Effects of progressive strength degradation on seismic-induced displacements of rock slopes

Seismic performance of slopes is typically assessed by evaluating the permanent displacements as a function of some earthquake response representative parameters. This paper presents the main results of a numerical study devoted to the evaluation of the influence of the progressive material strength reduction (from peak to ultimate values) induced by shear displacements on the seismic performance of jointed rock slopes. The parametric study refers to the simple one–dimensional problem of a rock slope characterized by the presence, at some fixed depth, of one planar joint. A simple modification of the Newmark rigid block model has been adopted in order to simulate the reduction of shear strength; different problem geometries (joint angle and depth) were considered in evaluating the distribution of permanent displacements induced by a selection of accelerometric records. Results seems to indicate that semiempirical relationships developed with reference to the original Newmark model (with constant shear strength) may be considered valid also in the case of gradually reducing shear strength, if the final value of yield acceleration is properly estimated. With increasing initial joint roughness only minor differences in the distribution of permanent displacements as obtained from constant or reducing shear strength rigid block models were found.