Study On The Risk Assessment And Active Protection About The Project Of Metro Tunnel Crossing The Urban Specially-shaped Slab Bridge

With the acceleration of the development of underground engineering in our country,the construction of urban subway project is ushering in a new round of high tide.Considering the complexity of urban construction,it is inevitable for subway tunnel to cross the city bridge foundation.As the weakest part of the urban bridge system,the safety of the special-shaped slab bridge must be paid enough attention by engineers and technicians.This paper is based on the Beijing Metro Line 7 engineering crossing the Guanganmen specially-shaped bridge,through the risk pre-assessment about engineering,the residual bearing capacity evaluation of the specially-shaped slab bridge,the determination of the foundation settlement control standard of the specially-shaped slab bridge and the optimization of the key parameters of the active lifting support,realizing the safety control for conduction of shield tunnel crossing the urban specially-shaped bridge.In this paper,a method for crossing project risk grading and the design of key parameters for actively supporting is validated in the practical engineering.It can be used as a reference for the risk assessment and design of the lifting support in the future.The main contents of this paper including:(1)On the mechanism of disturbance of surrounding soil by shield tunnel constructio,the article studied the influence of shield tunnel construction on single-pile and pile group foundation,focusing on the analysis of the shielding effect of pile group foundation and soil arching effect,and carries out numerical simulation analysis about the influence of shield tunnel construction on adjacent pile foundations deformation under the use of FLAC3D software.(2)Through the introduction of one-way compression spring to simulate the role of rubber bearings,the structural characteristics and the mechanical properties of the settlement about urban specially-shaped bridge are analyzed by finite element method.The vulnerability index is used to evaluate the settlement vulnerability of the specially-shaped slab bridge foundation.(3)Based on analyzing the influence of shield construction on stratum and pile foundation,the article introduced the improved Kent law risk assessment model,By improving parameter optimization and evaluation index and combining with the actual engineering situation,realizing the risk grading of project of shield tunnel crossing Guanganmen specially-shaped slab bridge with the help of numerical simulation analysis by using FLAC3D and Midas civil.(4)On the basis of the analysis of the structural mechanical characteristics of Guanganmen specially-shaped slab bridge,this paper introduces the method of radar chart to evaluate the residual bearing capacity of special-shaped slab bridge.Based on the analysis of the foundation settlement of the special-shaped slab bridge with Midas Civil,the settlement control standard of the single pier of Guanganmen specially-shaped slab bridge is determined.On this basis,the control method of different foundation combination settlement is obtained.(5)Through the finite element simulation of various conditions in the process of actively jack up for special-shaped slab and the reduction analysis about the bearing capacity of special-shaped slab,the article obtained the control limition of jacking one pier in the process of lifting Guanganmen specially-shaped bridge,and then the combined jacking control of different jacking quantity of each pier is realized.(6)Based on finite element analysis,through the comparison of the results of the internal force response of the special-shaped plate under different lifting conditions,obtaining the optimum parameters of the key parameters in the process of jacking up the special-shaped slab bridge,Optimizing the design of the actively lifting parameters of the special-shaped slab bridge.