真三轴条件下应变型岩爆孕育过程研究

Strain rockburst is an unstable, dynamic, failure phenomenon that is caused by excavation-induced abrupt release of energy storied in rock mass. True triaxial test is used here to investigate the crack initiation mode, magnitude of post-peak stress drop along with declining rate of stress at a variety of places with different distances from tunnel periphery by means of varying stress paths. Combination of positioning technology of acoustic emission and moment tensor is capable of revealing crack initiation modes, like tensile, tensile-shear, and shear. Based on the energy ratio of release magnitude to peak storied energy and decreasing rate relative to the strain change, we proposed an energy criterion associated with risk classification, occurrence place, and failure zone as well as rockburst depth. The numerical discrete element DDA method is enhanced to obtain, quantitatively, the elastic strain energy, the dissipated energy of shear sliding, and the kinetic energy of the block system during rock bursting, in order to understand the development of strain rockburst along with the corresponding influencing factors. The influence of the intermediate and minimum stresses on the development process of rockburst is explored here to clarify the stress conditions for brittle-ductility transformation. These results can be verified by typical rockbursts recorded at Jinping hydropower station. This project can help predict energy release and dynamic failure during development of strain rockburst.

应变型岩爆是开挖强卸荷引起岩体内储存弹性应变能急剧释放的一种非稳定破坏动力失稳过程。项目拟采用真三轴试验系统开展不同应力路径加卸载试验，确定洞周不同部位、距离洞壁不同深处硬岩起裂应力，测定峰后应力降相对大小和应力跌落速率；结合声发射定位技术和矩张量分析方法，揭示起裂模式(拉裂纹、混合裂纹和剪切裂纹)，提出一种建立在峰后应变能释放量相对峰前应变能比值和应变量释放量相对应变跌落速度乘积的基础上、能够表征应变型岩爆风险等级、位置、潜在范围和破坏深度的的动力失稳能量判据。二次开发DDA，定量化计算岩爆发生过程中应变能、摩擦能、系统动能及其相互转化，解译应变型岩爆孕育过程与主要影响因素。研究中间主应力、最小主应力对岩爆孕育的影响，获得脆性—延性破坏转换应力条件。以锦屏记录的典型岩爆实例进行验证。项目可为预测应变型岩爆孕育演化过程中能量释放和动力失稳破坏提供理论支持。

岩爆是高地应力赋存环境下开挖卸荷引起洞壁硬岩突然性破坏的动力过程，其本质是储存在硬岩中弹性能瞬间释放转化成动能的一种地质灾害。本项目采用理论分析、数值模拟、室内真三轴试验与工程现场相结合方法，研究真三轴条件下应变型岩爆孕育过程。解析推导了开挖后考虑颗粒粒径与微裂纹长度关联的硬岩三维起裂模型，预测岩爆的范围和深度。采用硬岩真三轴加卸载系统，开展了洞壁不同位置不同深度处硬岩脆性破坏性真三轴试验，测试应力应变全过程曲线、声发射信号、微观断口形貌等，系统考虑了非对称应力条件下洞周硬岩的特征强度，探索非连续变形、微裂纹时空演化和岩爆破坏模式，揭示了应力诱导下应力路径、应力状态和岩性对硬岩岩爆的影响。当最大主应力σ1与隧道轴线平行或近似平行，开挖后围岩稳定性取决于σ2和σ3，甚至主应力就会发生旋转(σ2增加数倍并超过σ1，且σ1保持不变)，研究应力旋转对岩爆孕育演化的影响。分析中间主应力σ2和最小主应力σ3对岩爆的影响作用，确定了脆性—延性破坏转换的力学条件。中间主应力σ2会增加起裂应力σci、损伤应力σcd、峰值强度σp和残余强度σr，增强围岩破裂脆性。σci约为σp的50%；σcd约为σp的75%；σ3变化对起裂应力与损伤应力阈值的影响更为明显。随着与洞壁的距离增加，中间主应力方向ν2整体呈增加趋势，最小主应力方向ν3呈下降趋势。提出了一种基于三维应力状态、考虑岩爆位置、能量释放量相对大小和释放速率的岩爆动力失稳脆性判据，补充和完善现有二维平面单点岩爆判据。推导硐室开挖前后的总能量变化解析公式，二次开发DDA，引入非连续结构面特征，提出了岩爆过程中应变能、损耗能、动能相互转化定量化计算方法。从能量的角度，确定岩爆过程中各种能量与岩体结构、岩体质量、地应力场关系，揭示阐明三维应力路径下应变型岩爆孕育过程、成灾机制。