Discrete element investigation of the mobility of granular mass flows

The gravitational flows of granular materials are omnipresent in industrial processes such as handling and transportation of material and in natural events such as landslides, rock and snow avalanches; however, their mobilities remain elusive due to the arbitrary slope geometry and the sliding volume. By means of three-dimensional discrete element simulations, this paper investigates the flow mobility characterized by its energy evolution, run-out distance, and movement of the center of mass of granular materials collapse on an inclined-upstream region, then plunge and deposit on a horizontal-downstream region. A specific case of numerical simulation is first compared with a theoretical prediction published previously to validate the capability of this numerical approach for simulating the mobility of granular flows. Based on this theoretical validation, a series of numerical experiments is generated by varying a broad range of values of the inclination angle of the inclined-upstream surface and the volume of granular blocks. The results show that the kinetic energy increases significantly with increasing the inclination angle but slightly increases with the volume of granular materials changing along the inclined direction. In which, the rate of reaching the peak values of the vertical and horizontal kinetic energies on the upstream and downstream regions, respectively, increases linearly with increasing the inclination angle. More interestingly, the flow mobility enhances with increasing the sliding volume, represented via the increase of the run-out distance and the decrease of the apparent friction coefficient which is defined as a ratio of the total drop and horizontal movement of the center of mass. Remarkably, the run-out distance of the flows can be nicely scaled by the maximum kinetic energy in the whole process and in horizontal region. These findings robustly declare the origins of the run-out distance from the spreading stage of granular materials in the downstream area and strongly provide evidence for describing the mobility of granular flows on the complex surface.