5.5 m. H = 22.0 m hD = (22.0 − 13.0) = 9.0 m l = 15.42 m Say 15.5 m Assume h0 = hD = (22.0 − 13.0) = 9.0 m H − hD = 17.5 − 12.0 = 5.5 m

Scheme for Well Point Dewatering

169

Trial-1 l 15.5 b 0.05 = = 1.72 and = ≈ 0.0 hD 9.0 H 17.5 From Fig. 3.22 (Leonards): C 1 = 0.98 and C 2 = 1.45. As before, distance of line source: L = 50 m [ ] C1 C2 h D = h0 (H − h 0 ) + 1.0 = 11.17 L i.e. h D |1 = 11.17 m Trial–2 H D − h0 = 11.17 − 9.0 = 2.17 m Assume h0 = 9.0 − 2.17 = 6.83 m b 0.05 l 15.5 = 2.27 and = ≈ 0.0 = hD 6.83 H 17.5 From Fig. 3.22 (‘Foundation Engineering’ by G. A. Leonards): C 1 = 1.02 and C 2 = 1.45 Substituting values of C 1 and C 2 and (H − hD ) = (5.5 + 2.17) = 7.67 m hD |2 = 8.38 m which is reasonably close to required value of 9 m. Therefore, hD = 9.0 m and h0 = 6.83 m ∴ (H − h0 ) = (17.5 − 6.83) = 10.67 m Assume (h0 − hw ) ≈ 0.01 H = 0.01 × 17.5 = 0.175 m ∴ hw = 9.0 − 0.175 = 8.825 m Spacing of well points (a) is given by the following equation: a h 2D − h 2w a ln = 2π L 2πrw H 2 − h 2D Substituting the following values and solving for a: h D = h 0 = 9.0 m, h w = 8.825 m, L = 50.0 m, H = 17.5 m, rw = 0.075 m Substituting above values in the equation: a = 2.565 m Adopt spacing of well points: a2 = 2.5 m c/c. Discharge per well is given by:

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8 Seepage Control

] [ ) H − h0 k ( 2 H − h 20 Q P = a 0.73 + 0.27 H L Substituting a = 2.5 m, k = 0.095 m/day, H = 17.5 m, h0 = 9.0 m, H − h0 = 8.5 m QP = 0.929 m3 /day per well say QP = 1.0 m3 /day per well Increasing discharge by 30%: yield per well: Q = 1.3 × 1.0 ∼ = 1.3 m3 /day/well

Number of Wells Stage-1 (Upper Level) Actual length of upper-level berm = 80 – 2 × (3.33 + 0.75) = 71.84 ≈ 72 m Considering spacing of wells: a1 = 3.5 m No. of wells on one side = (72/3.5 -1) ≈ 19 Nos. For both sides, No. of wells = 2 × 19 = 38 Nos. Discharge from Stage-1 wells: 38 × 1.5 = 57.0 m3 /day Stage-2 (Lower Level) Actual length of upper-level berm = 80 − 2 × (14.5) = 51 m. Considering spacing of wells: a2 = 2.5 m. Number of wells on one side = (51/2.5 -1) ≈ 19 Nos. For both sides, No. of wells = 2 × 19 = 38 Nos. Discharge from Stage-1 wells: 38 × 1.3 = 49.4 m3 /day. Estimated total discharge: Upper wells (38 Nos.): 57.0 m3 /day Lower wells (38 Nos.): 49.4 m3 /day Total (76 Nos.): 106.4 m3 /day.

Cross-Check (Approximate Method) It is recommended to verify total discharge determined above by approximately assessing flow quantity to dewater an excavation following Eq. (14.4), pp 818 of ‘Foundation Analysis and Design’ 5th Ed. by J. E. Bowles (Ref. Figure 8.22).

Installation and Operation of Wells

171

Fig. 8.22 Cross-checking flow to dewater excavation by approximate method

B = 60 m

L=85 m rw

50 m

R r

8.5 m H = 17.5 m hw rw

R

) ( π k H 2 − h 2w ( ) Q= ln rRw / where rw = 80×60 = 39.09 m Say 40 m π Substituting the following values in above equation rw = 40 m;

R = 50 + 40 = 90 m;

H = 17.5 m h w = (17.5−8.5) = 9.0 m

k = 0.095 m/day q = 82.9 m /day 3

Increasing by 30%, q = 107.8 m3 /day which compares very well with 106.4 m3 / day. Estimated total discharge from 76 wells may be considered at 110 m3 /day. Estimated discharge from (a) detailed calculations match very well with that from (b) approximate method which is encouraging. The pumping system can be planned accordingly.

Installation and Operation of Wells Stage-1 wells to be installed after excavation upto 2.0 m below EGL, i.e. upto 1st berm level with header located at RL-4.22 m. 9.0 m long wells (6.0 m stand-pipe and 3.0 m strainer, bottom plugged) are required to lower water level (WL) from RL-4.5 to RL-10.0 to permit progress of excavation upto 3rd berm level (RL-8.5). Stage-2

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8 Seepage Control

wells shall be installed after excavation approaching 3rd berm level. Length of wells shall be 10.7 m (7.7 m stand-pipe and 3.0 m strainer, bottom plugged). Stand-pipes and strainers of 50 mm diameter shall be installed in 400–500 mm diameter casing-protected boreholes. Strainers (bottom closed) to be wrapped with non-woven geotextile and the annular space between bore and strainer to be filled with shrouding material comprising of clean graded granular materials parallel with withdrawal of casing pipes. General arrangement of wells on both sides of excavation is shown in Fig. 8.23. General arrangement and details for two-stage well point dewatering system shown in Fig. 8.21 are reproduced below for preparation of plan and cross section of design drawing. It is to be noted that after completion civil works above GWL at one location, the system of wells will be shifted progressively to next section and the process is repeated until completion of construction of all foundations upto above local GWL. After installation of Stage-1 wells, pumping will start and continue till stable condition is reached. Excavation below 1st berm level shall start only after achieving stability. Similar procedure shall be followed after installation of Stage-2 wells and continuous pumping needed to maintain stability of sides of excavation. It is important to note that simultaneous pumping of both Stage-1 & Stage-2 pumps are necessary at initial stage. It is advised to install piezometers for monitoring actual water level in the aquifer. Sequence of operation of pumps shall be controlled / regulated based on site condition.

Fig. 8.23 Excavation plan showing general arrangement of wells

Hazards Due to Failure of Groundwater Control

173

Fig. 8.21 Profile of excavation with two-stage well points and phreatic surface

General arrangements of well points and connection to common header pipe to pump are shown in Fig. 8.21.

Importance of Well Point Dewatering System Deep excavation in soft soil without controlling groundwater can lead to serious side collapse and bottom heave. Side collapse during initial stage of excavation at a project site in Haldia, West Bengal, is shown in Fig. 8.25a. Subsequently, the risks were eliminated by implementing one- and two-stage well point dewatering (WP) systems. The sites became safe and construction-friendly. Installation of WP system (Fig. 8.25b); construction of foundation and civil work for track hopper with singlestage WP system (Fig. 8.25c, d) and two-stage WP system for excavation and civil works for junction house are shown in (Fig. 8.25e, f).

Hazards Due to Failure of Groundwater Control Improvements in site condition achieved after controlling groundwater in deep excavation have been demonstrated in Fig. 8.24. On the other hand, failure due to inadequate planning, execution and maintenance of seepage control system may lead to disastrous consequences as seen at a few sites (Fig. 8.26a–d). The failures could have been avoided provided properly designed dewatering systems installed, monitored and maintained properly.

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8 Seepage Control

(a) Typical detail of Well Point

(b) Multiple wells connected to common header pipe

Fig. 8.24 Arrangement of well points and connection to common header pipe a Typical detail of well point, b Multiple wells connected to common header pipe

(a) Side Collapse during Initial Excavation

(b) Installation of Well Point System in Progress

(c) Single-Stage WP System for Track Hopper

(d) Construction of Track Hopper in Progress

(e) Two-Stage WP System for Junction House

(f) Civil Works for Junction House in Progress

Fig. 8.25 Importance of groundwater control by well point system

Hazards Due to Failure of Groundwater Control

(a) Failure at Base due to ‘Quick Condition’

(c) Severity of Damaged Sheet Pile Wall

175

(b) Collapse of Sheet-Pile Wall due to Progressive Failure

(d) Enormous Force caused due to Side Failure

Fig. 8.26 Failures caused due to inadequate design and management of well point system

Chapter 9

Erosion Control and Retaining Wall

Introduction Slopes are seen almost everywhere in hills, plains, riverbanks and seashore. Natural or man-made slopes are not permanently stable and occasionally fail due to multiple causes. Common causes of slope failure are erosion due to rain, high/low tide in river and sea and flooding. Earthquake can cause minor or major slope failure. Accordingly, mechanisms for slope protection depend on location, site conditions and causes of failure. Technology for slope protection has advanced considerably with the development of new technology, products and methods of application. For example, artificial grass turf, vegetation over geojute fabric cover, tree plantation (horticulture) and many more. Objectives of plant-based approaches are to prevent surface erosion by rain and roots to reinforce surface soil layers. Literatures and product brochures can be referred for details. This section is not meant for browsing through different methods of slope protection. But to draw attention on certain points helpful for conceptualizing actual conditions and plan appropriate protective measures. Slope failure in riverbanks and seashores is mostly caused by erosion due to high/low tides and seasonal floods. Fluctuating water levels and velocity of flowing water loosen and scope out soil particles creating voids and loss of strength which finally leads to slope failure. Objectives of bank protection are to (a) prevent soil erosion caused by water and wind and (b) ensure stability of side slopes by constructing flexible retaining wall made preferably of natural materials. A simple, cost-effective, time-saving, durable technology for the protection of natural slopes is by Gabions. Methods for manufacture and placement of Gabions have been covered in detail in this chapter.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_9

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9 Erosion Control and Retaining Wall

For deep excavation in soft soil areas, sides of excavation need to be protected by ‘enclosing’ the excavation with temporary sheet pile walls. Initially, an engineer may feel design of retaining structure is difficult. Attempt has been made to demonstrate that retaining walls can be designed based on basic principles of earth pressure distribution in soil by hand calculation without dependence on software package. Main advantages of hand calculation are it gives ‘feel’ for the numbers (values) at intermediate steps, and design calculations are fully transparent for checking and revision as needed. The designer also feels confident in providing guidance in preparation of specification and working drawings for retaining wall. Over and above satisfaction gained from completing design and see successful implementation at project site is rewarding. Keeping above objectives in view, step-by-step analysis of multi-level braced retaining wall has been presented.

Important Points for Planning Prior to preparation of slope protection schemes, the designer needs to identify destabilizing factors. Following information and data on site should be helpful in identifying sources of problem and plan economic scheme keeping the site constraints, constructability and cost factors in mind. Following studies are recommended. 1. Topographical and contour survey preferably with closer contour intervals covering target and adjoining areas. Although slope failure truly is multidimensional phenomenon, more often analysis is done on two-dimensional (2D) basis. Having 3-D vision of the area is helpful in preparing representative design model. 2. Detailed geotechnical investigation to evaluate subsurface stratification and soil parameters for use in analysis. Stratification of the area is important as it reflects formation mechanism which impacts stability. 3. As water has tendency to destabilize slope, pattern of regional rain to be collected from local authorities. From contour drawing or topographic survey drawing, mapping of probable catchment area and natural rainwater channels on slopping surface are to be developed and studied. The data might lead to re-aligning or training rainwater flow through alternative course. 4. In case of slope on canal or riverbank, high and low tide levels, seasonal variation, flow pattern, vulnerability to erosion near bends and natural drainage of rainwater on banks need to be studied. 5. Reconnaissance on adjacent locations to understand topographic pattern of the region. 6. Information from local bodies on protection schemes adopted in past and their performance. 7. Accessibility and availability of local construction agency and raw materials for construction, e.g. boulder, stone, sand, earth, etc.

Slope Protection with Gabions

179

8. Information on growth of natural vegetation, bush, weeds, trees, etc., is important for natural protection system. Several companies provide protection service applying new technology and products. 9. It is necessary to adhere to statutory environmental restrictions and guidelines. These are to be collected for study as protection scheme has to meet the regulations both on land and water.

Slope Protection with Gabions Gabions are commonly used to protect hill slope and riverbank because these can be assembled near site with local manpower, transported to site and placed as per design under supervision. Gabions are box-like crates made of GI or steel wires and wire mesh, tied or welded. The crates are filled with select graded broken stone pieces, hand-packed and face-tied. Alternately, the crates can be assembled at fabrication yard and transported to site for placement, filled with stone metal, hand-packed and top close. Prior to placement of Gabions, area for placement is to be prepared by removing roots, topsoil, loose mud and dressing to safe design profile. The Gabions are placed ensuring joints are not aligned vertically like the practice in brick masonry work.

Gabions for Erosion Control and Slope Protection Geotechnical engineers normally engaged in urban projects may not be familiar with concepts, manufacturing, ground preparation and placement of different types of Gabions for efficient and economic solution for slope protection and erosion control. It therefore is felt; brief discussion on key points on the types and application of Gabions would be helpful. These are covered in the following paragraphs. Gabions are commonly used in different configurations to serve specific purpose. Typical details of manufacturing Gabions are shown in Fig. 9.1 for reference and are modified based on design for a project.

(a) Typical Gabion Crate made of GI wires

Fig. 9.1 Fabrication detail of crates for Gabion

(b) Hexagonal Wire Mesh used for Gabion

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9 Erosion Control and Retaining Wall

Gabion Manufacturing (a) Materials specification for Gabion (Ref. Fig. 9.1) 1. Gabion crates are made of PVC/zinc-coated steel wire of 2.7/3.7 mm diameter. 2. Gabion mattress is formed with mechanically woven hexagonal-shaped (12 × 10 cm) steel wire mesh. 3. Non-woven geotextile placed as separator between soil and Gabion blocks or mattress. 4. Stone for rock fill: Size: 150–250 mm, γ ∼ = 26 kN/m3 , porosity > 35%, hard and durable 5. Unit size of crate: 1000 × 1000 × 500 mm (Typ.) to 2–3 m length, breath and height about 1.0 m or more depending upon protection scheme. (b) Stone Filling in Crates 1. Rock filling to be done in three layers of near-equal height. 2. Lacing to be done in single- and double-lacing fashion @ 100 mm spacing. 3. Front face should be neatly packed with good fascia rock pieces at face of Gabion wall. 4. To prevent bulging, bracing wires shall be provided @ 300 mm c/c

Slope Protection with Gabions Scour due to rain on hill slope or riverbank of moderate height can be protected with single-stage Gabion wall. However for greater height or steeper slope, general arrangement and configuration will be different. For vertical retention, Gabion retaining wall is provided. Please note, before placing Gabions, the slope needs to be profiled to safe slope conforming to geotechnical design. General guidelines before placement of Gabions: (Ref. Fig. 9.2). 1. Excavation/trimming/filling/dressing and compaction at base/side of stable profile and bottom of slope before placement of Gabions. 2. Placement of a layer of geotextile separator to prevent scour/loss of soils from base/seat. 3. Place empty Gabion crates (top open) in position row-wise, tie together with steel wire. 4. Fill crate with select stone, hand-packed tightly and neatly avoiding bulging/ deshaping. 5. Close top with steel wire and twist properly and securely. 6. Place next layer or row of Gabion crates as above. 7. Care shall be taken to ‘anchor’ Gabion blocks at edges to prevent scour or formation of cavity.

Gabion Wall

181

Fig. 9.2 Slope protection with Gabion

8. For sloping surface, Gabions shall rest on properly prepared base. 9. Surface of Gabion wall/mattress should be finished plane without any sharp corner or bend. 10. In order to prevent top and bottom erosion and ensure stability, Gabions are to be placed at least 2 m from top edge and continue about 3 m at bottom of slope.

Gabion Wall Gabions can be used for construction of (a) vertical retaining wall of nominal height and (b) multi-stage Gabion walls for greater height. However, general arrangements and sizes of Gabions need to be modified accordingly. Typical Gabion retaining wall and multi-stage wall are shown in Fig. 9.3. Steps for construction of Gabion walls are discussed briefly. For detailed design, reader needs to refer books, literature, brochures, etc.

Vertical Gabion Retaining Wall Gabion retaining wall is designed as gravity wall. Sizes of Gabions at different levels are selected to ensure stability. For ease in handling and placement, height of Gabions is about 1.0–1.2 m, length and breadth are proportioned according to design. Typical design of 6–7 m high vertical Gabion retaining wall is shown in Fig. 9.3 along with dimensions of different Gabions. It can be seen, according to design, lengths of Gabion blocks vary from 1.0 to 3.0 m in steps of 0.50 m. The retaining wall will be built from bottom level after preparing seat of the wall. The Gabion wall will be built-in steps of 1.5–2.0 m height and backfilling with earth and compaction

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9 Erosion Control and Retaining Wall

Fig. 9.3 Gabion retaining wall

to be carried out simultaneously. As before, non-woven geotextile shall be laid at interface between soil and Gabion blocks. For prevention of scour at top and bottom of wall, 500 mm thick Gabion apron for about 2.0 m at top and about 3.0 m at bottom are to be provided. Gabion blocks have been marked and dimension as shown in Fig. 9.3.

Multi-stage Gabion Retaining Wall For protecting slope of greater height say about 12.0 m, design of single vertical retaining wall will be difficult and uneconomic. The protection system can be divided into stages, and multi-stage system will be economic and easy to construct. The ‘model’ vertical retaining wall can be used in two steps with intermediate berm of about 3.0 m wide. Stability of gravity wall can be improved by providing little inclination of about 8° to 10° toward the slope as shown in Fig. 9.3. Top and bottom of protective Gabion wall should be protected by providing 500 mm thick Gabion apron for about 2.0 m at top and about 3.0 m at bottom. However, length of apron to be decided based on site condition. Gabion blocks can be used effectively for slope protection and erosion control on tidal riverbanks. Slope face to be finished plane before Gabion blocks are placed on geotextile laid on finished surface. Key at toe is to be built first, and Gabion blocks shall be placed starting from bottom and ending at Gabion beam at top of slope. River bed erosion needs to be protected with Gabion mattress as shown in Fig. 9.4.

Block Gravity Wall

183

Fig. 9.4 Bank protection and erosion control using Gabion blocks and mattress

Block Gravity Wall Block Gravity Wall is used for slope protection and erosion control in hills and riverbank/seashore. As the name suggests, the wall is built by placing ‘blocks’ and stability maintained by ‘gravitational’ forces. Gravity wall is advantageous on many counts. Precast PCC/RCC, flyash or Gabion blocks are manufactured in casting/ fabrication yard for carrying to work site for placement. Blocks are placed in designed pattern over prepared base. Concrete blocks are cast with built-in ‘key’ for self-locking upon placement. Gabion blocks are tied with galvanized steel wires. The wall is flexible and can re-adjust to settlement/movement within permissible limits. Wall design is based on assessing static equilibrium and stability of each block by resolving restoring and overturning forces in vertical and horizontal components individually and collectively. Main overturning forces on wall are earth pressure mostly active, lateral component of surcharge at ground surface but no water pressures as weep holes are kept in concrete and masonry wall. Self-weight and shear between blocks and resistance at foundation against slip are stabilizing forces. Stability is assessed starting from top block to bottom taking forces from all upper blocks and surcharge from backfill on projected portions into account. Stability of bottom block against overturning and sliding is designed with comfortable factor of safety against each mode. If desired passive resistance from soil for depth of embedment of foundation may be considered provided backfill is done to ensure the development of passive resistance at base. General arrangement of 3-Block Gravity Wall is shown in Fig. 9.5. Typical model of 4-Layer vertical wall is shown in Fig. 6a. For additional stability against rotation (moment), the wall may be battered toward backfill as shown in Fig. 6b. Analysis is based on static equilibrium of forces and moments of the blocks as shown in Fig. 6a, b. But steps for resolving components of forces in vertical and horizontal directions for battered wall are somewhat elaborate. A spreadsheet program for analyzing 4-block wall (vertical and/or batter) has been developed.

