Dynamics of rearrangements during inclination of granular packings: the avalanche precursor regime
Résumé
The dynamics of inclined 3D granular packings driven towards their stability limits is studied experimentally through the dynamics of rearrangements of grains at their surfaces. Two regimes are identified in that way: a regime of limited and independent rearrangements of grains at small angles and a regime of extended events, called 'precursors of avalanches', at large angles. Both regimes are characterized. The transition between the two regimes is attributed to the emergence of slidings smaller than one grain diameter at the surface of the packing with a stick-slip dynamics which reflects the emergence of long-range correlations at the approach of the avalanche. The observed superficial events are shown to depend strongly on the microscopic details of the interaction between grains. In addition to the study of precursors, we discuss the consequences of this macroscopic correlation length on the packing stability. We show in particular that the avalanche angle θa depends not only on the width of the packing but also on its length.
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