Wet granular bed eroded by a dry granular flow

Using three-dimensional discrete element method simulations, we investigate the erosion dynamics of a cohesive bed composed of wet spherical particles subjected to the shear flow of an overlying noncohesive granular layer. Cohesion is modeled through a capillary attraction law, where the erosion process is governed by the irreversible rupture of liquid bridges at the interface. By systematically varying the liquid-vapor surface tension and the inclination angle of the bed, we analyze the influence of cohesive strength and flow intensity on the mass entrainment rate. We propose a robust scaling law for the surface erosion rate based on the interplay between two dimensionless parameters: the inertial number (I) and the cohesion index (ξ). This framework reveals that the threshold for erosion is determined by the ratio of the geometric mean of the driving stresses (kinetic and pressure) to the cohesive resistance. These findings provide a comprehensive description of the coupling between inertial and capillary forces, offering a predictive tool for the stability of cohesive interfaces in sheared granular flows.