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9 Erosion Control and Retaining Wall

Fig. 9.5 GA of block gravity wall

(a) Placed Vertically Fig. 9.6 Four-layer block gravity wall

(b) Battered for Additional Stability

Sheet Pile Protection for Deep Excavation

185

Fig. 9.7 4-Level (nano) block gravity wall

The program can be used to design 8–10 m high wall. Foundation for laying blocks should be competent to carry loads and (maximum and minimum) stresses due to moment within permissible limits. Dimensioning of bottom block must ensure ‘No Tension’, i.e. loss of contact with ground. Therefore, ground should be inspected for irregularity or weak pocket, rectified and compacted thoroughly and graded smooth. In case of battered wall, the foundation surface must be provided with proper camber. It may be noted gravity wall of height > 10 m may not be economic. For protecting hill slope, commonly height of wall required is more than 10 m. In such situation, system of multiple gravity walls of smaller height (Nano) walls as shown in Fig. 9.7 may be adopted. However, this approach should not be followed in areas with high rainfall and steep slopes. The method is generally suited for protecting hill slope for mine roads and should be used with caution in areas of importance. The ‘Nano’ Wall concept has been used in protecting slopes of ‘Slag Dumps’ and construction of new units in old slag-filled areas in steel plants. It is important to check global (overall) stability of combined slope upto full height and the wall including backfill. Combination of Gabion block, gravity wall and Gabion mattress can be used effectively for slope protection and erosion control at river/sea bank with high tidal variation. Height of fill behind wall can be raised by controlled fill. Slope surface should be protected from rain by plantation or similar treatment as shown in Fig. 9.8.

Sheet Pile Protection for Deep Excavation As indicated in the beginning, design of retaining walls may appear difficult at first. But it is not so because retaining walls can be analyzed based on theories of lateral earth pressure in soil avoiding dependence on software package solution. This has been demonstrated through an example of multi-level braced steel sheet pile retaining wall for protecting sides of deep excavation for a power plant. Detailed

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9 Erosion Control and Retaining Wall

Fig. 9.8 Block gravity wall, Gabion blocks and mattress for slope protection and erosion control

steps for analysis have been presented. For the selection of sectional properties of sheet piles and structural design of struts, stresses and moments on sheet piles and compressive loads on struts/props have been estimated. Special attention has been given on ‘full-cycle’ analysis from start of excavation upto withdrawal of last prop.

Introduction In steel and thermal power plants, ore/coal transported by rail wagons is unloaded by ‘toppling’ wagons on a series of underground hoppers in ‘Wagon Tippler’ (WT) unit. In general maximum depth of foundation for WT is about 12 or more from GL depending upon design of equipment manufacturer. Design of open excavation to such depth in soft soil with high groundwater will require excavation in about three levels with intermediate berms. As a result, overall length and width of excavated area will be large and volume of excavated earth will be enormous. Standard engineering practice is to ‘enclose’ the core area of construction by driving interlocking steel sheet pile wall braced with composite structural members called ‘strut’ placed at differing depth levels. At the outset it seemed geotechnical and structural design of ‘Braced Sheet Pile Wall’ would be difficult and may need to be carried out using software package. Such package cover wide varieties of analytical models, colorful display of results and are expensive not generally affordable for design office. Moreover, the package needs to be handled by person experienced in using the package. Preparation of input data is difficult because of so many options to choose from. Also, selection of desired design data from large output files may be difficult.

Sheet Pile Protection for Deep Excavation

187

Instead, it is possible to design complete protection system based on basic principles of soil mechanics available in textbooks. Input soil data are selected from geotechnical reports, technological parameters from design assignments supplied by equipment manufacturer. Geotechnical engineer can analyze by hand calculations and sketches based on basic principles of soil mechanics. In packaged solution, intermediate steps remain opaque. But in hand calculation, the designer calculates each step and gets a feel for the values of entities. Calculations are fully transparent for re-check and revision as needed. He/She can visualize contribution of certain parameters their advantages and constraints and have greater freedom in design and decision making. In Chap. 8, excavation for construction of foundations for Track Hopper (TH) and Junction House (JH) by open excavation after controlling seepage of groundwater adopting single- and two-stage well point dewatering system has been presented. At the same site, construction of Wagon Tippler (WT) was carried out by enclosing the area with steel sheet piles braced at intermediate levels. Step-by-step design procedure for braced retaining wall is presented to demonstrate that calculation is not that difficult and can be carried out in-house.

Braced Sheet Pile Protection for Deep Excavation in Soft Soil Design Parameters RCC Base Raft (B × L): 32.5 m × 13.1 m, Depth: 11.45 m from EGL. RCC Sump Pit (B × L): 4.0 m × 10.0 mm, Depth: 13.45 m from EGL. EGL: + 2.7 M (RL + 5.3 corresponds to EL ± 0.0).

Geotechnical Data Sub-soil layering and parameters based on field and laboratory test results are summarized in Table 9.1. Table 9.1 Soil profile and engineering parameters Layer

Description

Depths (m)

N-value

Shear strength

1

Soft silty clay

GL–6.0

4

C = 29 kPa, φ = 0

2

Very soft clayey silt

6.0–9.0

3

C = 25 kPa, φ = 0

3

Med. dense silty sand

9.0–22.0

23

C = 0, φ = 28°

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9 Erosion Control and Retaining Wall

Table 9.2 Correlation among EL, RL and depths Description Reference level

EL (M)

RL (M)

Thickness

Depth from EGL

0.0

+ 5.3

–

–

− 2.6

+ 2.7

–

–

Bot. of layer-1

− 3.3

6.0 m

6.0 m

Bot. of layer-2

− 6.3

3.0 m

9.0 m

1.50 m

9.95 m

EGL (layer-1)

Top of base raft

− 12.55

− 7.25

Bot. of base raft

− 14.05

− 8.75

Top of sump raft

− 14.55

− 9.25

Bot. of sump raft

− 16.05

− 10.75

11.45 m 1.50 m

11.95 m 13.45 m

Note Both elevation (EL) and reduced level (RL) have been included to refer levels

Control Levels For clarity EL, RL and depth (from EGL) of different entities are summarized in Table 9.2. It is standard practice in industry to define levels by EL or RL.

Estimation of Lateral Pressure on Sheet Pile It is seen in Table 9.2, depth from EGL to bottom of base raft is 11.45 m. Sheet pile wall is required to protect excavation upto bottom of base raft ~ 12.0 m from EGL. Analysis for 11.5 m long sheet pile has been carried out following principles of ‘braced single-wall cofferdam’ in soil mechanics. Length of sheet pile in Layers-1 and 2 is 9 m and in Layer-3 is 3 m. Water table shall be lowered at least to 13 m below EGL by well point dewatering system and maintained throughout construction period. Lateral earth pressure and thrust per unit length have been estimated based on principles mentioned above and forces are shown in Fig. 9.9: (a) for Layers-1 and 2 and (b) for Layer-3 respectively along with point of application from GL. The results are summarized in Table 9.3. Note all dimensions are in meter (m). Q1 = 16.20 kN, point of application: 9.125 m below GL. Q2 = 124.74 kN, point of application: 10.125 m below GL. Q3 = 17.82 kN, point of application: 11.350 m below GL Q=

∑

(Q 1 + Q 2 + Q 3 ) = 158.76 kN

Total lateral thrust on sheet pile wall =

∑

(P + Q) = 523.26 kN/m

Sheet Pile Protection for Deep Excavation

189

Fig. 9.9 Earth diagram on sheet pile wall

Table 9.3 Estimated lateral earth pressure in layers (per unit length) Layer-1 and 2

Layer-3

Referring Fig. 9a γ = 18 kN/m3 H1 = 9 m p1 = 0.375 γ H 1 = 60.75 kPa P1 = 205.03 kN, point of application 4.5 m below GL p2 = 0.5 γ H 1 = 81. kPa P2 = 159.47 kN, point of application 7.93 m below GL

Referring Fig. 9b γ = 18 kN/m3 H 2 = 2.5 m φ = 28°. ⇒ K A = 0.36 q1 = 0.8 γ H 2 K A = 12.96 kPa Surcharge from upper layers (Layer-1 and 2): q = γ H 1 = 162 kPa q2 = γ H 1 K A = 58.32 kPa (lateral pressure due to surcharge from Layer-1 and 2

Estimation Strut Loads Struts have been provided at three depth levels: Level-1: 3.00 m below GL (Mkd. S1). Level-2: 5.65 m below GL (Mkd. S2). Level-3: 9.00 m below GL (Mkd. S3). Forces on struts (S1, S2 and S3) have been determined by solving moment and equilibrium equations. Resultant forces on struts listed below: Force on strut S1 = 88.97 kN/m. Force on strut S2 = 112.10 kN/m. Force on strut S3 = 322.18 kN/m. Total = 523.25 kN/m.

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9 Erosion Control and Retaining Wall

Overall pressure diagram, lateral load and depth of resultant of Layers-1, 2 and 3 summarized in Fig. 9.10. Common practice is to increase design length of sheet pile by about 20–40%. Considering 25% increase and localized deeper excavation for sump, total length of sheet pile works out to 15 m (driven length of 14.5 m and projection of 0.5 m above ground). Wales and struts should be designed considering maximum force. Result of analysis is schematically shown in Fig. 9.11. Depth from GL(m) 0.0

EGL (RL + 2.7)

3.0 m Sheetpile

4.5 7.93 m

Layer-1 Firm Silty Clay N=3-5

6.75 m

Strut : S1 6.0

2.65

6.0 m

P1 = 205.03 kN

Strut : S2 9.0 3.35 m

Strut : S3 11.5 Exvn. Lvl. (RL-8.75)

Layer-2 P2 = 159.47 kN Very Soft Clayey Silt 3.0 m q 2.25 m N=2-4 0.125 m Q1= 16.20 kN 1.125 m Layer-3 Q2= 124.74 kN Med Dense Silty Sand 2.33 m N=18-29 13.0 m Q3= 17.82 kN

12.96

58.32

22.0

NOTE : Units used : Pressure (kPa), loads (kN) & distance (m)

S1 = 88.97, S2 = 112.10, S3 = 322.18 kN/M

∑S = 523.25 kN/m

Fig. 9.10 Pressure diagram of sheet pile wall Fig. 9.11 General arrangement for sheet pile wall

0.5 m (Projection)

Strut S3 (322.18 kN)

11.5

Strut S2 (112.10 kN)

Sheet Pile

3.35 m 2.65 m

Strut S1 (88.97 kN)

3.0 m

Exvn. Lvl.

EGL

Sheet Pile Protection for Deep Excavation

191

Table 9.4 Results of 3th trial designs and 4th trial for final design Description

Trial-1

Trial-2

Trial-3

Trial-4

No. of struts

1

3

3

2

Depth of sheet pile

19.0 m

14.0 m

15.0 m

12.0 m

Load on struts

466 kN/m

391 kN/m

523 kN/m

396 kN/m

WT of sheet pile/100 m

246.7 T

207.1 T

220.8 T

176.6 T

2.47

2.07

2.21

1.77

Cost (crores) per 100

m**

Depth of sheet pile reduced from 17.4–12.0 M

30%

Reduction in total load on struts

12.5%

Reduction in weight of sheet pile Remarks **

Not used

31% Not used

Not used

Adopted

Design was carried out on the same lines of worked-out example

Optimization on Number of Struts and Design Loads Sample design of braced sheet pile has been presented above. But excavation from top to bottom and civil works starting from bottom will face major obstacle from horizontal struts placed at three levels. Therefore, aim was to optimize number and locations (depths) of struts. Design (Trial-1) submitted by sheet pile manufacturer was unacceptable and further designs (Trials-2 and 3) were carried out keeping (a) minimum obstruction to excavation and (b) civil works and (c) cost and time factors in view. Results of three trial designs are summarized in Table 9.4. As seen in Table 9.4, none of initial designs (Trials-1 to 3) was acceptable because of length of sheet piles was greater than standard rolling length of 12 m and cost factors. Having gained experience from three trial runs, an alternative scheme (Trial-4) was attempted considering two struts.

Salient Features of 4th Trial (Fig. 9.12) (a) General excavation at ground surface by about 3.0 m deep from GL in the area. (b) Groundwater level brought down by two-stage well point dewatering system to 13.0 m depth and maintained as required during entire construction period. (c) In order to reduce number of struts from three, struts were provided at two levels: Strut-1 (S1) at 2.65 m below general excavation level (3 m from EGL). Strut-2 (S2) at 3.35 m below S1, i.e. 6.0 m below excavation level.

(d) Design loads on struts at full excavation stage were: S1 = 90 kN/M and S2 = 306 kN/m.

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9 Erosion Control and Retaining Wall

Fig. 9.12 Results of design: Trial-4

Results of all four trial design have been summarized in Table 9.4 which is selfexplanatory.

Importance of Full-Cycle Design (from Start of Excavation to Backfilling)

193

Importance of Full-Cycle Design (from Start of Excavation to Backfilling) Commonly, design of braced sheet pile protection system ends after calculation of forces, shear and moment, etc., upto full depth excavation stage. But the design is incomplete. With the progress of civil works and simultaneous backfilling on sides, the struts are removed from bottom-most level in stages. In most instances, forces on upper struts increase considerably with the removal of strut at lower level. Therefore, design of braced excavation should cover full cycle of operations starting from first stage excavation and placement of strut at 1st level (S1) to full depth of excavation with the placement of strut (S2) and subsequent civil construction along with backfilling and removal of struts upto ground level in stages. Importance of full-cycle design is demonstrated in the worked-out example of Trial 4. Estimated design axial loads on struts S1 and S2 at (a) full depth of excavation and (b) after removal of bottom strut (S2) are summarized in Table 9.5. It is noticed, axial load on S1increased drastically by about 2.7 times after removal of strut S2. If structural design of strut (S1) was based on the basis of loads at full excavation stage (90 kN/M) the design becomes ‘highly unsafe’ during removal of lower level strut. Therefore, strut S1 should be designed for 240 kPa/M and not for 90 kPa/M design load. Modified design of sheet pile in Trial-4 considering 3.0 m general excavation at ground surface and struts at two instead of three levels was carried out as before covering full cycle of operation. After completion of geotechnical analysis of sheet pile protection system, the geotechnical engineer needs to prepare design drawing for use in design of sheet pile section, struts and other details. Design drawing based on Trial-4 analysis is shown in Fig. 9.12. Structural and civil designs will be based on the drawing. After completion of civil works upto a meter or so above ground level and backfilling on sides, sheet piles are extracted by pulling with vibratory equipment. The construction site is restored for further works. Table 9.5 Increase of load on strut after removal of bottom level strut Strut No

Design axial load on strut (kN/M) Full excavation stage

After removal of bottom strut

Strut-1 (S1)

90

240

Strut-2 (S2)

306

NA

Chapter 10

Marine Projects

Introduction Traditionally, oceanic routes were and still are the prime mode of transport for intercontinental movement of bulk cargo and crudes for worldwide trade and cruise. Earlier, large sailboats and in recent days large ships/cargo vessels are used for the transportation of goods from source of production/manufacture to place of use/sale. For loading-unloading of goods, water-front structures are built on riverbank and sea coast. Geotechnical and foundation engineers have major role in design and construction of stable and safe foundation system for supporting sea-front structures and on-shore facilities. Vista of Marine Projects is as wide and deep as the ocean. Because of innumerable unknowns and uncertainties, projects in marine environment pose enormous challenge and risk. In spite of that, construction in marine environment must go on because intercontinental movement of bulk raw materials and finished products through sea is the most efficient and economic mode of transport. Moreover, vast explored/unexplored reserved ‘treasures’ of under-sea world are fascinating. Wide coverage on theory to practice on marine foundations is available in books, publications, print media and net world. However, aim of this chapter is to expose the reader mainly on topics pertinent to near-shore marine projects which practicing civil engineers may not be familiar with. At the same time, the chapter is not meant to be comprehensive coverage on the field. Contents are aimed to cover selected topics on planning for ground preparation and development, design and construction of foundations for water-front structures. This chapter has been arranged to include design aspects of land development to civil design basis, construction methodology of marine piles and concepts of Quay Wall for deep draft ports. Keeping the objectives in view, the chapter has been organized to include the following topics:

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_10

195

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• Strategy for ground development (raising level by filling) for marine facilities. • Civil design basis for marine piles. • Loads on water-front structures due to impact from approaching ship and anchoring. • Construction methodology of pile in river and sea. • Concept of Quay Wall—a must for deep water seaport. First and foremost step for any water-front project is to conduct detailed bathymetric survey covering port area, shipping channel from sea/river to port and beyond covering wide corridor. The survey data are used for finalizing several control parameters of jetty structure, finished ground/grade level (FGL) of port facility, piles in water and dredging in shipping channel for maintaining required draft for all-weather navigability of ship/barge. Bathymetric survey is a separate specialized field of underwater survey and not included in this book. Interested reader may refer appropriate references on the subject.

Strategy for Land Development Generally riverbank and seashore are low land, and finished ground needs to be raised to technically safe, technologically friendly and of course economically viable level. Determination of finished grade level (FGL) is important for selection of (a) method of filling and compaction, (b) preparation of general layout of port facilities and structure and (c) design of shallow and deep foundation. It is important that decision on FGL should not be taken judiciously and optimized. Filling and compaction are highly expensive and time taking work, even half (½) a meter difference in level will impact time and cost.

Selection of Finished Ground Level (FGL) Strategy for land development depends on three basic factors: (a) tide, (b) rain and (c) wind. Importance of each factor is explained through a case study of a proposed project site on an island in West Bengal.

Tidal Data Reported freshwater discharge in the estuary below Harbor varied between 550 m3 / s (Cumecs) and 11,000 m3 /s in monsoon. Maximum current of the order of 3.0–3.5 m/s occurs in deep channels.

Strategy for Land Development

197

Table 10.1 Tide table at the island Tide

At project site

In river

Mean high water springs (MHWS)

+ 5.7 m CD

+ 5.10 m CD

Mean high water neaps (MHWN)

+ 4.3 m CD

+ 3.66 m CD

Mean low water neaps (MLWN)

+ 2.1 m CD

+ 1.87 m CD

Mean low water springs (MLWS)

+ 0.8 m CD

+ 0.84 m CD

Highest high water level (HHWL)

+ 7.26 m CD

–

Mean sea level (MSL)

+ 2.82 m CD

–

Note CD stands for ‘Chart Datum’ (water level displayed on a nautical chart. CD for a zone is generally derived from some phase of tide commonly the lowest astronomical tide and mean lower low water)

Tidal data of river and from 2009 Admiralty Tide Table from nearby port are summarized in Table 10.1. From the above table, mean spring tide range is 4.9 m and mean neap tide range 2.2 m. The wave condition in the bay is said to be ‘calm’, the general wave height to be not more than 1.5 m. Topographical map of the island that shows average ground level is around 5.3 m CD which makes the island vulnerable to occasional flooding. There are reports of flooding the island in the past.

