Analysis of the effect of joint roughness on the failure mechanism of jointed rock mass under direct shear loading.

The mechanical properties of jointed rock bodies are important in guiding engineering design and construction. Using the particle flow software PFC2D, we conducted direct shear test simulations on joints with various inclinations and five different roughness levels to examine the models' crack extension penetration paths, damage modes, and strength characteristics. The findings indicate that the direction of the joint influences the pattern of the rock crack and its penetration route. Under forward shear, the rock bridge creates a notched through surface, whereas under reverse shear it creates two adjacent through surfaces, categorised into four types of crack consolidation between joints with different inclinations: 'end to end', 'the end is connected to the middle', 'end connection', 'first outward expansion and then rock bridge destruction'. Variations in joint inclination and roughness can alter the mechanical properties and damage patterns of joint specimens. The 'climbing' and 'gnawing' effects determine the peak shear strength of the rock body at the joint section. It is vital to consider these factors when assessing the joint's characteristics. The damage effect is determined by the joint inclination and joint roughness. When the main damage effect changes from 'creeping' slip to 'gnawing' damage, increasing joint roughness enhances the shear strength. Nevertheless, under the same 'gnawing' damage effect, augmenting joint roughness weakens the mechanical properties of the rock bridge, and as roughness increases, the shear strength decreases. For example, at a joint inclination of 30°, the shear strength increases by 20.1% as the JRC (Joint Roughness Coefficient) increases from 0 to 5. At a joint inclination of 60°, the shear strength decreases by 10.7% as the JRC increases from 0 to 10.