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Considering a 3D sheared granular layer modeled with discrete elements, it iswell known the rolling resistance significantly influences the mechanicalbehavior. Even if the rolling resistance role has been deeply investigated asit is commonly used to represent the the roughness of the grains and theinterparticle locking, the role of rolling viscous damping coefficient has beenlargely overlooked so far. This parameter is rarely used or only to dissipatethe energy and to converge numerically. This paper revisits the physical roleof those coefficients with a parametric study of the rolling friction and therolling damping for a sheared layer at different shear speeds and differentconfinement pressures. It has been observed that the damping coefficientinduces a frictional weakening. Hence, competition between the rollingresistance and the rolling damping occurs. Angular resistance aims to avoidgrains rolling, decreasing the difference between the angular velocities ofgrains. Whereas, angular damping acts in the opposite, avoiding a change in thedifference between the angular velocities of grains. In consequence, grainskeep rolling and the sample strength decreases. This effect must be consideredto not overestimate the frictional response of a granular layer.

Frictional weakening of a granular sheared layer due to viscous rolling revealed by Discrete Element Modeling