绿泥石片岩地层大跨度公路隧道大变形控制及合理支护形式现场试验

为了探索绿泥石片岩地层大跨度公路隧道大变形控制技术及合理支护形式,以陕西省宝(鸡)汉(中)高速公路连城山隧道工程为依托,针对采用单层I22b、双层I22b和双层HK200b钢架的3种初期支护形式,通过对围岩变形和支护结构受力进行现场量测,对比分析了不同初期支护形式的变形控制效果,提出了大跨度公路隧道软岩大变形控制方法和支护体系。研究结果表明:“大预留+双层HK200b钢架分次强支护+大管径长锁脚锚管+深仰拱”联合支护体系能有效控制隧道大变形灾害,避免初期支护变形侵限及频繁拆换拱;该支护体系中第1层初期支护钢架的刚度不宜太弱,以避免因其刚度不足导致的局部失稳和局部拆换问题;试验断面第2层初期支护的接触压力约占第1层初期支护围岩压力的61%,二次衬砌接触压力约占第1层初期支护围岩压力的40%;调整仰拱曲率对于优化结构受力和防治仰拱底鼓作用显著;基于对连城山隧道试验断面围岩压力和径向位移的统计分析,建立了不同支护阶段和不同刚度下的围岩-支护特征曲线,揭示了围岩与支护的相互动态作用机制和“多层分次强支护”大变形控制方法的支护作用机制;结合连城山隧道大变形处置实践,总结提出了“三台阶留核心土法+大预留、多层、分次支护+大管径长锁脚锚管+深仰拱”的大变形控制技术、“不侵限、不换拱、不破坏压密区”的大变形防控理念及“大断面、少分步、快挖快支”的施工原则。研究成果可为类似软岩隧道大变形控制提供重要借鉴。

In-situ Experimental Study on Large-deformation Control and Reasonable Support Forms for a Large-span Highway Tunnel in Chlorite Schist

To explore the large-deformation control technology and reasonable support forms for a large-span highway tunnel in chlorite schist, based on the Lianchengshan Tunnel of the Baoji-Hanzhong Expressway in Shaanxi Province, the deformation of surrounding rock and the stress of supporting structure under three primary support forms of single I22b, double I22b and double HK200b steel sets were in-situ measured, the deformation-controlled effects of different primary support forms were compared and analyzed, and the large-deformation control method and support system of large-span highway tunnels in soft rock were proposed. The study results indicate that the combined support system of “large deformation allowance + double HK200b steel sets + large-diameter long foot reinforcement bolt + deep invert” can effectively control large-deformation disasters in the tunnel and prevent the clearance invasion of primary lining and the multiple reconstruction of steel sets. To avoid the local instability and local reinstallation caused by insufficient stiffness, the stiffness of the first steel rib should not be too weak. The contact pressures of the second primary lining and secondary lining account for 61% and 40% of the ground pressure, respectively. It has a significant effect on optimizing structural stress and preventing floor heave by adjusting the invert curvature. Based on a statistical analysis of the ground pressure and radial displacement of the test sections in the Lianchengshan Tunnel, the characteristic curves of the surrounding rock and support under different supporting phases and stiffnesses were established. The dynamic interaction mechanism between the surrounding rock and support and the supporting mechanism of the large-deformation control method of “multilayer and staged strong support” were revealed. Combined with the engineering practice of large-deformation treatment in the Lianchengshan Tunnel, the large-deformation control technology of “three-bench method with reserved core soil + large deformation allowance, multilayer and staged strong support + large-diameter long foot reinforcement bolt + deep invert, ” the large-deformation control concept of “no clearance invasion, no support reconstruction, no damage to the compaction zone, ” and the construction principle of “quick excavation and quick support with larger section and fewer steps” were proposed and summarized. The research results can provide a significant reference for the large-deformation control of similar soft rock tunnels.