深埋条件下考虑裂纹扩展影响的围岩裂隙网络结构特征及演化规律研究

Under the deep environmental conditions, the surrounding rock of the cavern affect by many factors such as high in-situ stress coupling with high osmotic pressure and construction disturbance damage, and its fracture network is prone to structural changes such as expansion, penetration and obstruction. The three-dimensional characteristics of fracture network structure and evolution law of deep surrounding rock are of great significance for the disaster prevention and long-term stability of similar deep projects. This subject is intended to reveal the damage evolution law of surrounding rock fracture network under high ground stress and high permeability pressure coupling by visualized rock rheological test, tri-axial hydro-mechanical coupling test, electron microscope scanning and numerical modeling and simulation. The main content including: (1) A three-dimensional model of fracture network structure including damage factors, which based on multi-dimensional fractal theory; (2) Revealing the structure characteristics and evolution law of the surrounding rock fracture network in the deep environment through visualized macroscopic and microscopic experiments, developing a damage model which will consider crack propagation and revealing the intrinsic connection between micro-mechanism and macroscopic response by numerical experiments in high in-situ stress coupling with high osmotic pressure; (3)To propose an extended discrete element numerical calculation method considering the damage effect, which is suitable for deep environmental conditions, and numerical experiments based on the method can improve people's understanding of the evolution law and catastrophic mechanism of the surrounding rock fissure network in deep ground engineering, which is of great scientific significance to the deep ground development and utilization.

深部赋存环境洞室围岩受到高地应力高渗透压耦合作用以及施工扰动损伤等多因素影响，其裂隙网络极易产生扩展、贯通及阻塞等结构变化，研究其三维裂隙网络结构特征及演化规律对于深地工程的灾变规律研究及洞室围岩长期稳定性评价具有重要意义。本项目拟采用基于可视化改造的流变试验、渗流应力耦合三轴试验、电镜扫描试验及数值试验等方法，研究高应力-高渗透压耦合条件下围岩三维裂隙网络损伤演化规律（1）基于多维分形理论建立包含损伤因子的三维裂隙网络结构模型；（2）通过可视化宏细观试验，揭示深部赋存环境下围岩裂隙网络结构特征及演化规律，开发考虑裂纹扩展的损伤本构模型，结合数值试验揭示高应力高渗透压条件下裂隙网络演化的细观力学机理与宏观力学表现的内在联系；（3）提出适合深部赋存条件下考虑损伤的扩展离散元数值计算方法，结合数值试验研究提升人们对深地工程围岩裂隙网络演化规律及灾变机理的认识，对深地开发利用具有重要科学意义。

课题基于自主研发的真三轴水力压裂可视化试验装置，结合改进的DIC高精度测量系统，提出了一整套包含试样制备、荷载施加、数据记录、实时观测和图像分析的裂隙岩体水力压裂可视化试验流程，实现了复杂力学环境下裂隙岩体水力裂纹扩展全过程的可视化。在此基础上，开展了含不同裂隙结构特征岩样的单轴压缩、水力压裂与宏细观损伤观测试验，结合分形理论对单轴压缩条件下裂隙岩样全局应变场演化特征及损伤分形演化规律进行分析，提出了裂纹起裂机理分析方法。考虑注液流量、应力状态、裂纹倾角、岩桥角度等因素，根据水压变化、位移场和应变场分布演化等研究了水力裂纹扩展规律。通过PFC软件建立能够精细刻画岩样宏细观力学性质和裂纹起裂扩展特征的FJM模型，考虑水力耦合算法中流动通道打开或关闭的前提条件，实现了FJM模型中颗粒与流体的循环耦合作用，并改进能够适配平节理接触的水力耦合数值计算方法，利用数值试验对裂隙岩样在压缩断裂和水力压裂条件下的宏观力学行为和破坏模式进行分析，从细观应力场和位移场的角度研究了裂纹的起裂模式。综上，本课题通过水压-应力耦合加载试验开展了深部赋存环境高应力高渗透压作用下裂隙岩样损伤演化的系统研究，有效揭示了复杂应力条件下岩体裂隙网络结构特征与裂纹扩展演化机理。研究成果为耦合应力条件下岩体工程破坏的预测提供了理论依据，对于探究岩体工程的失效机理具有重要学术价值，对提高岩体的设计水平等具有重要的科学意义和工程实际意义。