To consider the roughness effect on shear strength and deformation of rock joint, this research proposed a joint model for the discrete element method. The background theory of the proposed model is based on Barton's shear strength criterion which is widely used to describe non-cohesive joint with roughness. To implement Barton's criterion in DEM software, three calculation modifications were performed, including exceeded force recapture, contact area equalization, and stiffness adjustment. Through the modifications, the force of each joint contact could be calculated, which reasonably reflect the joint mechanical behavior under different normal stress. Afterward, the proposed model was verified by comparing to the theoretical model. The results indicated that the proposed model rationally describes the shear stiffness influenced by mobilized joint roughness coefficient during the shear process. The comparisons showed that the proposed model is versatile in simulating the shear displacement with loading-unloading-reloading cycles, normal closure, and shear dilation of joint.
The strength and deformability of rock mass are heavily influenced by the properties of joints. The joint exhibits highly non-linear behavior under applied stress and is influenced by surface roughness. To describe the joint behavior, Barton proposed a non-linear model for rock joint (Barton, 1973). It not only provided the description of the failure envelope but also considered the evaluation of shear-displacement and dilation relationships. Therefore, it is widely used in the analysis of rock mechanics.
On the other hand, the discrete element method (DEM) has been widely adopted to explore the behavior of rock mass and successfully applied to rock engineering. Lots of models were developed to simulate joint behavior in DEM, including the bond-eliminate method, the smooth-joint method, and so on (Chiu et al., 2013). However, these methods can not reflect the phenomenon in experiments, such as shear-displacement curve and nonlinear failure envelope. To overcome this problem, this study proposed a rock joint model "rough-joint model". The theory of the proposed model is based on Barton's model. To implement Barton's criterion in DEM software, three calculation modifications were needed. After finishing the construction of the joint model, the direct shear test with reverse shearing has been simulated to show the performance. The failure envelope, shear-displacement curve, closure curve and dilation curve fit Barton's model very well. The above results show that rough-joint model can provide a way to simulated joint behavior with roughness in DEM, which is helpful for researchers to perform numerical analysis for the joint sliding problem.