Noncoaxiality considering inherent anisotropy under various loading paths in a strain space multiple mechanism model for granular materials

Inherent anisotropy is a crucial aspect to consider to improve one's understanding of the behavior of granular materials, in particular, noncoaxial responses under proportional and nonproportional loadings. This article investigates the capability of a strain space multiple mechanism model to reproduce complex responses of inherently anisotropic soils under various loading paths. The constitutive model has been expanded upon to account for the effect of inherent anisotropy by incorporating a new function along with three additional parameters; two of these parameters, a1 and a2, control the degree of anisotropy, whereas the third parameter, theta 0, represents the principal direction of inherent anisotropy. Laboratory experimental data regarding the complex anisotropic responses of Toyoura sand under various loading paths are used to validate the constitutive model. The model is found to successfully simulate the anisotropic drained soil responses under monotonic proportional and nonproportional loadings as well as those under loading involving the rotation of the principal stress axis by considering the additional anisotropic parameters. Furthermore, the simulated responses of inherently isotropic materials are compared with those of anisotropic materials to numerically investigate the influence of inherent anisotropy (ie, the anisotropic parameters) on soil behavior under such loading conditions.