Enhanced mobility of granular avalanches with fractal particle size distributions: Insights from discrete element analyses

Abstract

Granular avalanches are a form of hazardous landslide that rapidly travels long distances, with the grain-size distribution of their fragmented deposits developing fractal characteristics. In this study, we perform three-dimensional discrete element simulations of granular avalanches in a rotating drum to evaluate the effect of fractal particle size distributions on the flow mobility. The mobility of granular avalanches, measured as the inverse of the surface inclination angle, increases with the fractal dimension following a bilinear relationship with an abrupt slope change at a critical fractal dimension of 3.25, which delimits a roller-developing regime from a roller-active regime. The flow enters the roller-active regime when the fractal dimension is greater than 3.25, during which a complete basal layer of small particles separating the drum base and the flowing particles above is formed. Micro-mechanical evidence suggests that small particles at the drum base act as rotating bearings to reduce the effective basal friction, attenuate energy dissipation, and thereby enhance flow mobility.