Dynamic column collapse of dry granular materials with multi-scale shape characteristics

Understanding the fundamental principles governing granular flow dynamics has been a longstanding problem. The complexity is heightened when diverse particle shapes come into play, which thus necessitates a quantitative assessment of the impact of particle shape and especially, the interplay among multi-scale shape characteristics. In this study, we numerically study the combined effects of the particle’s overall form and surface asperity in dry granular columns, a simplified granular flow model, using spherical harmonics and the level-set discrete element method. Our results reveal that flow mobility for a given column aspect ratio decreases linearly with an adopted shape index known as the rotational resistance angle. This motivates us to propose a simple runout model incorporating shape effects for predicting flow mobility. Additionally, we analyze the energy evolution process and demonstrate that both the maximum kinetic energy and the final accumulated energy dissipation scale linearly with the shape index. Furthermore, column flow mobility is found to be correlated well with the front kinetic energy. Finally, we compare the static deposit angle from column collapse tests with the critical friction angle from triaxial compression tests, finding that they are approximately equal under short column conditions, which correspond to the quasi-static collapse regime. This provides potential alternative protocols to quickly measure the internal friction angle of dry granular materials.