| Soils exhibit pronounced nonlinear behavior under cyclic loading conditions. For saturated granular soil deposits, the analysis of ground movement due to earthquake shaking is more complicated since it is often followed by the buildup of excess pore water pressure. In this thesis, a finite-element (FE) model is proposed for effective stress analysis of perfectly saturated soils to seismic shaking. The formulation is based on theory of mixtures in which the soil is modeled as a two-phase medium composed of interacting solid and fluid phases. The finite element model is based on a general u-w-p formulation, where u is the solid displacement, w is the relative displacement of the fluid phase to that of the solid phase, and p is the pore pressure. The soil skeleton is modeled as a hyperelastic-plastic material with ellipsoidal bounding and loading surfaces. The FE model is implemented into a time-domain FORTRAN code SPECTRA-UWP with "stick" finite elements to accommodate vertically propagating seismic waves. SPECTRA-UWP is used to analyze the M6.2 earthquake of July 30, 1986 and the M7.0 earthquake of November 15, 1986 at a Large-Scale Seismic Test site in Lotung, Taiwan. Predicted responses in the form of ground surface accelerations and excess pore pressures are shown to replicate the recorded responses quite well. For the ground motions considered the coefficient of permeability and drainage boundaries have a direct impact on the predicted excess pore pressures but have little effect on the acceleration-time responses. |
