Fiberglass Pipe Design Manual 0898678897, 9780898678895

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Fiberglass Pipe Design

AWWA MANUAL M45

First Edition

FOUNDED 1881

American Water Works Association

Copyright (C) 1999 American Water Works Association All Rights Reserved

MANUAL OF WATER SUPPLY PRACTICES ---- M45, First Edition

Fiberglass Pipe Design Copyright © 1996 American Water Works Association All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information or retrieval system, except in the form of brief excerpts or quotations for review purposes, without the written permission of the publisher.

Project Manager and Technical Editor: Sharon Pellowe Copy Editor: Martha Ball Production Editor: Alan Livingston Production Artist: Karen Staab

Library of Congress Cataloging-in-Publication Data "Fiberglass pipe design manual." xviii, 159p. 17×25 cm.--(Manual of water supply operations: M45) Includes bibliographical (p. ) references and index. ISBN 0-89867-889-7 1. water-pipes. 2. Pipe, glass. I. Series. II. Series: /AWWA manual: M45 TD491.A49 no. M45 97-4036 628.1′ 5----dc21 CIP

Printed in the United States of America American Water Works Association 6666 West Quincy Avenue Denver, CO 80235

ISBN 0-89867-889-7

Printed on recycled paper

Copyright (C) 1999 American Water Works Association All Rights Reserved

Contents List of Figures, vii List of Tables, xi Preface, xiii Foreword, xv Acknowledgments, xvii Chapter 1 History and Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 1.2 1.3 1.4 1.5

Introduction, 1 History, 1 Applications, 2 Standards, Specifications, and Reference Documents, 2 Terminology, 6

Chapter 2 Materials, Properties, and Characteristics . . . . . . . . . . . . . 7 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

General, 7 Characteristics, 7 The Material System, 8 Glass Fiber Reinforcements, 8 Resins, 9 Other Components, 10 Physical Properties, 11 Mechanical Properties, 12

Chapter 3 Manufacturing

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1 Introduction, 15 3.2 Filament Winding, 15 3.3 Centrifugal Casting, 18 References, 20 Chapter 4 Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.1 Hydraulic Characteristics, 21 4.2 Preliminary Pipe Sizing, 21 4.3 Typical Pipe Diameters, 22 4.4 Pressure Loss Calculations, 23 4.5 Head Loss in Fittings, 27 4.6 Energy Consumption Calculation Procedure, 29 4.7 Transient Pressures, 31 References, 34 Chapter 5 Buried Pipe Design . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.1 Introduction, 35 5.2 Design Terminology, 35

iii

Copyright (C) 1999 American Water Works Association All Rights Reserved

Chapter 5 Buried Pipe Design—continued 5.3 Design Conditions, 36 5.4 Pipe Properties, 38 5.5 Installation Parameters, 38 5.6 Design Procedure, 39 5.7 Design Calculations and Requirements, 39 5.8 Axial Loads, 54 5.9 Special Design Considerations, 54 5.10 Design Examples, 54 References, 71 Chapter 6 Guidelines for Underground Installation of Fiberglass Pipe . . 73 6.1 Introduction, 73 6.2 Related Documents, 74 6.3 Terminology, 75 6.4 In Situ Soils, 77 6.5 Embedment Materials, 77 6.6 Trench Excavation, 80 6.7 Pipe Installation, 82 6.8 Field Monitoring, 87 6.9 Contract Document Recommendations, 88 References, 88 Chapter 7 Buried Pipe Thrust Restraints . . . . . . . . . . . . . . . . . . . 91 7.1 7.2 7.3 7.4 7.5

Unbalanced Thrust Forces, 91 Thrust Resistance, 92 Thrust Blocks, 93 Joints With Small Deflections, 95 Restrained (Tied) Joints, 99

Chapter 8 Aboveground Pipe Design and Installation . . . . . . . . . .

103

8.1 Introduction, 103 8.2 Test Methods and Physical Properties, 103 8.3 Internal Pressure Rating, 105 8.4 Thermal Expansion and Contraction, 107 8.5 Thermal Expansion Design, 107 8.6 Supports, Anchors, and Guides, 114 8.7 Bending, 120 8.8 Thermal Conductivity, 120 8.9 Heat Tracing, 121 8.10 Characteristics and Properties, 122 References, 124 Chapter 9 Joining Systems, Fittings, and Specials . . . . . . . . . . . . 9.1 9.2 9.3 9.4 9.5

Introduction, 125 Fiberglass Pipe Joining Systems Classification, 125 Gasket Requirements, 126 Joining Systems Description, 126 Assembly of Bonded, Threaded, and Flanged Joints, 131

iv

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125

9.6 Fittings and Specials, 134 9.7 Service Line Connections, 138 References, 138 Chapter 10 Shipping, Handling, Storage, and Repair . . . . . . . . . . . 10.1 10.2 10.3 10.4 10.5

Introduction, 139 Shipping, 139 Handling, 140 Storage, 142 Repair, 143

Glossary, 145 Index, 153 List of AWWA Manuals, 159

v

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139

Figures 3-1 Filament winding process, 16 3-2 Application of impregnated glass reinforcement of a filament wound pipe, 16 3-3 Continuous advancing mandrel method, 17 3-4 Finished pipe emerging from curing oven, 18 3-5 Preformed glass reinforcement sleeve method, 19 3-6 Chopped glass reinforcement method, 19 3-7 Application of glass, resin, and sand, 20 4-1 Friction loss characterisitics of water flow through fiberglass pipe, 23 4-2 Moody diagram for determination of friction factor for turbulent flow, 26 5-1 Definition of common variables used in chapter 5, 37 5-2 Distribution of HS-20 live load through fill for H C c > 3e

SP

Poorly graded sandi

Sands with fines More than 12% finesd

Fines classify as ML or MH

SM

Silty sandg,h,i

Fines classify as CL or CH

SC

Clayey sandg,h,i

Silts and clays Liquid limit less than 50

Inorganic

PI > 7 and plots on or above “A” line j PI < 4 or plots below “A” line j Liquid limit—oven dried

CL

Lean clayk,l,m

ML

Siltk,l,m

OL

Organic clayk,l,m,n

Gravels More than 50% of coarse fraction retained on No. 4 sieve

Clean gravels Less than 5% finesc

Organic

Liquid limit—not dried Silts and clays Liquid limit 50 or more

Inorganic

Organic

< 0.75

PI plots on or above “A” line PI plots below “A” line Liquid limit—oven dried

< 0.75

Organic siltk,l,m,o CH

Fat clayk,l,m

MH

Elastic siltk,l,m

OH

Organic clayk,l,m,p

PT

Peat

Liquid limit—not dried Highly organic soils a b

Primarily organic matter, dark in color, and organic odor

Based on the material passing the 3-in. (75-mm) sieve. If field sample contained cobbles and/or boulders, add “with cobbles and/or boulders” to group name. c Gravels with 5% to 12% fines require dual symbols: GW–GM well-graded gravel with silt GW–GC well-graded gravel with clay GP–GM poorly graded gravel with silt GP–GC poorly graded gravel with clay d Sands with 5% to 12% fines require dual symbols: SW–SM well-graded sand with silt SW–SC well-graded sand with clay SP–SM poorly graded sand with silt SP–SC poorly graded sand with clay e Cu = D60/D10 (D 30)2 Cc = D 10 ×D 60 f If soil contains ≥ 15% sand, add “with sand” to group name.

Organic siltk,l,m,p

g If fines classify as CL–ML, use dual symbol h

GC–GM or SC–SM. If fines are organic, add “with organic fines” to group name. i If soil contains ≥ 15% gravel, add “with gravel” to group name. j If the Atterberg limits (liquid limit and plasticity index) plot in hatched area on plasticity chart, soil is a CL–ML, silty clay. k If soil contains 15% to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. l If soil contains ≥ 30% plus No. 200, predominantly sand, add “sandy” to group name. m If soil contains ≥ 30% plus No. 200, predominantly gravel, add “gravelly” to group name. n PI ≥ 4 and plots on or above “A” line. o PI ≤ 4 or plots below “A” line. p PI plots on or above “A” line. q PI plots below “A” line.

Source: ASTM D2487; Reprinted with permission from the Annual Book of ASTM Standards, copyright ASTM, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959. NOTE: ASTM D2487 allows the use of “borderline” symbols when test results indicate that the soil classification is close to another group. The borderline condition is indicated by an en dash between the two symbols, for example CL–CH.

Copyright (C) 1999 American Water Works Association All Rights Reserved

48

FIBERGLASS PIPE DESIGN

Table 5-4 Values for the soil support combining factor Sc E′n/E′b 0.1 0.2 0.4 0.6 0.8 1.0 1.5 2.0 3.0 ≥5.0

Bd/D 1.5

Bd/D 2

Bd/D 2.5

Bd/D 3

Bd/D 4

Bd/D 5

0.15 0.30 0.50 0.70 0.85 1.00 1.30 1.50 1.75 2.00

0.30 0.45 0.60 0.80 0.90 1.00 1.15 1.30 1.45 1.60

0.60 0.70 0.80 0.90 0.95 1.00 1.10 1.15 1.30 1.40

0.80 0.85 0.90 0.95 0.98 1.00 1.05 1.10 1.20 1.25

0.90 0.92 0.95 1.00 1.00 1.00 1.00 1.05 1.08 1.10

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

NOTE: In-between values of Sc may be determined by straight-line interpolation from adjacent values.

pipe, separate E′ values for the native soil, E′n, and the pipe backfill surround, E′b, must be determined and then combined using Eq 5-16. Special cases are discussed later in this chapter. E ′ = Sc E ′b

(5-16)

Where: E ′ = composite modulus of soil reaction, psi (to be used in Eq 5-8 and Eq 5-21) Sc = soil support combining factor from Table 5-3, dimensionless E ′b = modulus of soil reaction of the pipe zone embedment from Table 5-5, psi To use Table 5-4 for Sc values, the following values must be determined: E ′n = modulus of soil reaction of the native soil at pipe elevation from Table 5-6, psi Bd = trench width at pipe springline, in.

