The influence of particle shape and particle size distribution on the macroscopic behaviour of granular materials is well established in experiments. However, the microscale mechanics which underly the macroscopic behaviour are not readily accessible in experiments. This research employs the discrete element method (DEM) which was proposed by Cundall & Strack (1979) to link the influence of particle shape and sample grading on the micromechanical behaviour of granular materials to the overall material behaviour.
To achieve the aim of this research, isotropic assemblies with different sample densities, particle shapes and coefficients of uniformity, C_u, were prepared and subjected to drained shearing via biaxial compression until the critical state was reached. Macroscopic characteristics such as strength and dilatancy were determined. The factors underlying the macroscopic behaviour were then investigated by considering the coordination number, fabric anisotropy, particle moment, friction mobilization at contacts and particle rotation.
The key macro-scale data from this research such as the strength and dilatancy confirm that the DEM simulations are effective analogues of sand. The macro-scale responses align with key expected behaviour characteristics of sand as observed in experiments. The critical state strength of the granular assemblies studied generally decreased with an increase in both the sphericity and the convexity of the particles; and increased as the aspect ratio, AR, increased. The critical state strength linearly increased with the Cu although at lower particle AR. The strength-dilatancy relationship established for sand was also established for the samples of various particle shapes studied here. The excess friction angle correlated highly with the dilatancy angles (R2 = 0.98) for the samples.
The critical state strength correlates highly with the critical state coordination number, the void ratio and the mechanical void ratio of the granular assemblies studied. The shear strength exhibited by the granular assemblies also correlates with the moment transmitted between the particles and the friction mobilised at contacts. For the samples studied here, the critical state strength generally increased as the moment transmitted by the particles and the friction mobilised at the contacts increased. The susceptibility of the particles to rotation when the granular assemblies were sheared correlates with the strength exhibited by the assemblies. The mean particle rotation exhibited by the samples at the critical state was found to increase as both the sphericity and the convexity of the particles increased; an increase in the particle AR resulted in a decrease in the mean particle rotation and a corresponding increase in strength.