Fully Coupled Finite Element Analysis for Consolidation of Unsaturated Soils Due to Hydraulic and Mechanical Loads

A constitutive model of unsaturated soils, referred as the σ′-S model (Zhou et al. 2012a, b), is implemented into ?nite elements to conduct fully coupled consolidation analyses for unsaturated soils subjected to various hydraulic and mechanical loads. The general form of the constitutive equations is derived for the net stress update, where the suction (s) is treated as a strain variable whereas the degree of saturation (S_r) is treated as a stress variable, and the hydraulic hysteresis and fully coupled hydro-mechanical interaction are considered. An explicit integration scheme is adopted to integrate the stress-strain-pore pressure-degree of saturation relationships (σ-ϵ-u_w-S_r) of the constitutive equations. The finite element implementation is then validated against Terzaghi's analytical consolidation solution for the saturated condition. Several one-dimensional consolidation and infiltration scenarios for different soils (hypothesis sand, silt, and clay) due to various mechanical and hydraulic loads are analysed by using the developed finite element codes, including a slow drying-wetting circle, and a fast loading with a pore pressure dissipation process after slow drying.