Effect of initial anisotropy on shear banding in granular materials

The present paper presents a new hypoplastic constitutive model to describe the behaviour of a cohesionless and initially transversely isotropic granular material. State changes are described using a nonlinear tensor-valued function depending on the current void ratio, the Cauchy stress, a structure tensor involving anisotropy effects and on the rate of deformation. The evolution of the anisotropic material parameters are related to the loading history. For large monotonic shearing the initial transversely isotropic property gradually vanishes and a stationary state can be reached which is independent of the initial state. It is shown that for plane strain compression the peak friction angle strongly depends on the current void ratio, the mean pressure and the orientation of the transversely isotropic plane. The possibility of a spontaneous strain localization in the form of a shear band is investigated and the influence of the state parameters on the shear band inclination is discussed.