Handbook of PVC pipe Chap6.pdf

8/10/2019 Handbook of PVC pipe Chap6.pdf

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CHAPTER VI

S U P E R I M P O S E D L O A D S

O N B U R I E D P I P E

Summary of Recommendations, Relationships, and Data

Relevant to the Evaluation of External Loads

on Buried PVC Pipe

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HANDBOOK OF PVC PIPE

CHAPTER VI

SUPERIMPOSED LOADS ON BURIED PIPE

Superimposed loads on buried PVC pipe fall into two categories -earth loads and live loads. In the design of any buried piping system,

both categories of superimposed loads must be considered. Inaccordance with common design practice, earth loads and live loads aretreated as separate design parameters.

Earth Loads: The first solution to the problem of soil-inducedloads on buried pipe was published by Professor Anson Marston at IowaState University in 1913. Since then, the Marston Theory of Loads onUnderground Conduits has been used in determination of loading on

buried pipe. Much of the work done on earth loading technology forburied conduits throughout the world is related, in part, to Marston'sload theory.

FIGURE 6.1

DEVELOPMENT OF LOADS ON

RIGID PIPE IN TRENCHES

Where: K'VhBd

= the frictional force resisting settlement

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FIGURE 6.2

SHEARING FORCES OVER RIGIDPIPE

Shearing Forces Increase the Load

FIGURE 6.3

SHEARING FORCES OVER FLEXIBLEPIPE

Shearing Forces Decrease the Load

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CHAPTER VI - SUPERIMPOSED LOADS ON BURIED PIPE

Marston recognized that most flexible conduits would fall into thecategory where the load imposed on the pipe is less than the weight of the

prism of soil over the pipe. The flexibility of the pipe insured that therelative prism settlement above the pipe would be greater than the side

column in nearly all cases. Rigid conduits, such as concrete pipe, fall intothe category where the prism above the pipe imposes a greater load thanthe weight of the prism itself. The lack of flexibility in a rigid conduitdictates that the relative settlement of the backfill will be greater on thesides of the pipe than over the pipe.

The inherent differences of the two types of pipe are expressed in theformulas Marston developed for calculating the earth loads imposed on

pipe buried in a trench. They are as follows:

EQUATION 6.1 EQUATION 6.2

Rigid Flexible

Wc= CdwBdBd Wc= CdwBdBc

Where: Wc = load on the pipe, lbs/Lftw = unit weight of backfill, lbs/ft

3

Bc = outside diameter of pipe, ftBd = width of trench at top of pipe, ftCd = load coefficient for conduits installed in trenches

Analysis of the two equations reveals that the ratio of the load on aflexible pipe or conduit to the load on a rigid pipe or conduit is equal tothe ratio of diameter of the pipe to the width of the trench, for identicalconditions of installation.

EQUATION 6.3

(Wc) Rigid

(Wc) Flexible=

CdwBdx Bd

CdwBdx Bc=

Bd

Bc

Therefore, if the trench is twice as wide as the pipe being buried (12 inpipe in a 24 in wide trench), the load imposed on a rigid pipe will be twicethe load imposed on a flexible pipe, as indicated by the Marston equations.

When calculating loads on buried pipe, the term Cdmust be determinedfor particular installation conditions. Cd is a function of the ratio of fill

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height (H) to trench width (Bd) and of the friction coefficient of the backfilland the sides of the trench. Cdis computed as follows:

EQUATION 6.4

Cd=1 - e-2k'H/Bd

2k'

Where: e is the natural logarithm basek = Rankine's ratio of lateral to vertical pressure' = the coefficient of friction between backfill

material and sides of trenchA diagram has been developed (Figure 6.4) for various values of k '

and ratios H/Bd

that eliminates the need for computation of Cd

in mostinstances. According to Marston's equation, the width of the trenchdirectly affects the loads imposed on flexible and rigid pipe. The height ofthe backfill material and the trench width again appear in the Cdcomputations.

An increasing width of trench does increase the load imposed on a

pipe, but the load does not continue to increase indefinitely. There is a

trench width for a given depth and size of pipe beyond which no

additional load is imposed on the pipe. This is called the "transition

width" and is a limiting value for calculating loads based on Marston's

trench formulas. At transition width and beyond, the loads can be

calculated using Marston's positive projecting conduit or "embankment"

equations. Embankment installation is realized if the top of the pipe

projects above the natural ground surface or is in a relatively wide trench

(beyond transition width). The maximum loads imposed on a pipe are

those obtained in the embankment mode of installation.

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FIGURE 6.4 - VALUES OF Cd

Computation diagram for earth loads on trench conditions (completely buried in trenches).

SOURCE: GRAVITY SANITARY SEWER DESIGN AND CONSTRUCTION. "MANUALS & REPORTS

ON ENGINEERING PRACTICE NO. 60," AMERICAN SOCIETY OF CIVIL ENGINEERS AND

"MANUAL OF PRACTICE FD-5," WATER POLLUTION CONTROL FEDERATION, 1982.

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Marston developed the following formula for computing loads on bothflexible and rigid positive-projecting conduits (embankment installation):

EQUATION 6.5

Wc= CcwBcBc

Where: Ccreplaces Cdas the load coefficient, andBcappears twice to replace the Bd

The load coefficient Cc in this case depends on the projection ratio(p), the settlement ratio (rsd), and the ratio of fill height (H) to pipe width(not trench width) (B

c).

As in the case for Cd, a graph has been developed for Cc(Figure 6.6)that eliminates the need for the complex computations required to generateCc. Settlements that influence loads on positive-projecting pipe areshown in Figure 6.5.

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FIGURE 6.5SETTLEMENTS THAT INFLUENCELOADS ON POSITIVE-PROJECTING

CONDUITS

Where: sg = settlement of natural ground adjacent to pipesm = compression of columnns of soil of height pBcdc = deflection of pipesf = settlement of bottom of pipe

rsd = settlement ratio = [(sm+ sg) (sf+ dc)]/smp = projection ratio




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FIGURE 6.6 - VALUES OF Cc

Diagram for coefficient Ccfor positive-projecting conduits.




For flexible pipe under most conditions, the product rsdP, is less thanzero (a negative value). Only flexible pipes with very high pipe stiffness

would ever have an rsdP product greater than zero. Therefore, use of arsdP product equal to zero will result in a conservative design approachfor most buried flexible pipe installations. As can be seen on the Cccomputation graph (Figure 6.6), when rsdPequals zero, the coefficient Ccis equal to the ratio of H/Bc.

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183

Replacing the Ccin Marston's embankment load formula with the ratioH/Bcyields:

EQUATION 6.6

Wc= HwBc

This is commonly known as the prism load, and simply stated, it is theweight of the column of soil directly over the pipe for the full height of the

backfill. This is the maximum load that will be imposed by the soil on aflexible pipe in virtually all cases and is a conservative design approach.

