Title: Fluid-filled granular media in confined geometries: a photoporomechanics study

Author (Talk): Wei Li, Stony Brook University

Abstract:

When fluid-filled granular media are confined in tight spaces, their behavior differs from that of bulk granular media because of fluid coupling and particle-wall interactions. Examples of granular media in confined geometries are fault gouge, concrete pumping and cathode material in lithium-ion batteries. Challenges in experimentally studying this problem arise from the difficulty in measuring physical parameters locally, such as, the pore pressure, particle-wall friction, the Janssen coefficient and, most importantly, effective stress that governs the behavior of granular media. Here we use a novel experimental technique, photoporomechanics, to visualize and quantify the effective stress of granular media in confined geometries and study the effect of particle-wall friction. We pack 2-mm photoelastic spheres into a monolayer cell made of a pair of glass plates and saturate the pack with glycerol. We consolidate the fluid-filled granular layer by applying a sudden load and record the deformation of the granular pack, the induced excess pore pressure and the effective stress, all as a function of time. We find that the pore fluid dissipation controls the rate of deformation of the granular pack during the consolidation tests. In contrast with classical Terzaghi’s 1D consolidation, however, the particle-wall friction controls the final effective stress profile of the granular pack when the excess pore pressure has fully dissipated. Higher particle-wall friction results in smaller deformation and thus faster excess pore pressure dissipation. Our study presents a new technique to study fluid-coupled granular media and provides insights into the rate and extent of granular compaction in confined geometries.