Collapse of wet granular materials: experiments and discrete element simulations

The presence of water strongly affects the behaviour of a granular material especially in the transition between static and dynamic conditions in which the attractive forces between particles become lower than the inertial ones and vice versa. The water effect is important especially in the pendular state (for saturation degree lower than about 5%) in many engineering applications: in geotechnics (e.g.. in slope stability problems), in many chemical processes (e.g. wet agglomeration) or granular transport and handling (discharge from silos, clogging, etc.). In comparison with other experiments, column collapse tests1,2 allow to better focus on phenomena involved in transition phases without introducing the effects of other variables, such as angular velocity and axial dispersion of particles occurring in rotating drums, or orifice geometry in case of discharge from silos. The Discrete Element Method (DEM) is particularly suitable to simulate this kind of tests providing that a capillary law is introduced in the model and a redistribution function of the liquid volumes is implemented, as it is shown in this work. The numerical analyses performed with this improved tool enhance the comprehension of the dependence of the mechanical behaviour of granular materials on particle diameter, wetting concentration, liquid surface tensions and contact angle.