The influence of particle elongations on direct shear behaviour of granular materials using DEM

This study examines the influence of particle elongation on the direct shear behaviour of granular materials using the discrete element method. A series of numerical direct shear test simulations were performed, and both the macroscopic and microscopic behaviour of elongated assemblies at the critical state were examined. The macroscopic response of elongated particles exhibits an initial hardening followed by post-peak strain softening, prior to reaching the critical state. The peak state friction angles initially increase and stay stable as the dimensionless elongation parameter ($$\eta$$) increases, whereas the critical state friction angles increase with the increase of $$\eta$$. Independent of the applied normal stresses, all samples reach a critical state at a unique normalized stress ratio (i.e., $$\tau /\sigma = 0.51$$) after ~ 25% shear strain. The stress-fabric relationship is mainly governed by the strong force subnetwork which is more affected by the change of η than the weak force subnetwork. Particle elongation generates a downward shifting of critical state lines (CSLs) in $$e - p^{{\prime }}$$ space. Furthermore, the correlations between CSL parameters and $$\eta$$ are well-fitted by a second-order polynomial function. These findings highlight the significance of particle elongation on direct shear behaviour of granular materials.