Below is a comparison of the Marston earth-load determinationformulas:

(EQUATION 6.1)

Rigid Pipe Load(Trench Condition) Wc= CdwBd2 (lbs/Lft)

(EQUATION 6.2)

Flexible Pipe Load(Trench Condition) Wc = CdwBdBc (lbs/Lft)

(EQUATION 6.5)

Pipe Load(Embankment Condition) Wc = CcwBcBc (lbs/Lft)

(EQUATION 6.6)

Flexible Pipe Load(Prism Load) Wc= HwBc (lbs/Lft)

The prism load may also be expressed in terms of soil pressure as

follows:

EQUATION 6.7

(Soil Pressure) P = wH =Wc

Bc

Where: P = pressure due to soil weight at depth H, lbs/ft2w = unit weight of soil, lbs/ft3


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H = depth at which soil pressure is desired, ftWc = trench load, lbs/LftBc = pipe outside diameter, ft

Calculation of soil pressure on both rigid and flexible pipes of thesame diameter in the same burial conditions demonstrates the differencebetween the load on flexible conduit in trench and embankment conditionsand load on rigid conduit in trench condition.

Example: Find the trench load for a rigid pipe and a flexible pipegiven the following information:

Pipe Outside Diameter (Do

or Bc) 12 inBurial Depth of Cover (H) 12 ftTrench Width (Bd) 3 ftRankine's Ratio (k) 0.33Soil Density (w) 120 lbs/ft3Coefficient of Soil Friction (') 0.5

Rigid Pipe Load (trench condition) Use Equation 6.1

Cd=1 - e-2(0.33)(0.5)(12/3)

2(0.33)(0.5) = 2.221

Wc= 2.221 (120)32= 2,398 lbs/Lft or16.7 lbs/in2

Flexible Pipe Load (trench condition) Use Equation 6.2

Wc= 2.221(120)(3)(1) = 800 lbs/Lft or5.6 lbs/in2

Flexible Pipe Load (assume prism condition) Use Equation 6.6

Wc= 120(12)(1) = 1440 lbs/Lft or10.0 lbs/in2

For all practical purposes, research and actual long-term data confirmthat the prism load provides a conservative, simplified approach for

designing flexible PVC piping systems to accommodate earth load. In atrench, friction forces can reduce the load on the pipe through arching

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action of the soil; however, frost and water action may dissipate theseforces, and in the long term, the load may approach the prism load.

The following tables have been developed for use in determiningMarston earth loads on PVC sewer pipe. The table is dependent on

outside-diameter dimensions and can be used with any flexible pipe withthe same or similar Do. Actual diameters appear parenthetically next tonominal pipe size in the table. If the condition of installation is known to

be a "trench" condition, then Table 6.1 will provide the computed earthload. For unknown conditions or in trenches beyond transition width, themore conservative prism earth-loads are recommended. Prism earth-loadsin lbs/lineal foot are listed in Table 6.2. Prism earth-loads in lbs/in2arelisted in Table 6.3. Tables 6.1, 6.2 and 6.3 utilize the most common rangesfor H (depth of cover, ft) and w (unit weight of soil, lbs/ft

3). The table

limits do not imply application limits.

TABLE 6.1 - EARTH LOADS IN TRENCH CONDITIONS (lbs/Lft)

Wc= CdwBdBc

Depth Trench 4" (Do= 4.215) PIPE 6" (Do= 6.275) PIPE

of Back- Width of Trench (ft)

Cover fill 0.75 1.00 1.25 1.5 1.0 1.5 2.0 2.5

Granular w/o Cohesion 56 66 72 77 98 115 125 132

Sand and Gravel 67 77 84 89 115 132 142 149

3 Sat. Top Soil 71 80 86 91 119 136 145 152

Dry Clay 79 88 94 99 131 147 156 162

Sat. Clay 91 100 106 111 149 165 174 179


Sand and Gravel 72 84 92 99 125 147 160 169

3.5 Sat. Top Soil 76 88 96 102 130 151 164 172

Dry Clay 85 97 105 111 144 165 176 184Sat. Clay 100 111 119 125 166 186 197 205


Sand and Gravel 76 90 100 107 134 160 176 187

4 Sat. Top Soil 81 94 104 111 140 166 181 191Dry Clay 91 105 114 122 156 181 196 205

Sat. Clay 108 121 131 138 181 206 220 229


Sand and Gravel 85 106 122 135 157 200 229 2496 Sat. Top Soil 92 112 128 141 167 210 238 257

Dry Clay 106 128 144 157 191 234 261 280

Sat. Clay 129 152 169 182 226 271 299 317

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TABLE 6.1 - EARTH LOADS IN TRENCH CONDITIONS (lbs/Lft) - Continued



Cover fill 0.75 1.0 1.25 1.5 1.0 1.5 2.0 2.5


Sand and Gravel 89 114 134 152 169 226 267 297

8 Sat. Top Soil 97 122 144 161 182 240 280 309

Dry Clay 114 142 164 182 211 272 312 341

Sat. Clay 141 172 196 215 256 320 362 390


Sand and Soil 91 118 142 163 176 243 294 334

10 Sat. Top Soil 99 128 153 175 190 260 311 350Dry Clay 118 150 177 200 223 298 351 390

Sat. Clay 147 185 215 240 275 357 412 452


Sand and Soil 91 120 147 171 179 254 314 362

12 Sat. Top Soil 100 131 159 184 195 273 335 382

Dry Clay 120 155 186 213 231 317 381 430

Sat. Clay 151 193 228 258 287 384 453 504


Sand and Soil 92 122 150 177 181 263 334 39315 Sat. Top Soil 101 133 164 192 198 286 359 418

Dry Clay 121 159 194 225 236 335 414 477

Sat. Clay 154 200 241 277 298 412 499 566


Sand and Soil 92 122 152 180 182 268 346 413

18 Sat. Top Soil 101 134 166 196 200 292 374 443

Dry Clay 121 161 198 232 239 346 436 511

Sat. Clay 155 204 249 289 303 430 533 614

Granular w/o Cohesion 72 96 120 143 143 213 279 340Sand and Soil 92 122 152 181 182 270 351 423

20 Sat. Top Soil 101 134 167 198 200 295 381 456

Dry Clay 121 161 199 236 240 351 447 528

Sat. Clay 155 205 252 295 305 439 550 640


Sand and Soil 92 122 153 183 182 272 349 439

25 Sat. Top Soil 100 135 168 201 200 299 391 476

Dry Clay 122 162 202 240 241 357 464 559

Sat. Clay 156 207 256 303 308 452 578 687


Sand and Soil 92 122 153 183 182 273 363 447

30 Sat. Top Soil 101 135 168 201 200 300 396 487

Dry Clay 122 162 202 242 241 360 473 577

Sat. Clay 156 207 258 308 309 458 595 717

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Cover fill 1.5 2.0 2.5 3.0 2.0 2.5 3.0 3.5


Sand and Gravel 177 190 199 206 238 249 257 263

3 Sat. Top Soil 182 194 203 209 243 254 261 266

Dry Clay 197 209 216 222 261 271 277 282

Sat. Clay 221 233 240 245 291 300 306 311


Sand and Gravel 196 214 226 234 268 282 292 300

3.5 Sat. Top Soil 203 219 230 238 274 288 297 304Dry Clay 220 236 246 254 295 308 317 324

Sat. Clay 249 264 274 281 330 343 351 357


Sand and Gravel 214 236 250 261 295 313 326 335

4 Sat. Top Soil 222 242 256 265 303 320 332 341

Dry Clay 242 262 275 284 328 344 355 363

Sat. Clay 275 294 307 315 368 384 394 402


Sand and Gravel 268 307 334 354 383 417 442 4616 Sat. Top Soil 281 318 344 363 398 430 454 472