Rainfall Data The project region is located in heavy monsoon rainfall area normally from midJuly to early October. For example, recorded average and peak monthly rainfall in monsoon are 225 and 540 mm respectively with high intensity duration for several hours (over 10 h). Based on various records, peak daily rainfall in the region varies from 232.4 to 294.6 mm.

Wind Data The area is prone to seasonal severe cyclonic storm with wind speed ranging from 89 to 117 km/h. Therefore, the most important criteria for land development should be positive and permanent protection from risks of (i) flooding due to high tide, (ii) heavy monsoon rain, (iii) wind-induced high wave. Average ground level of the island reportedly was + 5.3 m CD. Considering HHWL at + 7.26 m CD (Ref. Table 10.1), maximum wave height of (iv) 1.5 m and (v) 0.75 m provision for future sea level rise (effect of ‘global warming’) and ground settlement due to fresh fill, safe grade level

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works out as + 9.51 m CD, i.e. 6.69 m above MSL. Based on foregoing considerations, it emerges that logical choice for finished grade level (FGL) free from risk of flooding and at the same time facilitating natural drainage should be + 9.5 m CD. As existing average level of the island was + 5.3 m CD, average thickness of fill upto + 9.5 m CD will be 4.2 m. In case provision for ground settlement due to surcharge from fill is considered (say 300 mm): Average safe grade level should be + 9.8 m CD, i.e. average 4.5 m of fresh fill which demands huge volume of fill and compaction work which can be fulfilled only by dredging and reclamation. Filling by dredging has already been covered in Chap. 4. Generally for site on riverbank or seashore, formation level of ground needs to be raised to technically all-weather safe level. Determination of finished grade level (FGL) is important for (a) method of filling and compaction, (b) preparation of general layout of structure and (c) design of shallow and deep foundation.

Design Steps For Marine Piles General guidelines for geotechnical design for marine piles and civil design of marine structures are briefly outlined below for information. 1. For determining diameter and spacing of pile for Berth structures, geotechnical capacity as per sections B and C of IS 2911 (Part 1/Sec 2): 2010 can be followed. Both vertical and lateral capacity, depth of embedment and fixity will be calculated as per borehole data from geotechnical investigation report. 2. After determining the pile details, the structure shall be modeled in design software like STAADPro or equivalent package for analysis. Following loads shall be considered as per IS 4651 (Part III)—1974: • Dead Load—from preliminary design of superstructure • Live Load—Surcharge load due to storage and stacking of materials – Truck loading as per IRC 6-2017 – Mobile or Gantry Crane loading as per Crane Manufacturer specification. • • • • • • •

Berthing Load Mooring Load Differential Water Pressure, if any Wind force as per IS 875 (Part 3) Seismic force as per IS 1893 (Part 1) Wave force as per Shore Protection Manual Current force.

3. Load combination for Limit State of Collapse and Limit State of Serviceability, Table 4 and 1 of IS 4651 (Part 4) to be followed. 4. After analysis of structure, design of concrete structural members shall be carried out as per load combination for Limit State of Collapse.

Design Steps For Marine Piles

199

5. All concrete structural elements shall be checked for deflection and crack width as per load combination for Limit State of Serviceability. For deflection of RCC structures, Cl. 23.2 of IS 456-2000 and for permissible crack width, Table 3 of IS 4651 (Part 4) to be followed. Note Only latest versions of Codes referred above shall be applicable. The civil designer shall select above design loads/parameters from design assignment, codes, standards and other sources. It is noticed, the load list includes Berthing and Mooring loads, which a civil designer may not be familiar with. The loads are caused by impact by approaching ship on jetty and loads on capstan during loading/unloading of ship, wave and wind action. Concepts and simplified methods of estimating the loads are briefly discussed below for general information.

Berthing and Mooring Loads Preamble It is seen in the list for design loads that berthing and mooring have been included. These terms are connected with ship movement and may be unfamiliar to civil engineers. The question one may rise ‘what a geotechnical engineer has to do with ship movement’? The reasons are explained below. Unlike on-land vehicles which have positive breaking system, air-borne and marine vehicles don’t have such system. Movement is controlled only by regulating speed or reverse-propelling and direction control by rudder. Therefore, when a ship approaches shore, it has to be brought to jetty extremely cautiously before mooring (tying firmly) to jetty. Berth is the term used in ports and harbors where vessel will be moored for loadingunloading purpose. When a ship or barge comes ashore, it slowly approaches jetty, and the first or subsequent impacts of ship induce impact force on the jetty which is termed as berthing force. Berthing force can be estimated following codes and standards based on relevant ship and sea data. When a ship is ashore and tied firmly to fixed object called ‘capstan’ on the jetty/wharf/berth to keep it firmly connected during loading-unloading process. The process is called Mooring. Even under tied condition, ship exerts force on capstan due to wave and wind actions. The force is called mooring force. Safety of RCC members of berth structures and metal body of ship are of vital concern. Ship is never allowed to come in direct contact with concrete face of jetty. Because energy of impact (momentum) of heavy ship, even under low deceleration is quite high and can damage both ship and jetty. To prevent direct impact, jetties are protected with a series of long fenders to absorb majority of energy from impact. Fenders are like elastomeric bearings used in road and rail bridges. Fenders can be

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Table 10.2 Design parameters of barge DWT (t)

M D (t)

L OA (m)

L BP (m)

B (m)

D (m)

F (m)

150,000

179,000

290

276

44

17.5

6.8

of different shape, size and design. Basically, fenders are hollow cylindrical flexible tube-like member made specially to withstand large deflection under impact. They act as shock-absorber to prevent damage to ship and to jetty. Estimation of berthing and mooring loads are necessary for civil design of jetty structure. Civil designer will analyze the structure using standard software and finalize design loads on pile foundation. Role of geotechnical engineer comes in designing pile foundation for jetty. An example of assessing Berthing and Mooring loads is presented for general information. Before proceeding further, certain terminology related to specification of ship is defined for better understanding. Conventionally, category of cargo ship is designated by ‘DWT’. The deadweight (DWT) is a measure of ship’s ability to carry cargo. To calculate deadweight in tonnage, take weight of empty vessel at normal draft and subtract that from weight of vessel fully loaded with cargo to the point of maximum permissible immerged depth. Commonly, the ship manufacturer specifies DWT of the ship/vessel.

Computation of Berthing Force and Fender Spacing for Ship Ship Data For finalizing general arrangements and control parameters for jetty/wharf/berth structures, data on ship or barge planned to be handled are essential. This is important because all control levels are dependent on water level of sea and their normal and seasonal variation. Typical design parameters of ship/barge supplied by ship manufacture are presented in Table 10.2.

Specification of Ship Type of ship: Barge Ship size range = 150,000 DWT Parameters of Barge Where DWT: MD: L OA : L BP :

Rated carrying capacity of ship/barge in tons Displacement tonnage (weight of water displaced by fully loaded ship) Overall length (from tip to toe of ship) Length between perpendiculars (length of ship body at jetty level)

Design Steps For Marine Piles

B: D: F:

201

Beam (width of ship) Laden draft (depth of bottom of fully loaded ship from surface of water) Laden freeboard (height of fully loaded ship from surface of water).

Considering reader may be interested in knowing approaches for assessing berthing forces, fender arrangement, hull pressure and mooring forces, the design steps are discussed below for reference only.

Berthing Mode

Environment:

Moderate wind and swells

Density of seawater:

w = 1.025 t/m3

W D : Displacement tonnage (M D ) of the vessel:

= 179,000 t

V: Velocity of the vessel normal to the berth:

= 0.15 m/s

[For sheltered berthing condition as per Table 2 of IS 4651 (Part III), Clause No. 5.2.1.1.] = 9.81 ms−2

g = acceleration due to gravity:

As per of IS 4651 (Part III) Clause No. 5.2.1.2. Mass Coefficient: Cm = 1 +

π D 2 L BP w = 1.399 4W D

As per of IS 4651 (Part III) Clause No. 5.2.1.3, Angle of approach: θ = 10◦ 

 2 0.5  L BP B L BP 2 − R= + = 72.42 m 2 4 2   B = 62.31◦ γ = 90 − θ − A · Sin 2R   L BP L BP − Cosγ = 61.1 l= 2 4 r=

L BP = 69.0 4

Ce : Eccentricity coefficient =

1+

 l 2 r

1+

Sin2 θ = 0.57  l 2 r

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10 Marine Projects

Softness coefficient : C S = 0.9 As per of IS 4651 (Part III) Clause No. 5.2.1.4. Berthing Energy = 0.5 × C M × W D × (VB )2 × C E × C S /g = 148.31 tm Design berthing energy(Factor of safety = 1.4) = 207.638 tm ∼ = 2076.38 kNm [Refer Fentek Manual of Marine Fendering System] Using cell fender or super cone fender of type SCN 1800 with energy index E 1.0 from Fentek manual Rated energy corresponding to nominal rated deflection of 72% = 2185 kNm > 2076.38 kNm Rated reaction = 2350 kN = 235 T Calculated deflection for 1800 mm standoff distance = 990 mm

Fender Spacing Following parameters are related to Fender: Rb = Bow radius of smallest vessel = 130.5 m Pu = Uncompressed fender projection = 1.8 m δ f = Fender deflection = 0.99 m C = Clearance distance(10% of Pu) = 0.18 m Assuming single Fender contact (Ref. Fentec manual)   2 0.5 Fender spacing : S = 2 R 2B − R B − PU − δ f + C = 25.6 m Provided fender spacing(c/c) = 20 m

Hull Pressure Rated reaction = 2350 kN ∼ = 235 T from Berthing Mode (estimated above) Permissible Hull Pressure (Bulk carriers) = 200 KN/m2

Design And Construction Of Marine Piles

203

Minimum area of the frontal pad required for fender = (2350/200) = 11.75 m2 Frontal frame provided to cater to berthing of design vessel type Height = 4 m, Width = 3 m, Area 12 m2 > 11.75 m2

Mooring Force As per Table 4 of IS 4651 (Part 3III) For 200,000 DWT barge, mooring force = 150 T Therefore, in above example berthing load = 235 T and mooring load = 150 T Civil design of Berth/Jetty structure and piles needs to cater to the estimated forces and resulting moment.

Design And Construction Of Marine Piles Civil designs for the water-front structure are carried out indicated earlier in ‘Design steps for Marine Piles’ considering all loads, moments and load combinations. The civil designer prepares pile ‘design assignment’, based on which geotechnical and structural design of pile including reinforcement details to be completed by geotechnical engineer. Geotechnical and structural design and detailing of piles have been covered extensively in Chap. 7. Design of marine and offshore piles is carried out in (a) land and (b) marine mode depending upon several factors. Often, marine piles require steel liner over part or for full length of pile shaft to aid in driving and/ or protection from salinity and growth of sea weeds, fungus, etc. Design considerations for piles with steel liners have been covered in Chap. 7. The designer will furnish details of pile including reinforcement, installation guidelines and release for construction. Technical specification for pile construction should include basic control parameters and other details.

Piling for River Terminal (Jetty) on River Ganga Example of control parameters for piling work and details for a river terminal (Jetty) project on river Ganga are presented below for reference. Control Parameters for Design (All levels are in RL) River Ganga HFL: + 29.00 m; LFL: + 21.00 m; Riverbed Level: + 10.00 m (Avg.)

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Jetty: Top of Jetty: +33.50 m Piles: Cast-in-situ bored RCC piles with steel liners, Pile Dia.: 1000, 1200 and 1600 mm Termination level of piles: (−) 10.0 m, Depth of pile below bed level: 20.0 m CoL of piles: (a) Fender piles: + 21.00 m, (b) Jetty piles: + 31.20 m Liner: Tip level of steel liner: ± 0.0 m, Thickness of steel liner plate: 8 mm

Construction of Marine Piles Design loads of marine piles have been covered earlier in the section. Construction of piles in marine environment is in itself a vast subject and is highly specialized field requiring experience, understanding and skilled construction personnel. As works are carried out in water, it requires inventory of heavy equipment, electronic instruments and skilled operators. As the working areas are in shallow and deep water, safety measures for men and equipments are of utmost importance. Above all, quality checks at all steps are essential. Deep-sea piling has not been included in this edition. Both bored and driven cast-in-place piles are constructed in river and sea depending on several factors, namely (a) distance of piling site from shore/bank; (b) type of soil at sea/riverbed; (c) water depth; (d) tidal fluctuations; (e) approach to piling site by temporary platform, by boat, floating or jack-up barge; (f) topography of the site; (g) availability of suitable and adequate land for stores, fabrication yard, first-aid center, rail and road connectivity and other infrastructure facilities as required. Commonly, practicing geotechnical and civil engineers may not have exposure to construction in marine environment. In order to provide an impression on the support system required for piling work in water, examples from two projects in upper Ganga and Hooghly rivers close to Bay of Bengal are presented Example 1: Project: Riverbank—Approached By Temporary Platform Supported on Steel Piles Project: Piling for River Terminal (Jetty) over river Ganga Working Platform: 550 MT Marine Gantry made by assembling prefabricated steel substructures. Temporary steel platform built over temporary steel piles. The gantry is built from shore to end of jetty. Construction of piles starts from end of jetty and work backwards to end at bank/shore (Fig. 10.1a).

Design And Construction Of Marine Piles

(a) GA of Temporary Gantry for Pile driving

(c) Partly completed River Terminal

205

(b) Temporary Steel Platform built on Steel Piles

(d) View of River Terminal during Construction

Fig. 10.1 Views of pile construction by 550 T gantry crane operating from temporary platform

Construction of Pile Installation of working piles starts after construction of temporary platform and erection of Gantry. Inventory of equipments and sequence of operation for construction of piles are summarized below. (a) Inventory of Equipment: Crane, Vibratory-sinker, Hydraulic rotary piling rig, Transit concrete mixer all construction equipment move over the temporary platform to piling point. (b) Driving of liner with vibro-sinker. (c) Pile boring by hydraulic rotary rig. (d) Reinforcement cages assembled on shore, lowered in segments and welded. (e) Concreting by tremie method from bottom to top. After completion of piles over a stretch, the temporary gantry is dismantled for re-assembly at new location and steel piles for platform are extracted progressively. Sequence and different stages of pile construction are shown in Fig. 10.1a–d. Overall view of fender and jetty piles for the river terminal is shown in Fig. 10.2. Example 2: Project in River: Installation of piles from Jack-up Barge Project: 250 m Tall Four-Legged HT Transmission Tower for River Crossing As mentioned earlier, construction of marine piles is a highly specialized field of construction engineering requiring proper co-ordination among different disciplines. Few important activities are outlined below.

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Fig. 10.2 Overall view of construction of fender and jetty piles for the river terminal

On-Shore Activities A lot of back-up activities are to be carried out on-shore facilities. Except for common and standard facilities, fabrication yard for pile reinforcing cage and steel liner are important. These have to be made ready for the transportation to piling site. For near-shore sites, these are transported by material handling equipment like dumper, JCB, and hydra. But for offshore sites, these are transported by floating pontoon or barge.

Offshore Activities Working platform from shore to piling point supported on temporary timber or steel piles and wooden/steel platform is constructed. In deep water, floating barge or jackup barge erected at most convenient position and fixed above expected maximum tide level and anchored firmly in position. Pile driving equipment, support crane, accessories, power generator, survey and monitoring instruments are placed on barge. Start boring/driving of piles at prefixed pile point and to correct alignment and inclination for batter pile. (a) Driving data collected at regular interval are recorded and cross-checked with design parameters. (b) After completion of driving casing, reinforcement cages fabricated in segments are lowered in sequence and joined by welding. (c) Ready-mixed concrete is poured upto full height along with withdrawal of temporary casing.

Design And Construction Of Marine Piles

207

(d) After completion, the rig is shifted to next pile point and positioned for further pile installation. Above steps though sound simple, but require co-ordination among skilled operators and technicians. Steps for construction of fully steel-lined driven cast-in-place RCC pile for foundation for four-legged high-mast HT transmission tower crossing a river with high tidal and seasonal variation including high wave during high tide and high wind area from jack-up barge are shown in Fig. 10.3a–d. Completed pile group for one of a four-legged high-mast transmission tower is shown in Fig. 10.4, and the towers after erection on bank and in river are shown in Fig. 10.5a, b.

(a) Pile Driving from Jack-up-Barge

(b) On-board Heavy Duty Crane for Driving Pile from Barge

(c) DELMAG - Diesel Hammer for Pile Driving

(d) Bottom view of DELMAG Hammer

Fig. 10.3 Driving of piles with double-acting diesel hammer operating from jack-up barge

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10 Marine Projects

Fig. 10.4 15-Pile group (vertical and batter) for one leg of high mast HT transmission tower

(a) Tower on River Bank

(b) Tower in River Bed

Fig. 10.5 250 m tall HT transmission towers for river crossing

Quay Wall Introduction to Quay Wall So far marine structures on or near river/sea bank for medium size ship or barge have been discussed. For international trade, import/export of bulk volume of heavy cargo like containers, automobiles, coal, ore, crude oil, and LNG only large ships cursing through deep sea are used. The ships are huge and need deep water depth (draft) for smooth sailing. Generally, draft available near sea-front facilities is not

Quay Wall

209

adequate for sailing of large cargo ship to moor on jetty. To overcome the problem, high retaining walls are built some distance away from shore where water depth is more or can be increased by dredging sea floor. Space created between back of wall and shoreline is filled (technological filling) to match level (FGL) of terminal. The space developed is used for storage of cargo and onward transportation by rail/road. Loading-unloading of bulk cargo is handled by heavy-duty gantry crane operating on rail tracks laid on newly filled-up area. The wall needs to be constructed in deep water (depth upto 30 m or more). But, how the wall will be designed and built? It is not possible to design cantilever steel sheet pile or concrete retaining wall of that height in deep water. Actual practice is to build high wall with vertical sea-side face by placing precast concrete blocks in segments as per detailed design. These walls in marine terminology are called ‘Quay Wall’. Design of Quay Wall is quite interesting because it is based on hybrid models of ‘Gravity’ and ‘Balanced Cantilever’ wall concepts. Design basis for such wall is somewhat complex and should be carried out only by knowledgeable and experienced engineer. Commercial software packages are available. But, the packages are costly and should be handled only by trained engineers. Technologies for design, manufacturing in casting yard, transportation, lowering and accurate placement of precast RCC blocks under water are specialized jobs. Quay Wall is built by laying precast RCC blocks of designed dimensions, cast in construction yard and brought to site. The blocks have provision of self-interlocking ‘key’. Blocks are lifted by heavy-duty crane from floating barge and lowered in place one-by-one and layer by layer. A team of divers monitor proper placement of the RCC blocks. Backfilling with select granular material, e.g. stone (quarry run) in designed profile followed by dredged earth along with mechanical compaction, continues simultaneously with building-up of Quay Wall. A capping beam is cast on top of wall to help construction of terminal. Foundation for Quay Wall is designed by geotechnical engineer based on results of soil test at sea bed. He decides founding strata, estimates bearing capacity and settlement for wall and backfill considering variation in seawater level. The blocks are designed taking at least the following into consideration: i. Mix-design for precast RCC blocks considering durability under prolonged marine exposure. ii. Size/dimensions, weight of blocks as per design and taking stresses for lifting by hooks and lowering blocks under water by mobile crane. iii. Provision and detailing of keys on sides, top and bottom for self-interlocking with adjacent blocks. iv. Underwater supervision by divers with waterproof camera for on-ground monitoring on placement maintaining verticality at seaface. v. Backfilling space between wall and bank/shore with select material upto FGL/ FFL and compaction. Two examples of Quay Walls (a) of moderate height and (b) greater height are presented to reveal interesting features of design and construction.

