高应力强卸荷下双江口花岗岩岩爆中间主应力效应宏细观试验研究

Macro-meso experimental study of intermediate principal stress effect on rockburst of Shuangjiangkou granite under high stress and strong unloading

高应力强卸荷下的地下洞室围岩岩爆机制是当前亟待研究和解决的前沿课题。针对双江口水电站地下洞室群的花岗岩,利用新型真三轴加卸载试验系统开展不同中主应力下的三向五面真三轴岩爆模拟试验,并采用扫描电镜、能谱仪等综合分析岩爆破裂面的细观结构特征,分析了不同中主应力下试样的强度和变形特征、宏观破坏形态、岩爆破坏过程和破裂面及主要矿物细观破裂模式。试验结果表明:(1)随着中间主应力的增加,岩爆后的试样宏观破坏由拉伸破坏向剪切破坏转变;(2)随着中间主应力的增加,岩爆类型由迟滞应变型向即时应变型岩爆转变,岩爆剧烈程度先增大后减弱;(3)各中间主应力下试样爆坑断口为剪切断口,岩爆弹射碎屑上的断口为张拉断口;(4)主要矿物细观破裂模式与中间主应力无关:石英和钾长石发生沿晶和穿晶断裂的几率几乎相同,斜长石和云母则更易发生穿晶断裂。研究成果可为后续开挖阶段的岩爆防治提供技术支撑。

Rockburst mechanism of surrounding rock masses in underground cavern group under high stress and strong unloading is a frontier subject, and needs to be studied and solved urgently at present. The rockburst process of the granite from the Shuangjiangkou underground caverns under various intermediate principal stresses was simulated through three-directions and five-sides true triaxial tests. The fracture surface of the specimens after rockburst was observed by scanning electron microscope and energy dispersive spectrometer. The strength and deformation characteristics, macroscopic failure modes, rockburst process and meso-fracture modes of main minerals of the specimens under various intermediate principal stresses were analyzed. The experimental results show that: 1) With the increasing intermediate principal stress, the macroscopic failure of the specimens after rockburst changes from tensile failure to shear failure. 2) With the increasing intermediate principal stress, the specimen rockburst types change from time-delayed rockburst to immediate rockburst, and the rockburst intensity first increases and then decreases. 3) Under each intermediate principal stress, the fracture pits of the specimen after rockburst are primarily shear fracture, while the fractures of the ejection debris are tensile fracture. 4) The meso-fracture mode of main minerals in the studied granite is independence on the intermediate principal stress: the probability of intergranular and transgranular fracture of quartz and K-feldspar is almost the same, while plagioclase and mica are more prone to transgranular fracture. The research results can provide technical support for rockburst prevention during subsequent excavations.