Bifurcation prediction of shear banding in sand with non-coaxial critical state model considering inherent anisotropy

In view of phenomenological observations, the anisotropic state variable accounting for the effect of inherent fabric anisotropy, which can describe the microstructural characteristics of sand, is thought to influence the critical state of sand. Based on revised forms of the anisotropic state variable, the form for the anisotropic critical state line function is revised and the non-monotonically anisotropic effects are incorporated into the strength parameter in the re-adjustment of the elements of the model. The anisotropic plasticity model parameters of Toyoura sand are re-calibrated with triaxial compression and extension tests having various deposition directions. In comparison to the experiments on Toyoura sand, it is shown that the model can simulate the anisotropic stress-strain relationship reasonably well. Then, bifurcation analyses are conducted to predict the onset of strain localization with the corresponding non-coaxial anisotropic model. The results show that the modeling of shear band formation based on the non-coaxial model is in agreement with the tests considering the anisotropic characteristic.