5.7.4 Combined Loading The maximum stress or strain resulting from the combined effects of internal pressure and deflection should meet Eq 5-17 and Eq 5-18 or Eq 5-19 and Eq 5-20 as follows: For stress basis HDB and Sb: σpr HDB

≤

 σb rc   1 −   Sb E  FSpr

Copyright (C) 1999 American Water Works Association All Rights Reserved

(5-17)

Fine-grained soils with medium to no plasticity (CL, ML, ML–CL), or borderline soil (ML/CL), or any dual symbol or borderline soil beginning with one of these symbols, with 0–1 1–2 2–4 4–8 8–15 15–30 30–50 >50

E′n (psi)

Cohesive

Description

qu(Tons/sf)

Description

very, very loose very loose

>0–0.125 0.125–0.25 0.25–0.50 0.50–1.0 1.0–2.0 2.0–4.0 4.0–6.0 >6.0

very, very soft very soft soft medium stiff very stiff hard very hard

loose slightly compact compact dense very dense

50 200 700 1,500 3,000 5,000 10,000 20,000

*The modulus of soil reaction E ′n for rock is ≥ 50,000 psi. † Standard penetration test per ASTM D1586. For embankment installation E ′b = E ′n = E ′ . E′ special cases Geotextiles—When a geotextile pipe zone wrap is used, E′n values for poor soils can be greater than those shown in Table 5-6. Solid sheeting—When permanent solid sheeting designed to last the life of the pipeline is used in the pipe zone, E′ shall be based solely on E′b. Cement stabilized sand—When cement stabilized sand is used as the pipe zone surround, initial deflections shall be based on a sand installation and the long-term E′b = 25,000 psi. (Typical mix ratio is one sack of cement per ton or 1.5 sacks of cement per cubic yard of mix.) For embankment installation E′b = E′n = E′.

σb rc Sb E

≤

 σpr   1−  HDB 

For strain basis HDB and Sb:  εb rc   1− εpr  Sb  ≤ HDB FSpr εb rc Sb

≤

 εpr   1 −   HDB  FSb

Where: FSpr = pressure design factor, 1.8 FSb = bending design factor, 1.5 σpr = working stress due to internal pressure, psi =

(5-18)

FSb

PwD 2t

σb = bending stress due to the maximum permitted deflection, psi

Copyright (C) 1999 American Water Works Association All Rights Reserved

(5-19)

(5-20)

52

FIBERGLASS PIPE DESIGN

 δd   tt  = DfE      D  D rc = rerounding coefficient, dimensionless = 1 − Pw/435

(Pw ≤ 435 psi)

εpr = working strain due to internal pressure, in./in. =

PwD 2tEH

εb = bending strain due to maximum permitted deflection, in./in.  δd   tt  = Df      D  D δd = maximum permitted long-term installed deflection, in.

5.7.5 Buckling 5.7.5.1 Buckling theory. Buried pipe is subjected to radial external loads composed of vertical loads and possibly the hydrostatic pressure of groundwater and internal vacuum, if the latter two are present. External radial pressure sufficient to buckle buried pipe is many times higher than the pressure causing buckling of the same pipe in a fluid environment, due to the restraining influence of the soil. 5.7.5.2 Buckling calculations. The summation of appropriate external loads should be equal to or less than the allowable buckling pressure. The allowable buckling pressure qa is determined by the following equation: 1

EI 2  1  qa =   [ 32Rw B′ E′ ] D3  FS  Where: qa = allowable buckling pressure, psi FS = design factor, 2.5 Rw = water buoyancy factor, calculated as follows: Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h Where: hw = height of water surface above top of pipe, in. h = height of ground surface above top of pipe, in. B′ = empirical coefficient of elastic support, dimensionless. It is calculated as follows: B′ =

1 1 + 4e−0.065H

Copyright (C) 1999 American Water Works Association All Rights Reserved

(5-21)

BURIED PIPE DESIGN

53

Where: H = burial depth to the top of pipe, ft E′ = composite modulus of soil reaction, psi (see Eq 5-16) NOTE: Eq 5-21 is valid under the following conditions: Without internal vacuum: 2 ft ≤ H ≤ 80 ft With internal vacuum: 4 ft ≤ H ≤ 80 ft Where internal vacuum occurs with cover depths less than 4 ft but not less than 2 ft, qa in Eq 5-22 may be determined as the critical buckling pressure given by the von Mises formula. The 2 ft to 4 ft of soil cover provides a safety factor in excess of the recommended 2.5 value. In the 2-ft to 4-ft depth range, live loads plus dead loads should be checked by Eq 5-23 to determine the governing required wall thickness. The manufacturer should be consulted for further recommendations in this depth range. The von Mises formula is:  2n2 − 1 − vhl    2 2Ett   8EI  n qa =  1 − + +    3   2 2 K 1 + D [1 − (v ) (v )] hl lh      D (n − 1) (1 + K)  

(5-22)

Where: n = number of lobes formed at buckling ≥ 2 (The value of n must give the minimum value of qa obtained by iterative solution.) vhl = Poisson’s ratio, applied hoop stress vlh = Poisson’s ratio, applied longitudinal stress 2

 2nL  K =    πD  Where:

L = distance between rigid ring stiffeners, in. NOTE: For solid-wall (nonribbed) pipes, L should be the distance between joints, such as bells, couplings, flanges, etc. Typical pipe installations. Satisfaction of the buckling requirement is assured for typical pipe installations by using the following equation: γw hw + Rw (Wc) + Pv ≤ qa

(5-23)

Where: γw = specific weight of water (i.e., 0.0361 lb/in.3), lb/in.3 Pv = internal vacuum pressure (i.e., atmospheric pressure less absolute pressure inside pipe), psi

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54

FIBERGLASS PIPE DESIGN

In some situations, consideration of live loads in addition to dead loads may be appropriate. However, simultaneous application of live load and internal vacuum transients need not typically be considered. If live loads are considered, satisfaction of the buckling requirement is ensured by: γw hw + Rw (Wc) + WL = qa

(5-24)

5.8 AXIAL LOADS _______________________________________ Factors that contribute to the development of axial stresses in buried pipe are (1) hoop expansion due to internal pressure, which causes axial tensile stresses whenever the pipe is axially restrained; (2) restrained thermal expansion and contraction; and (3) pipe “beam” bending that may be induced by uneven bedding, differential soil settlement, or subsidence of soil. The minimum requirements for axial strengths are as specified by Sec. 5.1.2.4 and Sec. 5.1.2.5 and Tables 11, 12, and 13 of ANSI/AWWA Standard C950. These requirements include service conditions in typical quality underground pipe installations that comply with the guidelines provided in chapter 6 of this manual and that have thrust blocks provided at bends, blanks, and valves in accordance with chapter 7 and pipe manufacturers’ recommendations. When restrained joints are used, the pipe should be designed to accommodate the full magnitude of forces generated by internal pressure.

5.9 SPECIAL DESIGN CONSIDERATIONS ___________________ Pipe that meets the design requirements of ANSI/AWWA Standard C950 and Sec. 5.7 and that is installed in accordance with chapter 6 guidelines has adequate strength for service in usual buried applications. Special consideration should be made for the following conditions: (1) elevated temperature service; (2) broad temperature fluctuations; (3) shallow burial, where H < 4 ft (1.2 m) (Sec. 5.7.5); (4) uneven bedding or differential settlement of unstable native soils; (5) restrained tension joints; (6) extremely difficult construction conditions (for example, subaqueous installation); (7) heavy internal silt or sand loads; and (8) unusually high surface or construction loads.

5.10 DESIGN EXAMPLES _________________________________ Example design calculations are presented in this section for each of three specific situations. For reference, the set of design conditions, pipe properties, and installation parameters assumed for each design example are presented in Table 5-7. This summary is not repeated in the body of the example design calculations. The pipe material properties and characteristics presented in Table 5-7 have been assumed for illustrative purposes and should not be used as actual design values. Values for these parameters differ for various pipe constructions and materials and should be obtained from the manufacturer.

5.10.1 Design Example 1: Stress Basis Using the assumed set of design conditions, pipe properties, and installation parameters set forth under example 1 in Table 5-7 and following the procedural sequence for design calculations outlined in Sec. 5.6: 1. Calculate pressure class Pc from HDB using Eq 5-1 (Sec. 5.7.1.1):

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BURIED PIPE DESIGN

55

Table 5-7 Conditions and parameters for design examples Conditions and Parameters Design conditions: Nominal pipe diameter, in. Working pressure Pw, psi Surge pressure Ps, psi Vacuum Pv, psi Cover depth H, ft (min.–max.) Wheel load P, lb Soil-specific weight γs, lb/ft3 Service temperature, °F Native soil conditions at pipe depth Native soil modulus E′n, psi Groundwater table location Maximum hw, in. Minimum hw, in. Basis for HDB and Sb Pipe properties: Trial pressure class Pc, psi Reinforced wall thickness t, in. Liner thickness tL, in. Total wall thickness tt, in. Minimum pipe stiffness F/ ∆y, psi Hoop tensile modulus EH, psi Hoop flexural modulus E, psi HDB Sb Mean diameter D, in. Distance between joints L, in. Poisson’s ratio v, in./in. Hoop load vhL Axial load vih Installation parameters: Pipe/zone installation description Trench width, in. Shape factor Df Backfill soil modulus E′b, psi Deflection coefficient Kx Deflection lag factor DL Deflection: Maximum deflection permitted, δd/D

Sec. 5.10.1 (Example 1)

Sec. 5.10.2 (Example 2)

Sec. 5.10.3 (Example 3)

12 220 65 14.7 2.5–4 16,000 120 32–100 slightly compact clayey sand 3,000 at ground surface

36 115 55 8 4–8 16,000 125 32–90 dense silty sand

48 30

10,000 3 ft below ground surface 60 12

72 55 20 0 6–12 16,000 115 32–95 medium stiff, inorganic clay 1,500 10 ft below ground surface 24 0

Stress, psi

Strain, in./in.

Strain, in./in.

