Avalanche Occurrence on a Conical Bead Pile With Cohesion

A conical bead pile subject to slow driving is used as a model critical system to experimentally investigate variations in avalanche size and time between events. The pile is composed of roughly 20 000 steel spheres, 3 mm in diameter, atop a circular base. We add one bead at a time to the apex of the pile; avalanches are measured through changes in pile mass. We investigate the dynamic response of the pile by recording avalanches off the pile over the course of tens of thousands of bead drops. At low cohesion, the statistical properties of the avalanches, including probability of particular avalanche sizes, are well-characterized by universal power laws and scaling functions. As cohesion increases, we observe a deviation from the power law behavior. At both high and low cohesion, the experimental results match well with a mean-field model of slip avalanches [Dahmen et al., Nat Phys 7, 554 (2011)], as we have shown in detail in our recent work in Granular Matter [Lehman et al., Gran Matt 24:35 (2022)]. We report here some improvements for the experimental apparatus and discuss new techniques to analyze the time between avalanche events.