Macro viscous regime of natural dense granular mixtures

An experimental study was carried out on several dense-granular mixtures (debris flow mixtures and natural sand mixtures) using several rheometrical tools in order to investigate the rheological behaviour of the "fluid-like" material mixture. The results obtained on debris flow-water mixtures suggest that, in the fluid-like regime, the typical rheological behaviour is that of yield stress fluids and the rheology is strongly dependent on the grain concentration. The velocity profile obtained on natural sand-Newtonian fluid mixtures identify the shearing zone and 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.