Study On The Influence Of Small Spacing Shield Tunneling On The Existing Subway

With the rapid development of China ’s economic construction,the construction of subway has become an important way for cities to alleviate ground traffic congestion.With the gradual increase of subway lines,cross-transfer lines occur from time to time,and it is inevitable that there will be up-crossing and down-crossing situations and most of them are small clear distances.Therefore,it is of great application value in the actual construction to study the influence of the construction of the new tunnel with small spacing shield on the deformation of the existing subway tunnel structure and explore the deformation control effect under different reinforcement measures.In this paper,based on the project of a new subway tunnel with a small clear distance shield crossing the existing subway tunnel in Zhengzhou,combined with theoretical analysis,the surface settlement and the deformation law of the existing subway structure are analyzed by using the research methods of three-dimensional numerical simulation and field monitoring.Under different unloading factors,the uplift deformation law of existing subway tunnel is analyzed.The reinforcement measures suitable for this project are proposed to effectively control the structural deformation and surface settlement.The results of numerical simulation are verified by field monitoring data.The main research results are as follows :(1)Based on the hydrogeological characteristics of the project,the relevant technical specifications in China,the pre-construction overview of the existing tunnel structure and the previous research results,the control standards of the existing subway tunnel and surface settlement deformation of the project are determined,and the selection of the shield machine is analyzed.(2)Based on the numerical simulation,eight typical working conditions of the construction of the left and right lines of the new tunnel are selected as the research focus of this section.The research shows that when the construction of the new tunnel small clear distance shield is completed,the surface settlement curve shows a ’ W ’ shape;the vertical deformation trend of the existing subway tunnel finally presents an ’ M ’ shape,and the overall performance is uplift,indicating that the redistribution of soil stress caused by tunnel excavation unloading is the main reason for the uplift deformation of the existing tunnel.The horizontal displacement is less affected,accounting for only 16.80 % of the vertical uplift deformation peak.It shows that the deformation of the existing tunnel is mainly uplift deformation.(3)Based on the numerical simulation results,it can be seen that when the actual project allows,increasing the vertical clear distance and horizontal projection angle of the new and old tunnels and the horizontal clear distance of the new tunnel can reduce the influence of shield construction on the existing subway tunnel.The radial full-ring grouting of the existing tunnel combined with the secondary reinforcement grouting reinforcement measures of the new tunnel has a significant effect on the uplift deformation and surface settlement control of the existing subway tunnel.(4)The field measured data of the shield tunneling process are collated and compared with the numerical simulation results to verify the reliability and effectiveness of the numerical simulation method and the reinforcement scheme,so as to provide reference for similar engineering construction.