3D DEM investigation on the morphology and structure of landslide dams formed by dry granular flows

Large-scale landslide dams triggered by earthquakes or rainfall can cause disasters due to inundation upstream and outburst floods downstream after dam failure. Landslide dams formed by rock/debris avalanches are loose in structure and have a lack of stability; thus they are more susceptible to breaking. The morphological and structural features of landslide dams directly depend on the formation process, and greatly affect the dam stability as well as the dam failure modes. This study presents the transportation and deposition characteristics of dry granular flows with grains of mixed sizes during the formation of landslide dams via 3D discrete element method (DEM) simulations, mainly taking into consideration of the influence of the sliding area length, angle and roughness. The results show reverse segregation during grain transportation and deposition processes. The position of the particles forming the initial deposited layers was also reversed. It was found that when the sliding area angle was larger, the crest surface frontal angle and deposit width increased with the increment of the sliding area length. For lower sliding area angles, the deposit width and crest surface frontal angle showed little change. The increase of sliding length and base friction coefficient as well as the decrease of the sliding area angle will enhance the size segregation. As the slope angle increases, the dominant direction of the force drains shifts significantly and the sliding length mainly influences the magnitude of the normal contact force in the other directions. These considerations can contribute to a better understanding of the landslide dam morphology and structure after their formation.