Study On The Influence Of Shield Construction Of Small Spacing Metro Tunnel On The Surface Settlement And The Mechanical Performance Of Existing Tunnel

In order to put forward reasonable construction parameters and construction protection measures,then reduce the impact of shield tunnel construction in subway tunnels.The Fuzhou Metro Line 6 from Lianhua station to the section of the exit and entry line through the existing section of the Shajing Station to Lianhua station are taken as the engineering background,this paper studies on the influence of the clearance,the elastic modulus and the load release coefficient of the shield tunnel on the existing tunnel and the above ground surface during the shield tunnel construction of the small clear distance subway tunnel.After that,research work on the influence of shield tunneling in small spacing Metro tunnels are proposed as follows:1)Based on the background engineering situation,a threedimensional dynamic simulation of shield tunnel excavation process is established by using Midas/GTS finite element model.The calculation results of the finite element model under actual working conditions are analyzed,and the laws of surface subsidence,segment deformation and stress change in field deformation monitoring are compared.The reliability of the model and the rationality of the model parameters are verified,and the model parameters are adjusted according to the measured results when necessary.2)A three-dimensional finite element model of small net-distance tunnel with parallel left and right and overlapping upper and lower spacing is established.Then,the parameters of net-distance,elastic modulus of equivalent layer and load release coefficient are analyzed,on this basis,the transverse distribution of surface settlement,deformation and stress of existing tunnels caused by construction of tunnels are obtained.Based on the maximum surface subsidence as the evaluation criterion,the sensitivity of net distance,elastic modulus of equivalent layer and load release coefficient was evaluated by range analysis method,and the preliminary conclusion that net distance < elastic modulus of equivalent layer < load release coefficient was obtained.3)According to the conclusion of range analysis,the corresponding protective measures for shield tunnel construction with small net distance are put forward,such as controlling and adjusting the shield construction parameters timely,pre-reinforcing the existing tunnel segments with steel rings,reinforcing the surrounding rock and rock column,and real-time dynamic monitoring before and after construction to reduce the stratum and structural deformation,which put forward suggestions for the follow-up construction of the project.At the meantime,some references are provided for the construction of small net distance shield tunnel under similar conditions in the future.