Jamming transition of a granular pile below the angle of repose

TL;DR

This study investigates the relaxation dynamics of a granular pile after an avalanche, revealing complex intermittent behaviors and aging-like correlations that enhance understanding of the granular jamming transition.

Contribution

It provides experimental insights into the relaxation processes and intermittency in granular piles, linking them to aging phenomena and introducing a simple statistical model.

Findings

Observation of two coexisting dynamics: rapid independent grain moves and intermittent bursts.

Identification of long-lived transient states lasting over a thousand seconds.

Evidence of aging-like correlations in the relaxation behavior.

Abstract

We study experimentally the relaxation towards mechanical equilibrium of a granular pile which has just experienced an avalanche and discuss it in the more general context of the granular jamming transition. Two coexisting dynamics are observed in the surface layer: a short time exponential decay consisting in rapid and independent moves of grains and intermittent bursts consisting in spatially correlated moves lasting for longer time. The competition of both dynamics results in long-lived intermittent transients, the total duration of which can late more than a thousand of seconds. We measure a two-time relaxation function, and relate it via a simple statistical model to a more usual two-time correlation function which exhibits strong similarities with auto-correlation functions found in aging systems. Localized perturbation experiments also allow us to test the pile surface layer receptivity.