Critical angle of a dry binary mixture of granular materials

Abstract

A rectangular container, filled with a binary mixture of granular matter up to some height h, is opened at one wall to allow critical angle (θ_c) formation. Based on Mohr-Coulomb failure criterion, an accurate continuum description of θ_c as a result of different granular proportions is developed. Both our experiments and theory point to the existence for bidisperse granular mixtures of supramaximal θ_c, i.e. θ_c of mixed greater than θ_c of individual components. Our "flow-then-relax" type of pile shaping is a worthy addition to standard sandpile experiment (static repose formation) and rotating granular tumbler set-up (dynamic repose formation), where supramaximal angles are not observed during mixing.