(as given by [Equation (8)]), below it, and regard this line as the free surface of non-coherent earth of the same specific weight and angle of repose as the given earth; compute the thrust against the wall for such earth, devoid of cohesion, by methods pertaining to such earth; the thrust thus found is assumed to be approximately the true thrust on the wall for the original coherent earth. It is proper to state that Résal rejects the sliding-wedge theory for non-coherent earth, and uses a method of his own, which involves elaborate tables given in his book. The wedge theory is admittedly imperfect, mainly because the surface of rupture is a curve, but we have seen that it agrees with experiments on model walls or retaining boards, when properly interpreted, and it will be used, as before, in computing the earth thrusts,
, below, for earths devoid of cohesion. The graphical method has already been indicated.[Footnote 28] ]
In [Table 6] comparative results are given for various cases, including those already examined. Each retaining board was supposed to be 10 ft. high, the earth to have a natural slope of 1 on 1½, and to weigh 100 lb. per cu. ft.
TABLE 6.
| Case. | . | . | , in pounds per square foot. | , in pounds. | , in pounds. | |
|---|---|---|---|---|---|---|
| 1. | –⅓ | 0 | 100 | 1 440 | 880 | |
| 2. | 0 | 0 | 100 | 0 | 560 | 560 |
| 3. | 0 | 0 | 100 | 510 | 510 | |
| 4. | 0 | ½ | 100 | 660 | 750 | |
| 5. | 0 | ⅔ | 100 | 880 | 1 630 | |
| 6. | +⅓ | 0 | 50 | 18°26′ | 240 | 490 |
It is seen, by comparing the values of
and