Some effects of particle shape on the mechanical behaviour of granular materials

Abstract

The behaviour of a granular material depends on the shape, material proper- ties and packing of the grains. Starting with a particle characterization, the ability to make predictions of the macroscopic behaviour of an assembly of particles without re- course to laboratory or numerical experiments would be very useful. With this ultimate goal in mind, this work presents some first findings of an investigation into the effects on macroscopic behaviour of two key measures of particle shape: form and angularity. The form of a particle is quantified using the Longest (L), Intermediate (I) and Shortest (S) dimensions of an equivalent scalene ellipsoid; A sum of the local volumetric deviations of the particle from that ellipsoid as a ratio of the ellipsoid volume is used as a measure of angularity. Discrete element, periodic cell simulations of ellipsoidal and realistic par- ticle shapes sampled from railway ballast are used to investigate mechanical behaviour in terms of critical state friction angle. Characterization of the observed behaviour in terms of a single shape parameter is explored. It is found that deviation of particle form from that of a sphere together with increases in angularity both lead to higher angles of friction at critical state. It is argued that, at least to some extent, the higher critical state strength exhibited by non-spherical particles is due to their form and/or angularity suppressing particle rotation and leading to increased interparticle sliding, a mechanism that in comparison expends more energy.

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Identifiers

ORCID for John Harkness: orcid.org/0000-0003-0908-0791

ORCID for Antonios Zervos: orcid.org/0000-0002-2662-9320

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