Dynamical weakening by fluidization under oscillatory viscous flows

Abstract

Dynamical weakening of granular materials plays a critical role on diverse geological events such as seismic faulting and landslides. A common feature in the dynamics of these processes is the development of fluid‐solid relative flows, which could lead to fluidization by hydrodynamic viscous stresses. This work is focused on analyzing hydrodynamic fluidization under oscillatory viscous flows as a possible driving mechanism for dynamical weakening. The theoretical estimations and experimental observations presented and reviewed suggest that fluidization can be greatly promoted by oscillatory viscous flows, which are usually expected in geological events involving vibration of granular materials in viscous fluids. Fluidization under oscillatory viscous flows may occur at not excessively large vibration velocities of fine particles in gases or relatively larger particles in liquids or supercritical fluids. In particular, the enhancement of fluidization by high‐frequency vibrations would be a powerful mechanism to promote dynamical weakening of fine powders in dry fault gouges, failure of liquid‐ (or supercritical fluid‐) saturated beds, and sustained fluidization of pyroclastic flows and lahars.

Fluid-assisted brecciation of Lower Cretaceous Maiolica limestone in the Umbria-Marche Apennines: Hydrodynamical implications

“…The balance between the weight of the clasts in the fluid and the upward force exerted on the clasts can be expressed by For geological applications, the Ergun Equation or its modified forms are used in diverse situations to study the velocity needed for sediment motions, pyroclastic current flow, liquefaction of slope material, and fluidization of fault gouge, etc. (Allen, 1982;Cheng, 2003;Valverde, 2015;Breard et al, 2019). In particular, the two equations above are often modified for the computation of ν, the fluid velocity needed to stimulate clast entrainment in a fluid system.…”