卸围压条件下花岗岩强度特性及三维裂隙演化规律

为研究卸围压条件下花岗岩强度特性和三维裂隙演化规律,对花岗岩开展了常规三轴压缩、卸围压-加轴压和分级卸围压-加轴压循环加卸载3种不同应力路径力学试验,获得对应的轴、径向应力-应变曲线；采用CT扫描三维重构技术获得岩石卸围压过程中和破坏后内部裂隙分布三维图像.结果表明:相对于常规三轴压缩试验,试件在卸荷条件下脆性破坏特征更加显著,分级卸围压-加轴压循环加卸载会增大花岗岩的峰后延性,降低破坏轴压和破坏剧烈程度；两种卸围压方案都会使花岗岩的承载能力降低30%左右；卸荷作用下花岗岩宏观破裂为拉剪组合状,拉剪过渡不明显,表观裂隙是内部裂隙向外扩展的结果；花岗岩在卸荷作用下峰前产生的裂隙量较少,大量裂隙在峰后产生,破裂具有突发性和瞬时性,围压较低时宏观裂隙首先在试件边缘产生,围压较高时宏观裂隙首先在试件中部产生.

Strength characteristics and 3D fracture evolution law of granite under unloading confining pressure

To study the strength characteristics and 3D fracture evolution law of granite under unloading confining pressure, 3 different stress paths tests including conventional triaxial compression, unloading confining pressure-loading axial pressure, and graded unloading confining pressure-loading axial pressure cyclic loading and unloading were carried out on granite, and corresponding axial and radial stress-strain curves were obtained. Meanwhile, 3D reconstruction technique of CT scanning was used to obtain 3D images of the distribution of internal fracture during and after rock unloading confining pressure process. Results show that: 1) Compared with the conventional triaxial compression test, the brittle failure characteristics of specimens under unloading confining pressure were more obvious, and graded unloading confining pressure-loading axial pressure cyclic loading and unloading test could enlarge the post peak ductility of the granite, as well as reduce the axial compression of instability and the fierce of failure. 2) Both unloading confining pressure schemes reduced the bearing capacity of the granite by about 30%. 3) The macro-fracture of the granite under loading was a combination of tension and shear, and the transition between tension and shear was not obvious. The apparent fracture was the result of the outward expansion of the internal fracture. 4) The amount of cracks of the granite generated before the peak under unloading was small, while a large number of cracks were generated after the peak, and the fracture was sudden and transient. When the confining pressure was low, the macroscopic cracks were firstly generated at the edge of the sample, and when the confining pressure was high, the macroscopic cracks were firstly generated in the middle of the sample.