Influence of Cyclic Undrained Shear Strength Degradation on the Seismic Performance of Natural Slopes

Abstract

AbstractThe consequences of several large earthquakes occurred worldwide, reveal that the seismic stability conditions and the post-seismic serviceability of natural slopes are largely affected by the cyclic behaviour of soils. In fact, failures of natural slopes and large permanent displacements may be triggered by the weakening effects due to cyclic shear strength degradation, which may arise simultaneously with inertial effects. In this paper, effect of the cyclic behaviour of soils on the slope seismic response is accounted for in a displacement-based analysis using a simplified degradation model for the soil undrained shear strength. To assess the seismic performance of the slope, a modified Newmark-type analysis is proposed in which a time-dependent value of the slope yield acceleration coefficient kh,c is assumed. kh,c is expressed as a function of the number of equivalent loading cycles of the input motion, a degradation parameter T and a degradation ratio R, the latter quantifying the reduction of kh,c with respect to its initial value. The results of a parametric analysis were used to derive empirical predictive models for a safe estimate of the influence of cyclic undrained shear strength degradation on the seismic-induced permanent displacements.KeywordsSlope stabilityUndrained shear strength degradationPermanent displacements