=102. External Loads on Buried Pipe.=—Prof. Anston Marston and H. C. Anderson published[68] the results of a series of experiments on the loads on buried pipes which are of extreme value in the design of sewer pipe. The load on the pipe is given by the empirical expression _W_ = _CwB_^2, in which _w_ is the weight of the backfilling material in pounds per cubic foot, _B_ is the width of the trench in feet at the elevation of the end of a radius making an angle of 45 degrees upwards with the horizontal diameter of the pipe as illustrated in Fig. 80, and _C_ is a coefficient dependent on the character of the backfill and the ratio of the width to the depth of the trench. Values of _C_ are given in Table 42. The weights of various classes of backfilling are given in Table 43. TABLE 42 APPROXIMATE SAFE WORKING VALUES OF _C_ IN THE EXPRESSION _W_ = _CwB_^2 From Bulletin No. 31 of the Engineering Experiment Station, Iowa State College of Agriculture. ──────────────┬──────────────────────────────────────────────────────── Ratio of Depth│ Approximate Values of _C_ to Width │ ──────────────┼──────────────┬─────────────┬─────────────┬───────────── │Damp Top Soil │Saturated Top│ Damp Yellow │ Saturated │ and Dry and │ Soil │ Clay │ Yellow Clay │ Wet Sand │ │ │ ──────────────┼──────────────┼─────────────┼─────────────┼───────────── 0.5 │ 0.46 │ 0.47 │ 0.47 │ 0.48 1.0 │ 0.35 │ 0.86 │ 0.88 │ 0.90 1.6 │ 1.16 │ 1.21 │ 1.25 │ 1.27 3.0 │ 1.47 │ 1.51 │ 1.56 │ 1.62 2.6 │ 1.70 │ 1.77 │ 1.83 │ 1.91 3.0 │ 1.90 │ 1.99 │ 2.08 │ 2.19 3.6 │ 2.08 │ 2.18 │ 2.28 │ 2.43 4.0 │ 2.22 │ 2.35 │ 2.47 │ 2.65 4.6 │ 2.34 │ 2.49 │ 2.63 │ 2.85 6.0 │ 2.45 │ 2.61 │ 2.78 │ 3.02 6.5 │ 2.54 │ 2.72 │ 2.90 │ 3.18 6.0 │ 2.61 │ 2.81 │ 3.01 │ 3.32 6.6 │ 2.68 │ 2.89 │ 3.11 │ 3.44 7.0 │ 2.73 │ 2.95 │ 3.19 │ 3.55 7.5 │ 2.78 │ 3.01 │ 3.27 │ 3.66 8.0 │ 2.82 │ 3.06 │ 3.33 │ 3.74 8.5 │ 2.85 │ 3.10 │ 3.39 │ 3.82 9.0 │ 2.88 │ 3.14 │ 3.44 │ 3.89 9.5 │ 2.90 │ 3.18 │ 3.48 │ 3.96 10.0 │ 2.92 │ 3.20 │ 3.52 │ 4.01 11.0 │ 2.95 │ 3.25 │ 3.58 │ 4.11