A constitutive model for deformation of granular media under rotation of principal stress axes

During deposition of granular masses, the gravity field dictates the orientation of grains and their associated contacts. As a result, the mechanical behaviour of granular media becomes anisotropic. In this paper, an effort has been made to consider the effect of anisotropy in constitutive equations of granular media. To this aim, in the first stage, two joint invariant of stress ratio and fabric tensor are introduced to account for the effect of loading/soil fabric interaction. In the second stage, these joint invariants have been contributed in definition of plastic modulus, direction of plastic strain rate, and dilatancy rule of a conventional stress ratio based bounding surface hypoplasticity model. Finally, predictions of the proposed model have been compared with experimental results in order to show the model capability. It is shown that the presented model is able to account for anisotropy effects on various aspects of the mechanical behaviour of granular media including strength, dilatany, and non-coaxiality.