Experimental analysis of basal wall friction coefficient for a velocity controlled confined granular flow

This work presents a novel experimental design to measure the effective wall friction coefficient μw between a confined granular material and a flat wall under a controlled relative velocity and normal load, with concurrent monitoring of the solid volume fraction of the interacting layer. The design allows us to investigate the effects of initial packing configuration, in random or face-centered-cubic packing. The μw is further scaled by the particle-wall pure sliding friction coefficient, μpw, with the normal load considered to infer the degree of incoherent particle dynamics when discrete particles may develop rolling but not pure sliding contacts. Reverse μw/μpw variation trends with the sliding velocity are found and explained.