תהליכים פיסיקליים בניסויי גזירה של חומר גרגירי יבש ורווי – השלכות לתהליכי גזירה בטבע

Shearing of dense granular flow is common in natural settings ranging from crustal faults producing earthquakes through shallow slip in landslides and glaciers to surface shear as in moving sand dunes. Although these processes differ significantly in their boundary conditions, applied stresses, and shear velocities, they all involve shearing of grains. In many cases these shear zones are water saturated and the presence of water is crucial for the triggering and evolution of the slip event. Despite water’s importance, existing studies primarily concentrate on the shearing of dry materials. Here we experimentally investigate shearing of dry versus saturated quartz-rich sand to understand the effect of the fluid medium on the rheology and acoustic waves emission of the sheared sand. Increasing shear velocity dilates the granular system, however, dilation during water saturated experiments is about one-third the value measured for dry material. This reduced dilation is accompanied by lower acoustic energy emission from the shear zone. We suggest that the presence of fluid suppresses grain motion and particles impacts leading to mild increase in the internal pressure and therefore for the reduced dilation and acoustic energy emission. In contrast, for silicone oil as the liquid phase, the system dilates even over the dry case but the acoustic energy keeps descending. We suggest that higher viscosity fluids lubricate the contacts between grains and therefore reducing acoustic emission but increasing dilation. The competition between lubrication and damping effects in saturated granular flows are critical for the modeling of natural shear systems and the evolution of hazardous landslides.


תאריך 3/05/2018 11:15 - 4/05/2018
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