Dry Clay 313 350 375 393 437 469 491 508

Sat. Clay 363 400 424 442 500 530 552 569


Sand and Gravel 303 358 398 428 447 497 535 565

8 Sat. Top Soil 321 375 414 443 469 517 554 583

Dry Clay 363 418 456 485 522 570 606 633

Sat. Clay 429 484 523 551 605 653 688 715


10 Sat. Top Soil 348 417 469 509 521 586 636 676

Dry Clay 399 470 522 562 588 653 702 741

Sat. Clay 477 552 605 645 690 756 806 844


Sand and Soil 340 421 485 536 526 606 670 723

12 Sat. Top Soil 366 448 512 563 560 640 703 754

Dry Clay 424 510 576 627 638 720 783 834

Sat. Clay 514 606 674 726 758 843 908 958


Sand and Soil 352 447 526 591 559 657 739 808

15 Sat. Top Soil 382 480 560 625 600 700 782 849

Dry Clay 449 554 638 705 693 797 881 950

Sat. Clay 552 668 758 828 835 947 1035 1105

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TABLE 6.1 - EARTH LOADS IN TRENCH CONDITIONS (lbs/Lft) Continued



Cover fill 1.5 2.0 2.5 3.0 2.0 2.5 3.0 3.5


18 Sat. Top Soil 392 501 593 672 626 742 840 923Dry Clay 463 584 683 766 730 854 957 1042Sat. Clay 576 713 822 909 891 1027 1137 1226






Sand and Soil 365 484 598 705 606 748 881 100430 Sat. Top Soil 402 531 653 765 663 816 9956 1084

Dry Clay 482 633 772 897 791 965 1122 1261Sat. Clay 613 797 960 1103 996 1200 1379 1535

Depth Trench 12" (Do= 12.500) PIPE 15" (Do= 15.300) PIPEof Back- Width of Trench (ft)

Cover fill 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5

Granular w/o Cohesion 249 263 272 280 305 322 333 342Sand and Gravel 283 297 306 313 347 363 375 383



3.5 Sat. Top Soil 326 342 354 362 399 419 433 443Dry Clay 351 367 377 385 430 449 462 472Sat. Clay 393 408 418 425 482 499 512 521



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Cover fill 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5


30 Sat. Top Soil 790 971 1138 1291 967 1188 1393 1580Sand and Soil 721 890 1049 1195 882 1090 1284 1463

Dry Clay 942 1149 1335 1501 1153 1406 1634 1838Sat. Clay 1186 1429 1642 1827 1451 1749 2010 2237

Depth Trench 18" (Do= 18.701) PIPE 21" (Do= 22.047) PIPEof Back- Width of Trench (ft)

Cover fill 2.5 3.0 3.5 3.0 3.5 4.0

Granular w/o Cohesion 393 407 418 480 493 503

Sand and Gravel 444 458 468 540 552 562

3 Sat. Top Soil 452 464 474 548 559 568

Dry Clay 482 494 503 582 593 601

Sat. Clay 534 546 554 643 653 661

Granular w/o Cohesion 489 512 530 604 624 641Sand and Gravel 557 580 597 684 704 720

4 Sat. Top Soil 569 591 607 697 715 730

Dry Clay 612 632 647 745 763 777

Sat. Clay 683 702 717 828 845 858


Sand and Gravel 743 787 821 928 968 1000

6 Sat. Top Soil 767 809 841 953 991 1021

Dry Clay 835 875 905 1031 1067 1095

Sat. Clay 944 983 1013 1159 1194 1221


Sand and Gravel 885 953 1007 1124 1187 1237

8 Sat. Top Soil 922 987 1038 1163 1223 1271

Dry Clay 1016 1079 1128 1272 1330 1375

Sat. Clay 1164 1226 1274 1446 1502 1546


Sand and Soil 995 1087 1160 1281 1368 1439

10 Sat. Top Soil 1044 1133 1204 1336 1419 1486

Dry Clay 1163 1251 1320 1475 1556 1621

Sat. Clay 1347 1436 1504 1693 1773 1837


Sand and Soil 1079 1194 1288 1408 1518 1609

12 Sat. Top Soil 1140 1252 1343 1476 1584 1672

Dry Clay 1282 1395 1485 1645 1751 1837

Sat. Clay 1501 1617 1707 1906 2013 2098

190


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Depth Trench 18" (Do= 18.701) PIPE 21" (Do = 22.047) PIPE


Cover fill 2.5 3.0 3.5 3.0 3.5 4.0


Sand and Soil 1170 1316 1439 1552 1696 1818

15 Sat. Top Soil 1247 1392 1513 1641 1784 1903

Dry Clay 1420 1570 1691 1851 1994 2112

Sat. Clay 1687 1843 1968 2173 2320 2440


Sand and Soil 1232 1404 1553 1656 1830 1981

18 Sat. Top Soil 1321 1496 1644 1764 1938 2087Dry Clay 1522 1704 1856 2009 2189 2339

Sat. Clay 1830 2025 2183 2387 2574 2729


Sand and Soil 1261 1449 1612 1708 1901 2069

20 Sat. Top Soil 1358 1550 1714 1827 2021 2189

Dry Clay 1574 1777 1948 2094 2296 2467

Sat. Clay 1906 2125 2306 2506 2719 2897


Sand and Soil 1308 1525 1721 1798 2029 223525 Sat. Top Soil 1419 1645 1846 1939 2176 2385

Dry Clay 1665 1911 2124 2252 2505 2724

Sat. Clay 2047 2321 2553 2736 3010 3245


Sand and Soil 1332 1569 1788 1850 2108 2345

30 Sat. Top Soil 1453 1703 1931 2008 2277 2520

Dry Clay 1719 1998 2246 2355 2648 2909

Sat. Clay 2138 2457 2734 2896 3223 3509



Cover fill 3.0 3.5 4.0 3.5 4.0 4.5


Sand and Gravel 607 621 632 700 712 721

3 Sat. Top Soil 616 629 639 709 720 728

Dry Clay 655 667 676 752 762 770

Sat. Clay 724 735 743 828 837 845


Sand and Gravel 769 792 810 893 913 929

4 Sat. Top Soil 784 805 821 907 926 941

Dry Clay 838 858 874 967 985 998

Sat. Clay 932 950 965 1071 1087 1100

191


20/44


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Cover fill 3.0 3.5 4.0 3.5 4.0 4.5


