Shear Rate–Dependent Frictional Properties of a Wet Granular Layer

Abstract

Granular materials are a system of discrete particulates found practically in a variety of applications. Gouge particles along earthquake faults and rock joints behave as a granular material. In this article, the frictional properties of a wet granular layer are studied experimentally on a rock surface. Slide–hold–slide (SHS) tests show that static, steady, and residual stresses of the wet layer depend on the shear rate for a fixed hold time. Using Coulomb’s law of friction, adhesive stress and coefficient of friction are determined for all three stresses. Both components of friction are found to increase with shear rate. A friction model for soft solids is used to predict static friction of the granular layer. The scaling laws are also proposed for static friction concerning chain density, relaxation time, and extension of the molecular chains in terms of normal stress, and these results are justified.