X-ray observation of micro-failures in granular piles approaching an avalanche

TL;DR

This study uses X-ray imaging to investigate micro-failures in granular piles, revealing that small-scale rearrangements occur before avalanches, but are not reliable predictors of the macroscopic failure.

Contribution

It demonstrates that pre-avalanche micro-failures are influenced by factors beyond surface inclination, challenging their use as predictive indicators.

Findings

Micro-failures occur well before avalanches.

Energy from micro-failures increases approaching the threshold.

Pre-avalanche dynamics are affected by preparation methods.

Abstract

An X-ray imaging technique is used to probe the stability of 3-dimensional granular packs in a slowly rotating drum. Well before the surface reaches the avalanche angle, we observe intermittent plastic events associated with collective rearrangements of the grains located in the vicinity of the free surface. The energy released by these discrete events grows as the system approaches the avalanche threshold. By testing various preparation methods, we show that the pre-avalanche dynamics is not solely controlled by the difference between the free surface inclination and the avalanche angle. As a consequence, the measure of the pre-avalanche dynamics is unlikely to serve as a tool for predicting macroscopic avalanches.