Dense granular-fluid mixture: the effects of the natural grains characteristics and the interstitial fluid viscosity

An experimental study about the rheology of debris flow was carried out on debris flow soils and on natural sand using several rheometrical tools in order to investigate the rheological behaviour of the “fluid-like” material mixture. The results obtained on debris flow material mixtures suggest that, in the fluid-like regime, the typical rheological behaviour of this mixture is that of yield stress fluids and the rheology of the mixtures is strongly dependent on the grain concentration. The velocity profile obtained on natural sand-Newtonian fluid mixtures were analyzed in order to identify the shearing zone and to explain the dependence of the flow characteristics (i.e., transition from quasi-static regime to liquid regime) on viscosity and shear rate. The results suggest that, in that field, the interstitial fluid viscosity influence the sharing material layer and that no flow is possible for solid fraction higher than a maximum value.