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LOAD DISTRIBUTION <br />The surface load is assumed to be uniformly spread <br />on any horizontal subsoil plane. The spread load area <br />is developed by increasing the length and width of the <br />wheel contact area for a load configuration as illustrated <br />in Figure 3 for a dual wheel; in Figure 4 for dual wheels <br />of two trucks in passing mode; and in Figure 5 for two <br />dual wheels of two Alternate Load configurations in <br />passing mode. On a horizontal soil plane, the <br />dimensional increases to the wheel contact area are <br />based on height of earth cover over the top of the pipe <br />as presented in Table 2 for two types of soil. <br />Soil Type Dimensional Increase Factor <br />LRFD select granular 1.15H <br />LRFD any other soil 1.001-1 <br />As indicated by Figures 3, 4 and 5, the spread load <br />areas from adjacent wheels will overlap as the height of <br />earth cover over the top of the pipe increases. At shallow <br />depths, the maximum pressure will be developed by an <br />Table 3 r Critical Wheel Loads. Spread Dimensions of the Pipe for Select Granular Soil Fill <br />H, ft P, Ibs Spread a, ft Spread b, ft Figure <br />H<2.03 16,000 a+1.15H b+1.15H 3 <br />2.035H<2.76 32.000 a+4+1.15H b+1.15H 4 <br />2.765H 50,000 a+4+1.15H b+4+1.15H 5 <br />H, ft P, Ibs Spread a, H Spread b, ft Figure <br />H < 2.33 16,000 a + 1.00H b + 1.00H 3 <br />2.33 5 H < 3.17 32,000 , + 4 + 1.00H t + 1.00H 4 <br />3.17 < H 50,000 a + 4 + 1.00H b + 4 + 1.00H 5 <br />)ad Area <br />Sad Load Area <br />=© <br />Deslgn Data 1 <br />