Influence of particle shape on stress-dilatancy and critical state behavior of granular soils: a DEM study

Particle shape effect on the shear-dilatancy and critical state behavior of granular soils was investigated through a series of drained triaxial shearing tests utilizing a combined discrete element-finite difference framework. Elongated particles were modelled by 3D clump, and triaxial shearing tests were conducted on eight particle shapes under different initial densities and confining pressures. The results showed that increasing particle size ratio enhanced both maximum and critical state shear strengths due to an intensified interlocking mechanism. Exponential correlations were established between particle size ratio and the peak friction angle, excess friction angle, and dilation angle. Notably, the critical state friction angle and particle size ratio exhibited a robust exponential growth relationship regardless of confining pressure and initial density. A Bolton’s stress-dilatancy equation was examined for all samples, with the equation’s slope maintaining invariance across all tested conditions and particle shapes. Furthermore, microscopic analysis quantified the fabric anisotropy contributions: the fabric anisotropy coefficients, i.e., contact normal and normal contact force, accounted for approximately 80 % of the weight to the macroscopic strength regardless of particle shape. The contribution of contact normal increased, while the normal contact force decreased, with increasing particle size ratio at the critical state.