Stability of Granular Packings Jammed under Gravity: Avalanches and Unjamming

Granular avalanches indicate the sudden destabilization of a jammed state due to a perturbation. We propose that the perturbation needed depends on the entire force network of the jammed configuration. Some networks are stable, while others are fragile, leading to the unpredictability of avalanches. To test this claim, we simulated an ensemble of jammed states in a hopper using LAMMPS. These simulations were motivated by experiments with vibrated hoppers where the unjamming times followed power-law distributions\footnote{Lozano, C., Zuriguel, I., Garcimartín, A. (2015). Stability of clogging arches in a silo submitted to vertical vibrations. Physical Review E, 91(6), 062203.}. We compare the force networks for these simulated states with respect to their overall stability. The states are classified by how long they remain stable when subject to continuous vibrations. We characterize the force networks through both their real space geometry and representations in the associated force-tile space \footnote{Sarkar, S., Bi, D., Zhang, J., Behringer, R. P., Chakraborty, B. (2013). Origin of rigidity in dry granular solids. Physical review letters, 111(6), 068301.}, extending this tool to jammed states with body forces.