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This section has been planned only as a preliminary exposure on a relatively less familiar field of sea-front structures. To learn more, the reader is advised for further study and work with engineer experienced in the field. The geotechnical engineer needs to plan geotechnical investigation, select founding strata, estimate bearing capacity and settlement due to Quay Wall. Moreover, the geotechnical engineer needs to plan sequence and placement of select materials for backfilling work. Example 3: Quay Wall for Moderate Draft Quay Wall for 6.4 m Draft and Backfilling for Terminal Elevation and cross section of the Quay Wall are presented in Fig. 10.6a, b which are self-explanatory. Example 4: Quay Wall for High Draft 32 m high Quay Wall for Container Terminal Cross section of the Quay Wall showing arrangements of designed precast concrete blocks is presented in Fig. 10.7a. Dimensions of concrete blocks and volume of all layers are shown in Fig. 10.7b.

Dredging For Shipping Channel So far the chapter on Foundation for Marine Projects has covered activities from end point of ship movement, i.e. jetty, terminal, etc. But ship is not allowed to travel ‘on its own course’ but has to approach port from deep sea through designated route called ‘Shipping Channel’. In aviation industry, aircrafts approaching the airspace under the jurisdiction of an airport are guided by air traffic control (ATC). In similar manner when a ship approaches a port, its navigational control is taken over by designated port authority. When approaching port, movement of ship is escorted or guided by concerned port authority or pulled by tug boats. But in either case, draft required for ship must be available all along the route starting from deep sea to port of entry and beyond for ‘Ro–Ro’ (Roll-In and Roll-Out) facility. Siltation and deposition of suspended matters on seafloor and riverbed are a natural phenomenon and are contentious problems for port authorities. Siltation adversely affects effective draft. Therefore, bathymetric survey along entire shipping channel and port area and maintenance dredging is carried out routinely as required to maintain navigability in ports all over the world. In case of new port facility, there is no defined shipping channel. It is to be developed by dredging mud and sand from sea/ riverbed along the proposed shipping corridor. Safe side slopes of dredged cut along channel, which sometime may run into several meters in bay area, are to be designed by geotechnical engineer. Based on results of soil test, stability of underwater slope is analyzed taking marine factors, ship movement and allowing for Factor of Safety on conservative side. It is pointed out that, before proceeding on stability analysis

Dredging For Shipping Channel

211

(a) Elevation of Block Arrangements for Quay Wall for 6.4 m Draught

(b) Arrangement of Pre-Cast Concrete Blocks for Quay Wall of 6.4 m Draught & Built-up Terminal

Fig. 10.6 Quay wall for 6.4 m draft and backfilling for terminal

by conventional method, loads and forces for marine environments, e.g. tidal variation, under-current, thrust caused by ship movement, storm surge and scour are to be modeled properly following applicable design practice, codes, standards, etc. Mechanism for dredging is selected based on grain size and strength data from seabed samples. Underwater slope stability analysis must consider seismicity of the region. Scope of marine projects is vast and wide encompassing many specialized disciplines of engineering. Aim of the chapter was not to cover most of them but to expose practicing geotechnical and civil engineers on selected aspects of near-shore projects.

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The chapter includes geotechnical and civil design approach and construction practice. Normally civil engineers may not be familiar with design loads on structures due to ship movement. Therefore, a section on this aspect has been included for general guidance. The chapter covers selected portions from wide fields of marine projects. For further information and expertise on the subject, the reader needs to refer textbooks, literature and consult experts. However it is hoped, the chapter will be of interest to practicing geotechnical and civil engineers involved in design and construction of water-front and near-shore structures.

(a) Cross-Section showing Arrangements of Blocks for Tall Quay Wall

Fig. 10.7 Quay Wall of 32 m high for container terminal

Dredging For Shipping Channel

(b) Dimensions of Blocks Numbered as per Design of Quay wall

Fig. 10.7 (continued)

213

Chapter 11

Simplified Liquefaction Potential Assessment

Introduction In general, geotechnical investigation reports do not include effects of seismicity unless asked for. Incidences of earthquake and liquefaction in earthquake zones have significant effect in design of shallow and deep foundation. Earthquake of maximum zonal magnitude leading to liquefaction does occur only rarely. But earthquakes of lesser magnitude can occur causing ‘partial liquefaction’ in near-surface zones which can result in temporary loss of shear strength due to increased inter-granular pore water pressure. Civil designs of structures consider effects of seismicity through assigned factors, namely zonal, importance, amplification and other factors as per provisions of codes. But guidelines on design for partial liquefaction are difficult to find. Therefore, it may be prudent to study impact of partial liquefaction on design of foundation for site comprising of loose saturated silty, sandy soils with groundwater in earthquake prone regions. In case, saturated loose granular soil mass is subjected to rapid strain without allowing dissipation of pore water, it momentarily behaves as ‘fluid’ commonly termed as liquefaction. An upward gradient of [(G − 1)/(1 + e)] ≤ 1 can cause the state of complete liquefaction called quicksand. An upward gradient of lesser magnitude reduces the inter-granular pressure causing partial liquefaction, a condition that may occur when a fraction of existing inter-granular pressure is reduced due to increased pore pressure. Partial liquefaction can occur when large mass of saturated loose to medium sand is subjected to rapid shearing strains with partial or no escape of pore water during earthquake. Since the degree of liquefaction depends on combined pressure attained during earthquake, no general statement on degree of liquefaction can be made. Notionally, comparison of undrained and drained shear strengths under same loading condition can provide rough indication on degree of liquefaction. Broad boundaries of grain sizes susceptible to liquefaction are shown in Fig. 11.1.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_11

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11 Simplified Liquefaction Potential Assessment

Fig. 11.1 Grain sizes susceptible to liquefaction

Both Earthquake and Liquefaction are vast fields and covered exhaustively in books, literature, research reports etc. Basically, the fields are complex and multidirectional. Search on the subject will lead to large amount of references on theory and formulations to choose from. Only an expert can select a method appropriate for specific situation. But engineers engaged in projects may not be in a position to study the subject and analyze or seek help from expert. In order to overcome the barriers, attempt has been made to present methods for liquefaction potential assessment in simple and easy-to-understand format. Basic principles and governing formulations, methods for Preliminary Liquefaction Potential Assessment (LPA) have been compiled in simplified and transparent manner along with associated tables, curves, charts as far as practicable. Method for Step-by-Step LPA following two different approaches, namely (1) Indian Institute of Technology, Kanpur (IITK) and National Center for Earthquake Engineering Research (NCEER), USA, and (2) Seed & Idriss have been presented in tabular format. Spreadsheet programs with graphical display of results have also been developed. Geotechnical engineer can carry out LPA for a site following the methods and results from preliminary geotechnical investigation by the programs. Examples on application of LPA on effects of partial liquefaction on lateral pile capacity using above methods and program have been presented. Lastly, a startling case of extensive zonal destabilization caused by accidental puncturing of natural gas reserve field in Bangladesh due to deep-seated source of liquefaction has been described which should be of great interest. It is hoped, the chapter would be of great interest to geotechnical, civil engineers, faculty and professionals as well.

Methods for Simplified Liquefaction Potential Assessment (LPA)

217

Simplified Liquefaction Potential Assessment (LPA) Liquefaction depends on a large number of parameters, namely magnitude of earthquake, intensity and duration of ground motion, distance from source of earthquake (epicenter), site specific conditions, ground acceleration, type of soil, layer thickness, relative density, grain size distribution, fines content, plasticity of fines, degree of saturation, confining pressure, permeability characters, position and fluctuation of groundwater table, reduction of effective stress and degradation of shear modulus.

Geotechnical Design Considerations Liquefaction Potential Assessment (Methods) Methodology adopted for assessment of liquefaction potential based on geotechnical, seismological and other relevant data as per standard procedure are briefly outlined in following steps. • The geotechnical data such as SPT / CPT profile, dry density, wet density, grain size distribution and fines content from geotechnical investigation results on the site are tabulated. • The procedure involves standardization of SPT ‘N’ values measured in field by introducing corrections. • The expression for Cyclic Stress Ratio (CSR), which is the seismic demand induced by given earthquake, formulated by Idriss and Boulanger (2006) has been used. • The expression for Cyclic Resistance Ratio (CRR), which is the capacity to resist liquefaction formulated by Idriss and Boulanger (2006), has been followed. • Variation of both CSR and CRR with depth and hence profile of Liquefaction Potential throughout the depth evaluated using actual soil data. • Liquefaction Potential Index (LPI), which quantifies the severity to liquefaction proposed by Iwasaki et al. (1982), has been adopted.

Methods for Simplified Liquefaction Potential Assessment (LPA) Method of analysis is based on following references: (A) IS: 1893 (Part-1): 2002 & 1893 (Part-4): 2005 (B) IITK-GSDMA Guidelines for Seismic Design of Earth Dams and Embankments

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11 Simplified Liquefaction Potential Assessment

Provisions with Commentary and Explanatory Examples Indian Institute of Technology Kanpur & Gujrat State Disaster Management Authority August 2005: revised May 2007 (C) Simplified Procedure to Evaluate Liquefaction Resistance—Seed & Idriss (1971) (D) “Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and NCEER / NSF Workshop on Earthquake Evaluation of Liquefaction Resistance of Soils” Zone Factor for Maximum Considered Earthquake (MCE) Zone Factor (Z): [Table – 2: Cl. 6.4.2, IS: 1893 (Part 1): 2002] Seismic Zone

II

III

IV

V

Seismic intensity

Low

Moderate

Severe

Very severe

Zone factor (Z)

0.10

0.16

0.24

0.36

A. Analysis Based on: IITK-GSDMA Guidelines for Seismic Design of Earth Dams and Embankments 1. Data Required: SPT (N) or CPT(qc ), mean grain size, unit weight, fines content (FC) percent passing IS Sieve Size 75μ. 2. Evaluate total and effective vertical stress: (σ v ) & (σ ' v ) for all potentially liquefiable layers. 3. Evaluate stress reduction factor: rd rd = 1.0 − 0.00765 z for depth : z ≤ 9.15 m rd = 1.174 − 0.0267 z for depths : 9.15 < z ≤ 23 m 4. Evaluate Critical Stress Ratio (CSR) ) ( ) ( σv amax rd CSR = 0.65 g σv' where amax = Z × I × S × g where Zone Factor (Z) as in Table-2 (IS: 1893: 2002) I = Importance factor depending upon Category of Industrial structure (Table–5: IS-1893 Part-4, 2005) Importance Factor (I) for Various Industrial Structures (Table 2: Clause 8.3.2: IS-1893 Part-4, 2005)

Methods for Simplified Liquefaction Potential Assessment (LPA) Sl. No

Categories of structures

219

Importance Factor (I)

(i)

Structures in Category 1

2.0

(ii)

Structures in Category 2

1.75

(iii)

Structures in Category 3

1.50

(iv)

Structures in Category 4

1.00

S = Site Amplification Factor (Table – 2: IIT/K). Table 2: Site amplification factor, S II Seismic Zone

III

IV

V

Soil Type S1

1.0

1.0

1.0

1.0

Soil Type S2

2.0

1.5

1.2

1.0

Soil Type S1: Hard rock, Soft rock, Hard soil Soil Type S2: (i) For cohesionless soil: Average (N 1 )60 value over a depth equal to height of embankment is less than or equal to 15. (ii) For cohesive soil: Average su value over a depth equal to embankment height or width of footing is less than or equal to 25 kPa. 5. Corrections of SPT (N) and CPT (qc ) 5 A. Corrections of SPT (N) (a) Standardized SPT blow count (N60 ) N60 = N . C60 , where N is uncorrected / field SPT N-value C60 = CHT . CHW . CSS . CRL . CBD Correction factor from Table A.2 below. Table A.2: Correction Factors for Non-standard SPT Procedures and Equipment Correction for Correction Factor Nonstandard hammer type (DH = doughnut hammer, ER = energy ratio)

C HT = 0.75 for DH with rope and pulley C HT = 1.33 for DH with trip/auto and ER = 80

Nonstandard hammer weight or height of fall C H W = (H = height of fall in mm, W = hammer weight in kg

H ×W 63.5x762

Nonstandard sampler setup (standard samples with room for liners but used without liner)

C SS = 1.10 for loose sand C SS = 1.20 for dense sand

Nonstandard sampler setup (standard samples with room for liners but liners used)

C SS = 0.90 for loose sand C SS = 0.80 for dense sand

Short rod length

C RL = 0.75 for rod length 0–3 m (continued)

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11 Simplified Liquefaction Potential Assessment

(continued) Correction for

Correction Factor

Normalized borehole diameter

C BD = 1.05 for 150 mm borehole diameter C BD = 1.15 for 200 mm borehole diameter

(b) Normalized Standardized SPT: (N1 )60 . ( )0.5 . (N1 )60 = CN . N60 , where C N = σPa' v subject to C N ≤ 2, where Pa is atmospheric pressure (101.35 or 100 kPa). ( )0.5 Liao & Whitman (1986) proposed: C N = 9.79 σ1' . v

5 B. Corrections of CPT (qc ) (a) Normalized Cone Tip Resistance: ( (qc1N )cs = K c

Pa σv '

)n ( ) qc x Pa

where qc = corrected cone resistance Exponent ‘n’ = 0.5 for sand and 1.0 for clay K c = correction factor for grain characteristics K c = 1.0 for Ic ≤ 1.64 K c = − 0.403 I c 4 + 5.581 I c 3 − 21.63 I c 2 + 33.75 I c − 17.88 for I c > 1.64 Ic =

/

(3.47 − log Q)2 + (1.22 + log F)2

( )n f Pa v) where Q = (q cP−σ × and F = (qc −σ × 100 σv' a v) f = measured sleeve friction and ‘n’ = 0.5 for sand and 1.0 for clay. Soils with I c > 2.6 are deemed non-liquefiable. 6. Evaluate Critical Resistance Ratio (CRR7.5 ) Evaluate value of CRR7.5 (for earthquake magnitude of MW = 7.5) as below: (a) For SPT: CRR7.5 to be selected from Fig. A.5 for representative value of (N1 )60 (b) For CPT: CRR7.5 to be selected from Fig. A.6 for representative (qc1N )cs (c) Corrections of CRR7.5 for Design Earthquake Magnitude (MW ) CRR = CRR7.5 . K m . K σ . K α (i) K m : Magnitude Scaling Factor versus Earthquake Magnitude (MW ): Read from Fig. A.1 for given earthquake magnitude (MW ) or choose from table below

Methods for Simplified Liquefaction Potential Assessment (LPA)

221

MW

5.5

6.0

6.5

7.0

7.5

8.0

8.5

Km

2.4

2.0

1.6

1.2

1.0

0.8

0.6

(ii) K σ : Stress Correction Factor versus Vertical Effective Stress (σ' v ) (in atmospheric pressure unit) Read from Fig. A.2 for appropriate value of (σ' v ) for the depth NOTE: Figures A.1, A.2 … A.5 have been included in Addendum at end of chapter for quick reference ( )( f −1) ' K σ can also be estimated using formula: K σ = σv' , σ v (Atmospheric Pr. Unit) Values of ‘f ’ can be selected based on relative density (Dr ): Dr

40%

60%

80%

‘f’

0.8

0.7

0.6

If there is no initial static shear in the soil (e.g. embankment), normally value of K α = 1.0. 7. Factor of Safety (FoS): FS =

CRR CSR

Soil layers with FoS greater than 1.2 and between 1.0 and 1.2 are generally classified as non-liquefiable and marginally liquefiable respectively. B. Analysis Based on Simplified Procedure to Evaluate Liquefaction Resistance—Seed and Idriss (1971) 1. Cyclic Stress Ratio (CSR) After Idriss and Boulanger (2006) C S R = 0.65

1 1 amax σv rd ' g σv M S F K σ

where MSF = magnitude scaling factor and k σ overburden correction factor 1a) Stress reduction factor: rd rd = exp{α(z) + β(z)Mw } α(z) = −1.012 − 1.126 Sin

(

) z + 5.133 11.73

( z ) β(z) = 0.106 + 0.118 Sin 11.28 + 5.142 , the expression is valid up to z ≤ 34 m. Where z = depth in m, M w design earthquake magnitude

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11 Simplified Liquefaction Potential Assessment

The CSR value pertains to earthquake magnitude M w and is to be adjusted to earthquake of Magnitude M w = 7.5 through Magnitude Scaling Factor (MSF). 1b) Magnitude Scaling Factor (MSF) for M w ≤ 7.5 is given by (

−Mw MSF = 6.9Exp 4

) − 0.058 ≤ 1.80

1c) Overburden correction factor: K σ K σ : Equivalent Overburden pressure correction factor σ' v of 1 atmosphere ( ') σv K σ = 1 − Cσ ln pa ≤ 1.0, where pa is atmospheric pressure = 98 ∼ = 100 kPa. Cσ =

1 √ 18.9−2.5507 (N1 )60

≤ 0.30.

2. Corrections of Measured SPT Value Corrected (N1 )60 : (N1 )60 = Nm CN CE CB CR CS (N1 )60 corrected SPT value Nm measured N-value 2a) Overburden pressure correction: C N Normalization of overburden pressure with atmospheric pressure: C N ( )0.5 pa ≤ 1.70. σv' pa = 100 kPa (atmospheric pressure)

=

2b) Hammer energy ratio: C E =1.17 assuming energy ratio for standard rope-pulley system ∼ = 70% 2c) Borehole diameter correction: C B = 1.05 for 150 dia. borehole 2d) Rod length correction: C R : Depth: d (m)

d 35%, β = 1.2

For FC > 35%, α = 5.0 , For FC < 5%, β = 1.0, [ ( 1.5 )] For 5% 30 too dense to liquefy 3’a) Influence of Fines Content (FC) on (N1 )60 value (N1 )60 to (N1 )60CS (Idriss & Seed) (N1 )60CS = α + β (N1 )60 For FC < 5% α = 0 )] [ ( 190 For 5% < FC 1.5 OK Tan(δ) Tan(30)

This shows that the downstream raised dyke on sloping surface of old dyke is safe against sliding with Factor of Safety > 1.5. In order to ensure proper seating and good bond between old dyke and new construction, following precautions should be exercised. • Construction shall start from bottom at deepest section • Rock toe to be built first • Surface of existing face to be stripped removing all vegetation growth including uprooting • Surface of existing slope to be step-cut at about 1.0–1.5 m vertical interval. This is required for proper seating and compaction of new construction. Step height near top should be about 0.5–0.75 m interval • Top segment should be constructed after stripping and scarring crest of existing dam. Parapet wall of stone masonry or RCC may be built to fulfill requirement of design freeboard.