250 0.21 0 0.21 72 3.3E6 3.45E6 14,800 0.0100 12.21 240

150 0.61 0.04 0.65 36 1.8E6 1.9E6 0.0064 0.0115 36.69 360

100 0.61 0.05 0.66 9 3.25E6 3.5E6 0.0058 0.0058 72.71 480

0.35 0.15

0.30 0.20

0.35 0.15

slightly compacted silty sand, SM 27 3.5 400 0.1 1.05 0.05

moderately compacted moderately clayey sand, SC compacted gravel, GW 58 104 5.5 7.0 1,000 2,000 0.1 0.1 1.1 1.2 0.05

Copyright (C) 1999 American Water Works Association All Rights Reserved

0.05

56

FIBERGLASS PIPE DESIGN

 HDB   2t  Pc = 250 psi ≤      FS   D   14,800   2(0.21)  ≤      1.8   12.21 

≤ 282.83 psi ∴ OK 2. Check working pressure Pw using Pc and Eq 5-3 (Sec. 5.7.1.2): Pc ≥ Pw 250 psi ≥ 220 psi ∴ OK 3. Check surge pressure Ps using Pc and Eq 5-4: Pc ≥ (Pw + Ps) / 1.4 250 ≥ (220 + 65) / 1.4 250 psi ≥ 204 psi ∴ OK 4. Calculate allowable deflection, ∆ya, from ring bending using Eq 5-5 (Sec. 5.7.2):  ∆ya   tt   E Sb  σb = Df (E)     ≤  FS   D  D    ∆ya  3.5 (3.45E6)    12.21 

(3.45E6) (0.01)  0.21    ≤ 12.21 1.5  

17,009 ∆ya ≤ 23,000 Therefore, maximum ∆ya = 1.35 in. From Eq 5-8 (Sec. 5.7.3): ∆y D

≤

δd D

≤

∆ ya D

In this example, δd/D = 0.05: ∆ y/ D ≤ 0.05 ≤ 1.35/12.21 (5%) D ≤ (11%) D ∴ OK 5. Calculate external loads Wc and WL: Determine external load Wc using Eq 5-9:

Copyright (C) 1999 American Water Works Association All Rights Reserved

BURIED PIPE DESIGN

γs H

Wc =

144

For H = 2.5 ft Wc =

For H = 4 ft Wc =

120 (2.5 ft) 144

120 (4 ft) 144

= 2.08

= 3.33

psi

psi

Determine external load WL using Eq 5-13: WL = P (If) / [ 144 (L1) (L2) ] Solution of Eq 5-13 for WL requires determining If, L1, and L2: For H = 2.5 ft

If = 1.1

For H = 4 ft

If = 1.0

L1 is determined from Eq 5-10: L1 = 0.83 + 1.75 (H) For H = 2.5 ft

L1 = 0.83 + 1.75 (2.5 ft) = 5.21 ft

For H = 4 ft

L1 = 0.83 + 1.75 (4 ft) = 7.83 ft

Compute L2 using Eq 5-12: H ≥ 2.48 ft

L2 = [ (43.67) + 1.75 (H) ]/8

For H = 2.5 ft

L2 = [ (43.67) + 1.75 (2.5 ft) ] / 8 = 6.01 ft

For H = 4 ft

L2 = [ (43.67 ) + 1.75 (4 ft) ] /8 = 6.33 ft

Substituting in Eq 5-13: For H = 2.5 ft

WL = 16,000 (1.1)/[144 (5.21) (6.01)] = 3.90 psi

For H = 4 ft

WL = 16,000 (1.0)/[144 (7.83) (6.33)] = 2.24 psi

6. Calculate the composite modulus of soil reaction E′ using Eq 5-16: E′ = Sc E′b In order to determine E′, first determine Sc: E′n/E′b = 3,000 / 400 = 7.5 Bd/D = 27/12.21 = 2.21

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57

58

FIBERGLASS PIPE DESIGN

Using Table 5-4, by interpolation Sc = 1.52: Substituting in Eq 5-16: E′ = 1.52 (400) = 608 psi 7. Calculate deflection using Eq 5-8 (Sec. 5.7.3): ∆y D

=

(DL Wc + WL) KX 0.149 PS + 0.061 E′

3 100%

Substituting in Eq 5-8 for H = 2.5 ft: ∆y D

=

(1.05 × 2.08 + 3.90) (0.1) 0.149 (72) + 0.061 (608)

× 100 = 1.27 %

Check using Eq 5-7: ∆y

≤

D

δd D

≤

∆ya D

1.27% ≤ 5% ≤ 11% ∴ ΟΚ Substituting in Eq 5-8 for H = 4 ft: ∆y D

=

(1.05 × 3.33 + 2.24) (0.1) [ (0.149 (72) + 0.061 (608) ]

× 100

= 1.20 % Check using Eq 5-7: ∆y D

≤

δd D

≤

∆ya D

1.20% ≤ 5% ≤ 11% ∴ OK 8. Check combined loading stress δc using Eq 5-17 and Eq 5-18 (Sec. 5.7.4): Check using Eq 5-17:  σb rc   1 −  σpr  E Sb  ≤ FSpr HDB  (3.5) (3.45E6)   0.21   1 −  (0.05)   220 (12.21)    1−    12.21    0.01 (3.45E6)   2 (0.21)  ≤   1.8  14,800 

 220    435     

0.43 ≤ 0.47 ∴ OK

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BURIED PIPE DESIGN

59

Check using Eq 5-18: σb rc

≤

ESb

 σpr   1 −   HDB  FSb

 220   0.21   (3.5) (3.45E6) (0.05)   1 −  435  12.21      (3.45E6) (0.01)

≤

  (220) (12.21)    (2) (0.21)    1 −   14,800   1.5

0.15 ≤ 0.38 9. Check buckling pressure. NOTE: Vacuum load is present. Determine the allowable buckling pressure qa for H = 2.5 ft, using Eq 5-22:  2n2 − 1 − vhl    2 2Ett   qa =  n 1 − + +    2 2 1 + K     D (n − 1) (1 + K) 

8EI     3  D [1 − (vhl) (vlh) ] 

Solution of Eq 5-22 for qa requires determination of value of K: 2

 2nL  K =    πD 

2

 2 (2) (240)  =    π(12.21)  = 626.3

Substituting in Eq 5-22 and solving for qa:  2 (22) − 1 − 0.35    (8) (3.45E6) (0.213/12)   2 (3.45E6) (0.21)   qa =  + 22 − 1 +      2 2 1 + 626.3    (12.21)3 [1 − (0.35) (0.15) ]     (12.21) (2 − 1) (1 + 626.3) 

= 0.101 + 3.011 (12.35) = 37.29 psi Determine the allowable buckling pressure, qa, for H = 4 ft, using Eq 5-21: qa =

1 FS

 32Rw B ′E ′ 

0.5

 EI    3  D  

Solution of Eq 5-21 for qa requires determination of values for Rw and B′: Rw = 1 − 0.33 (hw/h)

Copyright (C) 1999 American Water Works Association All Rights Reserved

60

FIBERGLASS PIPE DESIGN

= 1 − 0.33 (48/48) = 0.67 B ′ = 1/(1 + 4e−0.065 H) = 1/ (1 + 4e−0.26 ) = 0.245 Substituting the values of Rw and B′ in Eq 5-21: 0.5

 3.45E 6 (0.21)3   1  qa = 32 (0.67) (0.245) (608)   3 2.5   12 (12.21)   = 27.34 psi

To satisfy the buckling requirement for normal pipe installation, use Eq 5-23: γw (hw) + Rw Wc + Pv ≤ qa In situations where consideration of live loads is appropriate, use Eq 5-24: γw (hw) + Rw Wc + WL ≤ qa Solutions of Eq 5-23 and Eq 5-24 both require determination of the value of the water buoyancy factor Rw at 2.5 ft depth also: Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h = 1 − 0.33 (30/30) = 0.67 Substituting in Eq 5-23 to check normal pipe installation condition with H = 2.5 ft: (0.0361) (30) + 0.67 (2.08) + 14.7 ≤ 32.29 psi 17.18 ≤ 32.29 psi ∴ OK and substituting in Eq 5-24 to check live load condition with H = 2.5 ft: (0.0361) (30) + (0.67) (2.08) + (3.9) ≤ 32.29 psi 6.38 ≤ 32.29 psi ∴ OK Substituting in Eq 5-23 to check normal pipe installation condition with H = 4 ft: (0.0361) (48) + 0.67 (3.33) + (14.7) ≤ 27.34 psi 18.66 ≤ 27.34 psi

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BURIED PIPE DESIGN

61

and substituting in Eq 5-24 to check live load condition with H = 4 ft: (0.0361) (48) + 0.67 (3.33) + (2.24) ≤ 27.34 psi 6.20 ≤ 27.34 psi ∴ OK Conclusion: Design is OK since all checks are satisfied.

5.10.2 Design Example 2: Strain Basis Using the assumed set of design conditions, pipe properties, and installation parameters set forth under example 2 in Table 5-7 and following the procedural sequence for design calculations outlined under Section 5.6: 1. Calculate pressure class Pc from HDB using Eq 5-2 (Sec. 5.7.1.1.):  HDB   2EHt  Pc = 150 psi ≤      FS   D   0.0064   2 (1.8E6) (0.61)  ≤     36.69   1.8   ≤ 212.81 psi ∴ OK 2. Check working pressure Pw using Pc and Eq 5-3 (Sec. 5.7.1.2): Pc ≥ Pw 150 psi ≥ 115 psi ∴ OK 3. Check surge pressure Ps using Pc and Eq 5-4 (Sec. 5.7.1.3): Pc ≥ (Pw + Ps) /1.4 150 ≥ (115 + 55) /1.4 150 psi ≥ 122 psi ∴ OK 4. Calculate allowable deflection, ∆ya, from ring bending using Eq 5-6 (Sec. 5.7.2):  ∆ya   tt   Sb  ε b = Df     ≤    D   D  FS   ∆ya   0.65   0.0115  5.5     ≤    36.69   36.69   1.5  0.00266 ∆ ya ≤ 0.00767 Therefore, maximum ∆ya = 2.89 in.

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62

FIBERGLASS PIPE DESIGN

From Eq 5-7 (Sec. 5.7.3.): ∆y D In this example,

δd D ∆y D

≤

δd

δya

≤

D

D

= 0.05 ≤ 0.05 ≤

2.89 36.69

5% ≤ 7.9% ∴ OK 5. Calculate loads Wc and WL: Determine external load Wc using Eq 5-9 (Sec. 5.7.3.5): Wc = For H = 4 ft

Wc =

For H = 8 ft

Wc =

γs H 144 125 (4) 144 125 (8) 144

= 3.47 psi = 6.94 psi

Determine external load WL using Eq 5-13 (Sec. 5.7.3.6): WL = P (If) / [144 (L1) (L2) ] Solution of Eq 5-13 for WL requires determining If, L1, and L2: For H = 4 ft

If = 1.0

For H = 8 ft

If = 1.0

L1 is determined from Eq 5-10: L1 = 0.83 + 1.75 (H) For H = 4 ft

L1 = 0.83 + 1.75 (4) = 7.83 ft

For H = 8 ft

L1 = 0.83 + 1.75 (8) = 14.83 ft

Compute L2 using Eq 5-12: H ≤ 2.48 ft

L2 = (43.67 + 1.75 (H) ) /8

For H = 4 ft

L2 = (43.67 + 1.75 (4) ) /8 = 6.33 ft

For H = 8 ft

L2 = (43.67 + 1.75 (8) ) / 8 = 7.21 ft

Copyright (C) 1999 American Water Works Association All Rights Reserved

BURIED PIPE DESIGN

Substituting in Eq 5-13: For H = 4 ft

WL = 16,000 (1.0) / [144 ( 7.83) (6.33) ] = 2.24 psi

For H = 8 ft

WL = 16,000 (1.0) / [144 (14.83) (7.21)] = 1.04 psi

6. Calculate the composite modulus of soil reaction E′, using Eq 5-16 (Sec. 5.7.3): E ′ = Sc E′b First determine Sc: En′ / Eb′ = 10,000 / 1,000 = 10 Bd / D = 58 / 36.69 = 1.58 Using Table 5-4, by interpolation Sc = 1.94 Substituting in Eq 5-16: E′ = (1.94 (1,000) ) = 1,940 psi 7. Calculate deflection using Eq 5-8 (Sec. 5.7.3): ∆y D

