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Abstract In-situ experimental investigations on thermal-mechanical coupled effects on physical and mechanical behavior of Beishan granites have been carried out through high temperature scanning electron microscope(SEM) testing system. Studies have clearly indicated that both mineral composition and mineral particle size are quite different for Beishan granite；and they have different thermal and mechanical properties(or hardness)，which greatly affect the failure mechanism and fracture toughness of granite. Thermal cracking，the initiation，propagation and coalescence of microcracks are greatly affected by thermal-mechanical coupled mechanism. In addition，these mechanisms will in turn affect other mechanisms，such as variations of seepage and chemical fields. For model I crack sample of Beishan granite，the crack propagation direction is proximately perpendicular to the direction of tensile stress. In addition，the initial defects and larger mineral particles have also greatly affected the granite fracture path. Especially with the temperature changing，granite fracture mechanism will change from the boundary(intergranular) fracture mechanism at low temperature to the coupled mechanism of boundary(intergranular) and grain(transgranular) fracture. Experimental data also show that the average fracture toughness of Beishan granite before 75 ℃ is about 4.728 MPa•mm1/2，while approximately 3.048 MPa•mm1/2 after 75℃，which deceases about 35%. The main reasons are due to the increasing thermal cracking with the increasing temperature and loads，which lead directly to the increasing microcrack and the decreasing cementation of mineral particles. All of these gradually affect the fracture toughness of granite. In addition，they will affect the seepage and chemical fields. Therefore，the thermal-mechanical coupling effects should not be ignored in nuclear waste repository design.
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Received: 17 October 2011
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2012, Vol. 31 