Sand and Soil 2081 2372 2639 2673 2974 3248

30 Sat. Top Soil 2259 2561 2835 2886 3195 3474

Dry Clay 2649 2979 3273 3358 3689 3983

Sat. Clay 3258 3626 3947 4087 4448 4765

Depth Trench 30" (Do= 31.496) PIPE


Cover fill 3.5 4.0 4.5

Granular w/o Cohesion 704 718 729

Sand and Gravel 789 802 813

3 Sat. Top Soil 798 811 821

Dry Clay 847 858 868

Sat. Clay 933 944 952



4 Sat. Top Soil 1022 1043 1060Dry Clay 1090 1109 1125

Sat. Clay 1207 1225 1240



6 Sat. Top Soil 1416 1458 1493

Dry Clay 1525 1565 1597

Sat. Clay 1705 1744 1774


Sand and Gravel 1696 1768 18278 Sat. Top Soil 1748 1816 1871

Dry Clay 1900 1965 2018

Sat. Clay 2145 2208 2259


Sand and Soil 1954 2055 2139

10 Sat. Top Soil 2027 2123 2203

Dry Clay 2223 2316 2392

Sat. Clay 2533 2624 2699


Sand and Soil 2169 2299 2409

12 Sat. Top Soil 2262 2388 2493

Dry Clay 2501 2624 2726

Sat. Clay 2875 2997 3098

193


22/44





Cover fill 3.5 4.0 4.5Granular w/o Cohesion 2025 2188 2329

Sand and Soil 2423 2597 2746

15 Sat. Top Soil 2548 2718 2862

Dry Clay 2849 3018 3160

Sat. Clay 3314 3485 3627


Sand and Soil 2615 2830 3016

18 Sat. Top Soil 2769 2981 3164

Dry Clay 3126 3342 3524

Sat. Clay 3677 3899 4084


Sand and Soil 2716 2956 3166

20 Sat. Top Soil 2887 3127 3334

Dry Clay 3280 3525 3735

Sat. Clay 3884 4139 4354


Sand and Soil 2898 3193 3458

25 Sat. Top Soil 3108 3407 3672

Dry Clay 3578 3891 4165

Sat. Clay 4301 4635 4923


Sand and Soil 3012 3351 3660

30 Sat. Top Soil 3252 3600 3915

Dry Clay 3783 4156 4488

Sat. Clay 4605 5012 5369






3 Sat. Top Soil 1014 1026 1036

Dry Clay 1073 1084 1094

Sat. Clay 1180 1190 1199



4 Sat. Top Soil 1304 1325 1342

Dry Clay 1387 1406 1422

Sat. Clay 1531 1550 1564

194


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6 Sat. Top Soil 1823 1866 1901

Dry Clay 1956 1996 2029

Sat. Clay 2180 2218 2249



8 Sat. Top Soil 2270 2339 2397

Dry Clay 2456 2522 2577

Sat. Clay 2760 2824 2876


Sand and Soil 2569 2674 2762

10 Sat. Top Soil 2654 2754 2837

Dry Clay 2895 2990 3070

Sat. Clay 3281 3374 3450


Sand and Soil 2874 3011 3127

12 Sat. Top Soil 2985 3116 3227

Dry Clay 3280 3408 3515

Sat. Clay 3747 3872 3976


Sand and Soil 3247 3432 3592

15 Sat. Top Soil 3397 3577 3732

Dry Clay 3772 3950 4100

Sat. Clay 4356 4534 4683


Sand and Soil 3537 3771 397418 Sat. Top Soil 3726 3955 4153

Dry Clay 4177 4406 4602

Sat. Clay 4873 5105 5303


Sand and Soil 3695 3958 4189

20 Sat. Top Soil 3908 4168 4394

Dry Clay 4406 4668 4895

Sat. Clay 5173 5443 5673

Granular w/o Cohesion 3258 3554 3823Sand and Soil 3992 4322 4619

25 Sat. Top Soil 4259 4591 4885

Dry Clay 4864 5207 5508

Sat. Clay 5794 6154 6467

195


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Sand and Soil 4188 4575 4927

30 Sat. Top Soil 4500 4894 5249

Dry Clay 5195 5610 5980

Sat. Clay 6265 6711 7104




Granular w/o Cohesion 1027 1040 1051Sand and Gravel 1145 1157 1168

3 Sat. Top Soil 1156 1168 1177

Dry Clay 1222 1233 1241

Sat. Clay 1341 1351 1359



4 Sat. Top Soil 1493 1512 1528

Dry Clay 1585 1603 1617

Sat. Clay 1747 1763 1777



6 Sat. Top Soil 2103 2143 2176

Dry Clay 2250 2287 2318

Sat. Clay 2500 2535 2564



8 Sat. Top Soil 2637 2702 2757

Dry Clay 2843 2904 2956Sat. Clay 3183 3242 3291


Sand and Soil 3014 3113 3198

10 Sat. Top Soil 3104 3198 3278

Dry Clay 3371 3460 3536

Sat. Clay 3802 3889 3962


Sand and Soil 3394 3525 3638


Sat. Clay 4364 4482 4582

196


25/44





Cover fill 4.5 5.0 5.5Granular w/o Cohesion 3282 3455 3607Sand and Soil 3869 4049 4206

15 Sat. Top Soil 4032 4206 4356Dry Clay 4452 4622 4768Sat. Clay 5110 5279 5422







Sat. Clay 6937 7289 7597







3 Sat. Top Soil 1331 1341 1350

Dry Clay 1405 1414 1423

Sat. Clay 1540 1549 1556



4 Sat. Top Soil 1723 1742 1757

Dry Clay 1826 1843 1857

Sat. Clay 2009 2025 2038



6 Sat. Top Soil 2442 2480 2512

Dry Clay 2606 2642 2672

Sat. Clay 2889 2922 2951

197


26/44







8 Sat. Top Soil 3079 3142 3195

Dry Clay 3310 3369 3419

Sat. Clay 3694 3751 3798


Sand and Soil 3548 3644 3728

10 Sat. Top Soil 3644 3735 3814

Dry Clay 3943 4030 4104

Sat. Clay 4432 4515 4586


Sand and Soil 4017 4146 4257

12 Sat. Top Soil 4146 4268 4373

Dry Clay 4514 4631 4732

Sat. Clay 5108 5221 5318


Sand and Soil 4614 4793 4950

15 Sat. Top Soil 4793 4965 5114

Dry Clay 5267 5433 5578

Sat. Clay 6016 6179 6321


Sand and Soil 5105 5334 5537

18 Sat. Top Soil 5334 5556 5752

Dry Clay 5911 6129 6320

Sat. Clay 6811 7029 7219


Sand and Soil 5381 5644 587820 Sat. Top Soil 5644 5900 6127

Dry Clay 6288 6541 6765

Sat. Clay 7287 7542 7765


Sand and Soil 5933 6275 6584

25 Sat. Top Soil 6275 6613 6916

Dry Clay 7075 7416 7720

Sat. Clay 8306 8658 8967


30 Sat. Top Soil 6742 7155 7530

Dry Clay 7681 8107 8490

Sat. Clay 9125 9571 9968

198


27/44





Cover fill 5.50 6.00 6.50 6.50 7.00 7.50


Sand and Gravel 1499 1510 1519 1691 1700 1708

3 Saturated Top Soil 1511 1521 1529 1702 1710 1718

Dry Clay 1593 1602 1610 1792 1800 1806

Saturated Clay 1744 1753 1760 1959 1966 1972


Sand and Gravel 1941 1960 1976 2199 2215 2228


Dry Clay 2076 2092 2105 2344 2357 2368

Saturated Clay 2281 2296 2308 2569 2582 2592


Sand and Gravel 2750 2790 2823 3143 3175 3204


Dry Clay 2976 3009 3038 3382 3410 3434

Saturated Clay 3292 3323 3351 3730 3756 3779


Sand and Gravel 3468 3533 3589 3995 4049 4097

8 Saturated Top Soil 3539 3599 3651 4064 4115 4160Dry Clay 3794 3851 3900 4341 4388 4429

Saturated Clay 4225 4278 4325 4814 4858 4898


Sand and Gravel 4105 4199 4281 4764 4845 4915


Dry Clay 4539 4622 4695 5225 5296 5358

Saturated Clay 5086 5166 5235 5827 5894 5953

Granular w/o Cohesion 4629 4802 4955 5515 5667 5804Sand and Gravel 5399 5575 5731 6379 6534 6672


