锦屏二级水电站大理岩不同应力路径下加卸载试验研究

针对锦屏二级水电站引水隧洞赋存于高地应力环境的特点，对隧洞内的大理岩开展常规三轴压缩试验及峰前、峰后卸围压试验，通过试验数据对比分析，研究大理岩的强度变形特征及破裂机制。主要研究成果：(1) 大理岩峰值强度与实时围压关系密切，应力路径不同、实时围压相同时，峰值强度相同。(2) 围压效应明显，峰值强度随初始围压增加而增加；相比三轴加载试验，峰前卸围压试验峰值强度降低约19.5%，峰后卸围压试验规律不明显，而峰后卸围压试验达到峰值强度时的围压值约占初始围压值的 97.2%，峰前卸围压试验结果较离散。(3) 相比三轴加载试验，峰前卸围压试验c值降低约27.5%， 值提高约22.6%，而与此相反，峰后卸围压试验c值增加约13.7%， 值降低约6.5%，表明大理岩抗破裂的主控因素峰前卸围压试验由摩擦力控制，峰后卸围压试验由黏聚力控制。(4) 峰后卸围压试验自卸荷点开始出现明显的应变平台，表现为理想塑性变形。(5) 峰前卸围压试验的体积应变自卸荷点开始出现明显的转折点。(6) 三轴压缩试验和峰后卸围压试验，大理岩的破坏模式主要为单一剪切破坏，随着围压增加，剪切破裂面端口的粗糙程度降低；峰前卸围压试验的破坏模式为：低围压时的劈裂破坏～中等围压时的“X”型共轭剪切破坏～高围压时的单一剪切破坏。这些研究结论揭示了锦屏大理岩加、卸载应力路径下的力学特性差异，可为西部深埋引水隧洞的开挖、支护设计及稳定性分析提供理论参考。

EXPERIMENTAL STUDY OF JINPING Ⅱ HYDROPOWER STATION MARBLE UNDER LOADING AND UNLOADING STRESS PATHS

In light of that the surrounding rock mass of diversion tunnel group of Jinping II hydropower station lies in the condition of high geostress,two different unloading tests of marble from the diversion tunnel were carried out.In order to analyze rock strength characteristics,deformation behavior and fracture mechanism under different stress paths,the conventional triaxial compression tests of marble were also performed.The results show that:(1) Even if the stress path and initial confining pressure are different,but as long as the real-time confining pressure is the same,the peak strength is equal.(2) The peak strength increases as the initial confining pressure increases.Comparing with triaxial compression test,it decreases by 19.5% of unloading confining pressure at pre-peak,and the peak strength appears when the real-time confining pressure accounts for about 97.2% of the initial confining pressure during the post-peak test.(3) The cohesion c decreases and the internal friction angle φ increases at pre-peak test,compared with the post-tests.The value of c decreases about 27.5% and φ increases about 22.6% at pre-peak test,but the value of c increases about 13.7% and φ decreases about 6.5% at pre-peak test.(4) From the unloading point to strain softening stage,the stress-strain curves have obvious strain platforms,which is the characteristics of the ideal plastic deformation.The strain platform increases with the confining pressure,which shows the feature of the marble from brittleness to plastic when the confining pressure increases.(5) The unloading confining pressure test at pre-peak shows that the marble expansion is limited.(6) The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test;and the fracture mode of the pre-peak test is the splitting failure—X conjugate shear rupture—single shear fracture as the confining pressure increases.These conclusions reveal the loading and unloading mechanical properties of marble under high geostress and provide reliable theoretical reference for the numerical simulation about excavation and design for the stability analysis of deep diversion tunnels in West China.