Simplified Finite-Element Model for Site Response Analysis of Unsaturated Soil Profiles

Abstract

A numerically stable and computationally efficient finite-element model for analyzing the dynamic response of unsaturated soil profiles in terms of total stresses is presented in this paper. The highly nonlinear, fully coupled governing differential equations are simplified by neglecting the relative accelerations and velocities of the pore fluids, and the simplified formulation is improved by incorporating an external viscous damping formulation for unsaturated soil. The surface spectral accelerations computed using the proposed model are qualitatively compared with that of DEEPSOIL and PLAXIS following a comparison of surface spectral accelerations computed using the underdamped and the damped simplified formulations. A detailed parametric study of the effect of viscous damping parameters and both elastoplastic and elastic constitutive models is also presented. A simplified soil–pile interaction study is presented to show the effect of soil–pile interaction on the computed responses. Analysis reveals that the proposed model is applicable to the seismic site response analysis of unsaturated soil profiles.