Earthquake Stability of Slopes of Cohesionless Soils

Evaluation of the effects of ground accelerations on the stability of slopes of cohesionless materials involves the determination of the yield acceleration, i. e., the acceleration at which slippage will begin to occur and the magnitude of the deformations developed. For accelerations of short duration it is shown that there is a marked difference between the yield acceleration and the acceleration inducing noticeable movement. Experimental evidence is presented to show that for dense cohesionless soils there is a small shear strength developed at zero confining pressure, termed the shear strength intercept, which can have a profound effect on the yield accelerations of small embankments. It is pointed out that the uniformity of surface conditions of a slope is also extremely important in determining the yield acceleration for any given case. Analyses for determining the yield acceleration and the position of the sliding surface are presented and the results are shown in graphical form. The computed values are shown to be in good agreement with experimental data. The effects of acceleration direction and the initial factor of safety of the slope on the yield acceleration are also examined.