Numerical Simulation of Flowslide Considering Transient Seepage Flow and Progressive State Transition

Flowslides are rapid gravity-driven flows of sediment-water mixture that typically occur following slope failures in soils, tailings, and municipal solid wastes, but the progressive state transition during the evolution of flowslides is still unclear. In this study, a practical method which couples elastic-plastic constitutive equations and Bingham fluid equations by a progressive transition criterion is developed within the framework of smoothed particle hydrodynamics (SPH). The elastic-plastic constitutive equations describe the mechanical behavior at a solid-like state and that at a fluid-like state is described by Bingham fluid equations. The progressive state transition can be described by a transition factor, which is governed by the degree of saturation and shear strain rate according to the experimental data. Transient seepage flow is also introduced into the SPH framework to describe the effect of water content on the evolution of flowslides. An infiltration boundary method based on ghost particles and smooth function symmetry is proposed to precisely model the rainfall infiltration process. The experimental data of ring shear tests and flume test are adopted to successfully verify the performance of the method, which can reasonably simulate the complicated solid-fluid transition processes. The method is further applied to simulate a full scale catastrophic flowslide at Payatas Landfill. As the overlying pressure on the slip surface increases, the material reaches the yield state. During the postfailure stage, the material at the slip surface first changes into an elastic-plastic state, and then partially transforms into a fluid-like state, leading to the large deformation of the failure material. The proposed method can contribute to a better understanding of the evolution of flowslides and is an applicable tool for hazard assessment.