Friction and dilatancy in immersed granular matter

TL;DR

This study demonstrates that the effective friction in immersed granular layers follows Amonton-Coulomb law and is largely independent of fluid viscosity and grain size, but surface properties significantly influence flow behavior.

Contribution

It provides comprehensive experimental evidence showing the independence of effective friction from fluid viscosity and grain size in immersed granular matter.

Findings

Friction obeys Amonton-Coulomb law in immersed granular layers.

Effective friction coefficient is independent of fluid viscosity and grain size.

Surface properties of grains significantly affect flow behavior.

Abstract

The friction of a sliding plate on a thin immersed granular layer obeys Amonton-Coulomb law. We bring to the fore a large set of experimental results which indicate that, over a few decades of values, the effective dynamical friction-coefficient depends neither on the viscosity of the interstitial fluid nor on the size of beads in the sheared layer, which bears out the analogy with the solid-solid friction in a wide range of experimental parameters. We accurately determine the granular-layer dilatancy, which dependance on the grain size and slider velocity can be qualitatively accounted by considering the rheological behaviour of the whole slurry. However, additional results, obtained after modification of the grain surface by a chemical treatment, demonstrate that the theoretical description of the flow properties of granular matter, even immersed, requires the detailed properties of the grain surface to be taken into account.