Rheology of a dense granular material

In order to understand the nature of friction in dense granular materials, a discrete element simulation on granular layers subjected to isobaric plain shear is performed. It is found that the friction coefficient increases as the power of the shear rate, the exponent of which does not depend on the details of the computational model. Using a nondimensional parameter that is known as the inertial number, this power law can be cast in a generalized form so that the friction coefficients at different confining pressures collapse on the same curve. We also show that the shear rate dependence of the volume fraction obeys a power law