Particle shape descriptors as a tool for classification of grain breakage

Abstract

This study explores particle breakage of a calcareous sand, utilising dynamic image analysis and direct shear tests at varying normal stress levels to analyse the sand crushing mechanism. Tests were arrested at four phase transition points encountered during shear. Particle breakage was traced along a proposed scale based on the literature. Distinct behaviours in shape descriptors for particles of different diameters were observed under changing stress conditions. Agglomerated particle-level behaviour indicates that applied stress levels lead to different soil responses; at low stress, grains roll or slide, whereas at high stresses, grain movement is restricted. Particle breakage was evident even at minimal stress, with increasing grain size reduction as shear strain and stress levels heightened. This study introduces a parameter loading intensity (LI), amalgamating the effects of force chains and loading duration to model grain crushing. Relationships among the shape-angularity group indicator (SAGI), convexity (Cx) and sphericity (S) were also established, enabling calculation of these descriptors, after any loading intensity is applied, based on the initial values. Finally, a methodology for forecasting changes in S and Cx, under any given LI for materials with a known SAGI is presented.