=

(DL Wc + WL) Kx × 100% 0.149 PS + 0.061 E′

Substituting in Eq 5-8 fo r H = 4 ft: ∆y D

=

(1.1 (3.47) + 2.24) 0.1 0.149 (36) + 0.061 (1,940)

× 100%

= 0.49 % Check using Eq 5-7: ∆y D

≤

δd D

≤

∆ya D

0.49 % ≤ 5 % ≤ 7.9% ∴ OK Substituting in Eq 5-8 for H = 8 ft: ∆y D

 (1.1 (6.94) + 1.04) 0.1  =   × 100%  0.149 (36) + 0.061 (1,940)  = 0.70%

Check using Eq 5-7: ∆y

D

≤

δd D

≤

∆ya D

Copyright (C) 1999 American Water Works Association All Rights Reserved

63

64

FIBERGLASS PIPE DESIGN

0.70% ≤ 5% ≤ 7.9% ∴ OK 8. Check combined loading strain, εc, using Eq 5-19 and Eq 5-20: Check using Eq 5-19: εpr HDB

≤

 εb rc  1 −    Sb  FSpr

 0.65   (5.5) (0.05)     36.69   (115) (36.69) 1 −   0.0115 2 (0.61) (1.8E6) ≤ 0.0064 1.8

115   1 − 435       

0.30 ≤ 0.38 ∴ OK Check using Eq 5-20: εb rc Sb

≤

 εpr  1 −    HDB  FSb

  (115) (36.69)       115    0.65    2 (0.61) (1.8E6)      − (5.5) (0.05)  1 −   435     36.69  1   0.0064             ≤      1.5 0.0115     0.31 ≤ 0.47 ∴ OK 9. Check buckling using Eq 5-21: qa =

1 FS

 32Rw B ′ E ′ 

0.5

 EI    D3    

Solution of Eq 5-21 for qa requires determination of values for Rw and B′: Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h For H = 8 ft: Rw k = 1 − 0.33 (60/96) = 0.794

Copyright (C) 1999 American Water Works Association All Rights Reserved

BURIED PIPE DESIGN

For H = 4 ft: Rw = 1 − 0.33 (12/48) = 0.917 B′ =

1 1 + 4e−0.065(H)

For H = 8 ft: B′ =

1 1 + 4e−0.065(8)

= 0.296 For H = 4 ft: B′ =

1 1 + 4e−0.065 (4)

= 0.245 Substituting the values of Rw and B′ in Eq 5-21 for H = 8 ft: 0.5

 1.9E6 (0.61)3  1  qa = 32 (0.794) (0.296) (1,940)   3 2.5   12 (36.69)  = 41.21 psi

Substituting the values of Rw and B′ in Eq 5-21 for H = 4 ft: qa =

 1.9E6 (0.61)3  1   32 (0.917) (0.245) (1,940)  3 2.5   12 (36.69)  = 40.30 psi

Check to satisfy the requirements of Eq 5-23: γw hw + Rw Wc + Pv ≤ qa and Eq 5-24: γw hw + Rw Wc + WL ≤ qa Substituting in Eq 5-23 for H = 8 ft: (0.0361) (60) + (0.794) (6.94) + 8 ≤ 41.21 psi 15.68 psi ≤ 41.21 psi

Copyright (C) 1999 American Water Works Association All Rights Reserved

65

66

FIBERGLASS PIPE DESIGN

and in Eq 5-24: (0.0361) (60) + (0.794) (6.94) + 1.04 ≤ 41.21 psi 8.72 psi ≤ 41.21 psi ∴ OK Substituting in Eq 5-23 for H = 4 ft: (0.0361) (12) + (0.917) (3.47) + 8 ≤ 40.30 psi 11.62 psi ≤ 40.30 psi and in Eq 5-24: (0.0361) (12) + (0.917) (3.47) + 2.24 ≤ 40.30 psi 5.86 psi ≤ 40.30 psi ∴ OK Conclusion: Design is OK since all checks are satisfied.

5.10.3 Design Example 3: Strain Basis Using the assumed set of design conditions, pipe properties, and installation parameters set forth in example 3 in Table 5-7 and following the procedural sequence for design calculations outlined in Sec. 5.6: 1. Calculate pressure class Pc from HDB using Eq 5-2 (Sec. 5.7.1):  HDB   2EHt  Pc = 100 psi ≤      FS   D   0.0058   2 (3.25E6) (0.61)  ≤     72.71   1.8   ≤ 175.713 psi ∴ OK 2. Check working pressure Pw using Pc and Eq 5-3 (Sec. 5.7.1.2): Pc ≥ Pw 100 psi ≥ 55 psi ∴ OK 3. Check surge pressure Ps using Pc and Eq 5-4 (Sec. 5.7.1.3): Pc ≥ (Pw + Ps)/1.4 100 ≥ (55 + 20)/1.4 100 psi ≥ 54 psi ∴ OK

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BURIED PIPE DESIGN

67

4. Calculate allowable deflection ∆ya from ring bending using Eq 5-6 (Sec. 5.7.2):  ∆ya   tt   Sb  εb = Df     ≤    D  D  FS   ∆ya   0.66  0.0058 7.0     ≤ 1.5  72.71   72.71  0.00087884 ∆ya ≤ 0.0038666 ∴ Maximum ∆ ya = 4.42 in. From Eq 5-7 (Sec. 5.7.3): ∆y D

≤

δd D

∆ ya

≤

D

In this example: δd D

= 0.05

∆y/d ≤ 0.05 ≤

4.42 72.71

(5%) D ≤ (6.09%) D ∴ OK 5. Calculate external loads Wc and WL. Determine external load Wc using Eq 5-9 (Sec. 5.7.3.5): Wc = For H = 6 ft

Wc =

For H = 12 ft

Wc =

γs H 144 115 (6 ft) 144 115 (12 ft) 144

= 4.79 psi = 9.58 psi

Determine external load WL using Eq 5-13 (Sec. 5.7.3.6): WL = P (If)/[ 144 (L1) (L2) ] Solution of Eq 5-13 for WL requires determining If, L1, and L2: For H = 6 ft

If = 1.0

For H = 12 ft

If = 1.0

L1 is determined from Eq 5-10: L1 = 0.83 + 1.75 (H)

Copyright (C) 1999 American Water Works Association All Rights Reserved

68

FIBERGLASS PIPE DESIGN

For H = 6 ft

L1 = 0.83 + 1.75 (6 ft) = 11.33 ft

For H = 12 ft

L1 = 0.83 + 1.75 (12 ft) = 21.83 ft

Compute L2 using Eq 5-12: For H ≥ 2.48 ft

L2 = (43.67 + 1.75 (H) ) /8

For H = 6 ft

L2 = (43.67 + 1.75 (6 ft) ) /8 = 6.77 ft

For H = 12 ft

L2 = (43.67 + 1.75 (12 ft) ) /8 = 8.08 ft

Substituting in Eq 5-13: For H = 6 ft

WL = 16,000 (1.0)/[144 (11.33) (6.77) ] = 1.45 psi

For H = 12 ft

WL = 16,000 (1.0)/[144 (21.83) (8.08) ] = 0.63 psi

6. Calculate the composite modulus of soil reaction E′, using Eq 5-16 (Sec. 5.7.3.8): E ′ = Sc E ′b First determine Sc: En′/ Eb′ = 1,500/2,000 = 0.75 Bd/D = 104/72.71 = 1.4303 Using Table 5-4, by interpolation Sc = 0.81: Substituting in Eq 5-16: E ′ = 0.81 (2,000) = 1,620 psi 7. Calculate deflection using Eq 5-8 (Sec. 5.7.3): ∆y D

=

( DL Wc + WL) Kx 0.149 PS + 0.061 E ′

× 100%

Substituting in Eq 5-8 for H = 6 ft: ∆y D

=

(1.2 (4.79) + 1.45) 0.1 0.149 (9) + 0.061 (1,620)

× 100%

= 0.72 % Check using Eq 5-7: ∆y D

≤

δd D

≤

∆ya D

0.72% ≤ 5% ≤ 6.09% ∴ OK

Copyright (C) 1999 American Water Works Association All Rights Reserved

BURIED PIPE DESIGN

Substituting in Eq 5-8 for H = 12 ft: ∆y D

=

(1.2 ( 9.58) + (0.63) ) 0.1 0.149 (9) + 0.061 (1,620)

× 100%

= 1.21 % Check using Eq 5-7: ∆y D

≤

δd D

≤

∆ya D

1.21% ≤ 5% ≤ 6.09% ∴ OK 8. Check combined loading strain, εc, using Eq 5-19 and Eq 5-20: Check using Eq 5-19:  εbrc  1 − S  εpr  b ≤ FSpr HDB

 (55) (72.71)     2 (0.61) (3.25E6)  ≤ 0.0058

 0.66   55   7 (0.05)   (1 −  435  )  72.71       1 −   0.0058   1.8

0.17 ≤ 0.29 ∴ OK Check using Eq 5-20: εb rc Sb

≤

εpr ) HDB FSb

1 − (

 (55) (72.71)   1 −  55   0.66   (2) (0.61) (3.25E6)   ( 72.71 ) (0.05) (7.0) (1 − 435 )   0.0058     ≤ 0.0058 1.5 0.48 ≤ 0.55 ∴ OK 9. Check allowed buckling pressure using Eq 5-21: 1   EI   qa =  32Rw B ′E ′  3   FS  D  

1 2

Copyright (C) 1999 American Water Works Association All Rights Reserved

69

70

FIBERGLASS PIPE DESIGN

Solution of Eq 5-21 requires determination of Rw and B′: Rw = 1 − 0.33 (hw/h) For H = 6 ft Rw = 1 − 0.33 (0/72) = 1.0 For H = 12 ft Rw = 1 − 0.33 (24/144) = 0.945 B′ =

1 1 + 4e−0.065H

For H = 6 ft B′ =

1 1 + 4e−0.065 (6)

= 0.270 For H = 12 ft B′ =

1 1 + 4e−0.065 (12)

= 0.353 Substituting the values of Rw and B′ in Eq 5-21 for H = 6 ft: qa =

 (1,620) 3.5E6 (0.613)  0.5 1    32 (1.0) (0.270)  2.5  (12) 72.71 3  

= 19.64 psi Substituting the values of Rw and B′ in Eq 5-21 for H = 12 ft:  (1,620) 3.5E6 (0.613)  0.5 1  qa =  32 (0.945) (0.353)   2.5  (12) 72.713   = 21.83 psi Since no vacuum is present, check to satisfy the requirements of Eq 5-24 only: qa ≥ WL + Rw (Wc) + γw hw

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BURIED PIPE DESIGN

71

Substituting for H = 6 ft: ≥ (1.45) + (1) (4.79) + 0.0361 (0 in.) = 6.24 ≤ 19.64 ∴OK Substituting for H = 12 ft: ≥ (0.63) + 0.945 (9.58) + 0.0361 (24) = 10.55 ≤ 21.83 ∴ OK Conclusion: Design is OK since all checks are satisfied.

