Effects of Particle Shape on the Shear Behavior and Breakage of Ballast: A DEM Approach

This paper presents results obtained from the discrete-element method (DEM) to study the effects of particle shape on the shear behavior and breakage of ballast aggregates. In this study, a series of direct shear tests have been performed on granular assemblies having various shape sphericity and roundness values. A clump-based degradation (breakage) model is incorporated into the DEM simulation to capture the breakage of aggregates during shearing. The results show that the decrease of particle sphericity and roundness results in an improvement in the shear performance of granular assemblies but subsequent exacerbation in particle breakage, which in turn reduces the shear strength and volumetric dilation. The breakage of particles localizes within an inclined band, with the width and inclination angle of the band increasing in assemblies comprising particles of low sphericity and roundness. A micromechanical analysis is conducted to examine the anisotropy of internal structures and particle motions in granular assemblies. It is observed that both the shape of particles and their breakage significantly influence these factors. Through microscopic analysis, a fundamental governing mechanism of particle shape effects on the shear strength and the breakage of granular materials is investigated at the macroscopic scale.