Study On The Safety Performance Of Prefabricated Open-Cut Subway Tunnels During Operation

Due to the existence of joints in the assembled lining structure,the stiffness of the structure is weakened at the joints,thus affecting the overall structural stress performance;the concrete at the edge of the pressure zone at the joints is prone to stress concentration and crushing,and the joints are prone to opening when bending,thus affecting the waterproof performance of the joint gasket.In this thesis,based on the urban rail transit project in Jinan City,Shandong Province,the new tramway project from Jinan to Jiyang District(Advance Zone)is studied for structural stress performance,flexural stiffness of assembled lining joints,waterproof performance of lining joints and long-term settlement of the subway during operation.The main research contents and results are as follows:(1)Force analysis of the structure through numerical simulation.According to the structural design drawings of the relying project,a fine model was established by the three-dimensional load-structure method,taking into account the reinforcement,prestressing rebar and strand,and assembly joints within the precast unit structure,etc.The structural force performance during the tunnel operation period was analyzed,as well as the influence of the placement position of the longitudinal joints on the internal force of the structure.(2)Analysis of the law of prefabricated structure joints subjected to bending.According to St.Venant’s principle,the location of the joint is in accordance with the assumption of a flat section,so there is a transition zone near the structural joint.(3)Improving the mechanical model of joint flexural stiffness.Based on the assumption of constant concrete volume during bending of the joint,the deformation geometry of the joint is derived,and the joint force-deformation and bolt forcedeformation relationships are combined with the force balance relationship,moment balance relationship,concrete force-deformation relationship,and bolt forcedeformation relationship to solve the unknown quantities and derive the joint force and deformation results,and an improved mechanical model of joint bending stiffness is established.The joint design parameters of related projects were substituted into the mechanical model to obtain the calculation results of structural edge tension,structural tension height,bolt stress,and joint flexural stiffness,which were compared with the experimental results of engineering studies to verify the correctness of the proposed mechanical model.(4)Study the waterproof performance of the joint waterproof gasket.Through numerical simulation to calculate the internal force of the structure,and into the joint bending stiffness mechanical model,the pre-stress loss in the case of joint opening analysis,the composite rubber gasket for a waterproof performance test,the pre-stress loss does not affect the waterproof performance of the gasket.Gasket waterproof performance increases with the increase in compression,and the impact is more sensitive when the compression is larger.The gasket corner and joint are the weak points of waterproofing;the corner should be changed to a curve arrangement,and the joint should be 6063 rubber special adhesive glued and wrapped with a layer of unvulcanized butyl rubber sheet.(5)Prediction of subway tunnel settlement during operation.The dynamic response of the soil under the train load is calculated by numerical simulation,and the settlement due to accumulated residual deformation without drainage and the consolidation settlement due to accumulated pore pressure dissipation are calculated separately,and the total settlement during the operation period is calculated by the layered sum method.The predicted settlement due to accumulated pore pressure dissipation is always significantly larger than that due to undrained accumulated residual deformation;both the predicted settlement subdivision and the predicted total settlement develop rapidly at the beginning and gradually slow down with time;the predicted total settlement is 30.36 mm at 15 years of operation and reaches 91.24% at6 years of operation.91.24% at 6 years of operation.