Statistics of intermittent granular flow from confined tabletop experiments

It is often said that “granular matter is ubiquitous”. Many natural components and human products look and behave like grains: stones, debris, soils, on the one hand; food, pharmaceuticals, building materials, etc., on the other. However, the physics involved is still poorly understood due to its inherent difficulties. In fact, granular materials are an example of frictional, dissipative, nonlinear, out-of-equilibrium systems. One consequence is that they exhibit, under various circumstances, large and irregular fluctuations, finite size effects, and poor reproducibility (as everyone knows from trying to slowly pour sugar or coffee powder). This article summarizes some experimental results on the response of horizontal grain beds subjected to low rate shear stress. In this case, the response is often intermittent and irregular, the so-called stick–slip regime, and can only be described statistically. Small-scale experiments are the best way to collect the necessary large amount of data and, despite the difference in scale, can provide the basis for a better understanding of larger scale phenomena such as avalanches, landslides and earthquakes.