Effect of Degradation on Seismic Response of Israeli Continental Slope

Abstract

Seismic site response analyses are often carried out using constitutive models for soil behavior under cyclic loading that incorporate Masing rules. In such analyses the effect of cyclic degradation of stiffness and strength on the seismic response of horizontal, soft clay strata is often ignored. In a recent publication, the authors have proposed a normalized form of the shear stress-strain relationship for undrained, cyclic simple shear of soft clay. Cyclic degradation is accounted for through a single fatigue parameter—the mean effective stress, utilized in normalization of stresses and strains. Cyclic degradation of the small strain shear modulus is neglected, i.e. the stiffness degrades only due to strength degradation. This normalized model has been combined with an effective stress model for simple shear loading and boundary conditions, developed within the framework of bounding surface kinematic and isotropic hardening plasticity, to provide an overall model that may be used in site response analysis. In the present paper, this model is utilized in one-dimensional propagation analysis to compare the expected response in a soft clay profile (comprising the Israeli continental slope) to that that would be predicted without accounting for cyclic degradation. Neglect of cyclic degradation is shown to be nonconservative, resulting in underestimation of velocities and accelerations developed in the profile.