深埋洞室软岩围岩开挖卸荷-流变特性研究

In the excavation of deep tunnels, the unloading rheological deformation of soft surrounding rock has great impact on the determination of the best supporting time. Taking the soft surrounding rock of deep tunnels as the study object, this research aims to investigate the excavation unloading and unloading-rheological mechanical characteristics of deep soft rock by conducting a series of laboratory triaxial tests and creep tests under unloading conditions according to the in-situ stress state of the soft surrounding rock. Then, in combination with the micro-structural change of the rock sample and the macroscopic deformation features observed in field, the characteristic of excavation unloading-rheological deformation and the deformation mechanism of surrounding rock are revealed, by which the boundaries of unloading deformation and creep deformation can be determined. Following that, an excavation unloading-rheological mechanical model for the surrounding rock of deep soft rock tunnels is built and revised by means of both spot monitoring and numerical simulation. The model describes the space-time stress-strain evolution law of the soft surrounding rock. In the meantime, the size, scope and developing trend of the unloading-rheological loose circle of the soft surrounding rock is defined and the reasonable optimal secondary support time and support scope are determined. The research results can provide helpful references for the deformation control of deep soft rock tunnels, and they can also provide helpful references to the deep soft rock engineering protection in areas such as transportation, mining, nuclear waste disposal.

深埋洞室软岩围岩的开挖卸荷-流变变形，关系到软岩围岩最佳支护时机的确定。课题以深埋软岩洞室围岩为研究对象，针对软岩围岩所处的应力状态，开展软岩室内三轴卸荷试验和三轴卸荷-流变试验，研究深埋软岩的开挖卸荷力学特性与开挖卸荷-流变力学特性，结合岩样细观结构变化与现场宏观变形破坏特征，分析软岩开挖卸荷-流变变形的特点，揭示围岩变形破坏机理，确定深埋软岩开挖卸荷变形与流变变形的界限范围。建立深埋软岩洞室围岩开挖卸荷-流变力学模型；利用现场监测资料与数值模拟相结合的手段，修正和完善软岩开挖卸荷-流变力学模型，掌握软岩围岩应力-应变时空演化规律；界定软岩围岩开挖卸荷-流变松动圈的大小范围及发展趋势，合理确定围岩的最优二次支护时机与范围。研究成果可为深埋软岩洞室变形控制提供依据，也可为交通、采矿、核废料处置等工程领域的软岩工程防护提供参考。

软岩洞室围岩开挖引起的大变形主要是开挖导致应力重分布产生的变形与软岩流变变形的叠加，且其流变持续时间长；特别是对于高地应力区地下软岩洞室，围岩与支护衬砌的变形现象将更加显著。如何界定软岩卸荷变形和流变变形的分界点，如何确定卸荷变形和流变变形的影响范围，关系到软岩开挖后二次支护时间及范围合理确定和支护结构的设计。因此，在地下工程尤其是软岩工程围岩稳定性分析中，迫切需要对深埋洞室软岩开挖卸荷-流变特性这一科学问题进行研究。本项目以四川省大渡河丹巴水电站引水隧洞工程为研究对象，采用室内试验、理论分析、数值模拟、现场监测数据对比验证等方法，开展了深埋软岩卸荷力学特性、洞室开挖施工卸荷-流变变形规律、围岩变形破坏机理，以及深埋软岩洞室围岩合理的二次支护时间与范围等方面的研究。主要研究结果有：确立了丹巴水电站右岸平硐深埋软岩抗压、抗剪强度和变形参数与应力路径的关系，分析了软岩卸荷条件-应变曲线延性-脆性转换机制；基于深埋软岩卸荷蠕变试验，分析岩石变形及损伤破坏规律，建立了考虑卸荷量的软岩卸荷蠕变本构模型并确定了相应参数的表征，并分析了单级卸荷与分级卸荷条件下的软岩稳态流变速率特征；通过大口径核磁共振成像系统NMR检测和外观破坏模式分析，从岩样内部微孔隙发育贯穿和宏观破坏的角度揭示了深埋软岩洞室围岩的破坏机理；分析了软硬相接围岩在开挖卸荷下隧洞围岩非协调变形破坏特征；以围岩变形演化为目标值，在不同洞型、洞泾及施工开挖方式优化分析的基础上，提出了以开挖面拱顶和拱底的相对位移为参考依据的二次支护时机确定方法。研究成果对深埋软岩洞室工程设计、施工控制和安全运行具有重要的理论意义，并在水电工程、交通工程、采矿工程及核废料地质处置等工程实践中对预防软岩工程的破坏、保证软岩工程的安全具有积极的实际意义。