Dry Clay 6120 6283 6425 7151 7291 7416

Saturated Clay 6960 7120 7258 8079 8215 8335


Sand and Gravel 6008 6237 6441 7169 7372 7554


Dry Clay 6904 7119 7309 8135 8322 8490

Saturated Clay 7918 8131 8318 9258 9442 9605


Sand and Gravel 6358 6621 6857 7632 7868 8081


Dry Clay 7368 7619 7842 8728 8948 9146

Saturated Clay 8495 8746 8967 9980 10198 10392

199


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Cover fill 5.50 6.00 6.50 6.50 7.00 7.50


Sand and Gravel 7068 7415 7730 8604 8922 9212


Dry Clay 8353 8696 9001 10019 10325 10601

Saturated Clay 9752 10100 10409 11586 11893 12169


Sand and Gravel 7594 8019 8408 9358 9755 10120

30 Saturated Top Soil 8059 8481 8865 9868 10258 10615Dry Clay 9131 9562 9951 11076 11468 11824

Saturated Clay 10780 11227 11627 12941 13341 13703

200


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Height of

Cover (ft)

Soil Wt.

(lb/ft3) 4 6 8 10 12 15 18 21 24 27 30 36 4

100 105 157 210 263 313 383 468 551 620 699 787 984 11

3 110 116 173 231 289 344 421 514 606 682 769 866 1083 12

120 126 188 252 315 375 459 561 661 744 839 945 1181 13

130 137 204 273 341 406 497 608 717 806 908 1024 1280 14

100 141 209 280 350 417 510 623 735 827 932 1050 1312 14

4 110 155 230 308 385 458 561 686 808 909 1025 1155 1444 16

120 169 251 336 420 500 612 748 882 992 1118 1260 1575 17

130 183 272 364 455 542 663 810 955 1075 1211 1365 1706 19

100 211 314 420 525 625 765 935 1102 1240 1398 1575 1969 226 110 232 345 462 578 688 842 1029 1213 1364 1537 1732 2165 24

120 253 377 504 630 750 918 1122 1323 1488 1677 1890 2362 26

130 274 408 546 683 813 995 1216 1433 1612 1817 2047 2559 28

100 281 418 560 700 833 1020 1247 1470 1654 1864 2100 2625 29

8 110 309 460 616 770 917 1122 1371 1617 1819 2050 2310 2887 32

120 337 502 672 840 1000 1224 1496 1764 1984 2236 2520 3150 35

130 365 544 728 910 1083 1326 1621 1911 2150 2423 2730 3412 38

100 351 523 700 875 1042 1275 1558 1837 2067 2329 2625 3281 36

10 110 386 575 770 963 1146 1403 1714 2021 2274 2562 2887 3609 40

120 422 628 840 1050 1250 1530 1870 2205 2480 2795 3150 3937 44

130 457 680 910 1138 1354 1658 2026 2388 2687 3028 3412 4265 48

100 422 628 840 1050 1250 1530 1870 2205 2480 2795 3150 3937 44

12 110 464 690 924 1155 1375 1683 2057 2425 2728 3075 3465 4331 48

120 506 753 1008 1260 1500 1836 2244 2646 2976 3354 3780 4724 53

130 548 816 1092 1365 1625 1989 2431 2866 3224 3634 4094 5118 57

NOTE: For OD used in calculations, see end of Table.

TABLE 6.2 - PRISM LOAD (lbs/Lft)

Nominal Pipe Diameter, Inches


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Height of

Cover (ft)

Soil Wt.

(lbs/ft3) 4 6 8 10 12 15 18 21 24 27 30 36 4

100 492 732 980 1225 1458 1785 2182 2572 2894 3261 3675 4593 51

14 110 541 805 1078 1348 1604 1964 2400 2829 3183 3587 4042 5052 56

120 590 879 1176 1470 1750 2142 2618 3087 3472 3913 4409 5512 62

130 639 952 1274 1593 1896 2321 2836 3344 3762 4240 4777 5971 67

100 562 837 1120 1400 1667 2040 2493 2940 3307 3727 4199 5249 59

16 110 618 920 1232 1540 1833 2244 2743 3234 3638 4100 4619 5774 65

120 674 1004 1344 1680 2000 2448 2992 3528 3968 4472 5039 6299 71

130 731 1088 1456 1820 2167 2652 3242 3821 4299 4845 5459 6824 76

100 632 941 1260 1575 1875 2295 2805 3307 3720 4193 4724 5906 6618 110 695 1035 1386 1733 2063 2525 3086 3638 4092 4612 5197 6496 73

120 759 1130 1512 1890 2250 2754 3366 3968 4465 5032 5669 7087 79

130 822 1224 1638 2048 2438 2984 3647 4299 4837 5451 6142 7677 86

100 703 1046 1400 1750 2083 2550 3117 3675 4134 4659 5249 6562 73

20 110 773 1150 1540 1925 2292 2805 3429 4042 4547 5125 5774 7218 81

120 843 1255 1680 2100 2500 3060 3740 4409 4961 5591 6299 7874 88

130 913 1360 1820 2275 2708 3315 4052 4777 5374 6056 6824 8530 96

100 773 1150 1540 1925 2292 2805 3429 4042 4547 5125 5774 7218 81

22 110 850 1265 1694 2118 2521 3086 3771 4446 5002 5637 6352 7940 89

120 927 1381 1848 2310 2750 3366 4114 4850 5457 6150 6929 8661 97

130 1005 1496 2002 2503 2979 3647 4457 5255 5911 6662 7507 9383 105

100 843 1255 1680 2100 2500 3060 3740 4409 4961 5591 6299 7874 88

24 110 927 1381 1848 2310 2750 3366 4114 4850 5457 6150 6929 8661 97

120 1012 1506 2016 2520 3000 3672 4488 5291 5953 6709 7559 9449 106

130 1096 1632 2184 2730 3250 3978 4862 5732 6449 7268 8189 10236 115


TABLE 6.2 (continued) - PRISM LOAD (lbs/Lft)



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Height of

Cover (ft)

Soil Wt.

