Evaluation of the anisotropy and directionality of a jointed rock mass under numerical direct shear tests

The characteristics of the anisotropy and directionality of jointed rock masses are the key to simplifying it as a transversely anisotropic material. Experimental direct shear tests were performed on stratified rocks cored from granulite rocks. The influence of normal stresses and joint orientations was tested and the anisotropy and directionality of the shear strength were evaluated. Numerical shearing tests on stratified rock models and discrete fractures network (DFN) models were subsequently conducted. In addition, the shear anisotropy and directionality in the DFN models were tested and discussed. The results demonstrate that the peak shear stress was more sensitive to the inclination angles than the normal stress. The stratified rocks in the experimental test showed apparent shear anisotropy and directionality. The maximum value of directionality coincided with the direction of the strike of the bedding plane. The more apparent the anisotropy was, the higher the directionality became. The failure patterns of stratified rocks exhibited more complex characteristics under higher normal stress. Significant variation of the shear strength distribution occurred due to the different orientations of fractures relative to the directions of the shear load. The failure patterns of DFN models of varied scales differed, and no apparent convergence was discovered. The shear strength of the DFN model showed an apparent principal direction. The numerical results presented in this paper are valuable for evaluating the prediction of the failure behaviour of rock masses, and can be further applied to the study of the failure mechanism of surrounding rock in engineering.