Granular friction: Triggering large events with small vibrations

Henri Lastakowski (1) , Jean-Christophe Géminard (1) , Valérie Vidal (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon

Triggering large-scale motion by imposing vibrations to a system can be encountered in many situations, from daily-life shaking of saltcellar to silo unclogging or dynamic earthquakes triggering. In the well-known situation of solid or granular friction, the acceleration of imposed vibrations has often been proposed as the governing parameter for the transition between stick-slip motion and continuous sliding. The threshold acceleration for the onset of continuous slip motion or system unjamming is usually found of the order of the gravitational acceleration. These conclusions are mostly drawn from numerical studies. Here, we investigate, in the laboratory, granular friction by shearing a layer of grains subjected to horizontal vibrations. We show that, in contrast with previous results, the quantity that controls the frictional properties is the characteristic velocity, and not the acceleration, of the imposed mechanical vibrations. Thus, when the system is statically loaded, the typical acceleration of the vibrations which trigger large slip events is much smaller than the gravitational acceleration. These results may be relevant to understand dynamic earthquake triggering by small ground perturbations. Granular assemblies are athermal systems, often used as paradigms to study the dynamics of industrial or natural processes, such as fault gouge and earthquake nucleation 1–6. When submitted to mechanical vibrations, granular media can behave as thermalized fluids when the vibrations are large enough, or remain in a solid-like state for small enough vibrations. Such a transition between jammed and unjammed states has been reported to occur when the peak-acceleration characterizing the vibration is of the order of the gravitational acceleration 7,8

Domaines: Physique Générale [physics.gen-ph]

Henri Lastakowski, Jean-Christophe Géminard, Valérie Vidal. Granular friction: Triggering large events with small vibrations. Scientific Reports, 2015, 10.1038/srep13455. ⟨10.1038/srep13455⟩. ⟨hal-01198563⟩