Shear behavior of Beishan granite fractures after thermal treatment

In this study direct shear tests on a series of thermally-treated Beishan granite samples including a rough fracture were conducted, and the thermal treatment temperature was up to 400 degrees C. Particle mechanics models for Beishan granite were also built up to examine the characteristics of thermally-induced and shear-induced microcracks in granite samples. The results showed that fracture shear stiffness and peak strength decreased with increasing thermal treatment temperature. Thermally-induced microcracks are the main source of the change in fracture shear properties with increasing themral treatment temperatures. Generally the randomly distributed thermally-induced microcracks mainly play a role in reducing the fracture toughness of the asperities, which contributes to the decrease in fracture shear stiffness and peark strength. However, some thermally-induced microcracks may be at large angles to the fracture plane, and can blunt the crack tip and trigger the shear-induced cracks to propagate deeper into fracture walls, which can increase the fracture shear strength and surface damage.