(1. State Key Laboratory of Coal Resources and Safe Mining，China University of Mining and Technology，Beijing 100083，China
2. School of Mechanics and Civil Engineering，China University of Mining and Technology，Beijing 100083，China)
Abstract：It becomes more and more important to study and understand the fracture behavior of rocks under thermo-mechanical coupled effects to meet the increasing demands of the future nuclear waste disposal geological engineering in China. We focus on granite from Beishan region，a potential future nuclear waste repository site in our country. The scanning electron microscope(SEM) high temperature test system has been employed to investigate three-point bending fracture behavior of Beishan granite after heat treatment. In the range of 25 ℃–100 ℃，Beishan granite exhibits mainly brittle failure. Under low stress，crack propagation is mainly controlled by the coupled effects of stress concentration，minerals mechanical behavior and the adhesive force among mineral particles. The final crack initiation normally occurs along the weaker cemented surface between the mineral particles. Crack initial spreading angle usually has an included angle with the horizontal plane. With the increasing loads，cracks gradually propagate along the horizontal direction. This is due to the direction subjected to the maximum bending tensile stress. However，the tensile strength of the rock is usually low. The average fracture toughness of Beishan granite does not almost change from room temperature to 100 ℃. Slight fluctuations may be due to mineral inhomogeneity. Based on digital speckle correlation calculation method，the full deformation field of rock at mesoscopic scale has been successfully measured. The measurement results obviously indicate that the surface deformations of mineral particles are very complicated. The results of the interface of mineral particles moving toward two different directions indicate the particles are subjected to tensile stress. Though the deformation occurs mainly along the surface subjected to the maximum bending tensile stress in the initial stage，the final failure may occur in the other places. At this case，the failure process is mainly affected by nonuniform weak surface. Therefore，rock failure at meso-scale is obviously affected by the coupled effects the maximum stress state and inhomogeneous deformation of local mineral particles.
2013, Vol. 32 
