Mechanism of bed scour erosion in narrow and steep debris-flow channels based on SPH–DEM–FEM coupling

Debris flows are a powerful and devastating form of geological hazards. Notable deep and lateral erosion of the channel bed occurs during debris-flow transport. Narrow and steep debris-flow channels cause more severe bed scour erosion. Moreover, the impact erosion caused by the transition from a rigid to an erodible bed owing to debris flows is highly destructive. Clarifying the mechanism of scour erosion is important for research on the erosion rate and estimation of the sediment volume transported by debris flows. Therefore, in this paper, we conduct a flume test of debris flows propagating over an erodible bed. Moreover, we use numerical simulation to reconstruct the flume test. The simulation is validated based on the parameters obtained from the flume test. Based on the calibrated model, we reveal the erosion process between the debris flows and channel materials. The simulation is based on a coupled approach involving smoothed particle hydrodynamics (SPH), discrete element method (DEM), and finite element method (FEM). Based on both the simulation and test results, an erosion resistance factor (ERF) is proposed to quantify the scour erosion resistance of bed particles. Utilizing the definitions of erosion rate, we explore the relationship between ERF and erosion rate. The results demonstrate that ERF can effectively describe the erosion process. A method of calculating the maximum erosion depth is derived using ERF. The error between calculated results and experimental results of the maximum erosion depth is <5 %.