Thermo-Mechanical Coupling Deformation of Gas Coal and Its Failure Mode and Mechanism

Using the 600°C 20MN servo-controlled triaxial rock testing machine of high temperature and high pressure, which is developed independently by China University of Mining and Technology (CUMT) coupled thermo-mechanical deformation and failure experiments under full stress-strain loading at 200°C and 400°C were carried out with Φ200mm × 400mm gas coal specimen from Xinglongzhuang coal mine, Shandong Province. The results indicated that at 200°C, the deformation of the specimens were minor before destruction, only 1.1%, and brittle fracture occurred. Compression-shear failure happened significantly in coal under high stress. And the whole specimen fractured along the shear plane. At 400°C, deformation of specimens were transformed to ductibility, and large deformation occurred in coal before failure, up to 15.1%. The failure mechanism of the specimens was the frame instability that was caused by pore development derived from large numbers of pyrolysis gas discharging. Coal loses carrying capacity with dramatic deformation. The main controlling factors of coal damage is stress at 200°C but temperature at 400°C.