深部复合地层TBM开挖扰动模型试验研究

针对全断面隧道掘进机（TBM）开挖过程掌子面岩体软硬交替变化的特点，以兰州水源地建设工程为背景，采用模型试验与数值模拟方法研究了复合地层TBM开挖过程隧洞围岩的动态响应规律。通过开展相似配比试验配制了不同围岩强度比的复合地层岩体相似材料，运用光纤光栅技术全程捕捉了隧洞开挖过程复合地层应变演化规律，并分析了隧洞围岩的宏观破裂形态。模型试验结果表明：TBM推进过程中复合地层应变变化规律体现了掌子面推进的空间效应，软岩部分应变要大于硬岩部分应变，且随着开挖步数的增加两种岩层应变差值越大；隧洞内岩体完全挖除后，围岩宏观破裂形态表明因复合地层岩体物理力学性质的差异，上覆软岩变形破坏较为严重，破裂和变形较为显著，在软、硬岩层交界面出现“变形不协调”现象。选取工程沿线某洞段的地质力学参数，基于破坏接近度（FAI）指标评价了隧洞开挖过程中复合地层围岩的稳定性，数值结果表明：开挖过程软岩中FAI变化较为明显，塑性区和破坏区分布范围更广，而下部硬岩受开挖扰动影响较小，只有拱底小范围岩体进入破坏状态。模型试验和数值结果均说明交替变化的掌子面岩体在开挖过程中其围岩在变形破坏等规律方面存在明显差异，因此，TBM在复合地层施工可采取重点部位监测预警、提前采取相应措施等手段，减少或避免卡机事故的发生。该研究成果对于指导复合地层TBM施工具有一定的借鉴和指导意义。

Physical experimental study on excavation disturbance of TBM in deep composite strata

In view of the alternating change of soft and hard rock mass in the work face, physical model test and numerical simulation were conducted to investigate the dynamic response of tunnel surrounding rock during the process of TBM excavation in composite strata at the Lanzhou water source construction project. Similar composite rock mass materials with different strength ratios of surrounding rock were prepared by performing analogous proportion experiments. The fiber grating technology was used to capture the strain evolution law of surrounding rock in composite strata during tunnel excavation, and the macroscopic fracture morphology of the surrounding rock of the tunnel was also analyzed. The physical experimental results show that the variation law of strain in composite strata during the TBM propulsion process reflects the spatial effect of the face thrust. The strain of soft rock is greater than that of hard rock, and with the increase of excavation steps, the difference of strain between two rock strata becomes greater. After the excavation, the macroscopic fracture morphology of surrounding rock indicates that the deformation and failure of the overlying soft rock is more serious and significant due to the difference in physical and mechanical properties of the composite rock mass. The phenomenon of “uncoordinated deformation” can also be found at the interface between soft and hard rock layers. The geomechanical parameters of a tunnel section along the project are selected to evaluate the stability of surrounding rock in composite strata during tunnel excavation based on the failure approach index (FAI). The numerical results show that FAI changes obviously in soft rock during excavation, and the plastic zone and failure zone are more widely distributed, while the lower hard rock is less affected by excavation disturbance, and only a small range of rock mass at the arch bottom enters the failure state during excavation. Both the model test and the numerical results indicate that there are differences in change laws in the deformation and failure of the surrounding rock during the excavation process. Therefore, the construction of TBM in the composite stratum can take measures such as monitoring and early warning of key parts as well as early corresponding measures reduce or avoid the occurrence of TBM jamming accidents.