Scale-free channeling patterns near the onset of erosion of sheared granular beds

Abstract

Erosion shapes our landscape and occurs when a sufficient shear stress is exerted by a fluid on a sedimented layer. What controls erosion at a microscopic level remains debated, especially near the threshold forcing where it stops. Here we study experimentally the collective dynamics of the moving particles, using a set-up where the system spontaneously evolves toward the erosion onset. We find that the spatial organization of the erosion flux is heterogeneous in space, and occurs along channels of local flux $\sigma$ whose distribution displays scaling near threshold and follows $P(\sigma )\sim J/\sigma$, where $J$ is the mean erosion flux. Channels are strongly correlated in the direction of forcing but not in the transverse direction. We show that these results quantitatively agree with a model where the dynamics is governed by the competition of disorder (which channels mobile particles) and particle interactions (which reduces channeling). These observations support that for laminar flows, erosion is a dynamical phase transition which shares similarity with the plastic depinning transition occurring in dirty superconductors. The methodology we introduce here could be applied to probe these systems as well.

8 pages, 6 figures

References in corpus (2)

• Depinning and nonequilibrium dynamic phases of particle assemblies driven over random and ordered substrates: a review
• Interface-resolved direct numerical simulation of the erosion of a sediment bed sheared by laminar channel flow

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• Crossover from Jamming to Clogging Behaviors in Heterogeneous Environments