(lbs/ft3) 4 6 8 10 12 15 18 21 24 27 30 36 4

100 913 1360 1820 2275 2708 3315 4052 4777 5374 6056 6824 8530 96

26 110 1005 1496 2002 2503 2979 3647 4457 5255 5911 6662 7507 9383 105

120 1096 1632 2184 2730 3250 3978 4862 5732 6449 7268 8189 10236 115

130 1187 1767 2366 2958 3521 4310 5267 6210 6986 7873 8871 11089 124

100 984 1464 1960 2450 2917 3570 4364 5144 5787 6522 7349 9186 103

28 110 1082 1611 2156 2695 3208 3927 4800 5659 6366 7175 8084 10105 113

120 1180 1757 2352 2940 3500 4284 5236 6173 6945 7827 8819 11024 124

130 1279 1903 2548 3185 3792 4641 5673 6688 7524 8479 9554 11942 134

100 1054 1569 2100 2625 3125 3825 4675 5512 6201 6988 7874 9843 11030 110 1159 1726 2310 2888 3438 4208 5143 6063 6821 7687 8661 10827 122

120 1265 1883 2520 3150 3750 4590 5610 6614 7441 8386 9449 11811 133

130 1370 2039 2730 3413 4063 4973 6078 7165 8061 9085 10236 12795 144

100 1124 1673 2240 2800 3333 4080 4987 5879 6614 7454 8399 10499 118

32 110 1236 1841 2464 3080 3667 4488 5486 6467 7276 8200 9239 11549 130

120 1349 2008 2688 3360 4000 4896 5984 7055 7937 8945 10079 12598 142

130 1461 2175 2912 3640 4333 5304 6483 7643 8598 9690 10919 13648 153

100 1194 1778 2380 2975 3542 4335 5299 6247 7028 7920 8924 11155 125

34 110 1314 1956 2618 3273 3896 4769 5828 6871 7730 8712 9816 12270 138

120 1433 2134 2856 3570 4250 5202 6358 7496 8433 9504 10709 13386 150

130 1553 2311 3094 3868 4604 5636 6888 8121 9136 10296 11601 14501 163

100 1265 1883 2520 3150 3750 4590 5610 6614 7441 8386 9449 11811 133

36 110 1391 2071 2772 3465 4125 5049 6171 7276 8185 9224 10394 12992 146

120 1517 2259 3024 3780 4500 5508 6732 7937 8929 10063 11339 14173 159

130 1644 2447 3276 4095 4875 5967 7293 8598 9673 10902 12283 15354 173





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Height of

Cover (ft)

Soil Wt.

(lbs/ft3) 4 6 8 10 12 15 18 21 24 27 30 36 4

100 1335 1987 2660 3325 3958 4845 5922 6982 7854 8852 9974 12467 140

38 110 1468 2186 2926 3658 4354 5330 6514 7680 8640 9737 10971 13714 154

120 1602 2385 3192 3990 4750 5814 7106 8378 9425 10622 11968 14961 168

130 1735 2583 3458 4323 5146 6299 7699 9076 10211 11507 12966 16207 182

100 1405 2092 2800 3500 4167 5100 6234 7349 8268 9318 10499 13123 147

40 110 1546 2301 3080 3850 4583 5610 6857 8084 9094 10249 11549 14436 162

120 1686 2510 3360 4200 5000 6120 7480 8819 9921 11181 12598 15748 177

130 1827 2719 3640 4550 5417 6630 8104 9554 10748 12113 13648 17060 192

100 1475 2196 2940 3675 4375 5355 6545 7716 8681 9784 11024 13780 15542 110 1623 2416 3234 4043 4813 5891 7200 8488 9549 10762 12126 15157 170

120 1770 2636 3528 4410 5250 6426 7854 9260 10417 11740 13228 16535 186

130 1918 2855 3822 4778 5688 6962 8509 10031 11285 12719 14331 17913 201

100 1546 2301 3080 3850 4583 5610 6857 8084 9094 10249 11549 14436 162

44 110 1700 2531 3388 4235 5042 6171 7543 8892 10004 11274 12703 15879 178

120 1855 2761 3696 4620 5500 6732 8228 9701 10913 12299 13858 17323 195

130 2009 2991 4004 5005 5958 7293 8914 10509 11823 13324 15013 18766 211

100 1616 2405 3220 4025 4792 5865 7169 8451 9508 10715 12073 15092 170

46 110 1777 2646 3542 4428 5271 6452 7886 9296 10459 11787 13281 16601 187

120 1939 2887 3864 4830 5750 7038 8602 10142 11409 12858 14488 18110 204

130 2100 3127 4186 5233 6229 7625 9319 10987 12360 13930 15696 19619 221

100 1686 2510 3360 4200 5000 6120 7480 8819 9921 11181 12598 15748 177

48 110 1855 2761 3696 4620 5500 6732 8228 9701 10913 12299 13858 17323 195

120 2023 3012 4032 5040 6000 7344 8976 10583 11905 13417 15118 18898 213

130 2192 3263 4368 5460 6500 7956 9725 11464 12898 14536 16378 20472 230





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Height of

Cover (ft)

Soil Wt.

(lbs/ft3) 4 6 8 10 12 15 18 21 24 27 30 36 4

100 1756 2615 3500 4375 5208 6375 7792 9186 10335 11647 13123 16404 184

50 110 1932 2876 3850 4813 5729 7013 8571 10105 11368 12812 14436 18045 203

120 2108 3138 4200 5250 6250 7650 9351 11024 12402 13977 15748 19685 221

130 2283 3399 4550 5688 6771 8288 10130 11942 13435 15141 17060 21325 240

The following values were used for OD:

4" = 4.215 27" = 27.953

6" = 6.275 30" = 31.496

8" = 8.400 36" = 39.370

10" = 10.500 39" = 41.385

12" = 12.500 42" = 44.375

15" = 15.300 45" = 47.370

18" = 18.701 48" = 50.570

21" = 22.047 54" = 56.960

24" = 24.803 60" = 63.360




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TABLE 6.3 - PRISM LOAD SOIL PRESSURE (lbs/in2)

P = wH

Height of Soil Unit Weight (lbs/ft3)

Cover (ft) 100 110 120 125 130

1 0.69 0.76 0.83 0.87 0.902 1.39 1.53 1.67 1.74 1.813 2.08 2.29 2.50 2.60 2.714 2.78 3.06 3.33 3.47 3.615 3.47 3.82 4.17 4.34 4.51

6 4.17 4.58 5.00 5.21 5.42

7 4.86 5.35 5.83 6.08 6.328 5.56 6.11 6.67 6.94 7.229 6.25 6.88 7.50 7.81 8.13

10 6.94 7.64 8.33 8.68 9.03

11 7.64 8.40 9.17 9.55 9.9312 8.33 9.17 10.00 10.42 10.8313 9.03 9.93 10.83 11.28 11.7414 9.72 10.69 11.67 12.15 12.6415 10.42 11.46 12.50 13.02 13.54

16 11.11 12.22 13.33 13.89 14.4417 11.81 12.99 14.17 14.76 15.3518 12.50 13.75 15.00 15.63 16.2519 13.19 14.51 15.83 16.49 17.1520 13.89 15.28 16.67 17.36 18.06

21 14.58 16.04 17.50 18.23 18.9622 15.28 16.81 18.33 19.10 19.8623 15.97 17.57 19.17 19.97 20.7624 16.67 18.33 20.00 20.83 21.6725 17.36 19.10 20.83 21.70 22.57

26 18.06 19.86 21.67 22.57 23.4727 18.75 20.63 22.50 23.44 24.3828 19.44 21.39 23.33 24.31 25.2829 20.14 22.15 24.17 25.17 26.1830 20.83 22.92 25.00 26.04 27.08

31 21.53 23.68 25.83 26.91 27.9932 22.22 24.44 26.67 27.78 28.8933 22.92 25.21 27.50 28.65 29.79

34 23.61 25.97 28.33 29.51 30.6935 24.31 26.74 29.17 30.38 31.60

206


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207

TABLE 6.3 - Continued

Height of Soil Unit Weight (lbs/ft3)Cover (ft) 100 110 120 125 130

36 25.00 27.50 30.00 31.25 32.5037 25.69 28.26 30.83 32.12 33.4038 26.39 29.03 31.67 32.99 34.3139 27.08 29.79 32.50 33.85 35.2140 27.78 30.56 33.33 34.72 36.11

41 28.47 31.32 34.17 35.59 37.0142 29.17 32.08 35.00 36.46 37.9243 29.86 32.85 35.83 37.33 38.8244 30.56 33.61 36.67 38.19 39.7245 31.25 34.38 37.50 39.06 40.63

46 31.94 35.14 38.33 39.93 41.5347 32.64 35.90 39.17 40.80 42.4348 33.33 36.67 40.00 41.67 43.3349 34.03 37.43 40.83 42.53 44.2450 34.72 38.19 41.67 43.40 45.14

Live Loads: Underground, PVC pipe may also be subjected to live

loads from different sources such as highways and railways. Live loadsshould always be considered when designing for shallow burial depths.However, under conditions of deep burial, the effect of live loads diminishand can be ignored.

