A three-phase two-point MPM for large deformation analysis of unsaturated soils

This paper presents a three-phase two-point formulation of the material point method (MPM) for modeling unsaturated soils involving large deformation. In the formulation, solid phase material is represented by one layer of material points while liquid and gas phases are modeled by another layer of material points. The formulation is a u-U formulation. It eliminates advection term between solid and liquid phases and is capable to address large relative deformations between the two phases. The advection term between liquid and gas phases are assumed to be small and not considered. The proposed formulation is validated with numerical models for small and finite deformation problems. The capacity of the method for study of geomechanics problems is demonstrated with simulation of seismic-induced ground liquefaction with an unsaturated embankment. The method is able to simulate large ground deformation due to soil liquefaction and generation of excess pore pressure, and captures pore pressure dissipation through the rapid water drainage through high-permeable soils.