REFERENCES _____________________________________________ AASHTO H-20. Washington, D.C.: American Association of State Highway and Transportation Officials. Cagle, L., and B.C. Glascock. 1982. Recommended Design Requirements for Elastic Buckling of Buried Flexible Pipe (Report of ANSI/AWWA Standard C950 Ad-Hoc Task Group on Buckling). In Proc. of AWWA Annual Conference and SPI 39th Annual Conference (January, 1984). Denver, Colo.: American Water Works Association. Luscher, U. 1966. Buckling of Soil Surrounded Tubes. Jour. Soil Mech. & Found., 92(6):213. Molin, J. 1971. Principles of Calculation for Underground Plastic Pipes—Calculations of Loads, Deflection, Strain. ISO Bull., 2(10):21. Spangler, M.G. and R.L. Handy. 1982. Soil Engineering. New York: Harper & Row. Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System.) 1993. ASTM D2487. West Conshohocken, Pa: American Society for Testing and Materials. Standard for Fiberglass Pressure Pipe. 1995. ANSI/AWWA C950. Denver, Colo.: American Water Works Association. Standard Practice for Determining Dimensions of ‘Fiberglass’ (Glass-Fiber-Reinforced Thermosetting Resin) Pipe and Fittings. 1991. ASTM D3567. West Conshohocken, Pa.: American Society for Testing and Materials.

Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading. 1993. ASTM D2412. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density. 1991. ASTM D4254. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Penetration Test and Split-Barrel Sampling of Soils. 1984. ASTM D1586. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table. 1993. ASTM D4253. West Conshohocken, Pa.: American Society for Testing and Materials. Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort. 1991. ASTM D698. West Conshohocken, Pa.: American Society for Testing and Materials. Von Mises, R. 1914. Critical Pressure of Cylindrical Tubes. Zertschorft des Vereins Deutscher Ingenieure, 28:19.

Copyright (C) 1999 American Water Works Association All Rights Reserved

AWWA MANUAL

Chapter

GUIDELINES FOR UN DERGROUND INS TALLATION OF FIBERGLAS S PIPE

M45

6 Guidelines for Underground Installation of Fiberglass Pipe

6.1 INTRODUCTION ______________________________________ The structural and installation designs of fiberglass pipe, or almost any buried pipe, are closely related. The structural design process, discussed in chapter 5, assumes that a pipe will receive support from the surrounding soil, and the installation process must ensure that the support is provided. The guidelines in this chapter suggest procedures for burial of fiberglass pipe in typically encountered soil conditions. Recommendations for trenching, placing, and joining pipe; placing and compacting backfill; and monitoring deflection levels are included. ANSI/AWWA Standard C950 specifies pipe that encompass a wide range of product variables. Diameters range from 1 in. to 12 ft., pipe stiffnesses range from 9 psi to 72 psi (62 kPa to 496 kPa), and internal pressure ratings range up to 250 psi (1,724 kPa). Designers and installers should recognize that all possible combinations of pipe, soil types, and natural ground conditions that may occur are not considered in this chapter. The recommendations provided may need to be modified or expanded to meet the needs of some installation conditions. Section 6.9 lists areas that may be influenced by project, local, or regional conditions and should be given consideration when preparing specifications. Guidance for installation of fiberglass pipe in subaqueous conditions is not included.

73

Copyright (C) 1999 American Water Works Association All Rights Reserved

74

FIBERGLASS PIPE DESIGN

These guidelines are for use by designers and specifiers, manufacturers, installation contractors, regulatory agencies, owners, and inspection organizations that are involved in the construction of buried fiberglass pipelines.

6.2 RELATED DOCUMENTS _______________________________ The following are several ASTM standards that provide engineers with additional information related to installing buried pipe. D8 D420 D653 D698 D883 D1556 D1557 D2167 D2216 D2321 D2412 D2487 D2488 D2922 D3017 D3839 D4253 D4254 D4318 D4564 D4643 D4914

Standard Terminology Relating to Materials for Roads and Pavements Standard Guide to Site Characterization for Engineering, Design, and Construction Purposes Standard Terminology Relating to Soil, Rock, and Contained Fluids Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3) Standard Terminology Relating to Plastics Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft [2,700 kN-m/m]) Standard Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon Method Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System) Standard Practice for Description and Identification of Soils (Visual–Manual Procedure) Standard Test Methods for Density of Soil and Soil-Aggregate in Place by Nuclear Methods (Shallow Depth) Standard Test Method for Water Content of Soil and Rock in Place by Nuclear Methods (Shallow Depth) Standard Practice for Underground Installation of “Fiberglass” (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table Standard Test Method for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils Standard Test Method for Density of Soil in Place by the Sleeve Method Standard Test Method for Determination of Water (Moisture) Content of Soil by the Microwave Oven Method Standard Test Methods for Density of Soil and Rock in Place by the Sand Replacement Method in a Test Pit

Copyright (C) 1999 American Water Works Association All Rights Reserved

GUIDELINES FOR UNDERGROUND INSTALLATION OF FIBERGLASS PIPE

D4944

D4959 D5030 D5080 F412

75

Standard Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester Method Standard Test Method for Determination of Water (Moisture) Content of Soil by Direct Heating Method Standard Test Method for Density of Soil and Rock in Place by the Water Replacement Method in a Test Pit Standard Test Method for Rapid Determination of Percent Compaction Standard Terminology Relating to Plastic Piping Systems

6.3 TERMINOLOGY ______________________________________ Terminology used in this chapter is in accordance with ASTM Standards F412, D8, D653, and D883, unless otherwise indicated. The following terms are specific to this manual. Bedding. Backfill material placed in the bottom of the trench or on the foundation to provide a uniform material on which to lay the pipe; the bedding may or may not include part of the haunch zone (see Figure 6-1). Compactibility. A measure of the ease with which a soil may be compacted to a high density and high stiffness. Crushed rock has high compactibility because a dense and stiff state may be achieved with little compactive energy. Deflection. Any change in the diameter of the pipe resulting from installation and imposed loads. Deflection may be measured and reported as either vertical or horizontal and is usually expressed as a percentage of the undeflected pipe diameter.

Excavated Trench Width

Final Backfill 6 to 12 in. In Situ Soil (native)

In Situ Soil (native) Backfill Initial Backfill

Pipe Zone Embedment

Foundation (if required)

Bedding Haunch Zone

Reprinted with permission from the Annual Book of ASTM Standards, Copyright ASTM, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.

Figure 6-1 Trench cross-section terminology

Copyright (C) 1999 American Water Works Association All Rights Reserved

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FIBERGLASS PIPE DESIGN

Engineer. The engineer in responsible charge of the work or the duly recognized or authorized representative. Final backfill. Backfill material placed from the top of the initial backfill to the ground surface. Foundation. Backfill material placed and compacted in the bottom of the trench to replace over excavated material and/or to stabilize the trench bottom if unsuitable ground conditions are encountered (see Figure 6-1). Geotextile. Any permeable textile material used with foundation, soil, earth, rock, or any other geotechnical engineering related material, as an integral part of a synthetic product, structure, or system. Haunching. Backfill material placed on top of the bedding and under the springline of the pipe; the term only pertains to soil directly beneath the pipe (see Figure 6-1). Initial backfill. Backfill material placed at the sides of the pipe and up to 6 in. to 12 in. (150 mm to 300 mm) over the top of the pipe, including the haunching (see Figure 6-1). Manufactured aggregates. Aggregates such as slag that are products or by-products of a manufacturing process, or natural aggregates that are reduced to their final form by a manufacturing process such as crushing. Maximum standard Proctor density. The maximum dry density of soil compacted at optimum moisture content and with standard effort in accordance with ASTM D698. Native (in situ) soil. Natural soil in which a trench is excavated for pipe installation or on which a pipe and embankment are placed. Open-graded aggregate. An aggregate that has a particle size distribution such that, when compacted, the resulting voids between the aggregate particles are relatively large. The voids are expressed as a percentage of the total space occupied by the material. Optimum moisture content. The moisture content of soil at which its maximum density is obtained when compacted with standard effort (see ASTM D698). Pipe zone embedment. All backfill around the pipe, including the bedding, haunching, and initial backfill. Processed aggregates. Aggregates that are screened, washed, mixed, or blended to produce a specific particle size distribution. Relative density. A measure of the density of a granular soil based on the actual density of the soil “relative” to the soil in its loosest state and the soil in its densest state (see ASTM D653 for a precise definition) as obtained by laboratory testing in accordance with ASTM D4253 and D4254. Soil stiffness. A property of soil, generally represented numerically by a modulus of deformation, that indicates the relative amount of deformation that will occur under a given load. Split installation. An installation where the initial backfill is composed of two different materials or one material placed at two different densities. The primary initial backfill extends from the top of the bedding to a depth of at least 0.5 times the diameter, and the secondary initial backfill extends from the top of the primary backfill to the top of the initial backfill.

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GUIDELINES FOR UNDERGROUND INSTALLATION OF FIBERGLASS PIPE

77

6.4 IN SITU SOILS _______________________________________ It is important to understand in situ conditions prior to construction in order to prepare proper specifications and planning construction methods. Classification of soils according to ASTM D2487 and D2488 is useful in gaining an understanding of in situ conditions. Other tests, such as the standard penetration test, are also useful in determining soil stiffness. Depending on actual installation conditions, such as trench geometry, the in situ soil conditions may also have a significant impact on pipe design. Refer to chapter 5 for further discussion. Consideration should also be given to seasonal variations in groundwater level when evaluating groundwater conditions. For example, if the soil exploration program is conducted in August, the groundwater level may be quite low compared to levels in April or May.

6.5 EMBEDMENT MATERIALS ____________________________ Soil types used or encountered in burying pipes include those classified in Table 5-3, and natural, manufactured, and processed aggregates. The soil classifications are grouped into soil “stiffness categories” (SC) in Table 6-1, based on the typical soil stiffness when compacted. Soil SC1 indicates a soil with high compatibility, i.e., a soil that provides the highest soil stiffness at any given percentage of maximum Proctor density and a soil that provides a given soil stiffness with the least compactive energy. Each higher number soil stiffness category is successively less compatible, i.e., it provides less soil stiffness at a given percentage of maximum Proctor density and requires greater compactive energy to provide a given level of soil stiffness. See chapter 5 for a discussion of how soil stiffness affects buried pipe behavior. Table 6-2 provides recommendations on installation and use of embedment materials based on stiffness category and location in the trench. In general, soil conforming to SC1 through SC4 may be used as recommended unless otherwise specified, but SC5 materials should be excluded from the pipe zone embedment.

