高围压高水压条件下岩石卸荷强度特性试验研究

Unloading strength properties of rocks under high confining pressure and hydraulic pressure

为了探讨高围压、高水压对岩石卸荷强度特性的影响,取锦屏二级水电站引水隧洞岩石(大理岩、砂岩及板岩)分别进行高围压、无水压峰前卸荷,高围压、无水压峰后卸荷及高围压、高水压峰前卸荷3种工况下的三轴压缩对比试验.试验结果表明,高围压、无水压工况下,岩石达到峰值强度后,与峰前卸荷相比,已经有很多的细小裂纹,其损伤程度远远大于峰值前岩石的损伤程度.高围压、无水压峰后卸荷时的黏聚力c、内摩擦角φ与峰前卸荷的黏聚力c、内摩擦角φ相比,有很大程度的降低.而高水压力的存在相当于降低了初始围压,也就是降低了岩石裂隙面及破坏面上的有效正应力,加速了岩石的破裂,从而降低了岩石的强度,因此高围压、高水压峰前卸荷的黏聚力c、内摩擦角φ与高围压、无水压峰前卸荷相比,有很大程度的降低,且黏聚力c比内摩擦角φ更加敏感.

In order to study the effect of high confining pressure and hydraulic pressure on the unloading strength properties of rocks, triaxial compression tests of rock specimens （marble, sandstone and slate） sampled from the rocks surrounding the diversion tunnel of Jinping Hydropower Station （GradeⅡ） were performed under three different states that is, the pre-peak unloading under high confining pressure and no hydraulic pressure, the post-peak unloading under high confining pressure and no hydraulic pressure, and the pre-pcak under high confining pressure and hydraulic pressure. The test results indicate that under the state of high confining pressure and no hydraulic pressure, after the rocks reach the peak strength, many cracks appear, and their damage degree is larger than that of rocks pre-peak unloading. The cohesion and the internal friction angle of rocks post-peak unloading under high confining pressure and no hydraulic pressure are much lower than those of rocks pre-peak unloading. In addition, the occurrence of high hydraulic pressure is equivalent to the decrease of the initial confining pressure, namely, the decrease of effective normal stress of the fracture surface and failure plane of rocks, resulting in the cracking acceleration of rocks and the decrease of rock strength. The cohesion, internal friction angle of rocks pre-peak unloading under high confining pressure and hydraulic pressure are also much lower than those of rocks pre-peak unloading under high confining pressure and no hydraulic pressure. Furthermore, the cohesion is more sensitive than the internal friction angle.