Effect of spontaneous rearrangements in the disorder of packing of discs

The motion of discs in a granular 2D packing slowly tilted till the system loses its stability is studied by image analysis. As in the 3D case (packing of spheres), before the avalanche takes place, the system undergoes several rearrangements of different magnitudes which do not imply lose of mass. Small rearrangements and displacements of large clusters of discs are observed. Velocity fields of large rearrangements are analyzed and it is concluded that the main effect of the rearrangements is to lead the system to a more disordered state.