6.5.1 Soil Stiffness Classes Soil stiffness category 1 (SC1). SC1 materials provide maximum pipe support for a given density due to low content of sand and fines. With minimum effort these materials can be installed at relatively high soil stiffnesses over a wide range of moisture contents. In addition, the high permeability of SC1 materials may aid in the control of water and are often desirable for embedment in rock cuts where water is frequently encountered. However, when groundwater flow is anticipated, consideration should be given to the potential for migration of fines from adjacent materials into the open-graded SC1 materials. Refer to Sec. 6.5.2 for a discussion of use of soil in backfill. Soil stiffness category 2 (SC2). SC2 materials, when compacted, provide a relatively high level of pipe support; however, open-graded groups may allow migration and the sizes should be checked for compatibility with adjacent material; see Sec. 6.5.2. Soil stiffness category 3 (SC3). SC3 materials provide less support for a given density than SC1 or SC2 materials. Higher levels of compactive effort are required and moisture content must be controlled. These materials provide reasonable levels of pipe support once proper density is achieved. Soil stiffness category 4 (SC4). SC4 materials require a geotechnical evaluation prior to use. The moisture content must be near optimum to minimize

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FIBERGLASS PIPE DESIGN

Table 6-1 Soil stiffness categories Soil Stiffness Category*,†

Soil Group Crushed rock and gravel with 70 RD f Gravel or 90 SPD Sand Bed

r1 + r2 2 But not less than 150 mm

f≥

Bed

a. Spacing between pipes in the same trench

b. Cross over

Source: Owens Corning Engineered Pipe Systems, Brussels, Belgium.

Figure 6-4 Adjacent piping systems and damage the pipe. Use compaction equipment and techniques that are compatible with materials used and located in the trench. Compaction of soils containing few fines (SC1 and SC2 with less than 5 percent fines). If compaction is required, use surface plate vibrators, vibratory rollers, or internal vibrators. The compacted lift thickness should not exceed 12 in. (300 mm) when compacted with surface plate vibrators or vibratory rollers; when compacted with internal vibrators, it should not exceed the length of the internal vibrators. Density determination should typically be in accordance with ASTM D4253 and D4254 (relative density). In some cases, the density of SW or SP soils may be determined by ASTM D698 (standard Proctor) if the test results in a clearly defined compaction curve. Compaction of soils containing some fines (SC2 with 5 to 12 percent fines). These soils may behave as a soil containing few fines or as a soil containing a significant amount of fines. The methods of compaction and density determination should be based on the method that results in the higher in-place density.

Using board or other device to push and compact embedment material under pipe.

WRONG!

First lift of embedment

Pipe

Bedding

Correct: Pipe firmly supported

Pipe

Bedding

a. Ensuring firm pipe support

First lift of embedment

Wrong: Poor pipe support b. Improper haunch

Source: Owens Corning Engineered Pipe Systems, Brussels, Belgium.

Figure 6-5 Proper compaction under haunches

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FIBERGLASS PIPE DESIGN

Compaction of soils containing a significant amount of fines (SC3, SC4, and SC5 [CH and MH]). These soils should be compacted with impact tampers or with sheepsfoot rollers. Density determination should be in accordance with ASTM D698 (standard Proctor). The maximum density occurs at the optimum moisture content. Less effort is required to reach a given density when the moisture content is within 2 percentage points of the optimum moisture. A rapid method of determining the percent compaction and moisture variation is described in ASTM D5080. For compaction levels of 90 percent standard Proctor or higher, the compacted lift thickness should not exceed 6 in. (150 mm). Determination of the in-place density of soils. The in-place density of any in situ or fill soil may be determined in accordance with ASTM D1556, D2167, D2922, D4564, D4914, or D5030. The applicable test method will depend on the type of soil, moisture content of the soil, and the maximum particle size present in the soil. The moisture content of the soil may be determined in accordance with ASTM D2216, D3017, D4643, D4944, or D4959. When using nuclear density-moisture gages (ASTM D2922 and D3017), the gauge should be site-calibrated in the proximity of the pipe and in the excavation unless otherwise indicated by the gauge manufacturer. Minimum density. The minimum embedment density should be established by the engineer based on an evaluation of specific project conditions. Higher or lower densities than those recommended in Table 6-2 may be appropriate. Minimum densities given in Table 6-2 are based on attaining an average modulus of soil reaction E′ of 1,000 psi (6.9 MPa) and are intended to provide satisfactory embedment stiffness in most installation conditions. (See chapter 5 for the significance of E′.) Consolidation using water. Consolidation of pipe zone embedment using water (jetting or saturation with vibration) should be done only under controlled conditions and when directed by the engineer. Minimum cover. To preclude damage to the pipe and disturbance to pipe embedment, a minimum depth of backfill above the pipe should be maintained before allowing vehicles or heavy construction equipment to traverse the pipe trench. The minimum depth of cover should be established by the engineer based on an evaluation of specific project conditions, such as pipe diameter and stiffness, soil type and stiffness, and live load type and magnitude. In the absence of an engineering evaluation, the following minimum cover requirements should be used. For embedment materials installed to the minimum densities given in Table 6-2 and live loads similar to AASHTO H-20, provide cover (i.e., depth of backfill above top of pipe) of at least 24 in. (0.6 m) for SC1 embedment; a cover of at least 36 in. (0.9 m) for SC2, SC3, or SC4 embedment, before allowing vehicles or construction equipment to traffic the trench surface; and at least 48 in. (1.2 m) of cover before using a hydrohammer for compaction unless approved by the engineer. Where construction loads may be excessive (e.g., cranes, earth-moving equipment, or other vehicles where wheel loads exceed the AASHTO H-20 loading) minimum cover should be increased as determined by the engineer, or special structures, such as relief slabs at grade, may be installed to reduce the load transferred to the pipe. If there is a risk of pipe flotation, then the minimum cover should be one pipe diameter. If a specific analysis is made of the buoyant force of an empty pipe compared to the submerged weight of soil over the pipe, this minimum cover may be reduced.

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GUIDELINES FOR UNDERGROUND INSTALLATION OF FIBERGLASS PIPE

87

6.7.4 Connections and Appurtenant Structures Connections to manholes and rigid structures and changing foundation soils. When differential settlement can be expected, such as at the ends of casing pipe, when the pipe enters a manhole, at anchor blocks, or where foundation soils change stiffness, provide a flexible system capable of accommodating the anticipated settlement. This may be accomplished by placing a joint as close as practically possible to the face of the structure and a second joint within one to two pipe diameters of the face of the structure (see Figure 6-3). Alternatively attach the pipe to the rigid structure with a flexible boot capable of accommodating the anticipated differential movement. Other methods of accommodating differential settlements are available. Vertical risers. Provide support for vertical risers as commonly found at service connections, cleanouts, and drop manholes to preclude vertical or lateral movement. Prevent the direct transfer of thrust due to surface loads and settlement, and ensure adequate support at points of connection to main lines. Exposing pipe for making service line connections. When excavating for a service line connection, excavate material from above the top of the existing pipe before removing material from the sides of the pipe. When backfilling excavations of existing lines, the materials and construction methods used should restore the installation to its condition prior to excavation. Pipe caps and plugs. Secure caps and plugs to the pipe to prevent movement and resulting leakage under test and service pressures. If lines are to be tested under pressure, any plugs and caps must be designed to safely carry the test pressure. Adjacent piping systems. Space parallel piping systems laid within a common trench sufficiently far apart to allow compaction equipment to compact the soil between the pipes. The minimum distance that should be allowed between pipes is the average of the radii of the two adjacent pipes, but not less than 4 in. (100 mm); see Figure 6-4(a). When mechanical compaction equipment is used, a clearance of 6 in. (150 mm) greater than the width of the widest piece of equipment may be considered as a practical clearance between the pipes. Compact the soil between the pipes in the same manner as the soil between the pipe and the trench wall, taking special care to compact the soil in the haunch zone of each pipe. When one piping system will cross over another, the minimum vertical clear space between the two pipes should be the average of the radii of the two pipes but not less than 12 in. (300 mm); see Figure 6-4(b). The trench in which the lower pipe is installed should be backfilled with SC1 or SC2 material compacted to a minimum of 90 percent of standard Proctor density, or 70 percent relative density.

6.7.5 Thrust Blocks Installation requirements related to thrust blocks are discussed in chapter 7.

6.8 FIELD MONITORING _________________________________ Compliance with installation requirements for trench depth, grade, water conditions, foundation, embedment and backfill materials, joints, density of materials in place, and safety should be monitored according to the contract documents. Leakage testing specifications are not within the scope of this manual. Deflection. Monitor the deflection level in the pipe throughout the installation process for conformance to the requirements of the contract specifications and the manufacturer’s recommendations. Conduct deflection measurement programs early

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FIBERGLASS PIPE DESIGN

in a project to verify that the construction procedures being used are adequate. The allowable deflection at the time of installation is the long-term allowable deflection reduced by the effects of deflection lag. If necessary, also consider the effects of vertical ovalling during compaction.

6.9 CONTRACT DOCUMENT RECOMMENDATIONS _________ The following guidelines may be included in contract documents for a specific project to cover installation requirements. ASTM D3839 provides similar guidelines and is written in a specification-type format. In either case, applications for a particular project may require that the engineer provide more specific requirements in several areas, including: • Maximum particle size if different from Sec. 6.5.2. • Restrictions on use of categories of embedment and backfill materials. • Specific gradations of embedment materials for resistance to migration. • State-specific restrictions on leaving trenches open. • Restrictions on mode of dewatering and design of underdrains. • Requirements on minimum trench width. • Restrictions or details for support of trench walls. • Specific bedding and foundation requirements. • Specific restrictions on methods of compaction. • Minimum embedment density if different from these recommendations; specific density requirements for backfill (e.g., for pavement subgrade). • Minimum cover requirements. • Detailed requirements for support of vertical risers, standpipes, and stacks to accommodate anticipated relative movements between pipe and appurtenances. Detailing to accommodate thermal movements, particularly at risers. • Detailed requirements for manhole connections. • Requirements on methods of testing compaction and leakage. • Requirements on deflection and deflection measurements, including method and time of testing.

REFERENCES _____________________________________________ AASHTO H-20. Washington, D.C.: American Association of State Highway and Transportation Officials. Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System). 1993. ASTM D2487. West Conshohocken, Pa.: American Society for Testing and Materials. Standard for Fiberglass Pressure Pipe. 1995. ANSI/AWWA C950. Denver, Colo.: American Water Works Association. Standard Guide to Site Characterization for Engineering, Design, and Construction Purposes. 1993. ASTM D420. West Conshohocken, Pa.: American Society for Testing and Materials.

