Study On The Influence Of Subway Approaching Onstruction On The Existing Tunnel Based On MJS Construction Method

The vault of line 5 is only 3.9m away from the floor of line 1.The stratum condition of the tunnel is complex and it belongs to the soft fluid-plastic stratum with specific regional characteristics.Aiming at the conditions above,Nanjing metro design department plan to adopt MJS(Metro Jet System)construction method for a pre-reinforcement to control the sedimentation of existing tunnels so as to ensure the safety of metro line 1.In order to master the influence law of soft fluid-plastic stratum approaching construction on the existing tunnel thus making sure of the construction safety,the shield tunneling method is adopted to underpass the existing subway line 1 project of the newly-built subway line 5 in Nanjing,and the physical similarity model test and finite element numerical simulation method are used to study.This paper analyzes the changes of ground surface settlement,existing subway settlement rules and lining stress in the process of shield construction under unreinforced and pre-reinforced measures of MJS construction method.The main results are as follows:(1)The strata traversing by shield are mainly composed of silty clay and silty sand.The working principle and characteristics of MJS jet pile are analyzed.Combining with the MJS construction method pre-reinforcement scheme introduced in this project,the construction sequence of horizontal rotary grouting piles is put forward based on the construction required parameters and reinforcement area layout scheme in the case of asthenic-plastic stratum.(2)Aiming at the characteristics of Nanjing soft flow plastic formation on the basis of the similarity theory to carry out the indoor physical model test,under the shield by simulating line 5 in the process of line 1,get in the process of the construction monitoring of displacement and stress monitoring results,through comparing unreinforced and strengthened with the optimal parameters of pre-reinforcement MJS methods after measuring point displacement deformation and stress change rule,both in the process of analysis of shield tunnel subsidence displacement and stress change rule and the subsidence of surface displacement change rule,verifying the rationality of the pre-reinforcement MJS methods of construction parameters.(3)The use of MIDAS/GTS NX software research new shield tunnel line 5 nearly took the existing tunnel line 1 construction of wear,effects on the changes in displacement and stress characteristics of the existing tunnel and subsidence of surface displacement are present a single settling tank "u-shaped" the shape of a settlement,and displacement of tunnel vertical intersection part between sedimentation value,the largest increase with the distance between two tunnel axis and the displacement value reduced gradually.The reinforcement measures for the newly built tunnel need to be protected by the MJS construction method pre-reinforcement measures for the soil above the newly built tunnel.Data monitoring should be strengthened for the key parts near the construction section.The detection project should adopt the automatic monitoring system.