高地应力挤压碎裂断层区隧道开挖卸载效应研究

Squeezing fractured fault under high geostress condition is always appeared in deep buried tunnel structure. Because of the more complicated stress environment and mechanical properties of the surrounding rock，some serious engineering disasters are often occurred, such as rock collapse, deformation invading limit, the cracking of shotcrete, twisted steel frame, and so on. Based on the shear strength test curves of squeezing fractured rock under high geostress condition, it would be put forward that a new parameter named dynamic softening modulus. Then a new rock strain softing model could be established by studying on the strain softening rule of squeezing fractured rock under high geostress condition. The features of plastic softing and plastic flow would be shown in this model. On this basis, a new deformation pressure formula would be derived considering the space effect and the stress redistribution rule during excavation unloading process. Combined with model test and 3D numerical analysis based on strain softening model, the new strain softing model and the new deformation pressure formula could be further improved through the comparison of mechanical characteristics during the excavation unloading process. The research results can provide a theoretical basis for the flexible supporting time and deformation control of tunnel structure with squeezing fractured rock under high geostress condition.

本课题以深埋隧道工程中的高地应力挤压碎裂断层区隧道为研究对象，以基于大型剪切试验曲线的碎裂性围岩动态软化模量研究为切入点，深入研究高地应力挤压碎裂断层岩具有的应变软化规律，建立基于“塑性软化”和“塑性流动”的岩体软化模型。在此基础上，考虑开挖卸载过程中的空间效应，分析其应力重分布规律，推导高地应力挤压碎裂断层岩开挖卸载后的形变压力计算公式。通过隧道开挖支护模型试验和基于应变软化的三维数值分析，系统研究其在卸载过程中的力学特性，验证并完善高地应力挤压碎裂断层岩应变软化模型和开挖卸载后的形变压力计算公式，为高地应力挤压碎裂断层区隧道工程柔性支护时机和变形控制提供理论依据。

深埋隧道工程中，高地应力挤压碎裂断层区隧道在施工中极易发生大变形、侵限、塌方等灾害，导致人员伤亡，造价失控，工期延误。针对上述问题，结合现场试验和监控量测数据，采用理论分析、室内试验和数值模拟等方法，考虑高地应力挤压碎裂断层区围岩的工程力学特性，理论分析阐明了高地应力挤压碎裂断层区隧道形变压力形成机理，基于相似材料室内试验、模型试验与数值模拟研究，揭示了其施工力学特性。项目首先搜集国内外软弱围岩隧道的工程实例，通过阅读文献、现场调研与室内试验，分析高地应力软岩隧道施工现状与岩体力学参数；然后，基于室内试验与理论分析，获得相似材料与模型试验合理参数，结合模型隧道开挖与数值模拟结果，分析得知围岩变形特征以及围岩-支护结构相互作用体系，归纳总结高地应力软岩碎裂断层区应力-应变特征；通过室内钢筒模型，得知高地应力软岩碎裂断层软弱围岩开挖卸荷规律，通过多维方法得出实际地层围岩在开挖过程中的应力释放特性；结合上述研究，分别推导了基于岩体软化“直-曲-直”模型的高地应力挤压碎裂断层区隧道卡斯特耐尔公式扩展、原岩塑性状态下高地应力挤压碎裂断层区隧道支护力作用解析解、高地应力挤压碎裂隧道剪切滑移破坏法理论计算式并通过实例计算进行验证。研究结果表明：对于高地应力挤压碎裂断层区隧道，初始地应力对于掌子面前方预收敛变形影响显著，推导公式计算的支护力远大于经典公式计算所得支护力，研究成果可为高地应力挤压碎裂断层区隧道工程支护力计算、支护结构设计、结构施做时机和变形控制提供理论参考。