Numerical Modeling on Fluid-Solid Coupled Erosion in Sandy Gravel Soils Containing a Suspended Cut-Off Wall

A cut-off wall is the simplest and most effective preventive measure to mitigate the internal erosion of a dike foundation. However, flow directions around a cut-off wall vary and dike foundations are composed of various soil particles. Thus, to investigate the effects of flow direction and soil composition on internal erosion in a cut-off wall structure, we used a coupled distinct element method with the Darcy fluid model. We discovered that the hydraulic gradient is the main factor affecting internal erosion with larger hydraulic gradients producing faster increases in eroded mass. Moreover, the erosion mechanism along the cut-off wall was related to the flow direction and the fine particle content. Downstream of the cut-off wall, the upward flow made the soil matrix loosen gradually, which assisted soil particle erosion. Upstream of the cut-off wall, soil with higher fine particle content was compressed gradually under the action of the downward flow; however, the downward flow assisted the migration of soil particles with lower fine particle content.