A micro-mechanical approach for the study of contact erosion

In the present paper, a simulation framework is presented coupling the mechanics of fluids and solids to study the contact erosion phenomenon. The fluid is represented by the lattice Boltzmann method (LBM), and the soil particles are modelled using the discrete element method (DEM). The coupling law considers accurately the momentum transfer between both phases. The scheme is validated by running simulations of the drag coefficient and the Magnus effect for spheres and comparing the observations with results found in the literature. Once validated, a soil composed of particles of two distinct sizes is simulated by the DEM and then hydraulically loaded with an LBM fluid. It is observed how the hydraulic gradient compromises the stability of the soil by pushing the smaller particles into the voids between the largest ones. The hydraulic gradient is more pronounced in the areas occupied by the smallest particles due to a reduced constriction size, which at the same time increases the buoyancy acting on them. At the mixing zone, where both particle sizes coexist, the fluid transfers its momentum to the small particles, increasing the erosion rate in the process. Moreover, the particles show an increase in their angular velocity at the mixing zone, which implies that the small particles roll over the large ones, greatly reducing the friction between them. The results offer new insights into the erosion and suffusion processes, which could be used to better predict and design structures on hydraulically loaded soils.