Experimental Observation of Quasi-Static Avalanche Process of a Granular Pile

An experimental setup is developed to control a slow avalanche of a granular pile. The dynamical behavior of the quasi-static avalanche process is investigated systematically by directly tracking the displacement of particles in the avalanche. It is observed that the particles in the pile slide are in a layered structure, i.e., the pile can be divided into several parallel layers according to the displacement of the particles, at each layer the particles move with the same speed and in the same direction. The inclined angle of the layer is about 47°, which is also the direction of the movement of particles. We also find that there exists a critical layer below which the particles do not slide and above which the particles slide a lot, and the amount of its slippage is proportional to its distance from the critical layer.