Several methods exist for calculating these live loads. The designapproach presented here is based on the Boussinesq formula for a pointload at the surface of a semi-infinite elastic soil:

EQUATION 6.8

WL=12

)I(PC fL

Where: WL = live-load on pipe, lbs/Lin

CL = live-load coefficient per foot of effective length

P = wheel load, lbsIf = impact factor, dimensionless (If = 1.35 for 1


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Tables 6.4 and 6.5 give the live load coefficient CLfor a single wheel

load and for two passing trucks, respectively. The design approach taken

in these tables conservatively represents a wheel load as a point load.

Analytical expressions for CLare given below the tables in terms of the

pipe diameter or radius and the height of cover.

TABLE 6.4

LIVE-LOAD COEFFICIENTS FOR SINGLE-WHEEL LOAD

Height of Cover Over Pipe H -- ft

2 4 6 8 10 12 14 16 18

Pipe

Diameter

in. Live-Load Coefficient CL

8 0.055 0.018 0.008 0.005 0.003 0.002 0.002 0.001 0.001

10 0.068 0.022 0.010 0.006 0.004 0.003 0.002 0.002 0.001

12 0.080 0.026 0.013 0.007 0.005 0.003 0.002 0.002 0.001

14 0.092 0.031 0.015 0.008 0.005 0.004 0.003 0.002 0.002

16 0.104 0.035 0.017 0.010 0.006 0.004 0.003 0.002 0.002

18 0.114 0.039 0.019 0.011 0.007 0.005 0.004 0.003 0.002

20 0.125 0.043 0.021 0.012 0.008 0.005 0.004 0.003 0.002

24 0.143 0.051 0.025 0.014 0.009 0.007 0.005 0.004 0.003

30 0.165 0.062 0.030 0.018 0.012 0.008 0.006 0.005 0.004

36 0.183 0.072 0.036 0.021 0.014 0.010 0.007 0.006 0.004

42 0.196 0.082 0.041 0.024 0.016 0.011 0.008 0.006 0.005

48 0.206 0.090 0.046 0.028 0.018 0.013 0.009 0.007 0.006

54 0.214 0.097 0.051 0.031 0.020 0.014 0.011 0.008 0.00760 0.219 0.104 0.055 0.034 0.022 0.016 0.012 0.009 0.007

NOTE 1: An effective length of 3.0 ft of pipe is assumed.

NOTE 2:

CL=1

3-

2

3ARCSIN

HR2+ H2+ 1.52

(R2+ H2) (H2+ 1.52) +

RH

1

R2+ H2+

1

H2+ 1.52

R2+ H2+ 1.52

WHERE: H = earth cover, ft; R = pipe radius, ft; ARCSIN must be in radians.

208


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TABLE 6.5

LIVE-LOAD COEFFICIENTS FOR TWO PASSING TRUCKS

Height of Cover Over Pipe H -- ft

2 4 6 8 10 12 14 16 18

Pipe

Diameter

in. Live-Load Coefficient CL8 0.0523 0.0296 0.0169 0.0112 0.0081 0.0062 0.0049 0.0039 0.0032

10 0.0654 0.0369 0.0211 0.0140 0.0101 0.0077 0.0061 0.0049 0.004112 0.0785 0.0443 0.0253 0.0168 0.0122 0.0093 0.0073 0.0059 0.0049

14 0.0916 0.0517 0.0295 0.0196 0.0142 0.0108 0.0085 0.0069 0.005716 0.1047 0.0591 0.0338 0.0224 0.0162 0.0124 0.0098 0.0079 0.006518 0.1177 0.0665 0.0380 0.0252 0.0182 0.0139 0.0110 0.0089 0.007320 0.1308 0.0739 0.0422 0.0279 0.0203 0.0155 0.0122 0.0099 0.008124 0.1570 0.0887 0.0506 0.0335 0.0243 0.0186 0.0147 0.0118 0.009730 0.1962 0.1108 0.0633 0.0419 0.0304 0.0232 0.0183 0.0148 0.012236 0.2355 0.1330 0.0760 0.0503 0.0365 0.0279 0.0220 0.0178 0.014642 0.2747 0.1552 0.0886 0.0587 0.0426 0.0325 0.0256 0.0207 0.017148 0.3140 0.1773 0.1013 0.0671 0.0486 0.0371 0.0293 0.0237 0.019554 0.3532 0.1995 0.1139 0.0755 0.0547 0.0418 0.0330 0.0266 0.021960 0.3925 0.2217 0.1266 0.0838 0.0608 0.0464 0.0366 0.0296 0.0244

NOTE 1: An effective length of 3.0 ft of pipe is assumed.

NOTE 2: Coefficients are for 6-ft axle widths, 3.0 ft between passing wheels.

NOTE 3:

CL=3D

H2

cos tan

-11.5

H

5+ cos tan

-17.5

H

5

WHERE: D = pipe diameter, ft; H = earth cover, ft.

209

As mentioned previously, the influence of live loads on theperformance of PVC pipe is only significant in shallow depths. This isgraphically demonstrated by Figures 6.7 and 6.8, which show the totalload on a pipe exposed to live loads and earth loads for highway and forrailway traffic. As can be seen in both of the graphs, as the depth of coverincreases, the influence of the live load diminishes rapidly, illustrating thatthere is a depth of cover at which the total load is a minimum. This is

approximately 5 feet for an H20 truck and 13 feet for an E80 RailwayLoad. The influence of live loads on PVC pipe as projected for highway,railroad and airport installations is shown in Table 6.6. The values shownin Table 6.6 account for the impact and loading factors and can beconverted to live load per unit length (as used in Equation 6.8 - WL) bymultiplying these values by the outside diameter of the pipe.


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With an AASHTO H-20 live load, a 20 ton truckload is simulated inwhich 80% (32,000 lbs) is distributed to the rear axle, and evenly dividedinto two 16,000-lbs wheel loads. The remaining 20% (8,000 lbs) isdivided over the front axle into two 4,000-lbs wheel loads. The distance

between the front and rear axles is assumed to be 14 feet, with two dual-tire wheel loads on each axle. One is centered over the point in question,and the other located 6 feet away. With impact, the AASHTO LRFDBridge Design Specification distribution of the tire foot print is taken as1.5 feet by 1.67 feet. Similarly, the AREMA

2 Cooper E-80 live load

simulates the effect of four 80,000-lbs axles, located 5 feet apart. Eachaxle load is assumed to be distributed over a 2-ft by 8-ft area.

