Acoustic Emissions in Granular Structures under Gravitational Destabilization
Abstract
In this work, we perform experiments in an acoustic tank to record acoustic emissions (A Es) occurring when a granular medium is submitted to a gravitational destabilization. The granular medium is composed ofmonodisperse glass beads filling a box which can be inclined From a =O° up to the avalanche threshold angle ao=28 °. To respect quasi-static conditions, the angle increases by steps less than 3°/mn. An omnidirectional hydrophone records the continuous acoustic field in the bead structure until the avalanche occurs. We compare the results for different experimental configurations, in particular for dry and water saturated granular media, but also for different bead diameters (d=8, 3 and 0.3 mm) in order to span the viscosity range of the granular structure. We show that the AE signatures strongly depend on the viscosity parameter, which can be related to the Stokes number and the fluid/solid density ratio. The transition From a viscous to an inertial dynamic of the granular structure is discussed, based on these experimental results.