The mobility of high-altitude and long-runout landslides in cirque terrain: Insights from movement in grain silos

Complex terrain is one of the main factors affecting the mobility of high-altitude and long-runout landslides. The gravity flow in silos provides information about dynamic landslide processes in cirque terrain. Based on simulations of numerical flume tests, in this study, we analyzed the influences of the funnel shape, lateral erosion, ice-grain mixing and melting, and inter-grain friction on the motility of high-altitude and long-runout landslides. The results show that (i) the kinematic process of the sliding mass can be divided into bulk flow, funnel flow, pipeline flow, and diffusion flow in cirque terrain. In the funnel flow movement stage, due to gradual narrowing of the terrain, lateral extrusion of the grains can form a dynamic arch effect, increasing the radial stress and lateral erosion intensity. (ii) Due to the formation of a dynamic arch, the inter-grain friction coefficient is proportional to the lateral pressure. The top angle of the wedge in funnel terrain is inversely proportional to the lateral pressure and the peak flow rate. The larger the top angle of the wedge is, the more significant the dead zone is, and the more scattered the grains in the accumulation body are. (iii) When lateral erosion and ice mixing and melting occur, they can cause a decrease in the lateral pressure and can enhance the break of the dynamic arch due to widening of the channels and decrease in the inter-grains friction, thus amplifying the mobility of the long runout landslide. Based on the above research results, the influences of the grain silo terrain should be fully investigated, and the impact of the lateral erosion effect should be fully considered.