水力耦合作用下三维裂隙岩体破裂的时空演化机理研究

The fracturing evolution of jointed rock mass under hydromechanical coupling condition is an important cause of the instability of deep underground structures and engineering accidents, and it is also a key issue involved in the hydraulic fracturing process of oil and gas resources exploitation. In this project, a series of laboratory experiments, theoretical analyses and numerical simulations will be performed systematically to investigate the space-time evolution mechanisms of three-dimensional fracturing of jointed rock mass under hydromechanical coupling condition. First, hydromechanical coupling experiments will be carried out to study the initiation condition of three-dimensional cracks, the propagation and coalescence patterns of cracks and the interaction effect between adjacent cracks, and the influences of the geometric and distributive characteristics of cracks and the loading conditions on crack growth will be analyzed to help understand the space evolution mechanism of rock mass fracturing. Besides, the correlation rules between the crack growth and coalescence as well as the rock mass fracturing behavior with the loading time will also be investigated, aiming to reveal the time-dependent characteristics of rock mass fracturing. Then theoretical analyses will be conducted on the basis of experiment data to investigate the mechanical and deformational behavior of jointed rock mass under hydromechanical coupling, and the initiation criterion of three-dimensional crack as well as the strength evolution criterion of jointed rock mass will be presented. Finally, a mechanical model of jointed rock mass that considering the fracturing process under hydromechanical coupling condition will be established and will also be programmed on the basis of distinct element method. The study results can provide scientific basis and technical support for the stability evaluation of underground engineering, the prevention of engineering accidences and the efficient exploitation of resources.

水力耦合作用下裂隙岩体的破裂演化是导致深部地下结构失稳及工程事故发生的重要原因，同时也是油气资源开发中进行水压致裂增产所必须关注的核心问题。本项目拟综合采用室内试验、理论分析和数值模拟方法，系统研究水力耦合作用下三维裂隙岩体破裂的时空演化机理。通过开展水力耦合室内试验，调查三维裂隙的起裂条件、扩展和贯通模式及裂隙间相互作用机制，分析裂隙几何分布特征及加载条件对裂隙空间扩展贯通的影响，阐明裂隙岩体破裂的空间演化机理；通过调查裂隙扩展贯通及岩体宏观破裂行为与加载时间的相关性规律，阐明裂隙岩体破裂的时效特征。在大量试验数据的基础上开展理论研究，分析水力耦合作用下裂隙岩体的受力变形行为，提出岩体三维裂隙的起裂判据以及岩体强度演化准则，构建水力耦合作用下三维裂隙岩体破裂演化过程的力学分析模型并实现离散元程序化。上述研究成果可为地下工程稳定性评价、事故防治以及资源高效开发提供科学依据和技术支撑。

水力耦合作用下裂隙岩体的破裂演化是导致地下结构失稳及工程事故发生的重要原因，也是深部资源开发中进行水压致裂增产所必须关注的核心问题。本项目综合采用室内试验、理论分析和数值模拟等方法，系统研究了水力耦合作用下三维裂隙岩体破裂的时空演化机理。.在裂隙岩体破裂的空间演化方面，调查了三维裂隙的起裂条件、扩展和贯通模式及裂隙间相互作用机制，分析了水力加载条件及裂隙几何分布特征的影响。结果表明：水压能够有效驱动裂隙起裂并倾向原裂纹面扩展，增强张拉破裂模式，增大岩体失稳破裂风险；双向受压状态下的裂隙岩体较单轴加载时更为安全，而拉压共同加载时则更易破裂；随裂隙倾角在一定范围内增大，翼裂纹临界扩展长度减小，而试件破裂模式经历了张拉为主—拉剪复合—剪切为主的转变过程；裂隙间距减小使双裂隙外侧端部应力集中增强，导致翼裂纹更易萌生，并改变岩桥贯通特征和岩体破坏模式。.在裂隙岩体破裂的时效特征方面，调查了水力耦合条件下裂隙扩展贯通及岩体破裂行为与加载时间和加载模式的相关性规律。研究表明：在轴压恒定状态下，水压增大显著提升了裂隙亚临界扩展和非稳定扩展速率，使岩体破裂具有突发性；围压增大显著延长了岩体加速变形至失稳破坏的时间，增加了岩体延性变形；倾角对裂隙扩展的时效性特征具有明显影响，45°裂隙最容易起裂并发生非稳定扩展，而含较大倾角裂隙的岩体长期稳定性较好。.在试验数据的基础上，分析了水力耦合作用下裂隙岩体的受力变形特征及强度演化规律，并结合声发射技术提出了岩体三维裂隙起裂扩展的阶段性特征及判别方法。研究表明：随水压升高，起裂应力、损伤应力和峰值强度持续降低，且水压的影响存在阈值；试件破裂过程中声发射撞击率变化呈现明显阶段性特征，为起裂应力和损伤应力判定提供了依据；根据破裂发展进程，岩体破裂可分为未开裂、小破裂和大破裂3个状态，其对应的声发射主频变化特征可为破裂状态的预测预警提供参考信息。