Standard Practice for Description and Identification of Soils (Visual–Manual Procedure). 1993. ASTM D2488. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Practice for Underground Installation of ‘Fiberglass’ (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe. 1994. ASTM 3839. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications. 1989. ASTM D2321. West Conshohocken, Pa.: American Society for Testing and Materials.

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GUIDELINES FOR UNDERGROUND INSTALLATION OF FIBERGLASS PIPE

Standard Terminology Relating to Materials for Roads and Pavements. 1994. ASTM D8. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Terminology Relating to Plastic Piping Systems. 1994. ASTM F412. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Terminology Relating to Plastics. 1993. ASTM D883. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Terminology Relating to Soil, Rock, and Contained Fluids. 1990. ASTM D653. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon Method. 1994. ASTM D2167. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Density and Unit Weight of Soil in Place by the SandCone Method. 1990. ASTM D1556. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Density of Soil and Rock in Place by the Water Replacement Method in a Test Pit. 1989. ASTM D5030. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Density of Soil in Place by the Sleeve Method. 1993. ASTM D4564. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading. 1993. ASTM D2412. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Determination of Water (Moisture) Content of Soil by Direct Heating Method. 1989. ASTM D4959. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Determination of Water (Moisture) Content of Soil by the Microwave Oven Method. 1993. ASTM D4643. West Conshohocken, Pa.: American Society for Testing and Materials.

89

Standard Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester Method. 1989. ASTM D4944. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock. 1992. ASTM D2216. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. 1995. ASTM D4318. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density. 1991. ASTM D4254. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Rapid Determination of Percent Compaction. 1993. ASTM D5080. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Method for Water Content of Soil and Rock in Place by Nuclear Methods (Shallow Depth). 1988. ASTM 3017. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Methods for Density of Soil and Rock in Place by the Sand Replacement Method in a Test Pit. 1989. ASTM D4914. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Methods for Density of Soil and Soil-Aggregate in Place by Nuclear Methods (Shallow Depth). 1991. ASTM 2922. West Conshohocken, Pa.: American Society for Testing and Materials. Standard Test Methods for Maximum Index Density and Unit Weight of Soils and Calculation of Relative Density. 1993. ASTM D4253. West Conshohocken, Pa.: American Society for Testing and Materials.

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90

FIBERGLASS PIPE DESIGN

Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort [56,000 ft-lbf/ft (2,700 kN-m/m)]. 1991. ASTM D1557. West Conshohocken, Pa.: American Society for Testing and Materials.

Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort [12,400 ft-lbf/ft3 (600 kN-m/m3)]. 1991. ASTM D698. West Conshohocken, Pa.: American Society for Testing and Materials.

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AWWA MANUAL

Chapter

BURIED PIPE THRU ST RES TRAINTS

M45

7 Buried Pipe Thrust Restraints

7.1 UNBALANCED THRUST FORCES ________________________ Unbalanced thrust forces occur in pressure pipelines at changes in direction (i.e., elbows, wyes, tees, etc.), at changes in cross-sectional area (i.e., reducers), or at pipeline terminations (i.e., bulkheads). These forces, if not adequately restrained, may cause pipeline movement resulting in separated joints and/or pipe damage. Thrust forces are: (1) hydrostatic thrust due to internal pressure of the pipeline, and (2) hydrodynamic thrust due to changing momentum of flowing fluid. Since most pressure lines operate at relatively low velocities, the hydrodynamic force is very small and is usually ignored.

7.1.1 Hydrostatic Thrust Typical examples of hydrostatic thrust are shown in Figure 7-1. The thrust in dead ends, tees, laterals, and reducers is a function of internal pressure P and cross-sectional area A at the pipe joint. The resultant thrust at a bend is also a function of the deflection angle ∆ and is given by: T = 2PA sin (∆/2) Where: T = hydrostatic thrust, lb P = internal pressure, psi

91

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(7-1)

92

FIBERGLASS PIPE DESIGN

PA0

T = 2PA sin ∆ 2

D

∆

∆ 2

PA

PA

PA sin ∆ 2

Bend

Wye

PA

∆

T = PA0

PA2

PA

∆ 2

T = PA

PA1

T Dead End ∆ 2

T = 2 PA2 cos ∆ – PA1 2

PA0 PA2

Bifurcation

PA2

PA1 T = PA0

T

T = P (A1 – A2 ) Tee

Reducer

Figure 7-1 Thrust force definitions A = (π/4) Dj2 = cross-sectional area of pipe joint, in., where Dj is the pipe joint diameter, in. ∆ = deflection angle of bend, degrees

7.2 THRUST RESISTANCE For buried pipelines, unbalanced horizontal thrust forces have two inherent sources of resistance: (1) frictional drag from dead weight of the pipe, earth cover, and contained fluid, and (2) passive resistance of soil against the pipe or fitting in the direction of the thrust. If this resistance is not sufficient to resist the thrust, then it must be supplemented by increasing the supporting area on the bearing side of the fitting with a thrust block; increasing the frictional drag of the line by “tying” adjacent pipe to the fitting; or otherwise anchoring the fitting to limit or prevent movement. Unbalanced uplift thrust at a vertical deflection is resisted by the dead weight of the fitting, earth cover, and contained fluid. If this type of resistance is not sufficient to resist the thrust, then it must be supplemented by increasing the dead weight with a gravity-type thrust block; increasing the dead weight of the line by “tying” adjacent pipe to the fitting; or otherwise anchoring the fitting to limit or prevent movement.

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BURIED PIPE THRUST RESTRAINTS

93

LB A

. . . . . . .. . . . .

. . . . . . ..

h

. . . .. . . . ... ... .

HB

Section A–A

A

Reinforcing Steel

. .. ... . . . .. .. .. . . . . . .. . . . . . ..

h

. .. .

HB

Alternate Section A–A

... .. ... . . . Piles

Alternate Section A–A

Figure 7-2 Typical thrust blocking of a horizontal bend

7.3 THRUST BLOCKS Concrete thrust blocks increase the ability of fittings to resist movement by increasing the bearing area and the dead weight of the fitting. Typical thrust blocking of a horizontal bend (elbow) is shown in Figure 7-2. Calculation of size. Ignoring the dead weight of the thrust block, the block size can be calculated based on the bearing capacity of the soil: Area of block = LB × HB = (T × FS)/σ

(7-2)

Where: LB × HB = area of bearingsurfac eo f thrust block, ft2 T = thrustforc e,lb σ = bearing valuefor soil, lb/ft2 FS = design factor, 1.5 Typical values for conservative horizontal bearing strengths of various soil types are listed in Table 7-1.

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94

FIBERGLASS PIPE DESIGN

Table 7-1 Horizontal soil-bearing strengths Soil Muck Soft clay Silt Sandy silt Sand Sandy clay Hard clay

Bearing Strength σ (lb/ft2)* 0 1,000 1,500 3,000 4,000 6,000 9,000

*Although the bearing strength values have been used successfully in the design of thrust blocks and are considered to be conservative, their accuracy is dependent on accurate soil identification and evaluation. The design engineer must select the proper bearing strength of a particular soil type.

If it is impractical to design the block for the thrust force to pass through the geometric center of the soil bearing area, then the design should be evaluated for stability. After calculating the concrete thrust block size, and reinforcement if necessary, based on the bearing capacity of soil, the shear resistance of the passive soil wedge behind the thrust block should be checked because it may govern the design. For a thrust block having its height, HB, less than one-half the distance from the ground surface to base of block, h, the design of the block is generally governed by the bearing capacity of the soil. However, if the height of the block, HB, exceeds one-half h, then the design of the block is generally governed by shear resistance of the soil wedge behind the thrust block. Determining the value of the bearing and shear resistance of the soil and thrust block reinforcement is beyond the scope of this manual. Consulting a qualified geotechnical professional is recommended. Typical configurations. Determining the bearing value, σ, is the key to “sizing” a thrust block. Values can vary from less than 1,000 lb/ft2 (48 kN/m2) for very soft soils to several tons per square foot (kN/m2) for solid rock. Knowledge of local soil conditions is necessary for proper sizing of thrust blocks. Figure 7-2 shows several details for distributing thrust at a horizontal bend. Section A–A is the more common detail, but the other methods shown in the alternate sections may be necessary in weaker soils. Figure 7-3 illustrates typical thrust blocking of vertical bends. Design of the block for a bottom bend is the same as for horizontal bend, but the block for a top bend must be sized to adequately resist the vertical component of thrust with dead weight of the block, bend, water in the bend, and overburden. Proper construction is essential. Most thrust block failures can be attributed to improper construction. Even a correctly sized block can fail if it is not properly constructed. A block must be placed against undisturbed soil and the face of the block must be perpendicular to the direction of and centered on the line of action of the thrust. A surprising number of thrust blocks fail because of inadequate design or improper construction. Many people involved in construction and design do not realize the magnitude of the thrusts involved. As an example, a thrust block behind a 36 in. (900 mm), 90 degree bend operating at 100 psi (689 kPa) must resist a thrust force in excess of 150,000 lb (667 kN). Another factor frequently overlooked is that thrust increases in proportion to the square of pipe diameter. A 36 in. (900 mm) pipe produces approximately four times the thrust produced by an 18 in. (450 mm) pipe operating at the same internal pressure.

Copyright (C) 1999 American Water Works Association All Rights Reserved

95

BURIED PIPE THRUST RESTRAINTS

Finished Grade

Concrete Collar

. . . . . . . . . . . . .. .

. . . . . . .. .

Figure 7-3 Typical profile of vertical bend thrust blocking

Adjacent excavation. Even a properly designed and constructed thrust block can fail if the soil behind the block is disturbed. Properly sized thrust blocks have been poured against undisturbed soil only to fail because another utility or an excavation immediately behind the block collapsed when the line was pressurized. If the risk of future nearby excavation is high, the use of restrained (tied) joints may be appropriate.

