中文摘要：

从三峡花岗岩常规三轴实验出发，通过研究裂纹应变的变化规律，得到不同围压下花岗岩的起裂应力。结果表明，起裂应力与围压变化幅度一致，与峰值强度相比，起裂应力一般保持在峰值应力的25％-50％。进一步的实验与理论分析认为，三峡花岗岩在簟轴、三轴瓜缩条件下的微观破裂机制主要是扣伸破裂，从起裂至裂纹稳定扩展阶段，其内部裂纹属I型裂纹，由此通过对压应力下椭圆裂纹的拉伸破坏分析，研究起裂应力、起裂角与围压的关系。比较基于裂纹应变分析得到的结论发现，二者在一定围压区间是比较接近的。

英文摘要：

Based on the conventional triaxial compression test of Three Gorges granites, the crack initiation stress under different confining pressures can be obtained by studying the crack strain curves. The result shows that the crack initiation stress changes at the same extent with confining pressure： compared with the peak strength, the crack initiation stress is generally located between 25% and 50% of the peak strength. Through experimental and theoretical analyses, it is found that the microcosmic failure of Three Gorges granites is mainly induced by tensile cracks under uniaxial and triaxial compressive conditions; and the cracks inside the granite belong to I-mode fracture in stable crack growth stage. Furthermore, the fracture mechanical model of Three Gorges granite is established in order to study the relationship between crack initiation stress, crack initiation angle and confining pressure. Some beneficial conclusions are drawn.