Two-phase dynamic MPM formulation for unsaturated soil

In this paper, a computational framework based on the Material Point Method is developed to study the coupled seepage-deformation process in unsaturated soils. Governing equations are derived from the balance equations of solid and liquid phases accounting for partial saturation effects, and the soil is discretized with a single set of material points which move according to the displacement of the solid phase. The implementation of different types of boundary conditions, such as transient hydraulic head, seepage face, and infiltration/evaporation, is discussed in detail. The method is applied to simulate levee collapse due to rapid drawdown and rainfall. The methodology proposed in this paper is a promising tool to advance the current practice, which customarily evaluates slope safety only by means of small deformation analyses based on FEM or LEM, while here a large deformation approach is presented.