THE ROLE OF SURFACE ROUGHNESS AND AMBIENT FLUID IN THE RUN-OUT OF FINE GRANULAR FLOWS.

Geophysical granular flows – such as debris flows, snow avalanches and pyroclastic flows – may cause substantial economic loss and fatalities. Different approaches have attempted modeling the motion of granular flows, still without capturing completely the vast and rich phenomena. In particular, energy losses resulting from fluid and particle interactions are still not well represented in applied granular models. The interstitial fluid appears as a key factor modulating energy loses by conferring high mobility to granular flows. Tied to the latter, pore fluid pressure can reduce particle frictional stress by local buoyant effects enhancing run-out distances and flow velocity. In this talk experimental results are reported on the run-out of fine particle granular flows, with emphasis in the effects of the initial pore fluid pressure, initial mixture density and bottom roughness in flow mobility.