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

This paper reports an experimental study on avalanches in a granular materi al contained in a confined geometry. The granular packing is made of monosi ze 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 stabi lity). The avalanche involves a decrease of the surface slope until a secon d 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 functi on of the height of the granular packing. In order to avoid cohesion effect s, experiments are carried out in a humidity controlled environment. For sm all packings, up to approximately ten layers, the stability of the system i s significantly affected by the rough surface at the bottom. In contrast, f or thicker systems, critical angles do not depend on the height.