Studying Avalanches on a Conical Bead Pile

Adam Deeley

2020

The height in which beads are dropped was investigated as a tuning parameter for a conical beadpile oscillating through critical states. The change is driven by dropping beads one at a time on to the apex of the pile. By comparing the probability distribution function of avalanche sizes to previ- ous data, we are able to verify the use of a new set of beads used for the experiment.

Also explored was the effect of drop height and threshold value on the inter-event time probability density. By varying the threshold we can closer approximate the shifting point where small avalanche regime behavior ceases. The point is determined by how well the data are fit by a Weibull distribution versus a Brownian passage-time distribution, typically used to fit data from small to large thresholds, respectively.

This experiment determined that with a drop height of 2 cm and no added cohesion, small avalanche behavior ceased at thresholds greater than or equal to 350 beads. For a drop height of 4 cm, small avalanche behavior ceased at thresholds greater than or equal to 375 beads. For a drop height of 6 cm, there was no threshold which displayed a shift from small to large avalanche behavior. The shift most certainly occurs somewhere, however the data sets do not have enough data points to accurately determine the peak of the probability density function, as there are a very small number of avalanches greater than 300 beads at this drop height.