深部非贯通裂隙岩体松弛损伤机制与数值模拟

The progressive evolution process of fractured zones, induced by the relaxation damage of hard rock at depth, is one of the most important reasons for the time-dependent failure of rock engineering at depth. However, the relaxation damage mechanism of hard rock at depth is not clear till now, and the numerical simulation method for the progressive evolution of fracture zones in rock mass needs further. In view of this, this project will focus on the relaxation damage mechanism of hard rock at depth and the progressive evolution of fractured zones trigged by relaxation. Various means will be adopted here, including positioning acoustic emission experiments under unloading relaxation condition, micromechanics theory and extended finite element method, etc. So, on one hand a series of relaxation tests with positioning acoustic emission equipment will be carried out stepwise under different confining pressure, loading grading and unloading rates. To obtain the fracture toughness under rheological condition, subcritical crack growth tests will be conducted. Through a combination of the micromechanics and rheology theory, a mesoscopic damage evolution model for the relaxation of crack-weakened rock mass will be established. Meanwhile, the fractured zones caused by relaxation will be analyzed to figure out the inelastic deformation mechanism of hard rock at depth. On the other hand, based on the extended finite element method and cohesive crack model, taking the rheological behavior of rock mass into account, a new simulation method for the relaxation damage of rock mass will be proposed. Then, the progressive evolution of fractured zones in surrounding rock mass around an opening will be simulated numerically. Finally, in order to validate the proposed theoretical and numerical models, these models will be used to simulate the relaxation damaged zones in the surrounding rock mass. Subsequently, comparisons between the monitoring data and numerical results will be made. In all, it can be expected that from this study a scientific guide would be provided for assessment of the long-term stability of rock engineering at great depth.

深部硬岩松弛损伤导致的围岩破裂区渐进演化是深部岩体工程流变破坏的重要原因之一，然而目前深部硬岩松弛损伤机制尚未明确，且在松弛损伤导致的破裂区渐进演化数值模拟方面也有待于进一步深入。鉴于此，本项目以深部硬岩松弛损伤机制及其引发的围岩破裂区渐进演化为研究对象，采用卸荷松弛声发射定位试验、细观损伤力学和扩展有限元法等手段，一方面开展不同围压、加载等级和卸荷速率下的硬岩松弛声发射定位试验，以及岩石亚临界流变断裂试验，结合细观损伤力学和流变理论，建立松弛过程裂隙岩体细观损伤演化模型，揭示深部硬岩松弛损伤导致岩体破裂区和非弹性变形发生机制；另一方面采用扩展有限元法，考虑围岩流变效应，分析深埋洞室卸荷松弛过程围岩损伤演化机制，模拟松弛损伤引起的围岩破裂区渐进发展过程。最后，通过与围岩变形和破裂区监测资料对比，验证本研究成果的合理性。研究成果将为深部地下工程设计、施工及长期稳定性预测提供理论依据。

非贯通裂隙岩体在岩土工程中是十分普遍的，因而对其中裂隙的力学响应以及岩体的变形破坏机制、强度准则等力学特性的研究具有十分重要的意义。岩体内部存在的大量节理裂隙改变了岩体的物理力学性质，使其变形模量及强度等力学参数发生变化。而对于深部岩体，由于其所处的高地应力环境，非贯通裂隙对岩体的物理力学性质，以及开挖后的松弛损伤影响更为明显。本项目以深部硬岩松弛损伤导致围岩破裂区渐进演化为研究对象，通过不同轴向应变水平下脆性岩石的松弛试验，验证了深部脆性硬岩的应力松弛特性，且应松弛试验中的应力变化量与轴向应变成正比。利用卸荷松弛声发射定位试验，通过多通道声发射仪以及VIC高速相机对岩样中裂纹扩展过程进行实时定位，结果表明裂纹两侧水平应变变化明显，试件最终的破坏主要由于张拉裂纹的扩展引起的劈裂破坏。通过比较不同松弛应力路径下的试件裂纹体积应变曲线可知，随着应力松弛历史的增加，裂纹扩展路径上的特征点起裂顺序依次延后，在临近破坏时，脆性材料表现出明显非线性特性。此外，在不同围岩和不同卸荷速率环境下，硬岩流变裂纹扩展长度与松弛试验中试件轴压与围压差值成正比。围压卸载越快，卸载后剩余的轴向应力越小，因此对应的松弛试验的初始轴向应力也越小，进而松弛过程中流变裂纹的扩展长度与扩展速率均呈现下降趋势。利用OLYMPUS SZX16座式显微镜以及DIC应变测量系统，观测到由于松弛试验的作用，主裂纹面的断裂由岩石晶体间破坏发展为穿晶破坏。同时，试件宏观破坏模式也由张拉破坏发展为张拉-剪切破坏，或者纯剪切破坏。最后以扩展有限元法为基础，结合岩体松弛损伤演化方程和流变起裂准则，建立深部岩体平面问题非线性流变数值模型，分析得出开挖速率过快以及岩体中细微裂纹的大范围分布都会导致大规模开挖损伤区的快速产生。本研究成果为深部地下工程设计、施工及长期稳定性预测提供理论支撑。