TABLE 6.6LIVE LOADS ON PIPE

Height Live Load Transferred to Pipe, lbs/in2 Height Live Load Transferred to Pipe, lbs/in2

Of Of

Cover Highway Railway Airport Cover Highway Railway Airport

(ft) H201 E802 3 (ft) H201 E802 3

1 12.50 14 * 4.17 3.06

2 5.56 26.39 13.14 16 * 3.47 2.29

3 4.17 23.61 12.28 18 * 2.78 1.91

4 2.78 18.40 11.27 20 * 2.08 1.53

5 1.74 16.67 10.09 22 * 1.91 1.14

6 1.39 15.63 8.79 24 * 1.74 1.05

7 1.22 12.15 7.85 26 * 1.39 *

8 0.69 11.11 6.93 28 * 1.04 *

10 * 7.64 6.09 30 * 0.69 *

12 * 5.56 4.76 35 * * *

40 * * *

1 Simulates 20 ton truck traffic + impact (Source: ASTM A 796)

2 Simulates 80,000 lbs/ft railway load + impact (Source: ASTM A 796)

3 180,000 lbs dual tandem gear assembly. 26 inch spacing between tires and 66 inch center-to-center spacing

between fore and aft tires under a rigid pavement 12 inches thick + impact.

* Negligible live load influence.

210


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211

FIGURE 6.7 - H20 HIGHWAY LOADING

Vertical Soil Pressure (lbs/ft2)

SOURCE: AMERICAN IRON AND STEEL INSTITUTE, WASHINGTON, D.C.

FIGURE 6.8 - COOPER E-80 LIVE LOADING

Vertical Soil Pressure (lbs/ft2)

SOURCE: AMERICAN IRON AND STEEL INSTITUTE, WASHINGTON, D.C.


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AASHTO Design MethodThe American Association of State Highway and Transportation

Officials (AASHTO) currently has published two design documents,which provide specifications for estimation of the effects of live loads Section 3, in the LRFD Bridge Specifications Manual, is entitled Loadsand Load Factors and from the Standard Specifications for HighwayBridges, Division 1, Section 3 is entitled, "Loads." A summary of themethod of the former reference, being the more recent of the two, iscaptured below.

The contact area of a dual-tire is assumed to be a singular rectanglewith a width (W) of 20 inches and a length (L) of 10 inches. Theequivalent area of loading distribution, realized at pipe depth, can becalculated as follows:

EQUATION 6.9

A = (W + H)(L + H)

where: A = area of load distribution under fill, ft2

W = width of dual-tire, ftL = length of dual-tire, ft

= 1.15 for granular soils=1.0 for all other soil typesH = height of cover, ft

Similar to the 60o rule often found in soil mechanics texts, the equation

above applies for burial depths exceeding 2 feet, but not exceeding 8 feet.The distributive effect of the fill can be ignored at cover depths less than2 feet, and live loads can be neglected where depth of fill is more than 8feet. The enlarged contact area, defined in Equation 6.9, is used to

compute the distributed load experienced at the pipe surface, by simplydividing the wheel load (P) by the area (A).

Design Software External Load Design for Flexible ConduitsThe Uni-Bell PVC Pipe Association offers design software that can

calculate the loads described in this chapter, as well as apply the loadingsto estimate the long-term deflection discussed in Chapter VII, Design ofBuried PVC Pipe.

The program can account for either of the earth-loading scenarios

described earlier in this chapter. The Marston earth load (defined byEquation 6.2) and the prism earth-load options (defined by Equation 6.6)are both available to the user. Through interactive screens, such as that

212


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shown in Figure 6.9, the design specifics are obtained (backfill material,height of cover, compaction effort, etc.), in which the user is prompted toinput data or select from a listing of typical values. Furthermore, units forinput and output are user-defined, allowing for either metric or Englishunits.

FIGURE 6.9 SAMPLE INPUT SCREEN

With regard to live loads, several options are available. The softwarehas the capability to simulate standard highway (H20), railway (E80), andairport live loads, as well as provide for custom live load situations. Thesingle-wheel, two-trucks-passing, and custom live-loads (in which theloads and the pattern are user-defined) are all computed, using a methodsimilar to the Boussinesq method presented earlier in the text. Thesoftware determines the live loads at user-defined depths using Holls and

Newmarks integration of the Boussinesq formula.5 Furthermore, the

software can be used to calculate long-term deflection for flexible pipe

using principles explained in the next chapter, Design of Buried PVCPipe.

213


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FIGURE 6.10 LIVE-LOAD MENU SCREEN

214


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CHAPTER VI

BIBLIOGRAPHY

1. Airport Runway Depth of Cover Tables, National Corrugated Steel Pipe Association,Shiller Park, IL.

2. American Railway Engineering Association Manual for Railway Engineering,Landover, MD (2000).

3. Barnard, R. E., "Design and Deflection Control of Buried Steel Pipe Supporting Earthand Live Loads," American Society for Testing and Materials, Philadelphia, PA, Proc.57 (1957).

4. Cohn, Morris M., By the Magic of Chemistry: Pipe Lines for Progress, CertainTeed

Products Corp., Valley Forge, PA (1975).

5. Gravity Sanitary Sewer Design and Construction, "Manuals & Reports on EngineeringPractice No. 60," American Society of Civil Engineers and "Manual of Practice FD-5,"Water Pollution Control Federation (1982).

6. Handbook of Steel Drainage and Highway Construction Products, American Iron andSteel Institute, Donnelley and Sons, Co., New York, NY (1971).

7. Howard, A. K., "Laboratory Load Tests on Buried Flexible Pipe," Journal AWWA,Denver, CO (Oct. 1972).

8. LRFD Bridge Design Specifications, American Association of State Highway andTransportation Officials, Washington, DC (1999)

9. Manual of Recommended Practice, American Railway Engineering Assoc., AREASpec 1-4-28, Chicago, IL.

10. Marston, Anson and A. O. Anderson, "The Theory of Loads on Pipes in Ditches andTests of Cement and Clay Drain Tile and Sewer Pipe," Bul. 31, Iowa EngineeringExperiment Station, Ames, IA (1913).

11. Molin, J., "Principles of Calculation for Underground Plastic Pipes - Load, Deflection,Strain," ISO/TC 138/WG6 (Sweden - 3) 47 (Jan. 1971).

12. Moser, A. P., R. K. Watkins and O. K. Shupe, "Design and Performance of PVC PipesSubjected to External Soil Pressure," Buried Structures Laboratory, Utah StateUniversity, Logan, UT (June 1976).

13. Pipeline Design for Water and Wastewater, American Society of Civil Engineers,New York, NY (1975).

14. Spangler, M. G., "The Structural Design of Flexible Pipe Culverts," Bulletin 153, IowaEngineering Experiment Station, Ames, IA (1941).

15. Spangler, M. G. and R. L. Handy, Soil Engineering, Intext Educational Publ., NewYork, NY (1973).

215


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16. Standard Practice for Structural Design of Corrugated Steel Pipe, Pipe Arches, andArches for Storm and Sanitary and Other Buried Applications, ASTM A796,American Society for Testing and Materials, West Conshohocken, PA (1993).

Documents

Handbook of PVC pipe Chap6.pdf