Shear strength of assemblies of ellipsoidal particles

A series of drained tests were performed numerically on specimens with ellipsoids of two different shapes. The drained tests include axial extension, constant mean stress compression, lateral compression, lateral extension, plane strain, triaxial compression, triaxial extension and six constant-b tests. The six constant-b tests were conducted by varying the intermediate principal stress with b = (σ2 − σ3)/(σ1 − σ3) = 0, 0·2, 0·4, 0·6, 0·8 and 1. These tests were performed using the discrete element method (DEM) with pressure boundaries. Two specimens composed of 1170 ellipsoids with two different aspect ratios were created. The two specimens were consolidated isotropically before being loaded along different stress paths. The effects of intermediate principal stress, mean stress, particle shape and stress path were investigated. The results show that the stress–strain behaviour of constant-b tests was affected by mean stress. Similar behaviours were observed for the drained tests with b = 0 regardless of the stress path. The friction angles of these tests were then compared with four failure criteria that have been proposed in the literature. Overall, the Lade and Ogawa models are better than the models proposed by Matsuoka & Nakai and Satake. The Ogawa model has a slightly better performance than the Lade model.