New Technology on Filtration of Tailing for Storage Management As mentioned earlier, construction of new tailing pond poses several challenges mainly due to non-availability of land, environmental, statutory regulations and cost. The closed-end situation can be overcome by adopting new technology of treating (artificial dehydrating) tailings and storage of dry tailing on dead or closed pond. If excess water from slurry can be extracted, properties of dehydrated (dry) tailing are quite similar to soil. Handling, transportation, storage in high stack and compaction of dry tailings can be controlled fairly easily. Technologies for extraction of water in filtration plant are available. In this process, large volume of tailings can be ‘dried’ and stacked to great height in relatively small area, and mining activities can be continued for many years. The filtration process designed by process engineers is to be verified in pilot plant tests. Based on the outcome, scheme for storage management (multi-disciplinary engineering) is developed. The scheme comprises testing geotechnical parameters and variations of dried tailing for design of engineered stacking, safe slope profile, layer thickness, compaction mechanism, slope protection, drainage and erosion control measures. Modalities for handling and transport of dry tailings are planned by material handling team. Testing and ground preparation of closed/dead pond for fresh storage is to be carried out depending on bed condition. During stacking, the works must be supervised by geotechnical and safety engineers.

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12 Tailing Storage Management at Mines

Tailing can be treated in vacuum belt filtration plant to extract maximum amount of water to generate ‘paste’ or dry tailing called ‘cakes’ depending upon characteristics of tailing and process route. Paste is transported to dumping ground by heavy-duty pump and pipeline. Dry tailing is transported by belt or pipe conveyor, dumper trucks for stacking to great height, drying and mechanical compaction to stable configuration. In this manner, storage of large volume of dry tailing over relatively small area is possible. Height of stack depends on stack design based on engineering properties of cakes, control on deposition patterns and compaction mechanism. Figure 12.7 shows dry cakes transported through pipelines being discharged on storage ground. Figure 12.8 show heaps of dry tailing stacked in dumping area before spreading and compaction. Fig. 12.7 Temporary stacking of dry tailing

Fig. 12.8 Heaps of cakes before spreading and compaction

New Technology on Filtration of Tailing for Storage Management

261

Fig. 12.9 Diamond mine

Cake generated after vacuum filtration can be conveyed to temporary stockpile for onward transportation to stacking area by dumpers. Dumped cakes can be placed and mechanically compacted to design profile up to great height above dead pond. After reaching design height, the stack is to be closed permanently and protected from environmental hazards by covering with vegetation or coir mat fulfilling mandatory requirements of ‘stack closer plan.’ Storage management of dry tailing in the form of cakes is presented through two examples. Example 1: (Diamond Mine Project) After beneficiation of Lamproite containing ~ 45% solids is treated in vacuum filtration plant for generating cakes containing about ~ 16% moisture. The cakes are transported by conveyor to storage area up to a 50-m-high stack adequate for 20 year operation of the diamond mine. Software generated profile of the stack is shown in Fig. 12.9. Example 2: (Zinc Mine Project) Presently, slurry generated from beneficiation plant contains about 35–40% solids. Pilot plant tests on vacuum filtration showed cakes with ~ 14% of moisture can be generated. Dry tailings can be collected by a short conveyor and stockpiled for transportation by dumpers for stacking over full pond. Large quantity of dry tailings can be accommodated in 50-m-high stack build over the nearly-full tailing pond. Software generated profile of storage stack and approach ramp for movement of dumpers is shown in Fig. 12.10.

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12 Tailing Storage Management at Mines

Fig. 12.10 Zinc mine

Software Generated Views of Multi-layered Storage Stacks Up to Full Height Showing Different Layers It is pointed out the software generated views (Figs. 12.9 and 12.10) of storage profiles of dry tailing are prepared by software experts based on stacking patters (number of layers, thickness, side slopes, terrace level, etc.) supplied by team of engineers after geotechnical designs namely compaction; slope stability—individual layer and overall stack; safe side slope; berm width, approach ramp and other data required in the software. Purpose of presenting the general views of stacks is to expose readers to demonstrate power of vacuum filtration of wet slime for advanced storage management of tailings. It is true that initial costs for setting up filtration plant, conveyor routes, approach road, inventory of earth moving, compaction and their maintenance will have effect on initial CAPEX (capital expenditure). But the break-even point will be reached in a few years and thereafter it is a win–win situation for the management. It however is pointed out that proper maintenance, supervision and safety measures are key to success of dry stacking process.

Key Points on Filtration Technology and Stacking Dry Tailing

263

Key Points on Filtration Technology and Stacking Dry Tailing Key points on filtration technology and stacking of dry tailings are outlined below for information: • Grain sizes of tailings depending upon crushing and screening commonly range: (–) 75 μ • Water content in slurry: 40–45% (w/w) • Slurry can be treated in filtration plant to extract water down to about 14–18% water contents • Filtration plants, sub-station, tanks and utilities can be setup in small area near pond or beneficiation plant • Dry tailings can be transported by conveyor, dumper trucks and stored in layers as per stack design • Stacks can be profiled to stable configuration and compacted during deposition • Rainwater drainage and environmental safety measures are to be planned and implemented during stacking • ‘Closing’ of stacks is to be carried out ensuring permanent protection against erosion by wind and rain, surface protection by laying coir mat and plantation of vegetation. Several specialized agencies carry out surface protection work. Method of dump protection and closer with vegetation is shown in Fig. 12.11. • Prevailing environmental regulations are to be followed in ‘stack closer’ and maintenance plans. • Initial costs (CAPEX) for setting up filtration plant and fleet of transport equipment reach break-even point within few years of operation. The process is efficient, environment-friendly and economic in the long run. • Operational costs (OPEX) are moderate and are related to equipment maintenance and plant productivity.

Fig. 12.11 Arrange of slope protection with stone pitching and top protection by plantation

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12 Tailing Storage Management at Mines

It is seen, geotechnical engineers have major role to play in various aspects of tailing storage management in overall ore beneficiation process. A wide range of activities in connection with beneficiation of ore, storage of underflow in tailing pond, methods for raising height of existing dam, assessment of geotechnical parameters of dehydrated tailing, stack design and several other related topics. Active participation of experienced geotechnical engineers is essential in every step. For reference, branch-wise involvements of geotechnical engineering are listed under following broad heads. A. Raising height of existing dam i. Selection of method of raising height (U/S, D/S or Central) including geotechnical design ii. Provision of Masonry Parapet Wall (at crest, toe or both) in case of space constraints iii. Design of foundation for U/S or D/S raised portion of new dam iv. Design of dam with provision for future raising v. Seepage analysis of raised dam vi. Logical approach for selection of Free-board vii. Stability analysis of ‘Slope-on-Slope’. B. Tailing Storage management adopting Filtration technology i. Exploration and assessment of load bearing capacity of operating or dead pond and method for ‘improvement’ of pond deposits and design ii. Assessment of geotechnical properties of ‘dried’ tailing (cakes or paste) after filtration iii. Mode of transportation, laying in layers, design of slopes and method of compaction (stack design) iv. Dump closer plan ensuring statutory mines and environmental regulations. C. Supervision and Testing i. Planning and supervision of geotechnical investigation at ponds ii. Testing of geotechnical parameters of dried tailing (paste or cakes) after filtration iii. Design supervision during ground improvement works at pond beds iv. Supervision during placement of dried tailing in layers and mechanical compaction v. QA and QC tests during progress of field works vi. Periodical inspection on ‘health of dump’ and take remedial measures in case of incipient risk. It is hoped, this chapter as a whole has been great interesting and informative to geotechnical engineers practicing in mining industry. The methods for raising height of existing dam can also be applied in raising of embankments for water retaining structures/storage ponds/reservoirs, canal in urban development projects.

Chapter 13

Failure During Construction

Introduction Even after careful planning and design, unexpected failure can and do occur during construction. Reasons behind failure are known only after post-failure studies are conducted. It may be revealed that failure was caused due to missed-out guidelines at planning/design stage or simple negligence/over-sight during execution. In some rare occasion, it may remain an unpleasant surprise (God’s act). But one thing is sure, failure does not occur without reason—known or unknown. However, it is to be kept in mind that reasons behind ‘similar-looking’ failure can be different. Therefore, forensic study needs to be conducted for each case of failure. A number of instances of ‘failure during construction’ at industrial and urban infrastructure project sites have reported. Out of them, twelve (12) selected case-histories of failures of varying degree of severity occurred over four (4) decades is presented along with outcome from failure studies. These should be of great interest to engineers practicing in industrial and urban infrastructure projects and might be helpful in avoiding failure in the future project.

Case History 1: ‘Sliding’ of RCC Base Raft on Sloping Base (1981) It is an interesting case of RCC base raft foundation for inclined tunnel for connecting Track Hopper to Ground Hopper in a steel plant at Visakhapatnam, sliding down during construction. Construction of tunnel was carried out adopting open cut method. Excavation, leveling and laying PCC mud mat were completed. High sulfate aggressivity of sub-soil required treating all concrete surfaces in contact with soil to be painted with two coats of hot bituminous paint. Accordingly, top and sides of mud mat were painted before casting first segment of (40 mm long, 12 m wide and 1.0 m thick) © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_13

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RCC base raft of the tunnel. Due to high summer temperature (~43 °C), the bitumen layer softened resulting in friction loss and the base raft started sliding downwards with little tilt (rotation). Fortunately, it was detected at early stage and further sliding was arrested by driving steel joists in front of raft. As preventive measure, a number of joists were driven before construction of remaining raft segments. The simple arrangement proved effective during construction of remaining rafts for the tunnel. As mentioned in the beginning, every event of failure must have reason/s. In this case, the source of problem was in planning for construction. In order to expedite progress, construction of base raft was started from top and construction of lower rafts to continue simultaneously. This was a case of lack of foresight / experience.

Case History 2: Restoration of Pile Foundation (1983) This is another interesting case of shifting pile foundation along with structural column of a factory building at Dankuni, West Bengal. Earlier the project site was paddy field and had to be developed by 2-m-thick earth filling. Sub-soil was soft to medium silty clay to clayey silt with low SPT up to about 15 m depth followed by medium dense to dense silty fine to coarse sand with SPT values increasing with depth. Groundwater table encountered within 2.0 m from OGL. The structural framed building was designed with steel columns and roof truss. Column foundation was designed on 8 Nos. of 550 mm diameter cast-in-situ driven piles of about 25 m shaft length. Piles were driven, pile cap and pedestal were cast, fabricated steel columns erected, roof truss and purlins were placed, and roof sheeting was in progress. As per shop layout, an 8 m wide, 6 m deep ‘sand tunnel’ was to be constructed below shop floor. For construction of sand tunnel, about 4 m deep excavation had to be carried out below OGL and accordingly depth of pile cap was kept below excavation level. While roof sheeting was in progress, excavation for sand tunnel started. One fine morning it was horrifying to see one column shifted about 500 mm toward tunnel tearing joints at roof truss and purlins. Immediately, the roof structure was structurally separated and supported on temporary derricks. The column was structurally disconnected from all other members and all works on roof and tunnel were suspended. Fortunately, there was no causality or serious damage to any structural member. What to do now? Studies were conducted on causes and effects of shift. Out of several schemes, selected rectification scheme included (a) measurement of actual shift, its direction and characteristics; (b) technical assessment on causes of shift; (c) if there was any damage to RCC raft, pedestal and piles; (d) how to restore the structures and (e) method of rectification of foundation ensuring safety of the building, cost and time factors.

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It was observed the solution was more difficult than the cause itself. This was challenging for geotechnical, civil, structural and construction engineers. Within days, an innovative but bold restoration and rehabilitation scheme was prepared for presentation to the management. Main findings from technical studies, pros and cons, risks, guidelines of proposed restoration scheme and final outcome are summarized below. Cause of Shift: A tunnel for carrying sand was to be constructed below shop floor. An underground sand tunnel passed through middle of shop floor and coming out at side with 90º bent near the ‘failed’ column. Excavation was carried out on two sides of column base raft with other two sides remaining up to ground level. Lateral earth pressure acting on two perpendicular sides of pedestal pushed the pedestal diagonally by about 500 mm and thereafter remained stable. Forensic studies on effects of shift were carried out on: (a) column pedestal; (b) extent and characteristics of settlement; tilt / rotation if any to assess (c) health of RCC piles; (d) condition of fabricated structural column. Outcome of forensic studies: (a) Piles were unaffected, no damage to pile shafts; (b) tilt of base raft resulted from unequal penetration / lifting of few outer piles; (c) RCC pile cap and pedestal was intact and sound. Restoration scheme: ‘pushing back’ the foundation by jacking the pile cap with extreme care; (b) complete civil construction of tunnel and (c) re-erect column and complete balance structural fabrication. Method for Jacking: (a) Excavation to expose RCC pile cap up to cut-off level; (b) trim corner of RCC raft; (c) construct temporary bulkhead by driving joists and placing timber planks; (d) earth-filled bags for bulkhead; (e) setting one 160 T capacity reversible remote-controlled motorized jack between raft and bulkhead. After detailed techno-economical deliberation, the proposal received ‘green signal’ from the owners’ side and also assurance for full support and cooperation. Views of excavation, pile cap chamfered for fixing steel plate for jacking, hydraulic jack placed between pile cap and bulkhead are shown in Fig. 13.1a, b, respectively. Operation: ‘Push’ back piled foundation at extremely slow rate and taking various measurements. Extreme care was exercised to monitor if there was any sudden drop in jack pressure or movement of column and soil at excavated level. During middle of operation it was interesting to notice water coming out from edge of pile cap. Jacking operation continued round the clock for nearly 40 h till shift was brought down within 25 mm from original position. Monitoring continued for several days before allowing civil construction and backfilling prior to resuming structural works. Full view of final setup for jacking before start of pushing operation is shown in Fig. 13.2. Restoration work was carried out on war-footing and completed within two weeks time to the satisfaction of all concerned. The process building remained stable and functioning satisfactorily.

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(a) General view of pushing pile cap

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(b) Close-up view of chamfered pile cap & jack

Fig. 13.1 Setup for jacking pile cap with remote controlled reversible jack

Fig. 13.2 Jacking system fully assembled and ready for Start

Construction of underground sand tunnel should has been completed up to ground level before construction of the pedestal. The best approach should have been to construct tunnel and pedestal simultaneously along with earth backfilling. The cause of failure was faulty construction planning. Excavation up to 4 m deep on two perpendicular sides of pedestal was due to lack of foresight and experience.

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Case History 3: Settlement of Building Due to ‘Buried Water Channel’ (1984) This was case of excessive unequal settlement and tilt of a single-storied health center building at Raipur. The building supported on open foundation was constructed and commissioned. But after few months during first rainy season, aprons at one corner started cracking and settling, thereafter diagonal cracks appeared on walls and floors of the building. The defects were repaired but damages continued to recur. It was thought cracks were caused due to initial unequal settlement and expected to stabilize after few months. But that was not so. The defects started re-appearing progressively at different locations of the building. After about one year of continued subsidence problems, the plant management was fed-up with the ‘sick’ health center and decided to abandon it and build a new health center at other location. Post-failure study on nature and extent of damages along with a few exploratory shallow boreholes revealed the culprit was an active ‘buried water channel’ which was washing away silty soil from bottom of foundation forming small and medium size cavities. From the outcome of studies, it was apparent either thorough soil test was not carried out or existence of buried channel was ‘not identified’ during investigation. It therefore is important to carry out soil test even for minor structures.

Case History 4: Differential Settlement Due to ‘Swelling Soil’ (1985) It was a case of differential settlement of two-storied project office building in a steel plant at Durgapur. Considering existence of ‘swelling-shrinkage’ type soil, the RCC framed building was supported on 6.5 m deep (450 mm and 750 mm diameter) under-reamed pile foundation. The building was completed and Project Office was opened. After about 1½ years, cracks started appearing on tiles of toilet and pantry floors. Gradually, cracks progressed and appeared on outer walls of ground floor. This was embarrassing for the project engineers. Afterward, cracks widened and level difference between door and floor became risky for walking. Thick floor mats were placed at entry. Civil engineer failed to point finger at any valid reason. Geotechnical engineer recommended carrying out few shallow (~10 m deep) boreholes along periphery of outer walls including field tests and sample collection. Laboratory tests included swelling, shrinkage limits and swelling index along with other routine tests. Results revealed existence of expansive soil from about 2.0 to 5.0 m depth below surface which was responsible for seasonal differential settlements. Once diagnosis was complete, cure was simple. As remedial measure, it was decided to create a ‘grout curtain’ along outer periphery. Grout mix comprising of bentonite, lime and cement was injected under low to moderate pressure in two stages. A two-layer grout curtain was completed and the floors repaired. The treatment stopped further settlement.

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Case History 5: Influence of Underground Connectivity of River—Experience During Construction of Calcutta N–S Metro Rail (1980’s to 1990’s) The first ever in India, fully underground Calcutta Metro Rail from Dumdum to Esplanade lovingly called PATAL RAIL (meaning train moving below ground) was commissioned on October 24, 1984 (1st Stage) and February 1995 (2nd Stage). Almost the entire 20 km stretch lies below mean Hooghly river water level. Construction of tunnel was planned on open cut method and sides protected by thick RCC Diaphragm Walls braced with fabricated structural members. Entire project was planned, designed, constructed, commissioned and maintained by the engineers of Indian Railway. It never had any structural collapse, derailment and serving daily commuters nicely till today. During construction of the project, several instances of geotechnical interest were noticed. Selected few of them having influence of connectivity with Hooghly River are presented below. 1. Near the Statesman Building (Central Avenue Side) During excavation for metro tunnel within diaphragm walls, dewatering and maintaining stability of diaphragm walls became extremely difficult due to excessive bottom heave and gushing water causing serious stability problems. Cracks appeared on walls and basement floor of nearby Statesman Building. Metro rail undertook extensive grouting work at outer faces of diaphragm walls and heavy dewatering inside tunnel. The area was stabilized and construction of tunnel progressed. 2. Construction of Park Street Flyover on J. L. Nehru Road Construction of flyover on J. L. Nehru Road started several years after regular operation of the Metro Rail. Foundations for flyover were supported on RCC bored piles. During progress of pile load test, it was noticed even under maintained final test load, pile head settlement varied at different times of day and night which could not be explained. For investigation purpose, test load was maintained for few more days and time-settlement recorded at regular interval. It may be noted the load test was done in January and winter that year was severely cold with chilling wind blowing from Hooghly River at night. Initially, it was thought, change in day and night temperature could be the reason. Brain storming sessions were not fruitful. In those days I used to stay in a suburb town (Sreerampur) in Hooghly district and commute to office in Calcutta by local train and cross Hooghly River by ferry launch. One morning when crossing by ferry, noticed the river was full during high tide. After attending office, went to site, checked pile settlement records and noted reduction in settlement. Requested site supervisors to record hourly settlement for rest of the day. On my way back visited the site again to check settlement records and noticed increase in settlement in afternoon and requested site to continue hourly recording till midnight. At the Ferry Ghat office, enquired about times of high and low tides in the river for the day. Next day while checking times of settlements and tides, sinusoidal patterns of both were noticed.

