Dynamics of irregular particles in the passive layer under the slumping regime

Abstract Previous study of our group showed that the compaction of sand particles is observed before while dilatancy occurs during avalanches in the active layer (es. Chen et al., Sci Sin Phys Mech Astron 49(6), 2019). In current works, we investigated the dynamic of irregular particles in the passive layer by speckle visibility spectroscopy, discovering two types of cycle rearrangements. We determine that one kind of rearrangement corresponds to the compaction of the pre-avalanche granular bed, and the other rearrangement is triggered by granular avalanches occurring in the active layer. The rearrangement caused by avalanche has a greater dissipation energy by comparing the other rearrangement. We describe simple mechanisms which account for the non-uniformity of dissipated energy. We further found that the propagation speeds of the rearrangements in the passive layer are an order of magnitude faster than that in the active layer and the propagation directions for both rearrangements are opposite to each other.