Granular flows on erodible and non erodible inclines

Granular flows occur in nature on hard surfaces but more frequently on erodible layers of different origin, thickness and properties. Experimental test results are available for testing analytical and numerical solutions, validating them and the definition of the material properties. A series of numerical simulations was performed via FEM analyses considering the granular material to behave as an elasto-plastic Mohr–Coulomb solid. The obtained results were compared with experimental observations of spreading over horizontal and inclined chutes, on both rigid and erodible layers. It turns out that the numerical model is able to capture the influence of the test geometry in case of both rigid and erodible surfaces, but it fails to replicate the excessive runout observed in the presence of layers close to the critical slope angle. It is suggested that this difference could be originated by the meta-stable conditions in which erodible layers are deposited in the experiments considered from the literature. For granular flows moving over a rigid surface both runout and peak front velocity increase with the column aspect ratio, whereas runout increases more rapidly for chute slope larger than 15∘, in agreement with published experimental results. Much more complex is the understanding of granular flows over erodible layers. The simulations replicate the generation of waves due to the erosion of the erodible layer, as well the sequential formation of multiple shear bands inside the collapsing column causing the rapid release of multiple subvolumes.