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Records of settlement-rebound and high-low tides were plotted vs. real (clock) time. Striking matching of sinusoidal patterns of variation in pile settlement-rebound and low–high tide data with time lag of about one (1) hour was evident. It was then concluded beyond doubt that variations in settlement were due to tidal variation in river Hooghly. Above findings indicate active connectivity between Hooghly River and adjoining areas. Incidents of river connectivity were experienced during construction of tunnel for Metro Rail toward south. 3. Tollygunge-Majerhat Rail Bridge on S. P. Mukherjee Road During construction of Metro Tunnel near Majerhat rail bridge, extensive problems in dewatering, base stabilization and ‘sand boiling’ were faced for quite some time. Situation was somehow managed after major dewatering from outside and inside tunnel, timber piling, sand bags, etc. Above cited events indicate active underground connectivity of Hooghly River along the alignment of Metro Rail corridor and beyond. The observations also show sub-surface complexities of Calcutta Soil. This was further evidenced during planning for A. J. C. Bose Flyover presented below. 4. A. J. C. Bose Road Flyover from Park Circus to Victoria Memorial Hall Soil investigation work from Circus Avenue (Patodia House) to Victoria Memorial (Roland Road Crossing) was carried out by 20 Nos. 40 m deep boreholes. Locations and cross section are shown in Fig. 13.3a–c. (a) Locations of borehole Nos. BH 01 to BH 20 along proposed flyover alignment (b) Sub-soil stratigraphy along the boreholes (c) Enlarged view of stratigraphy near Rabindra Sadan: BH 14 to BH 20. It is observed from Park Circus to Rabindra Sadan, sub-soil is ‘Normal Calcutta Soil’. From Rabindra Sadan to Victoria Memorial, the deposit is characterized as ‘River Channel Deposit’ continuing up to 25 m below EGL. This shows the original course of Hooghly River and present position after changing course toward west side over the years.

Case History 6: Liquefaction Due to ‘Blow-Out’ of Natural Gas Well (1997) A small village named Sreemangal in Sylhet district of Bangladesh is located on a proven vast reserve of natural gas. A US firm was contracted for drilling gas extraction wells, purification, processing and supply to tank farm 30 miles away. A heavy-duty deep drilling rig was deployed for exploration of locations suitable for sinking production wells. During progress of drilling, the bore accidentally punctured dome of gas reserve at about 800 m below ground. Gas started blowing out (gusting)

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(a) Boreholes Locations from Circus Avenue to Victoria Memorial RabindraSadan

KarayaRoad

(b) Subsoil Stratigraphy form Circus Avenue to Rabindra Sadan ctoria Memorial

(c) Enlarged Section from Rabindra Sadan to Victoria Memorial (BH 14 to BH 20)

Fig. 13.3 Lithology from Circus Avenue to Victoria Memorial

under high pressure spread over large area. Whole region became sensitive and virtually ‘boiling’. Gas bubbles along with water come out for several weeks. Local hutments were partially damaged, walking on ground was risky. Big trees tilted, bubbles coming out from pond and hill streams, fish died. ‘Pan’ cultivation, a major export commodity, was affected and beetle nut (Supari) trees tilted and discolored. Intensity of blow-out was so severe that ‘boiling’ condition developed and the 40 m

Introduction

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tall, 500 T drilling rig and accessories slowly and steadily sunk into ground and buried completely. In the beginning, the firm attempted to salvage the rig, but ultimately abandoned and allowed it to ‘rest in peace’ forever. Details of the incident have been covered in Chap. 11.

Case History 7: Settlement of Ground Storage Tanks (2003) A Tank Farm of 7 steel tanks of 15–35 m diameter and 10–12 m height were set up for storage and distribution of diesel, petrol, aviation fuel at Louisiana, USA, in 1970. The site was low soft ground and was used for garbage disposal since 1950s. Steel tanks were built on sand / granular pad of nominal thickness. Most of the tanks settled considerably during hydro-tests. During operation all tanks settled vertically, differentially and tilted causing distress on most of the tanks. Some tanks were reelevated by pumping sand under tank floor more than once. In spite of that, further settlement continued. It is understood that, the tanks settled several feet in initial years of use and some bottom valves settled below grade. The area drainage and outlets were poor. During heavy rain, the area gets flooded. Settlements of 30–50 cm appear reasonable and most of which occurred during hydro-test and initial years of use. Although, degree of settlement slowed down over the years it continued @ 2.5 to 7.5 cm in 4 years. Several tanks had to be decommissioned because usability of the tanks reduced drastically (75–50% of full capacity) due to depth of ‘dead storage’, limitation on maximum storage height, routine maintenance and cost etc. Rectification/restoration schemes ranged from lifting and temporarily removing tank to other location by ‘floating’, construction of ring wall, sand filling and reinstalling tank, pumping fiber reinforced concrete under pressure deep into ground, jet grouting around tank periphery, dry soil mixing below tank bed, construction of piles below tank bed and so on. Logical approach for selection of rectification scheme should assess (1) ultimate soil bearing capacity, (2) total settlement and (3) time to complete 50% and 90% settlement of tank foundations. Such ground tanks are commonly designed considering acceptable differential settlement between center and edge of tank. In case, tank settles vertically and uniformly the problem can be managed. However, considerable settlement difference along tank periphery is difficult to tolerate. Ring beam will help in reducing peripheral differential settlement but will do little to reduce total settlement. In view of this, strengthening around tank periphery will be of partial benefit. Proposal for complete improvement should consider both base and periphery.

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Case History 8: Failure of Sheet Piles During Deep Excavation (2006) For construction of Wagon Tippler (WT) in Haldia, excavation (28 m × 10 m, 12 m deep) was to be carried out. The site was located at about 150 m from a perennial canal. Sub-soil comprised of medium stiff silty clay (5 m) followed by very soft silty clay (5.5 m) underlain by medium dense silty fine sand up to 40 m. Groundwater was within 1.5 m below EGL. Scheme for 12 m deep excavation and dewatering called for side protection with interlocking braced steel sheet pile and lowering groundwater level at least to 13 m. Estimated critical depth of excavation before bottom heave (sand blowing) was between 7.5 m and 8.0 m below GL. Design Scheme for Excavation: • Driving interlocked braced steel sheet piles up to 18 m depth • Two layer well point dewatering system comprising of 6 inner wells of 17–18 m deep and 6 outer wells of 12 m deep in each layer around sheet piles. Work at site deviated from the scheme. Old, bent, rusted sheet piles were driven without proper interlocking. Dewatering by well points was replaced by ‘sump and pump’ method. Pace of work was slow even with several stoppages and quality of workmanship was poor. As a consequence what were feared did happen: • Bottom heave and ingress of water started from bottom and sides at about 8.5 m depth (Fig. 13.4) • Sheet piles started caving in, dislodged and water started rushing from all sides • Sump-pump was ineffective, water accumulated in excavation and further excavation was impossible • Removal of blown-out sand and earth aggravated the situation, operation of heavyduty pumps made the situation worse with side collapse, sheet piles caved-in with visible ground subsidence outside excavation • As the area become hazardous, further work was suspended. Fig. 13.4 Heave at bottom of excavation

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Fig. 13.5 Construction of base raft in segments

Civil works for Wagon Tippler was re-started in following sequence and civil works completed successfully. – Base raft was cast in smaller segments and walls with short lifts with great difficulty (Fig. 13.5). – Civil works for WT was delayed by about 3 months with cost overrun. – Excessive pumping, bottom heave, side collapse, caving and subsidence of ground disturbed in-situ consistency, increased pore water pressure, permeability and loss in shear strength of surrounding soil. It was later revealed, in order to save time and cost, the construction agency deviated from design schemes and proceed with simplified approach thinking well point system was over conservative and adopted sump-pump system. For deep excavation in soft soil with high water level, controlling groundwater and competent side protection are essential.

Case History 9: Failure at Deep Excavation Due to Poor Maintenance of Well Points (2007) Coal unloaded in Wagon Tippler (Ref. Case History 8) is to be conveyed to underground Junction House (JH) to Pent House at ground level by (4 m × 3 m) sloping-up tunnel. Based on bad experience during construction of WT, scheme for excavation for JH and tunnel included 18 m long interlocking sheet piles and dewatering by 12 Nos. well points system with submersible pumps were adopted. But quality of workmanship was poor.

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Sheet Piling • During construction, alignment and interlocking of sheet piles were not always maintained • Sequence and stages of excavation vis-a-vis simultaneous placement of props were not followed • Excavated earth dumped close to edge of excavation exerted additional surcharge on ground. Well Points • 150 mm dia. 24 m deep borehole filled with gravel from 24 to 18 m • 50 mm dia. 6–8 m long HDPE strainer (2–3 mm slits/drill holes) were used but without geotextile wrapping and shrouding with filter media to prevent chocking of strainer pipe • Submersible pumps were used for dewatering, and multiple wells were connected to common header pipe. Coal unloaded at WT is conveyed through JH (depth ~ 12 m) to Pent House at ground level through an inclined tunnel. But strangely, construction of tunnel started from Pent House at top instead from bottom. Sheet piling for JH was done keeping tunnel side open. As excavation reached about 7–8 m depth (critical depth) ingress of water increased, cracks appeared on ground surface with about 300–500 mm subsidence. Well points became ineffective due to soil clogging strainers eventually making them partially or fully ineffective. Heavy-duty in-pit pumps engaged for dewatering. These were clear warning of ensuing trouble but excavation continued. Work resumed after dewatering with heavy-duty pumps but without taking any corrective or preventive measure against damages caused by flooding and subsidence. As depth of excavation reached about 11–12 m (bracing and struts provided up to 9 m depth), subsidence and several new cracks appeared on ground surface. Entire excavation collapsed with devastating damage to sheet piles, bracings, supports, etc., at night on December 2007. The structural members and sheet piles were bent and twisted beyond imagination. Fortunately, there was no human causality or damage to costly construction equipment. Post-failure conditions of the site and severely twisted steel structural members shown in Fig. 13.6a–d speak for itself on severity of earth pressure. Causes of failure at JH are summarized below: – Dumping of excavated earth near edge of excavation–poor practice – Strainer piper were not wrapped with geotextile and encased with shrouding caused blockage of openings – As majority of well points were partly or fully chocked, pore pressure started building up – ‘Liquefaction’ condition of sandy strata started when depth of excavation approached critical depth of ~ 8 m – Heavy-duty pumping caused increased ingress of water in excavation carrying soil and sand particles with it

Introduction

(a) Failure Cracks and Subsidence on Ground

(c) View of Collapsed Sheet Piles and Bracings

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(b) Opposite side of Excavation after First Failure

(d) Close-up views of Distorted Structural Members

Fig. 13.6 Photographs for Failed Sheet Pile Protection system for Junction House

– Flooding of excavated pit due to heavy rain softened soil over large area causing loss in strength – Sheet piles started yielding due to excessive thrust exerted by transformation of surrounding soil from ‘active’ to ‘at rest’ to ‘residual’ shear strength condition exerting enormous lateral thrust on sheet piles. Developed series of slip surfaces with severe ground subsidence – Struts failed in compression and bending due to severe load leading to total collapse of protection system.

Case History 10: Failure of ‘Contiguous Pile’ Retaining Wall (2014) Scale Pit (40 m × 15 m, 17.5 m deep) and connecting Flume Duct was to be constructed inside a steel plant in Durgapur. The site was congested with existing heavy processing plants. Space constraints required only ‘vertical’ excavation up to about 19 m depth. Vertical sides of excavation were protected by ‘contiguous pile wall’ with horizontal bracings at two levels. Accordingly 184 Nos. of 750 mm dia, 20–23 m long RCC bored piles were cast along the periphery. Top of piles were connected with RCC capping beam and excavation started for scale pit from (deeper) end and progressed toward flume duct.

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Fig. 13.7 Layout of piles protecting excavation

When depth of excavation reached about 12–13 m, suddenly 2–3 piles along with soil behind collapsed and huge volume of water gushed into pit. Gushing water along with soil and mud filled excavated pit by several meters. Loss of soil from adjacent area caused ground subsidence by about 1.5 m and cavity causing loss of support to columns of adjacent RCC framed building. Failure happened at about 2 AM at night, as a result there was no human causality but some equipment was damaged. Figure 13.7 shows layout of scale pit, Flume Duct and arrangement of contiguous pile protection wall. Search for source of water leads to an old worn-out underground ~ 150 mm dia water main. Water at high pressure was coming out from the pipe washing out soil and developing large cavity. Closer view of failed piles and developed cavity are shown in Fig. 13.8. The damaged pipe was repaired and flow of water stopped. The failure was caused due to (a) Continued flow from leaking water main under pressure loosened soil and forming buried channel/s. (b) Water flow through buried channel washed out cement from green pile concrete in that area and pile shafts became weak. (c) When excavation progressed, weak piles could not sustain active earth pressure from surrounding earth (d) The weak piles failed and collapsed. Rectification measures included (a) propping corner column of adjacent building, (b) protecting failed area with steel sheets supported by joists, (c) cavity was backfilled with stone, earth and compacted. Balance works for the scale pit and duct were completed without any further difficulty.

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Fig. 13.8 Close-up view of failed piles

Case History 11: Failure of Flyover Over Canal (2013) So far failures at industrial project sites have been presented. Often, major failure occurs in urban infrastructure project sites. Geotechnical aspects of two such incidents occurred in and around Calcutta are highlighted. A new flyover over a canal was commissioned in 2011. But within two years, one 40 m span of structural carved steel girder along with concrete deck slab collapsed and fell into the canal. As the accident occurred in early morning hour, fortunately there was no human causality. Figures 13.9a, b show failed girder. As usual, blame-game started in news media pointing fingers at design, construction, material, workmanship, supervision, interference and what not. However, purpose of referring the failure is to look into probable causes from geotechnical angle. Original plan was to construct one column inside canal and majority of piles on both banks were completed. But due to inter-departmental conflicts on issue of unobstructed flow through canal, foundation system was revised avoiding column

(a)

(b)

Fig. 13.9 a Collapsed girder fell on canal, b truck hanging from fallen girder

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inside canal. Design of curved segment of steel girder over canal was modified accordingly. Balance construction was completed and the flyover opened to traffic. So where is the geotechnical issue? In short, revised design called for rearrangement of foundation resulting in revision in design loads. But piles on banks were already cast. Extra load might have caused excess and / or differential settlement between foundations. The settlement difference naturally gets magnified due to height of pier. This might have resulted in displacement of bearing pads at pier and girder adversely affecting proper transfer of load from girder to pier cap. When the heavy transport truck hit (probably at high speed on empty road) on one side of curve girder, one bearing might have slipped; the girder lost stability and dropped on canal. It is known foundation supported on group of friction piles in alluvium soil initially settle with time. I wonder if estimation of group settlement of foundation on friction piles is carried out for infrastructure projects. It may be pointed out that in steel and power plants, equipments and units (namely Crusher, ID fan, Sinter Machine, Rolling Mills) are highly sensitive to total and differential settlements. Foundations for sensitive units resting on open or deep foundation, settlement checks are mandatory practice in heavy industries.

Case History 12: Ground Subsidence During Tunnel Boring with TBM (2019) The East–West Metro Rail Project in Calcutta connecting Salt Lake to Howrah Maidan via Sealdah Station, Esplanade, crossing the Hooghly River, Howrah Station to Howrah Maida was planned with two parallel tracks. The stretch in Salt Lake was planned on elevated tracks and stations. Thereafter, the tracks and stations were planned with two underground tunnels. Tunnel Boring Machines (TBM) successfully completed major portion of tunneling work from Howrah and reached last leg close to Sealdah Station. On August 31, 2019, when the TBM was boring below Bowbazar (Central Kolkata), suddenly huge amount of water, mud and sand rushed in flooding the tunnel and portion of TBM. The incident caused wide-area ground subsidence and instability over large parts of Bowbazar. Major cracks developed on walls and pavements and many buildings partially collapsed (Fig. 13.10). A number of centuries-old and heritage buildings damaged. Local residents were evacuated / relocated, unsafe buildings demolished. It was later learnt the TBM did hit and puncher a ‘dormant’ aquifer. The event was an eye-opener on the formation and characteristics of ‘Normal Calcutta Soil’. Geotechnical engineers are familiar with ‘London Clay’, ‘Chicago City Clay’, ‘Mexico City Clay’ for their specific characteristics. In the same line, brief overview on ‘Normal Calcutta Soil’ based on old maps and reports known only to a few might be of interest to geotechnical, civil, construction engineers and

Introduction

(a) Damages to Pavement

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(b) Damages to Building

Fig. 13.10 Damages caused by ground subsidence in Bowbazar area

town planners as well involved in urban development project in and around Greater Calcutta. Search for history of Calcutta soil revealed existence of valuable documentations on events of natural furry the region underwent over centuries. Few such incidents starting from 1660s are highlighted. The author has compiled some of the data and documents collected from various sources which might be of interest to an engineer and general reader as well.

Map of 1660s East India Company engaged The “NEDERLANDS INDIA” to prepare map of the-then Bengal and vast adjoining areas. The map titled “BENGALE en RAAD” by MATTHEUS & BROUCKE cover eastern Indian states Orissa, Bihar, Bengal, Assam, Tripura, Arracan, Sundarbans, Bay of Bengal. The mapping team was in India during 1658–1664. Part of the map covering ‘pre-partitioned’ Bengal, Tripura, Arracan and Bay of Bengal is reproduced in Fig. 13.11. It shows large network of major and minor rivers, canals, lakes in South Bengal.

The ‘Ghost’ of Creek in Bowbazar On August 31, 2019, Metro tunnel hitting an aquifer body and crumbling whole of Bowbazar area raised the ghost of a centuries old dormant creek. What really tipped the behemoth is ghost of the city’s past which few people remember now. If old maps and reports were consulted to know what lay beneath, the tunnel part of

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Fig. 13.11 Map of ‘pre-partitioned’ Bengal, Tripura, Arracan and Bay of Bengal

Calcutta Metro might not have faced the devastation. The accident has woken up the ghost of a stream that once flowed through the heart of the city. • In Old Calcutta Map by Col. Mark Wood (1784–85) and by Upiohncin (1792–93), a creek can be found in the area. • The creek used to meander from Hooghly near Chadpal and Babu Ghat pass through Hastings Street, Princep Street, Wellington Square, Creek Row, Sealdah and Beliaghata to Salt Lake. It is the creek that gave names of existing roads Creek Row, Creek Lane. • The creek was navigable till 1737 for big barges by British East India Company to venture out of Fort William which was built where GPO stands today. • In fact the British officials excavated the creek for further navigability

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• When the Great Tropical Cyclones struck the city on Oct. 11, 1737, it left an incredible trail of death and destruction. Wind speed was felt at 200 mph (333 kmph). Thousands of vessels sunk. A big barge was blown nearly 4 km into creek up to Wellington Square (Raja S. C. Mallick Square).The area was called Dingah Bhanga Lane (means broken boat). It subsequently was renamed Wellington Lane. • The cyclone sounded the creek’s death nail as the storm caused the creek to silt up. The stretch of Hastings Street was filled up but the Creek Row stretch remained a creek for long though water flow from the river stopped as general gradient of the city was from east to west. As a result the creek turned into a ditch used to carry surface drainage water. The Wellington Square was the ditch. Memories of the creek remains in names of places like Jelepara Lane (Fisherman’s lane), Sareng Lane (Sailor’s lane) and Kaibarta Samaj. Fisherman used to catch fish and sale at Janbazar and Fenwick Bazar. Parts of broken boats were found during foundation work for some of the buildings in the area. Heritage of Bowbazar Bowbazar was the center of India’s Freedom Movement and Center of Excellence for academic and cultural activities not only in Bengal but of India. A number of centuries-old and heritage buildings damaged. Everything bearing the history of Bowbazar is destroyed after the tunnel boring machine hit the unmapped aquifer. The old maps of the city show that all the houses are sitting right on top of the erstwhile creek. Underground Railway Network • In 1905, The British Parliament requested The Advisory Board of Engineers co-opted with The Royal Commission of Traffic to look into the possibility of laying underground rail network (in line with Metropolitan Railway in London that started in 1863) in Calcutta, the then second capital of British Empire. Acting on the advice, the Board embodies in a Report that Calcutta is built on dangerously sloppy silt with very occasional thin bed of poor remains of carbonaceous clay and a creek running within the city making it hazardous to build an underground railway. • Negotiating Bowbazar, where a creek used to flow allowing water ingress or permeability, was not a cake-walk for Metro tunnel boring by TBM. When the body of water was filled up during rainy season, formation of underground water table can be highly fragmented and deceptive. The precarious geology of Bowbazar area, because of huge water flow points at the creek which might have got buried deep underneath the surface. One can obliterate canal or tank by filling it up but hardly erase their underground imprints. • One now wonders whether the authority consulted old maps and records to understand the situation below surface. The accident has woken up the ‘ghost of a stream’ that once flowed through the heart of the city.

