Experimental investigation on failure processes and characteristics of landslide dams with different inflow conditions.

Landslide dams are naturally formed dams with loose structures and poor stability. Whether and how landslide dams break after formation is directly affected by the upstream inflow conditions. In this study, different erosion patterns of landslide dam were achieved by controlling the water level through inflow conditions. Failure processes and characteristics of landslide dams with different erosion patterns were investigated by a series of physical model tests. The tested results showed that the failure process of landslide dam undergoing coupled erosion with seepage and overtopping included piping, slope erosion, settlement, breach evolution, large-scale scouring and formation of armor layer. With the increase in seepage duration before overtopping, the slope scouring and internal erosion were more serious. Headward erosion in coupled erosion occurred earlier and had a faster maximum erosion rate than that of rapid overtopping. When a landslide dam has been subjected to serious piping before overtopping, the peak discharge would increase, the emerging time of the flood peak would be early and the breaching duration would be short compared with that of rapid overtopping and failure triggered by seepage, respectively. The coupled erosion resulted in the smallest volume ratio of residual dam, the largest volume ratio of downstream alluvium and the longest transport distance. Failure processes and characteristic of landslide dams were influenced by seepage erosion that would alter the internal stress conditions and cause migration of fine particles to result in soil deformation. The results indicate that the coupled erosion is more harmful and is not conducive to risk assessment and timely rescue.