EPJ Web of Conferences 249, 03023 (2021)
https://doi.org/10.1051/epjconf/202124903023

Robust experimental study of avalanche precursory events based on reproducible cycles of grain packing destabilizations

¹ Univ. Rennes, CNRS, IPR [(Institut de Physique de Rennes)]-UMR 6251, F-35000 Rennes, France
² Univ. Rennes, CNRS, Géosciences Rennes-UMR 6118, F-35000 Rennes, France

^* e-mail: luc.oger@univ-rennes1.fr
^** e-mail: renaud.delannay@univ-rennes1.fr
^*** e-mail: yves.legonidec@univ-rennes1.fr

Published online: 7 June 2021

Abstract

Quasi-periodic collective displacements of grains at the free surface of a tilted grain packing constitute precursors of granular avalanches. Laboratory experiments are commonly performed by slowly tilting the packing from 0^° to the maximal stability angle θ_A. In these conditions, the number of precursors is too small to assess reproducible and robust statistical analyses of the precursor activity. To go beyond this limitation, we have developed a specific experimental protocol consisting of tilting the packing with successive oscillation cycles. We use a high-resolution optical camera and process the images of the packing free surface to identify precursory events during many consecutive cycles of a single packing. We observe the same behavior for all half-cycles, forth and back: appearance of the first precursors after the same variation of inclination, exponential evolution of the weak surface activity for the first precursors and linear growth of stronger surface activity for the following ones. The experimental protocol provides both reproducible precursor measurements based on large sample statistical inferences and a quasi-stationary state after one full-cycle. This approach is very promising for highlighting the effects of external parameters, including humidity and packing geometry.