TABLE 16. Weight of Pipe-Trench Fill
Fill lb/ft^3 kg/m^3
Dry sand 100 1601
Damp sand 115 1841
Wet sand 120 1921
Damp clay 120 1921
Saturated clay 130 2081
Saturated topsoil 115 1841
Sand and damp topsoil 100 1601Enter Table 15 at the depth-to-width ratio of 2.18. Since this particular value is not
tabulated, use the next higher value, 2.5. Opposite this, read k = 1.70 for a sand filling.
Enter Table 16 at damp sand, and read the weight as 115 lb/ft^3 (1842.1 kg/m^3 ). With
these data the pipe load relation can be solved.
Substituting in L = kWw^2 , we get L = 1.70(115)(5.5)^2 = 5920 lb/ft (86.4 N/mm). Study
of the properties of clay pipe (Table 17) shows that 36-in (914-mm) extra-strength clay
pipe has a minimum average crushing strength of 6000 Ib (26.7 kN) by the three,-edge-
bearing method.
- Apply the loading safety factor
ASTM recommends a factor of safety of 1.5 for clay sewers. To apply this factor of safe-
ty, divide it into the tabulated three-edge-bearing strength found in step 3. Or, 6000/1.5 =
4000 Ib(17.8 kN).
5. Compute the pipe load-to-strength ratio
Use the strength found in step 4. Or pipe load-to-strength ratio (also called the load fac-
tor) = 5920/4000 = 1.48.
TABLE 17. Clay Pipe Strength
Minimum average strength,
Ib/lin ft (N/mm)
Pipe size,
in (mm) Three-edge-bearing Sand-bearing
4(102) 1000(14.6) 1500(21.9)
6(152) 1100(16.1) 1650(24.1)
8(203) 1300(18.9) 1950(28.5)
10(254) 1400(20.4) 2100(30.7)
12(305) 1500(21.9) 2250(32.9)
15 (381) 1750 (25.6) 2625 (38.3)
18(457) 2000(29.2) 3000(43.8)
21(533) 2200(32.1) 3300(48.2)
24 (610) 2400 (35.0) 3600 (52.6)
27(686) 2750(40.2) 4125(60.2)
30(762) 3200(46.7) 4800(70.1)
33 (838) 3500 (51.1) 5250(76.7)
36(914) 3900(56.9) 5850(85.4)