Monolithically-coupled finite element analysis using implicit integration scheme for apartially saturated porous medium

This paper presents a comparison between a semi-implicit time integration linear finite element implementation and fully-implicit nonlinear Newton-Raphson finite element implementation of a biphasic small strain mixture formulation of an elastic partially saturated porous medium. The pore air phase pressure p_a is assumed atmospheric; i.e., p_a = 0 as reference pressure, although the formulation and implementation are general to handle an increase in pore air pressure as a result of loading, if needed. The solid skeleton phase is assumed linear isotropic elastic and partially saturated consolidation in the presence of surface infiltration and traction is simulated. The verification of the implementation against an analytical solution for partially saturated pore water flow (no deformation) and comparison between the two implementations is presented, and the importance of the porosity-dependent nature of the partially saturated permeability is assessed as a comparison with a commercial code for the partially saturated flow with deformation. As a result, the response of partially saturated permeability subjected to the porosity influences on the saturation of a soil, and the different behaviors of the partially saturated soil between staggered and monolithic coupled codes, is worthy of attention because of the difference of matric suction regarding shear strength of a deformable soil.