Flow of dry and wet granular materials: Numerical simulation results

We use a DEM method to simulate dense assemblies of frictional spherical grains in 3D steady shear flow under controlled normal stress P, either dry or in the presence of a small amount of an interstitial liquid, which gives rise to capillary menisci and attractive forces. We pay special attention to the quasi-static limit of slow flow. The system behavior is characterized by the dependence of internal friction coefficient and solid fraction on two dimensionless control parameters: the inertial number, I and the reduced pressure, P*, comparing confining forces to contact tensile strength. Capillary forces have a significant effect on the macroscopic behavior of the system, up to P* values of several unities, especially for longer force ranges associated with larger menisci. We relate this effect to fabric anisotropy parameters of contact and distant interactions.