The effect of the earth pressure coefficients on the runout of granular material

In the framework of a better territory risk assessment and decision making, numerical simulation can provide a useful tool for investigating the propagation phase of phenomena involving granular material, like rock avalanches, when realistic geological contexts are considered. Among continuum mechanics models, the numerical model SHWCIN uses the depth averaged Saint Venant approach, in which the avalanche thickness ( H) is very much smaller than its extent parallel to the bed ( L). The material is assumed to be incompressible and the mass and the momentum equations are written in a depth averaged form. The SHWCIN code, based on the hypothesis of isotropy of normal stresses ( σ xx = σ yy = σ zz ), has been modified (new code: RASH 3D) in order to allow for the assumption of anisotropy of normal stresses ( σ xx = Kσ zz ; σ yy = Kσ zz ). A comparison among the results obtained by assuming isotropy or anisotropy is given through the back analysis of a set of laboratory experiments [Gray, J.M.N.T., Wieland, M., Hutter, K., 1999. Gravity-driven free surface flow of granular avalanches over complex basal topography. Proceedings of the Royal Society of London, Series A 455(1841)] and of a case history of rock avalanche (Frank slide, Canada). The carried out simulations have also underlined the importance of using a different earth pressure coefficient value ( K) for directions of convergence and of divergence of the flux.