Evaluation of the effect of low normal stresses on the joint shear behavior using numerical simulation

In this study, the effect of low normal stress levels on shear behavior of jointed samples was investigated using discrete element method (DEM). Based on the experimental design, 50 jointed samples with different joint persistency (JP) were modeled under low normal loads. The results of numerical modeling showed that the effectiveness of the normal load is greater in the post-peak and enters operation after the failure point. Moreover, increasing the normal stress on the shear surface changes the behavior from brittle to ductile. Standard deviations of shear strengths showed that changes in normal stress at higher JP have less effect on the shear strength of jointed samples. Also, for a constant JP, the shear stiffness of the sample increases with normal stress, and increasing the JP does not have a significant effect on the shear stiffness of the sample. Increase in JP at a constant normal stress level decreases the sample dilation. Considering the crack formation in a constant JP, it was observed that up to the peak shear stress, the number of cracks increases with increasing the normal stress, and this is not continuous after the peak and shows different variations. The results showed that with decreasing the JP, the relative growth of cracks in the vertical direction decreased and more cracks were created in the direction of the shear plane. The propagation and coalescence of cracks and the creation of a failure surface can also cause stress relaxation, and the magnitude of the contact force between the particles depends on this issue.