Impact of Particle Morphology, Preparation Method, and Confinement on the Angle of Repose for Granular Materials

Understanding and predicting avalanches, mudslides, and other similar granular flows has many applications in geophysics, civil engineering, and mining. The angle of repose is an important parameter characterizing particle flow in granular piles. We investigate how the angle of repose depends the particle's aspect ratio, preparation method, and confinement. For piles made of prolate particles of aspect ratios ranging from 2.5 to 6 flowing down from a channel, the angle of repose decreases with increasing aspect ratio. By contrast, numerical studies report an opposite trend, although for particles within a smaller and narrower range of aspect ratios then the ones we tested. Interestingly, when the pile is formed by rotating the container, the angle of repose increases with aspect ratio, suggesting that pre-existing entanglement between longer particles helps sustain steeper slopes. We also observed that pile confinement has a relatively smaller impact on the angle of repose, with greater confinement making the angle of repose generally steeper regardless of aspect ratio.