软弱地层隧道钢架-锁脚锚管组合支护与拱脚地层相互作用机制

When tunneling in soft ground using the partial excavation method, it is vulnerable to the overall settlement of tunnel support. As a result, the disturbed zone of the rock mass is expanded and the stability of the rock mass is decreased significantly, which directly threaten the construction safety. The combined support of steel frame and feet-lock pipe is an effective measure to resist tunnel settlement. Taking tunnels in soft ground as the background, this research project aims to reveal the transfer characteristics of the foot load under the combined support of steel frame and feet-lock pipe, clarify the load transfer mechanism along the axis and transverse of the feet-lock pipe, and put forward the calculation method for foot settlement and foundation load. The research is based on theoretical and testing methods. The foundation load and foot settlement are measured to analyze the bearing ratio between the feet-lock pipe and foundation and illustrate the main influencing factors. Distribution rule of foundation reaction coefficient along the length of feet-lock pipe, and load transfer mechanism along the axis of feet-lock pipe under the combined action of the tunnel settlement and convergence are to be revealed based on the simulation test and theoretical analysis. According to the testing and theoretical results, the mechanics analysis model for the foundation stability is established considering the coordinate deformation among the steel frame, feet-lock pipe and foundation at the tunnel foot. The calculation formulas of foot settlement and foundation load are derived to evaluate the reasonability of feet-lock pipe parameters and the stability of the steel frame before and after the excavation below the tunnel foot. The research results can provide theoretical foundation for tunnel design and construction in soft ground.

软弱地层隧道分部开挖过程中，常因拱脚支撑力不足，导致支护出现整体沉降，随之松弛区扩大，引起围岩稳定性显著降低，直接威胁施工安全。钢架-锁脚锚管组合支护是抵抗隧道沉降的有效措施。本项目拟以隧道工程为背景，揭示软弱地层隧道钢架-锁脚锚管组合支护下拱脚荷载传递特性，阐明锁脚锚管横向和轴向的荷载传递机制，提出拱脚沉降和地基荷载计算方法。研究方法拟以试验与理论并重，通过监测拱脚沉降和地基荷载，分析锁脚锚管与拱脚地基各自承载比例及主要影响因素；通过模拟试验和理论分析，揭示锁脚锚管横向地基反力系数沿长度的分布规律，以及隧道沉降和收敛变形共同作用下锁脚锚管轴向的荷载传递机制；依据试验及理论分析结果，建立钢架-锁脚锚管-地基协调变形的力学分析模型，推导拱脚沉降和地基荷载计算公式，评价台阶下部开挖前、后钢架脚部稳定性以及锁脚锚管支护参数合理性。研究成果可为软弱地层隧道设计与施工提供理论依据。

软弱地层隧道分部开挖过程中，常因拱脚支承力不足，发生初期支护整体沉降，随之松弛区扩大，造成围岩稳定性显著降低，直接威胁施工安全。钢架-锁脚锚管组合支护是抵抗隧道沉降的有效措施。本项目以隧道工程为背景，围绕软弱地层隧道钢架-锁脚锚管组合支护与拱脚地层相互作用机制，通过模拟试验、理论分析和现场测试等手段，开展了以下研究：.在模拟试验方面，研发了锁脚锚管支护下隧道拱脚地基荷载传递试验装置及方法；研究了黄土地层锁脚锚管的承载性能及锁脚锚管打设角度对承载性能的影响；反算了锁脚锚管横向地基反力系数，揭示了m值随锁脚锚管端部竖向荷载和竖向位移的变化规律以及锁脚锚管打设角度对m值的影响。.在理论分析方面，提出了锁脚锚管承载性能简化分析方法，建立了钢架竖向加载与锁脚锚管分担荷载、拱脚地基荷载的关系表达式，研究了锁脚锚管在分担拱脚地基荷载方面的性能表现及主要影响因素，揭示了锁脚锚管支护下拱脚地基荷载的传递特性；基于锁脚锚管支护效应、初期支护拱脚约束条件、锁脚锚管对初期支护拱脚的约束作用等分析，提出了考虑锁脚锚管支护效应的初期支护结构计算方法，推导了隧道拱脚地基荷载和拱脚沉降计算公式。.在现场测试方面，制定了光纤光栅测力锁脚锚管测点及光纤保护方案，确保现场测试数据稳定、完整、有效；根据锁脚锚管现场测试结果，揭示了锁脚锚管管身应变分布变化规律。受施工扰动影响，锁脚锚管各测点处应变的变化规律较为复杂；从整体上看，锁脚锚管靠近钢架一端的受力明显大于管身其他部位，靠近围岩深处一端的受力明显较小；锁脚锚管管身左、右测点处应变并非对称分布，与锁脚锚管和钢架的连接方式密切相关；锁脚锚管打设角度越大，其承担的荷载越多，且荷载可传递至围岩更深处，承载性能越好；对于极软弱的绿泥石片岩地层，考虑工程经济性，φ50锁脚锚管长度不宜超过3m，建议取2.5m。.以上成果可提升锁脚锚管支护理论研究水平，为软弱地层隧道锁脚锚管设计提供重要依据。