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, partical-wall friction, the Janssen coefficient and, most importantly, effective stress that governs the behavior of granular media.
