Safety Management For A Large Diameter Shield Tunnel Traversing Existed Metro Station

In the process of large-scale development of urban underground space,the integrated rail transit mode dominated by rail transit construction has become an important and difficult problem in the future development of underground space.With the acceleration of construction,the engineering environment conditions become more and more complex and changeable.Urban network planning is becoming more and more intensive.Also,it is more and more common for new tunnels to be built close to underground structures.Safety is the core of the crossing project,including its impact on the structure and environment of the project.Therefore,it is of great significance to study the impact of urban shield tunnel crossing construction and process safety control.This paper is based on the project of Tsinghua Garden Shield Tunnel under Zhichun Road Metro Station on Beijing-Zhangzhou High-speed Railway.The theoretical analysis,numerical calculation and field measurement are adopted.The control standard formulation,deformation analysis and prediction of strata and subway structures,reinforcement of existing structures and safety management of construction process in shield tunnel underpass engineering are studied in depth.The main results are as follows:(1)Based on the structural damage assessment,the existing metro structural control standards are formulated.First,damage assessment of existing structures is needed.Using Analytic Hierarchy Process and Comprehensive Fuzzy Theory to Calculate Comprehensive Reduction Coefficient of Underground Structure Control Standard.The relationship between deformation and stress of Metro structure is obtained by numerical calculation and theoretical analysis.The control standard of metro station in the process of shield tunnel underpass construction is formulated.(2)An optimized Pasternak foundation model considering deformation joints is proposed.The structure between deformed joints is equivalent to a finite beam.The force acting on the deformation joint is taken as the boundary condition to simulate the effect of the deformation joint in Pasternak foundation model.Then the analytical solutions of structural displacement,bending moment and shear force are derived.The calculation method of differential settlement at deformation joints is given.Taking a project as an example,the optimized Pasternak foundation model,Winkler foundation model and numerical simulation results are compared.The results show that the optimized Pasternak foundation model can predict the deformation of existing structures more accurately.The influence of formation parameters,engineering parameters and structural parameters on structural deformation is analyzed.(3)Based on the numerical simulation of shield tunneling process,the optimal reinforcement scheme is proposed.Comparing the two working conditions of station structure and non-station structure,the influence of existing structure on stratum deformation is analyzed.The results show that the existing structure can block the transfer of deformation to a certain extent and reduce the influence of construction on surface deformation.When no reinforcement measures are taken,the settlement and horizontal displacement of the structure exceed the control value.The reinforcement effects of horizontal jet grouting pile,pipe curtain and multi-layer small pipe grouting are compared.Comparisons are made in terms of applicability,reinforcement effect,construction technology,environmental impact and cost.The grouting reinforcement of multi-layer small conduit is the most economical and reasonable.(4)Based on the measured data,the deformation law of subway structure during shield tunnel underpass is summarized,and the dynamic control system of crossing engineering is put forward.The characteristics and rules of Metro structure and track cross-section and time-history deformation are analyzed.The deformation process of the station structure can be roughly summarized as "stability before penetration～grouting reinforcement and lifting～slow settlement after penetration～continuous subsidence after construction～stability of deformation after penetration".The deformation process of track structure is similar to the tunnel structure.It can be summarized as "stability before penetration～grouting reinforcement with a small amount of lifting～slow settlement after penetration～continuous subsidence after penetration～rebound after construction～deformation stability".The whole process of shield construction is comprehensively analyzed.A dynamic safety control system for crossing engineering is proposed.The corresponding safety control measures are put forward in the three stages of pre-construction,during-construction and post-construction.It realizes the fine,dynamic and intelligent control of the crossing project.It has been successfully applied in the project of Tsinghua Garden Tunnel passing through Zhichun Road Station.