Micro-mechanical perspective on the role of particle shape in shearing of sands

Abstract

This study presents a micro-mechanical perspective on the role of realistic particle shapes in shearing of sands through calibration with physical experiments and parametric studies using discrete element method (DEM) to reveal the different mechanics between irregular particles and spherical particles incorporating rolling resistance (μr). To achieve this goal, particle shapes of Toyoura sand were captured by micro-computed tomography and reconstructed using a clump generation algorithm in DEM. The use of clumps in DEM led to closer match with experimental results of triaxial tests at various porosities and confining pressures, which could not be achieved by sphere models with μr. With realistic particle shapes, initial rotations of clumps were allowed until they became interlocked, while the load resistance built up gradually. High coordination numbers were observed, with force chains relatively evenly distributed. In contrast, the use of μr in sphere models promoted the formation of voids that were sustained during the loading process, because rotational motions of particles were hampered by μr and they did not easily collapse into the voids. This was accompanied by polarised strong force network around the voids, leading to more dilative and brittle macroscopic behaviour than observed in physical experiments. These findings illustrate that particle shapes cannot be sufficiently replaced by the use of sphere models and μr due to intrinsic differences in their micro-mechanics.