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Experience During N-S Metro Rail Work Difficulties caused from large network of major and minor rivers, canals, lakes existed in South Bengal (Ref. Figure 13.11), most of which got buried during development projects, were experienced during construction of the First North–South Metro Rail. Some of the incidents occurred in Central Calcutta stretches (The Statesman Building to Tollygunge) were discussed in Case History 5. Data Available on Calcutta Soil Not so long ago, Greater Calcutta area was explored length and breadth. Work done by eminent soil engineers like Amitabha Ghose Dastidar, Sudhin Gupta & P. K. Ghosh of Cementation India Ltd. deserves special mention. Comprehensive details of “Calcutta Soil” are documented well in published literatures. Select few examples presented below clearly show presence and extent of River Channel Deposit up to Portuguese Church and presence of high plasticity clay from 10 to 20 m below GL near Sealdah Station. Figure 13.12 shows cross section through boreholes from Ramrajatala to Salt Lake which show River Channel Deposit up to Dalhousie. Figure 13.13 shows cross section from J. L. Nehru Road to Beleghata. It is observed a layer of soft clay (CH) encountered from C. R. Avenue and continued to Beleghata. Sub-soil between C R Avenue to Sealdah Station show (CL) soil up to 10 m below GL and (CH) soil from 10 to 20 m below GL. Sandy Silty Clay (CL) with low plasticity (LL < 35) and low compressibility up to 10 m below GL. Soft Silt and Clay (CH) with high plasticity (LL > 50) and high compressibility from 10 to 20 m below GL. The authority might have missed this. This along with Case History No. 4 on construction of A. J. C. Bose Road Flyover from Park Circus to Victoria Memorial and Case History 5 on construction of N-S Metro rail are indicative of the Hooghly river changing course from east to west by more than a kilometer over the years. What was blamed for disaster at Bowbazar was ‘ghost of the city’s past’ which few people remember now. Colossal waste of money, time and extensive damage to

Fig. 13.12 Cross Section from Ramrajatala to Salt Lake. Note River Channel Deposit continued up to Dalhousie Area (Portuguese Church)

Common Cause of Failure During Construction J. L. Nehru Rd.

C R Ave .

285 Se aldah St .

To Beleghata

Fig. 13.13 Cross Section from J L Nehru Road to Beleghata

property and suffering to the local residents could have been avoided if available old maps and reports were consulted to know what lay beneath before going ahead with the tunnel alignment of East–West Metro Rail.

Common Cause of Failure During Construction In above cases, minor to major failures at industrial and urban infrastructure development project sites have been discussed. In fact construction sites often have to live with incidents of failures of lesser degree. A few common causes of failures, which if taken care may help avoided risk of failure during construction. Specification and working drawings including NOTES should be studied carefully and sequence of work is to be planned. Inventory of manpower and equipment, uninterrupted supply of raw materials are to be arranged. Based on available space, site plan for office, cement store, godown, first aid center along with water and power supply are to be arranged. Site should be approachable by road, maintained neat and clean avoiding water logging. Quality of work should be supervised and recorded routinely. Overall house-keeping at site is very important for smooth and trouble-free progress. Cash flow to site is necessary to avoid slow progress. Site practices which often lead to failure during construction are many. Only a few are listed below: • Excavated earth dumped close to edge of excavation—destabilize sides of excavation. • Water pumped out from excavation not discharged to proper outlet—chances of back-flow. • Precautionary measures not taken for draining out rain water—risks of inundation. • Missing or ignoring early signs of incipient failure—warning signal for major failure.

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• Leaving things to chance—taking risk knowingly or unknowingly. • Construction method, sequence of works often simplified at site to save time and cost—unwise practice. • Lack of supervision on quality of materials and workmanship—defects or failure in future. • Construction machinery and accessories not maintained, inexperienced operator—loss of productivity. • Smart Phone is blessing and distraction—time and attention diverted in responding phone, browsing, PR, etc. • Round-the clock work including night shift without adequate manpower and logistic supports. Extended working hours / overtimes act on efficiency of workers—poor quality of workmanship and output. • Air conditioned site offices—supervisor uninterested to go into hot, humid site and rains—not desirable. • Designer, construction engineer, contracting agency, management need to work in tandem as a team to see the project is completed without any failure or accident and handed over in schedules time. • Most important, design engineers should visit site periodically to conduct design supervision and modify design-based actual on site condition.

Chapter 14

Site Hazards and Remedy

Introduction In most green and brown-field industrial or infrastructure project, survey and soil investigation teams are the first entrants to site. They often face variety of unknown and unforeseen problems even before start or during progress of field work. The problems are to be solved all by themselves with limited resources available to them. Even during progress of civil construction, situation sometime can change drastically leading to accident. Under the circumstance, the site personnel feel helpless. Hazardous situations faced at some sites and how those were overcome by indigenous methods is presented which should be of interest for field personnel.

Dangers from Wild Animals Soil Investigation Work at Iron Ore Mine in Orissa (1982) The team for soil investigation (SI) work for an iron ore mining and processing project mobilized to site inside Barsua reserve forest in Orissa. The team mobilized to the forest in summer of 1982. In those days modern communication gadgets like cell phone, Internet were not available, even land phone were accessible in towns. The team at first was charmed at the calm and was mesmerized by serene and scenic beauty of forest environment with fruit-bearing trees, bananas even aroma of ripe jack fruits. The team was welcomed by chirping & humming birds, peacocks, under inquisitive eyes of whooping monkeys. Then came howling from wild black bear and lastly the heart-freezing trumpet of elephant from nearby forest. That’s not all; occasional hissing of poisonous snake was most terrifying. So the heavenly day turned into nightmare after sundown. The team tackled most of the unforeseen problems indigenously and completed the job more or less in time before start of © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_14

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monsoon. Interesting and innovative means and methods adopted by the team to tackle the situations are briefly described. At the beginning, the SI team engaged number of ‘native’ village boys who were familiar with the forests and behavior of wild animals. Their guidance was very valuable. A few interesting events on how fear and risk of harm from wild animals were averted at site are shared with the readers.

Monkey In the beginning, monkeys started roaming around tents stare at the strangers. After few days they started eating the waste and left-over food thrown away by the workers. The monkeys developed taste for cooked spicy food. In search for food they sometime enter unguarded tent silently and not only enjoy rice-curry meal but topple vessels spoiling lunch for hungry workers. As a precaution, vessels of cooked food were kept covered with metal sheets. Deprived of lunch, monkeys got visibly upset and vandalized tents. Fed-up with the ‘monkey-business’, one day food for the jungle guests was blended with high dose of country liquor (from worker’s stock). The monkeys seemed to like it much better and ate full belly. After about an hour or so, they got intoxicated. Unable to stand erect or walk straight, missing grip while galloping between tree branches fell on ground and walked away unbalance. It was a rare enjoyable scene to watch dull faced monkeys sitting with sleepy eyes. After some time they recovered and managed to walk back to jungle before dusk. From next day, they were not seen near the sites. After few days, the monkeys although came back, but never ventured to come close to the tents. This was an example of innovative initiative by the workers.

Bears Wild black and brown bears often came around work sites and near tent to inspect what was going on in their very own territory. But they never came close to workmen and did no harm. But their very presences were frightening enough for workers, and they kept close vigil on the dark-haired inhabitants. Interestingly, the situation was tackled rather easily. When the bears came around, winch operator removed silencer box from diesel engines of winch and run it at different speeds for some time. Dark smoke and blasts from engines were enough to scare them away. After few days, they stopped coming near work sites.

Elephant Elephants were in no mood to tolerate intrusion into their own territory. Their anger was avenged mostly at night. Once in a while they topple drilling rig, empty water drum. It was a matter of surprise that they invariably squeeze grease drums. This

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caused hardship as getting fresh supply of grease from distant town was difficult. Technique used for bears was partly successful in tackling elephants. But it is important to be extremely cautious and keep a safe distance from a group of elephants having baby elephant.

Snake Forest snakes are dangerously venomous, speedy and are real threat at site. Snakes can sneak into conspicuous places almost anywhere and not detectable. Preventive measures are the only way to be safe from danger of snake. Some common methods are mentioned for reference, but site-specific measures are essential. Snake Trench An all-round snake trench (~0.6 m wide, 350–400 mm deep) needs to be dug around tents ensuring loop-like continuity. Carbolic acid and Gamaxine powder to be sprayed liberally in and around trench and tents. Care at Work Site Special care must be exercised in handling drilling rod, casing tube, wire rope, pipe stack, where snakes normally hide. Before picking-up these items from stack, workers were instructed to hit rods repeatedly with hammer to check for snake. The working areas were sanitized every morning by spraying carbolic acid. The workers must wear boots and use industrial hand-gloves along with safety glass. Although the team managed all dangers from wild animals, they could not avoid mosquito and insect bites. All of them used mosquito net at night. Still some workers suffered from malaria. Risks from snakes are part of professional hazards for soil investigating and survey agencies. But such dangers need to be tackled. An instance on precautionary and safety measures taken to avert risks from snake at a green field project site in the year 2005 is described below. It was a site for Coke Oven & Byproducts Plant at Haldia, West Bengal. The site was part of an old closed fertilizer plant setup during initial stage of developing industries in Haldia industrial belt. Huge area was lying idle for decades, factory buildings faced natural destruction and vast land turned into thick jungle. Part of the closed fertilizer plant was acquired for setting up the coke oven project. A number of ponds and water bodies caused obstacles. But presence of large number of poisonous snakes in ponds and jungle were very risky and scary. As usual soil investigation (SI) team mobilized to site. Fear of snake was managed as described below. First ‘snake trenches’ were dug around tents and storage areas for drilling rods, wire rope, sampling tubes, boring rig and accessories in which the serpentine might hide. The areas were sprayed with carbolic acid and DDT regularly. In those days, ‘pager’, a device for messaging service only, was available that too only in cities. A doctor having a ‘pager’ (it was rare in those days) and a two-wheeler was engaged on condition of his availability on call day and night. Snake charmers were invited

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for their expert advice. Jungle clearance and site leveling work started slowly from two corners to ‘divert’ snakes to one side of site. During construction of the old fertilizer plant, main roads and drainage system were built nicely. The concrete drains and gully pits were covered with cast-iron slabs. Quality of construction was very good and drainage system was functional except some siltation. Advantage of covered drainage network was taken. Snakes took shelter in gully pits and hide there. When some workers opened cover of a pit, they were terrified by hissing sounds from snakes in pit. They immediately closed the chamber. Later, snake charmers were called. They captured large number of snakes and happily took them away. Fortunately, there was no case of snake bite except for a cow. Grave dangers from snakes were averted successfully in this manner.

Damages by Tornado at Construction Site (1983) Installation of cast-in-situ RCC driven piles for construction of Wheel and Axle plant at Dankuni, West Bengal was in progress. The site was located by the side of state highway passing through vast paddy fields. Field works on site development, construction of site office, store buildings, boundary wall and piling with four driven piling rigs were continuing in full swing. On summer of June 1983, day temperatures were approaching 38ºC and windy. One day in late afternoon suddenly a Tornado developed in the wide open paddy fields and crossed through the site. After it settled down it was surprising to see about 10 ft. (3 m) wide section of brick boundary wall was literally ‘cut’ out without any damage on remaining part of the wall. Most interestingly, the bricks were ‘gone with the wind’ and not even a single piece of brick could be traced anywhere near the area. But the tornado toppled one driven piling rig standing on the path of tornado fell down side-wise. Obviously there was no remedy for natural phenomenon like Tornado.

Failure of Driven Piling Rigs at Construction Sites (2006 and 2013) At a site in Haldia (2006), installation of large number of driven cast-in-situ piles was in progress deploying large fleet of piling rigs. An accidental situation occurred in a flick of a second. The rig while engaged in piling work deformed in a peculiar shape as shown in Fig. 14.1. To common eye, it might look as an improvised design of rig. But it was not so and structural engineers were at a loss to explain how the rig can deform to such unique shape. The fact was while pulling out steel casing shale during progress of concreting, one of the guy wires (may be old worn out) connected to the rig gave in and snapped. Instantly, the main frame was subjected to tremendous ‘compression-bending’ force with sudden jerk and the rig deformed.

Dangers from Wild Animals

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Fig. 14.1 Deformed shape of driven piling rig due to tearing of single guy wire rope

This shows importance of using good wire rope for holding high mast piling rig. Enlarged view of deformed zone is shown in Fig. 14.2. At another project site in Haldia (2013), construction of a large number of 600mm-diameter-driven cast-in-situ piles was progressing in full swing deploying a fleet of driven piling rigs. All of a sudden, two steel tie members of one rig snapped from main frame. The rig bent immediately as shown in Fig. 14.3.

Unfortunate Incident at Bored Piling Site (2010) As part of expansion project at IISCO, Burnpur, West Bengal, large area inside plant premises earlier used for dumping slag for decades was selected for setting up new rolling mills. Height of slag dump was about 10–12 m. For construction, the slag dump was cleared and leveled. The long mill building and equipment were designed on large diameter bored pile foundation. Hydraulic rotary rigs were deployed for piling work. At one location during boring at 7–8 m below ground color of return slurry turned reddish. Boring was stopped forthwith and drilling tools withdrawn. Workers were astonished to find small pieces of flesh in return slurry. Pile area was cordoned off, dug up with JCB and Poclain. After a few hours, to every one’s horror and sadness, it was discovered that the flesh were parts of full grown python. The forest department was informed by the plant authority. Experts from forest department came prepared

292 Fig. 14.2 Close view of deformed area

Fig. 14.3 Failure of driven piling rig due to snapping of tie members from main frame

14 Site Hazards and Remedy

Dangers from Wild Animals

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Fig. 14.4 Full-grown python rescued from piling site

with gears and carefully rescued the second python of the pair totally unharmed (Fig. 14.4). It was one of sad experience in my professional practice.

Safety Belts Caused Fatal Accident (1985) It was the saddest incident I came across in my professional career. It was the site for Wheel and Axle plant at Dankuni, West Bengal. On a Sunday morning, repair and maintenance works of elevated oil pipeline was undertaken after taking proper shut-down and closing oil supply the day before. The single road-crossing pipeline was about 14 ft. (4.3 m) above road. A welder and a helper both wearing waist safety belt climbed and crawled to location for repair. During welding, residual oil left in pipe trickled down and dropped on road. Suddenly oil caught fire by falling red hot metal droplets from welding rod. The welder tried to jump but due to high heat, he could not unbuckle himself from safety belt. The helper rushed for his rescue. He also was wearing safety belt. When he reached near fellow worker, he lost control due to high heat of burning oil below. As it was Sunday morning, nobody was around to rescue the victims. Both of them met with horrific death. The safety gears turned into death trap. It was a clear a case of negligence on safety and fire protection. The work should have been carried out from a proper platform under supervision of safety inspectors. There was no fire extinguisher in the area. In fact nobody could think of serious risk and fire hazard from working on oil pipeline and gas developed in oil pipes. Two unfortunate workers got burnt. So Safety First should be the motto for all construction sites and must not be compromised on any excuse.

Chapter 15

Practice in Geotechnical and Foundation Engineering

Introduction Main focus of excellence in professional practice in Geotechnical and Foundation Engineering (GFE) in Industrial Projects is on technological requirements, economy and on-time completion. Factors like constructability, quality of workmanship, safety and ensuring rated productivity are other major considerations. Few instances of failure during construction or after commissioning have been presented in Chap. 13. Failures occurred generally due to lack of knowledge or experience that could have been avoided during engineering and construction stages. Can it be due to shortage of knowledgeable and experienced personnel in projects? It calls for introspection and rectification of the system starting from education to training to practice. There can be other angles too namely professional growth, modern business models, nontechnical interferences and others. These aspects as seen and felt by the author during his profession spanning over 45 years in several heavy industrial projects have been laid bare candidly without prejudice. Differing views and disagreements are always welcomed. But shortage of knowledgeable and truly experienced geotechnical and foundation engineers in projects is undeniable.

Professional Practice in Geotechnical and Foundation Engineering After completion of college education, pass-outs normally opt either for (a) education, i.e. higher studies, pursuing teaching and research or (b) professional practice, i.e. planning, design and construction. During practice, engineers often face several challenges. Following issues are believed to be relevant in that respect.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6_15

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Projects often face shortage of knowledgeable and experienced personnel reasons for that needs to be looked into. Normally, dream of fresh engineers toward professional practice is an airconditioned chamber in modern design office, decent compensation package and perks. But work at site means hot sun, rain and hardship which can lead to lack of interest and may even lead to frustration. Whatever could be the reason/s, some of the following causes might be responsible. It is pointed out following ‘observations’ must not be generalized but cannot be ruled out either.

Education In recent years, several engineering colleges offering geotechnical engineering diploma/degree have cropped up. In many such institutions faculty members mostly are part-time or visiting engineers who have little time or say over course management. Their role is similar to specialist doctors attending different clinics. Majority of the colleges do not even have equipped and maintained laboratory facility. The pass-outs are handicapped to take up job responsibility.

Training Very few pass-outs get opportunity to participate in field investigation work, don’t have access to laboratory of commercial establishment. As a result fresh engineers are poorly equipped to take up actual work either in design office or in soil testing company. Ironically, there is demand for qualified soil engineer. Earlier there used to be a system of 3–6 months training at office and job sites. After completion of training period, formal report was to be submitted. The report was evaluated by competent body who if satisfied would issue certificate (Certified Engineer) in recognition of training.

On-Job Training Some employer now require fresh graduates to undergo training period from 1 to 3 months to work under the guidance of senior engineers. This practice is fading out or diluted.

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Personal Initiative Practicing engineers need to allocate time, energy and budget to upgrade theoretical and technical knowledge by getting involved in professional activities. One should attempt to contribute on improvement in a project so that he feels proud and claim ownership. Above all, he/she should have respect for and devotion to geotechnical engineering profession.

Job Prospect and Career Opportunity Job opportunity for fresh geotechnical engineers is somewhat limited and compensation packages are not comparable to other branches of engineering. Opportunities for career growth of geotechnical engineering in a company or corporate are not bright.

Knowledge in Associated Branches of Engineering Working knowledge in civil design, detailing and methods of construction are essential for success in foundation engineering practice. Basic principles of structural engineering are welcome. These experiences help produce economic and constructible foundation design. Geotechnical engineer should make frequent visit to investigation and construction sites to gain practical experience.

Internal Discussion Earlier engineers used to discuss freely and frankly among colleagues and seniors combined on certain problem over a cup of tea. In most cases, practical solutions used to be evolved out of the discussion. Recent practice is ‘brain storming’ sessions through video-conferencing with head and branch offices. Under the circumstance, the atmosphere may not be conducive for participants to ask question or express idea/ opinion freely or fearlessly unless one is bold enough to come forward.

