Slip Avalanches 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 the distributions of avalanche sizes and time between events. The pile is composed of roughly 20 000 steel beads, 3 mm in diameter, and driven by adding one bead at a time to the pile apex. We record the changes in pile mass over tens of thousands of bead drops to characterize the distribution of avalanche sizes. The experimental results match well with a mean-field model of slip avalanches [Dahmen et al., Nat Phys 7, 554 (2011)], as shown recently with particular emphasis on the effect of cohesion [Lehman et al., Gran Matt 24:35 (2022)]. The effects of cohesion on the statistics and the time series properties of the experimental avalanches correspond closely to the effect of dynamic weakening on the slip avalanches in this simple model used both for earthquakes and the plastic deformation of brittle solids. In addition to the avalanche size data, we also record the activity on the pile directly with a camera located above the pile. Here we extend the comparison between the experiment and the model to characteristics of individual avalanches, such as avalanche duration and extent on the pile, by using the particle image velocimetry to analyze the avalanche motion.