7.4 JOINTS WITH SMALL DEFLECTIONS The thrust at pipe joints installed with angular deflection is usually so small that supplemental restraint is not required. Small horizontal deflections. Thrust T at horizontal deflected joints is resisted by friction on the top and bottom of the pipe as shown in Figure 7-4. Additional restraint is not required when: T ≤ fLp (Wp + Ww + 2We)

(7-3)

Where: T = 2PA sin (θ /2) = result and thrust force, lb where θ is the deflection angle created by the deflected joint, degrees f = coefficient of friction Lp = length of pipe, ft Wp = weight of pipe, lb/lin ft

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96

FIBERGLASS PIPE DESIGN

θ T = 2PA sin 2

T

T

Lp

Lp Lp 2

Lp 2

A

θ θ

A

Lp

θ

F= T

Plan View

We f Lp We

Wp Ww

F

T

f Lp (Wp + Ww + We ) Section A–A

Figure 7-4 Restraint of thrust at def lected joints on long-radius horizontal curves

Ww = weight of fluid in pipe, lb/lin ft We = earth cover load, lb/lin ft The passive soil resistance of the trench backfill against the pipe is ignored in the previous analysis. Depending on the installation and field conditions, the passive soil resistance of the backfill may be included to resist thrust. The selection of a value for the coefficient of friction f is dependent upon the type of soil and the roughness of pipe exterior. Design values for the coefficient of friction generally vary from 0.25 to 0.50. Determination of earth cover load should be based on a backfill density and height of cover consistent with what can be expected when the line is pressurized. Values of soil density vary from 90 lb/ft3 to 130 lb/ft3 (14 kN/m3 to 20 kN/m3), depending on the degree of capaction. We may be conservatively determined using the Marston equation for loads imparted to a flexible pipe, as follows: We = (Cd) (W) (Bd) (Bc) Where: We = earth load, lb/lin ft Cd = a coefficient based on type of backfill soil and on the ratio of H (depth of fill to top if pipe, ft) Bd (see Figure 7-5)

Copyright (C) 1999 American Water Works Association All Rights Reserved

(7-4)

BURIED PIPE THRUST RESTRAINTS

1.5 E D C B A 1.0

Computation Diagram for Earth Loads on Trench Conduits (conduits buried in trenches)

0.9 0.8 0.7 0.6

Coefficient Cd

0.5

0.4

0.3 0.25

0.2

A = Cd K µ and K µ' = 0.1924 for granular materials without cohesion B = Cd K µ and K µ' = 0.165 maximum for sand and gravel C = Cd K µ and K µ' = 0.150 maximum for saturated topsoil D = Cd K µ and K µ' = 0.130 ordinary maximum for clay E = Cd K µ and K µ' = 0.110 maximum for saturated clay

0.15

0.1 0.1

0.15

0.2

0.3

0.4

0.5

0.6

0.7

0.8 0.9 1.0

1.5

Values of H/Bd 5 E 4 D C B

Coefficient Cd

3

A 2 Expanded Scale of Computation Diagram for Earth Loads on Trench Conduits

1.5

1 1

1.5

2

3

4

5

6

7

8

9 10

15

20

25

30

Values of H/Bd

Figure 7-5 Computation diagram for earth loads on trench conduits

Copyright (C) 1999 American Water Works Association All Rights Reserved

40

97

98

FIBERGLASS PIPE DESIGN

A

T T = 2PA sin

θ 2

Lp T

Lp

Lp 2

Lp 2

θ θ

ϕ

( ϕ– θ ) 2 F=T

A Horizontal Plane

Lp θ

Profile View

We

Wp Ww Wt = (Wp + Ww + We ) Section A–A

Figure 7-6 Restraint of uplift thrust at deflected joints on long-radius vertical curves

W = unit weight of soil, lb/ft3 Bd = ditch width at top of pipe, ft Bc = outside diameter of pipe, ft Small vertical deflections with joints free to rotate. Uplift thrust at deflected joints on long-radius vertical curves is resisted by the combined dead weight, Wt, as shown in Figure 7-6. Additional restraint is not required when: T ≤ Lp (Wp + Ww + We) COS (ϕ – θ/2) Where: T = 2PA sin (θ/2) Lp = length of standard or beveled pipe, ft

Copyright (C) 1999 American Water Works Association All Rights Reserved

(7-5)

BURIED PIPE THRUST RESTRAINTS

99

Wp = weight of pipe, lb/lin ft Ww = weight of water in pipe, lb/lin ft We = earth cover load, lb/lin ft ϕ = slope angle, degrees θ = deflection angle, degrees, created by angular deflection of joint

7.5 RESTRAINED (TIED) JOINTS ____________________________ Unbalanced thrust forces at fittings or deflected joints may be resisted by using restrained joint(s) across the deflected joint or by tying adjacent pipes to the fitting. This method fastens a number of pipe on each side of the fitting to increase the frictional drag of the connected pipe to resist the fitting thrust. Since thrust diminishes from a maximum value at a fitting to zero at distance L from the fitting, requirements for longitudinal strength to resist thrust can be calculated for the pipe length immediately adjacent to the fitting and prorated on a straight line basis for the remainder of the pipe within the tied distance L. Frictional resistance on the tied pipe acts in the opposite direction of resultant thrust T. Section A–A in Figure 7-4 shows a diagram of the external vertical forces acting on a buried pipe with horizontal thrust and the corresponding frictional resistance. Uplift thrust restraint provided by gravity-type thrust blocks, shown for the top bend in Figure 7-3, may also be provided by the alternate method of increasing the dead weight of the line by tying adjacent pipe to the vertical bend. Section A–A in Figure 7-6 shows a diagram of the vertical forces acting on a buried vertical (uplift) bend used in determining the thrust resistance by dead weight.

∆ T = 2PA sin __ 2

L

∆

L

F = 2Lf(Wp+Ww+2 We) = T Joint Not Tied

Figure 7-7 Thrust restraint with tied joints at bends

Copyright (C) 1999 American Water Works Association All Rights Reserved

100

FIBERGLASS PIPE DESIGN

As previously stated, both of these analyses ignore the passive soil resistance of the backfill against the pipe. Depending on the installation and field conditions, the passive soil resistance of the backfill may be included to resist thrust. Horizontal bends and bulkheads. As illustrated in Figure 7-7, the frictional resistance F needed along each leg of a horizontal bend is PA sin (∆/2). Frictional resistance per lin ft of pipe against soil is equal to: Frictional resistance/ft of pipe = f (2We + Wp + Ww)

(7-6)

Where: f = coefficient of friction between pipe and soil We = overburden load, lb/lin ft Wp = weight of pipe, lb/lin ft Ww = weight of water in pipe, lb/lin ft F = frictional resistance Therefore, the length of pipe L to be tied to each leg of a bend is calculated as: L =

PA sin (∆/2) f (2We + Wp + Ww)

(7-7)

Where: L = length of pipe tied to each bend leg, ft P = internal pressure, psi A = cross-sectional area, in.2 ∆ = deflection angle of bend, degrees f = coefficient of friction between pipe and soil We = overburden load, lb/lin ft Wp = weight of pipe, lb/lin ft Ww = weight of fluid in pipe, lb/lin ft The length of pipe to be tied to a bulkhead or tee leg is: L =

PA f (2We + Wp + Ww)

Where: L = length of pipe tied to bulkhead to tee leg, ft with all other variables as defined previously.

Copyright (C) 1999 American Water Works Association All Rights Reserved

(7-8)

BURIED PIPE THRUST RESTRAINTS

T = 2PA sin

101

∆ 2

L1

L2

∆

ϕ1

2

ϕ

Horizontal Plane PA PA

Figure 7-8 Length of tied pipe on each leg of vertical (uplift) bend

Vertical (uplift) bends. As illustrated in Figure 7-8, the dead weight resistance needed along each leg of a vertical bend is 2PA sin (∆/2). Dead weight resistance per lin ft of pipe in a direction opposite to thrust is: Dead weight resistance/ft of pipe = (We + Wp + Ww) COS (ϕ–∆/2)

(7-9)

Where: We = overburden load, lb/lin ft Wp = weight of pipe, lb/lin ft Ww = weight of fluid in pipe, lb/lin ft ϕ = slope angle, degrees (see Figure 7-8) ∆ = deflection angle of bend, degrees (see Figure 7-8) Length of pipe L to be tied to leg of a vertical (uplift) bend is calculated as: L =

PA [ sin (∆/2) ] (We + Wp + Ww) COS [ ϕ − (∆/2) ]

(7-10)

with variables as defined previously. L1 =

PA sin ∆/2 (We + Wp + Ww) COS ( ϕ1 − ∆/2)

Copyright (C) 1999 American Water Works Association All Rights Reserved

(7-11)

102

FIBERGLASS PIPE DESIGN

L2 =

PA sin ∆/2 (We + Wp + Ww) COS (ϕ2 − ∆/2)

(7-12)

Vertical downward bends are resisted by bearing of the trench against the bottom of the pipe. Properly bedded pipe should not have to be investigated for this condition. Transmission of thrust force through pipe. In addition to calculating pipe length to be tied to a fitting, designers must be sure that tied pipe lengths have sufficient strength in the longitudinal direction to transmit thrust forces. The maximum thrust force for which the pipe adjacent to a bend must be designed is equal to:  5.43∆ + 0.063 ∆2  Fy =   PA for 0 < ∆ ≤ 90° 1,000  

(7-13)

Fy = PA

(7-14)

for ∆ > 90°

Where: Fy = maximum axial thrust force for which the pipe adjacent a bend must be designed, lb P = internal pressure, psi A = cross-sectional area, in.2 ∆ = bend deflection angle, degrees

Copyright (C) 1999 American Water Works Association All Rights Reserved

AWWA MANUAL

Chapter

ABOVEGROUN D PIPE DES IGN AND IN STALLATION

M45

8 Aboveground Pipe Design and Installation

8.1 INTRODUCTION ______________________________________ This chapter addresses the design and installation of fiberglass pipeline systems in aboveground applications for sizes 16 in. (400 mm) and smaller, and only for pipe lines that have restrained joints. Different design provisions and supporting methods may be applicable for specific project requirements, larger diameters, or a particular piping product. Consult with the manufacturer and the piping engineer for appropriate design considerations.

8.2 TEST METHODS AND PHYSICAL PROPERTIES ___________ The ultimate and allowable design stresses and physical properties for aboveground fiberglass pipe are based on standardized test methods; these properties are based on the minimum reinforced wall thickness. Table 8-1 provides a list of various American Society for Testing and Materials (ASTM) standardized test methods and the type of data the tests provide. The comments column provides information on safety factors for design stresses. Most manufacturers provide data obtained at both 75°F (24°C) and at the maximum allowable working temperature of the pipe. Some manufacturers take exception to various aspects of ASTM test methods and use modified techniques. Prior agreement relative to modified test methods is essential.

103

Copyright (C) 1999 American Water Works Association All Rights Reserved

104

FIBERGLASS PIPE DESIGN

Table 8-1 Standard test methods and design properties Property

Test

Comments

Axial tensile Ultimate stress Design stress Modulus of elasticity

ASTM D2105 or ASTM D638

Axial compression Ultimate stress Design stress Modulus of elasticity

ASTM D695

Short-term failure pressure Ultimate hoop tensile stress

ASTM D1599

Hydrostatic design stress Procedure A cyclic pressure

ASTM D2992

Commonly = 25% ultimate Usually