Modified two-phase dilatancy SPH model for saturated sand column collapse simulations

The high mobility of landslides generates a serious risk of death and property damage. In this study, we develop a two-phase smoothed particle hydrodynamics (SPH) model based on mixture theory to investigate high mobility landslide mechanisms by simulating the process of saturated sand column collapse for different solid volume fractions and permeabilities. The dilatancy coefficient of volume fraction dependence and the Drucker-Prager criterion are introduced into an elastic-perfectly plastic model to describe the solid phase mechanic behavior, and the fluid phase is described as a slightly compressible Newtonian fluid. We present the deposition profile shape and apparent slope evolution trends of collapse examples for different initial solid volumes and permeability changes. We then analyze the effective stress, pore pressure, and velocity during the collapse process of extremely low permeability sand columns to explain the mechanism behind collapse evolution trends. We conclude that shear contraction behavior improves the mobility of the solid-fluid mixture by increasing the pore pressure and decreasing the effective stress, and vice versa. During the shear contraction process of column collapse, the lower permeability, slower seepage rate of the fluid phase, and lower pore pressure diffusion rate result in stronger mobility, but the larger drag force coefficient retards sand column collapse. Numerical simulation results show that the proposed model corrects some limitations of existing three-dimensional SPH models and can be applied to research the motion mechanism of solid-fluid mixtures such as landslides and debris flows.