Introspection Factors attributable to problems relating professional practice are classified under different categories starting from site investigation to design, construction and modern business policy. Some of them are highlighted below.

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Problems Faced by Small and Medium Investigating Agencies In general difficulties/challenges faced by small and medium soil investigation (SI) firms are many. A few hurdles commonly faced by SI agencies are listed below without prejudice. • Allocation of time and cost for completion of SI work sometimes are unrealistic and unworkable • Land may not be acquired and approach not available—the contractor has to arrange everything within contract price and time • Test locations falling in water body were not spelt out in bid documents leading the contractor face serious difficulties during field work • In open competitive bidding, generally there is no lower limit for quoting price. As such, bidder can quote price without justification. In this process absurdly low unworkable price can be quoted. Under the eyes of many departmental and other watch dogs, soil engineer’s hands are tied making it impossible to disqualify a bid on unworkable price issue. • A contractor has to face many hurdles almost from all quarters: public roads, land owners, plant entry gate, safety and training department, political, local body, on-site checking it goes on and on which can be tackled only by non-technical means. Some bidder account for such unforeseen costs under a common cost head “NHT” (Non-Harassment Tax) but can rarely meet all such cost heads. • Next hurdle is multi-layered checking of reports (Interim, Preliminary, Draft, Final, Addendum); unending series of comments and getting approval for billing take unjustifiably long time. Simply because no one is willing to take responsibility so they opt for route of ‘shared responsibility’. Decision making and taking has become rare in recent days. But there are exceptions. • Lastly, payments of work bills are deferred several times by accounts section on various procedural and statutory regulation issues. Getting final payment is a marathon process. Most agencies need to offer “PUJA” to right sets of ‘GOD’ to get payment after completing a job. • Earlier, senior soil engineers insisted on personally inspecting and comparing bore logs with soil samples, checking laboratory test results before finalizing bore logs, selection of design soil parameters. On the contrary, some ‘expert’ does not take the trouble of visiting site or laboratory. • Reports are often prepared by academician or persons who do not have exposure in design and construction of heavy foundation. So while designing and detailing, constructability of foundation may be missed. • Certain ‘Design and Build’ (D&B) contracts come with an option for adopting foundation as per tender design or revise based on fresh SI by successful contractor. At times, even if say pile lengths mentioned in tender are adequate for the structure, the D&B contractor insists SI agency to provide longer pile in

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support for Extra Claim. By that time, the SI agency is stuck up to neck deep into financial muck. Only option left for survival is to ‘compromise’ and prepare soil report as per direction from D&B contractor. The SI agency is forced toward unethical practice. • With so many barriers, bumps, risks, how one can expect medium SI agency to execute field work, collect sample, carry out all laboratory tests and submit report in truly professional manner and spirit? As a result, some practicing civil designer feels skeptic about data and recommendation in soil reports and prefers in ‘over-design’ of foundations. A. Changing business policies Contracts for construction of infrastructure projects are commonly awarded to big companies of repute. Still unsatisfactory construction is not avoidable. Changed business model may be a reason. During last few decades, large construction houses changed business policies and execution modes, a few of them are highlighted below. • Diversification of big corporate separating construction wing into subsidiary ‘profit centers’ with set targets and growth plans. This encourages sub-contracting to agencies for execution and in turn earns profit both by main and sub-contractors out of the main contract price at the cost of quality of materials and workmanship. • New recruits (some with business management background) enter projects. Thrusts are on incentivizing progress, control on cash flow, procurement and sometime interference on engineering issues. • Number of QA/QC forms to fill, reporting to manager, attending progress/review meetings, answering mails increased many fold without new recruitment resulting in distraction from actual engineering services. • Unavoidable influence and interference from non-technical, preferential and interested quarters. B. Importance of Field Tests Present day trend in construction practice is to reduce (even avoid) number of confirmatory (proof) tests during progress of construction (may be to save costs of test) instead rely on QA/QC reports. Pile load tests are done few and far between, instead Non-Destructive Tests (NDT) are conducted on a number of working piles. But replacement of field test by indirect tests can at best be considered as supplementary. Only a few engineers are familiar with interpretation of data/profile from NDT. As such ‘health’ of piles as inferred by the testing agency is to be accepted without verification. (I personally have seen few cases of NDT agency reporting as per direction of piling agency). I am not aware of recent practice on number (percent) of working piles are subjected to load test. I personally found conducting more field tests has built-in advantages. For instance:

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(a) Direct verification of load carrying capacity of pile (b) By not knowing which pile will be selected for load test, piling agency takes extra care on quality of materials and workmanship for all piles (c) More tests improve overall quality without much additional financial burden. C. Personal Motivation Out of personal inquisitiveness, I informally raised following points to practicing engineers with a request for candid response (response is omitted her). Answer to following points can be indicative of their professionalism. • Seminar, conference, short courses, training, special lectures (employer or selfsponsored) attended. • Journals, technical reports, etc., collected from other sources for study/reference but actually studied. • Search Google for any query and get multiple answers. How many of these are checked for applicability to specific problem before adoption. • Use equation/formula not fully understanding basic considerations, assumptions and limitations but use it for solving problem. Are the results verified or cross checked by alternate method? • Commercial software packages are used to solve problems. Analysis is carried out for multiple options. The output depends on development of realistic ‘design model’, quality and reliability of input data. Are the output results cross checked and validated by alternate method before adoption? • Number of specialized field tests, e.g. (a) Footing load test, (b) Pile load test, (c) Field Permeability test, (d) Dynamic tests (Block vibration test, Cross-hole) being conducted are becoming few and far between. Why? • Lack of experience in construction leads to uneconomic/impractical/difficult-toconstruct design and recommendation. Exposure to actual construction site is important. Interested in site visits? • Mobile phone, laptop, digital camera, music system purchased vs. no. of books/ journals acquired. • Updates/new versions of various Apps, OS, links, etc., on modern gadgets are to be done on regular basis as these are imposed upon to stay connected. Similarly, there is need to upgrade on developments in modern day geotechnical and foundation engineering theory and practice. • Does one really respect geotechnical engineering profession as foundation for all developmental projects?

‘E-Classes’ Leading to ‘Learning Gap’ in Higher Education Modern education system is oriented toward ‘E-classes’ (‘online’ mode of education) replacing traditional class room lectures by faculty facing students. In any case, it is necessary to verify outcome of modern teaching system and learning. An

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Table 15.1 Worrying factor on ‘learning gap’ Country

No. of universities

No. of students (Millions)

Institution closure (weeks per year)

Estimated learning loss (%)

France

631

3

12

9.84

Germany

464

3

38

25

Italy

240

2

38

31.16

UK

282

2

27

20–31

US

3254

19

58

13.8

988

35

60

40–60

India

Source The Times of India, Kolkata Edition, July 17, 2021

education technology solution provider ‘Team Lease Edtech’ surveyed over 700 students and senior officials from 75 Indian universities to assess the learning gap in higher education during the pandemic years. Nearly, 85% of respondents believe they failed to learn 40–60% of course materials. The gap in learning is acknowledged across the world. The worrying factors on ‘Learning Gap’ revealed by the survey are summarized in Table 15.1. Dean (Academics) of a university said grades did not reflect learning loss since exams were conducted online. Everybody is getting high marks but when you interact with them you realize learning is not happening except for a small number who are self-motivated student. A VC pointed out online education couldn’t be used to train in skills. Registrar of a university pointed out sixty percent of student who would not have been promoted is currently getting promoted with good marks. Director of the Center for Distance Education said the learning gap is visible also in teachers. In view of discussions on professional practice in geotechnical and foundation engineering and worrying factors, it is evident teaching and skill-building need to be overhauled especially for practice in industrial projects. Obviously, one cannot change prevailing systems of education and training. But to succeed in professional practice the ‘learning gap’ can and should be filled by interested student/professional by themselves. The author is of the opinion that guidelines for improving engineering skills of practicing geotechnical and foundations engineers given below will be of great help.

Guidance for Improving Engineering Skills • Understanding basic principles of soil mechanics, foundation engineering an seepage analysis • Active participation in field work at geotechnical investigation sites • Personally carryout laboratory tests and calculations relating to soil parameters • Study local geology and search literature relating the project area

302

15 Practice in Geotechnical and Foundation Engineering

• Classify soils/rocks establish stratigraphy and assign ‘design’ soil parameters with probable range • Calculate safe bearing capacity, settlement of shallow and deep foundation, prepare foundation recommendation • Interaction with civil designer and construction engineer • Assist construction engineer to prepare technical specification commensurate with design • Skill in writing and communication in English and regional language is helpful • Visit site to experience how construction is done vis-à-vis adherence to design considerations • Understanding site problems, provide constructive solutions safe-guarding design parameters • Initiate measures to ensure quality in construction • Review design data, considerations, calculations and scope for improvement in next project • Continue study literature, textbooks, journals, papers, etc., on new technology, process • Keep updated on new technological development in the country and abroad • Enhance knowledge and data base and new developments • Participate in discussion with colleagues to exchange views on technical matters • If opportunity comes, involve in trouble shooting for failure study and rectification • Join technical seminar, discussion/presentation, conference and study articles of interest • It is a good idea to prepare technical papers for publication/presentation • Never shy away from a problem—there is a solution waiting to find and modify to suit the problem • Try to build-up own technical library for quick reference. In medical colleges, students learn basics of anatomy, medicine and medical science. They have to accompany senior doctors during check-up rounds to patient in hospital wards and assist in diagnosis, line of treatment and also in different medical procedures. After completion of course, pass-outs are posted as interim doctor in hospital for specified period before getting independent responsibility. In engineering practice, similar modality existed earlier through special lectures, site visits and promotional demonstration sessions. But the practice is fading out in recent days. It is believed that apart from learning in institution, unless engineers solve problems by themselves based on theoretical principles with minimum support from computer packaged solution, learning may remain incomplete. There is broad consensus on the problem on availability of knowledgeable and experienced geotechnical and foundation engineers in heavy industrial projects. There is hesitation in real devolution of powers to young practicing engineers. Instead they are burdened with targets on time and cost aspects with limited or no technical

‘E-Classes’ Leading to ‘Learning Gap’ in Higher Education

303

or financial support. In my opinion give young engineers power to carry out engineering professionally. Why not celebrate slightly-above average performance. If failures even small ones should not be memorialized. Why not crave notches for other success and give them more chance to rectify and reform. It is hoped, the book on Geotechnical and Foundation Engineering Practice in Industrial Projects has succeeded in fulfilling its main objectives on professional practice, motivation on theoretical concepts, self-assessment, confidence building, writing concept note and engineering report chapter, attending technical meeting in own or client’s office, respect for the profession and last but not the least feel pride of ownership on contribution in a project.

Appendix A

Units and Conversion Tables

Introduction While going through textbooks, literatures, reports, codes, etc., of previous and recent years and foreign publication, one may face difficulty in comprehending or comparing actual magnitude of data due to use of different measuring unit systems, e.g., foot-pound-second (FPS), centimeter-gram-second (CGS), international system of units (SI) is the modern form of metric system world’s most widely used, etc. The reader may also face difficulty in identifying conventional symbols unique to a parameter and corresponding conversion factors from one to other system. Conversion tables and charts are generally available in print form and online. Still, one may prefer to have them handy. Keeping above difficulties in view, basic units, standard symbols and conversion factors for different entities are furnished in tabular forms for convenience. SI System of Measures: Unit, Symbol and Definition of Quantity Quantity

Unit

Symbol

Definition

Force

Newton

N

1 N = 0.10197 kg. m/s2 (kgf)

Pressure/stress

Pascal

Pa

1 Pa = 1 N/m2

Frequency

Hertz

Hz

1 Hz = 1 cycle/sec (c/s)

Energy

Joule

J

1J=1Nm

Power

Watt

W

1 W = 1 J/s

Electromotive force

Volt

V

1 V = 1 W/A

Current

Ampere

Flux

Weber

Wb

1 Wb = 1 V s

Flux density

Tesla

T

1 T = 1 Wb/m2

Electric conductance

Siemens

S

1 S = 1 A/V

A

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Roy, Geotechnical and Foundation Engineering Practice in Industrial Projects, https://doi.org/10.1007/978-981-99-7906-6

305

306

Appendix A: Units and Conversion Tables

Basic Units and Conversion Tables (SI to CGS, CGS to SI) Load/Force SI → CGS

CGS → SI

1 N ≃ 0.1 kg

1 kg = 10 N (≃ 10.193 N) 1 T = 10 kN = 0.01 MN

1 kN = 100 kg = 0.1 T 1 MN =

106

N=

105

1 T = 0.01 MN

kg

1 MN = 100 T

100 T = 1 MN

Pressure SI → CGS

CGS → SI

1 N/mm2 = 10 kg/cm2

1 kg/cm2 = 100 kPa = 0.1 MPa 1 T/M2 = 10 kPa

1 Pa = 1 N/M2 = 0.1 kg/M2 1 kPa = 1000

N/M2

= 0.1

T/M2

= 100

100 T/M2 = 1 MPa

kg/M2

1 MPa = 100 T/M2 = 10 kg/cm2

1 T/M2 = 0.01 MPa

1 MPa = 1000 kPa

1 kg/cm2 = 105 Pa

100 kPa = 10

T/m2

=1

1 cm2 /kg = 10–2 M2 /kN

kg/cm2

1 kPa = 0.01 kg/cm2 1 Bar = 1 kg/cm2 = 10 Ton/m2 = 100 kPa = 100,000 Pa

Density SI → CGS

CGS → SI

1 kN/M3 = 100 kg/M3 = 0.1 T/M3

1 T/M3 = 10 kN/M3

1 kN/M3 = 0.1 gm/cm3

1 gm/cm3 = 10 kN/M3

Area

1 Acre = 4046.85 m2 1 Hector = 100 m × 100 m = 10,000 M2

Nautical Mile (NM)

1 kM2 = 247.1058 Acres 1 NM = 1852 M ∼ = 6076 Ft

Velocity

1 knot = 1.852 km/hr

Appendix A: Units and Conversion Tables

307

Conversion Table (SI to FPS and FPS to SI) To convert

SI to FPS From

Length

Area

Volume

Force

Stress

FPS to SI To

Multiply by

From

To

Multiply by

m

ft

3.281

ft

m

0.308

m

in

39.37

in

m

0.0254

cm

in

0.3937

in

cm

2.54

mm

in

0.03937

in

mm

25.4

m2

ft2

10.764

ft2

m2

929.03 × 10–4

m2

in2

1550

in2

m2

6.452 × 10–4

cm2

in2

0.155

in2

cm2

6.452

mm2

in2

0.155 × 10–2

in2

mm2

645.16

m3

ft3

35.32

ft3

m3

28.317 × 10–3

m3

in3

61.0234

in3

m3

16.387 × 10–6

cm3

in3

0.06102

in3

cm3

16.387

N

lb

0.2248

lb

N

4.448

kN

lb

224.8

lb

kN

4.448 × 10–3

kN

kip

0.2248

kip

kN

4.448

kN

US ton

0.1124

US ton

kN

8.896

N/m2

lb/ft2

20.885 × 10–3

lb/ft2

N/m2

47.88

kN/m2

lb/ft2

20.885

lb/ft2

kN/m2

0.04788

kN/m2

US

0.01044

US

kN/m2

kip/ft2

20.885 × 10–3

kN/m2

lb/in2

kN/m3

lb/ft3

kN/m3

lb/in3

Moment

N-m

lb-ft

N-m

lb-in

8.851

lb-in

Nm

0.11298

Moment of Inertia

mm4

in4

2.402 × 10–6

in4

mm4

0.4162 × 106

m4

in4

2.402 × 106

in4

m4

0.4162 × 10–6

mm3

in3

6.102 ×

10–5

in3

mm3

0.16387 × 105

m3

in3

6.102 ×

104

in3

m3

0.16387 × 10–4 6.452

Unit Weight

Section Modulus

ton/ft2

Coefficient of cm2 /s in2 /s consolidation m2 /year in2 /s cm2 /s

ft2 /s

ton/ft2

kN/m2

95.76

kip/ft2

kN/m2

47.88

0.145

lb/in2

kN/m2

6.895

6.361

lb/ft3

kN/m3

0.1572

0.003682

lb/in3

kN/in3

271.43

0.7375

lb-ft

Nm

1.3558

in2 /s

cm2 /s

10–5

in2 /s

m2 /year 20.346 × 103

1.076 × 10–3

ft2 /s

cm2 /s

0.155 4.915 ×

929.03 (continued)

308

Appendix A: Units and Conversion Tables

(continued) To convert

SI to FPS From

Hydraulic Conductivity

FPS to SI To

Multiply by

From

To

Multiply by

m/min

ft/min

3.281

ft/min

m/min

0.3048

cm/min

ft/min

0.03281

ft/min

cm/min

30.48

m/s

ft/s

3.281

ft/s

m/s

0.3048

cm/s

in/s

0.3937

in/s

cm/s

2.54

Conversion Factors—FPS to SI To convert from

To

Multiply by

Microns

inches

3.9370079 × 10–5

Pounds

dynes

4.44822 × 105

grams

453.59243

kilograms

0.45359243

grams

1 × 106

kilograms

1000

pounds

2204.6223

kips

2.2046223

Tons (short or US ton)

1.1023112

lbs/in2

6.94445

lbs/ft2

1000

US tons/ft2

0.500

kg/cm2

0.488244

Tons (Metric)

Ksf (kips/ft2 )

metric Pounds/in3

ton/ft2

4.88244

gms/cm3

27.6799

kg/m3

27,679.905

lbs/ft3

1728

ft/day

1440

ft/year

5256 × 102

ft/year

ft/min

1.9025 × 10–6

cm/s

m/min

0.600

ft/min

1.9685

ft/year

1,034,643.6

ft/min

Appendix A: Units and Conversion Tables

Intrinsic Solution for Quadratic Equation The Equation: Convert the equation in following form: ax 2 + bx + c = 0 Solution: b √ x = − ± b2 − 4ac 2 Intrinsic Solution for Cubic Equation Convert the equation in following form: y3 + p y2 + q y + r = 0 Substituting y = x − 3p , the equation transforms to x 3 + ax + b = 0, where ) ) 1( 1( 3 3q − p 2 and b = 2 p − 9 pq + 27r 3 27 ┌[ ┌[ ] ] / / | | 3 3 2 2 | | a a b b b b 3 3 + + A=√ − + − − and B = √ 2 4 27 2 4 27 a=

Intrinsic Solution of Cubic Equation: Solution: (1) x 1 = A + B (2) x2 = − A+B + 2 (3) x3 = − A+B − 2

√

A−B −3 2 √ A−B −3 2

Conditions: If p and q are real number (a) (b) (c) (d)

2

3

a > 0, ⇒ One real and two imaginary roots if b4 + 27 2 b a3 if 4 + 27 = 0, ⇒ roots are real and at least two roots are equal 2 a3 if b4 + 27 < 0, ⇒ all roots are real and different Then, y = x − 3p

309

Appendix B

Standard Correlations

Introduction Some common but helpful correlations of parameters and formulae may not be available when actually needed. The correlations are considered standard for different soil and rock types. A few often referred correlations and formulae from standard references have been complied for ready reference. SPT Correlation for Sand and Clay Ref, ‘Soil Mechanics’ by Lambe and Whiteman Standard Penetration Test Relative density of SAND

Strength of CLAY

N

N

Relative density

qu (kPa)a

Consistency

0–4

Very Loose