Particle shape effects on the shear behaviors of granular assemblies: irregularity and elongation

This study examines the influence of particle shape irregularity and elongation on the shear behaviors of granular materials using the 3D discrete element method (DEM). The particles are generated by combining a Fourier shape descriptor-based method with the random field theory and reconstructed in DEM using the overlapping sphere algorithm. A series of drained and undrained triaxial and true triaxial tests are performed to shear the samples with different particle irregularity and elongation to the critical state. The stress and the strain responses, the evolution of the fabric anisotropy and the coordination number are examined and analyzed within the framework of the anisotropic critical state theory. It is found that the consideration of complex shaped particles in DEM produces more realistic sand behaviors, and the shear strength and the dilation of the granular material increase with increasing irregularity and elongation. While elongation in the range of the study has insignificant influence on the location of the critical state line (CSL) on the void ratio-mean effective stress plane, irregularity is found to positively affect both the absolute slope and the intercept of the CSL. The unique fabric anisotropy norm at the critical state is also sensitive to the particle shape and is greater with larger irregularity and elongation.