The shear behavior of a fracture is very complicated due to its surface being rough. Different fracture shearing mechanisms have been introduced in the literature including normal dilation or sliding, asperity cutting and contact area failure. Majority of the existing models consider number of assumptions to simplify the problem, which leads to unrealistic results. In current study, shear behavior of real rock fractures is modeled numerically using the Particle Flow Code PFC2D. The shear behavior of simple synthetic symmetric profiles was studied first. Then the peak shear stress of several real rough fractures was estimated at different normal stress levels. The results of this study indicated that by increasing both profile roughness and normal stress, asperity degradation increases during shearing process followed by significant increase in residual shear stress of the natural rock fracture.
Amongst different fracture geometrical properties surface roughness influences the shear strength of the discontinuity surfaces significantly (Barton, 1977). When the applied shear and normal stresses are large, shear failure may take place by both sliding and cutoff along the fracture surface, with tensile fracturing being observed occasionally (Karami & Stead, 2008). JRC introduced by Barton and Choubey (1977) is perhaps the most commonly used parameter for fracture roughness. However, JRC is a subjective method based on observational comparison of real rock surface with 10 standard exemplar profiles (Asadi et al. 2009). Cundall (2000) used the bonded particle model in particle flow code, PFC to simulate shear tests on rough fractures. He found comparable results with those obtained from Barton shear strength criteria. Similarly, Karami and Stead (2008) performed numerical simulations using Hybrid FEM/DEM method and examined shear strengths of JRC profiles. Giacomini et al. (2008) performed FEM numerical simulation using Abacus code to simulate shearing behavior of synthetic saw-tooth profiles.