Numerical simulation of rock avalanches: Influence of a local dissipative contact model on the collective behavior of granular flows

Rock avalanches are a significant concern in developing mountain areas. Thus a reliable prediction of depositional areas from avalanches is needed. In order to improve the numerical modeling of such events and to provide information concerning the physical phenomena underlying this type of granular flow, a discrete element model, which takes into account frictional and collisional dissipation at grain scale together with angular-shaped elements, is used to investigate the collective behavior of granular masses propagating down a slope. The discrete element model (DEM) parameters are defined from drop tests involving the collision of an individual particle with a flat surface. The validity of the numerical model is estimated by comparison with the results of a laboratory experiment involving a dry granular flow on an inclined plane. The numerical model improves the understanding of rock avalanches by providing both valuable information about the way energy is dissipated either at the base or within the propagating granular mass and relevant information about the kinematics of the flow and the shape of the deposit. The influence of contact-law parameters is investigated using a sensitivity study. It is shown that the flow is strongly influenced by basal friction, while inter-particle friction and collisional dissipation phenomena intervene mostly in areas of flow perturbation (such as transition zones between two slopes). A macroscopic roughness of the slope surface induces an increased disorder in the particle motion which increases both frictional and collisional dissipation within the granular mass. Using a planar slope and increasing the frictional parameter can reproduce the apparent influence of this roughness.