A Fully Coupled Numerical Framework for Predicting Dynamic Behavior in Unsaturated Soils and Its Application to Embankment Seismic Analysis

Abstract

A soil–water–air fully coupled numerical framework is proposed to predict the deformation and hydraulic behavior of soils under different saturation states in response to dynamic loading. The proposed framework is developed based on the mixture theory of porous media and the governing equations are discretized with the finite-element method. The soil behavior is modeled by a sophisticated constitutive model. The hysteresis characteristic and the mutual dependence between volume change and the degree of saturation in the soil–water characteristic curve (SWCC) are considered. A consistent description for both unsaturated and saturated soils is achieved by taking the effective stress and the degree of saturation as the two independent variables, with only one set of unified mechanical/hydraulic parameters. The numerical framework is first validated at the element level against undrained and unvented strain-controlled cyclic triaxial test results of unsaturated Toyoura sand. The reliability of the proposed framework in addressing boundary value problems is further validated by the simulation of a dynamic centrifuge model test. The numerical framework is further applied to the dynamic stability analysis of unsaturated embankments with different initial water contents. The results show that initially unsaturated embankments with relatively high water content are susceptible to liquefaction during seismic loading. There is a significant correlation between the liquefaction and the deformation-induced soil saturation. Deformation-induced saturation initially occurs at the toe of the embankment and then gradually extends to the areas near the lateral surfaces of the embankment, which triggers the development of shear bands.