Precursors to avalanches in a granular monolayer

We investigate the stability of a granular monolayer composed of spherical grains on an inclined plate. When the tilt angle α increases, some reorganizations are observed throughout the pile. The packing fraction ρ of the packing evolves by successive jumps. Those discontinuous events precede the collapse of the pile at a critical angle αc. The occurrence of precursors before avalanches is modeled by stop-and-go motions of blocks due to the competition between sliding friction and the Janssen effect [J. Durand, Sands, Powders, and Grains: An Introduction to the Physics of Granular Materials (Springer-Verlag, New York, 2000)].