Influence of the number of layers on the equilibrium of a granular packing

This paper reports an experimental study on avalanches in a granular material contained in a confined geometry. The granular packing is made of monosize grass beads initially poured into a box that is slowly inclined until an avalanche takes place at a critical angle theta(M) (maximum angle of stability). The avalanche involves a decrease of the surface slope until a second critical angle theta(r) (angle of repose) is reached. Both angles and the mass displaced out of the box during the avalanche are studied as a function of the height of the granular packing. In order to avoid cohesion effects, experiments are carried out in a humidity controlled environment. For small packings, up to approximately ten layers, the stability of the system is significantly affected by the rough surface at the bottom. In contrast, for thicker systems, critical angles do not depend on the height.