Simulation of backward erosion piping based on coupled material point-characteristic finite element method

The backward erosion piping is a common form of seepage failure in embankments during flood seasons, and it mostly occurs in the dual-structure foundations with unprotected outlet downstream. Due to the high hydraulic gradient of the soil seepage at the water outlet, the soil near the solid-liquid interface is easy to be eroded away. Once there is an impervious clay layer on the upper layer of the eroded soil, a piping channel will be formed to continuously develop to the upstream side, and eventually lead to the instability and failure of the embankment. Based on the coupled material point - characteristic finite element method, a novel modeling approach for the backward erosion piping is developed by employing the local hydraulic gradient as the triggering criterion of piping. The novel approach divides the particles within the solution domain into three types, and deletes the particles that meet the triggering conditions of piping to represent the granular taken away by erosion. Since the fluid phase is described by the generalized Navier-Stokes equation, the proposed approach can simultaneously calculate the seepage of pore water and the free flow of piping channel. Finally, the small-scale erosion experiments are provided to perform the applicability of the proposed approach.