Laboratory and micromechanical investigation of soil anisotropy

This paper presents an experimental investigation revisiting the anisotropic behavior of geomaterials in drained monotonic shear using Hollow Cylinder Apparatus. The test program has been designed to cover the effect of material anisotropy, pre-shearing and material density on the behavior of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. The test results demonstrate that the stress-strain-strength behavior of the specimen shows strong dependence on the principal stress direction. The pre-shearing history, material density and particle shape are found to be influential. The deformation non-coaxiality, i.e., non-coincidence between the principal stress direction and the principal strain rate direction is observed. In particular, it was found that non-coaxiality is more significant in presheared specimens. This paper also explains the phenomenological observations based on the recently acquired understanding in micromechanics, with attention focused on strength and deformation non-coaxiality.