Effect of particle shape on the mechanical response of a granular ensemble

Abstract

The mechanical behaviour of a granular ensemble at a macro scale is an integration of the interparticle interactions. Even though manifold parameters at multiple length scales govern the behaviour of granular materials, particle shape and size are considered paramount in governing the ensemble level mechanical response such as the strength, stiffness and packing fraction (e(max), e(min)), friction angle etc. In this research programme, an experimental study using hollow cylinder apparatus is undertaken in order to study the effect of particle shape on the ensemble material behaviour. Two model materials are chosen for these series of experiments - angular sand and spherical glass ballotini. The mean grain size of both sand and glass ballotini used in this study is 0.5 mm. Also the specimens are prepared at a relative density of 30% using the same preparation technique, ensuring almost similar initial fabric. These specimens are subjected to a gamut of stresses by varying the intermediate principal stress ratio (b) such that the critical state surface (or yield locus) could be traced on an octahedral plane (in the principal stress space). The angular particles showed increased critical state strength when compared to the glass ballotini at different intermediate principal stress ratio. The volume change in the angular sand particles are seen to be mostly contractive, while at the same relative density, the glass ballotini showed a dilative response. Finally, the particle shape controls the size of the critical state locus on the octahedral plane, in that, the angular particles show an increased size when compared to the spherical particles.