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

Pascale Aussillous (1) , Zhenhai Zou (1) , Élisabeth Guazzelli (1) , Le Yan (2) , Matthieu Wyart (3)

1 IUSTI - Institut universitaire des systèmes thermiques industriels
2 UC Santa Barbara - University of California [Santa Barbara]
3 EPFL - Ecole Polytechnique Fédérale de Lausanne

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 setup where the systemspontaneously 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 σ whose distribution displays scaling near threshold and follows P(σ)≈J/σ, 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 that 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.

Domaines: Matière Molle [cond-mat.soft]

Pascale Aussillous, Zhenhai Zou, Élisabeth Guazzelli, Le Yan, Matthieu Wyart. Scale-free channeling patterns near the onset of erosion of sheared granular beds. Proceedings of the National Academy of Sciences of the United States of America, 2016, 113 (42), pp.11788 - 11793. ⟨10.1073/pnas.1609023113⟩. ⟨hal-01431924⟩