Shear behavior of Beishan granite fractures after thermal treatment

• Published in: Engineering fracture mechanics 2019-05, Vol.213, p.223-240
• Main Authors: Zhao, Zhihong, Dou, Zihao, Xu, Haoran, Liu, Zhina
• Format: Article
• Language: English
• Subjects: Beishan granite; Crack tips; Direct shear test; Fracture; Fracture mechanics; Fracture toughness; Granite; Heat treatment; Microcracks; Particle mechanics model; Shear properties; Shear stiffness; Shear strength; Shear tests; Thermal treatment
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2019.04.012

•The increasing thermal treatment temperatures can weaken fracture shear properties.•The distributions of thermal microcracks determine fracture shear properties.•Thermal over-closure causes a slight increase in fracture shear strength. 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 °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.