中文摘要：

开挖卸荷岩体裂隙面通常处于拉剪应力状态。在裂隙应力和变形状态分析的基础上，采用线弹性断裂力学理论和物理模型试验研究了拉剪应力状态下裂隙扩展的力学机制。岩体裂隙在拉剪应力状态下沿裂隙面间的滑动抗剪摩擦力消失，裂隙起裂沿I型张拉裂隙断裂韧度K1最小的方向起裂，并最终发展与卸荷拉应力方向垂直；拉剪应力状态下岩体的总位移方向平行于拉应力方向，通过合理的位移假设，基于能量及线弹性断裂力学理论，求解了拉剪应力状态下分支裂隙扩展过程中尖端的动态应力强度因子和扩展长度判据；通过拉剪应力状态下单裂隙扩展物理模型试验验证了理论推导的正确性。

英文摘要：

The rocks cracks are in tension-shear stress state when excavated and unloading. Based on the analysis of stress and deformation for the crack in tension-shear sress state, the mechanism of its expanding is studied by linear elastic fracture mechanics theory and physical model test. The researches show that the frictional force along crack plane is vanished when cracks are in tension-shear stress state; the cracks expanding is started up in the direction of the fracture toughness K1 of mode I tensile crack being minimal, and ultimately perpendicular to tension stress. The total displacement is parallel to tension stress under tension-shear stress state, the dynamic stress intensity factor of branching cracks tip in the process of expanding and its expanding length are solved based on energy and linear elastic fracture mechanics theory on the logical displacement hypothesis. The theory results are examined and certified by physical model experiment of some single crack under tension-shear stress.