The Numerical Simulation Study Of Surface Subsidence In Shield Construction Of Subway

The construction environment of subway engineering is complex and the technical requirements are very high.The key link of the project is the tunnel construction.But in the process of shield tunneling,stratum deformation and surface subsidence are unavoidable.Large area settlement will affect the progress of construction,especially the safety of adjacent buildings,structures and municipal pipelines.How to reduce the disturbance of soil around the tunnel and how to control the surface deformation and settlement is of great significance for practical engineering application.Combined with the theory of time and space effect of stratum movement,starting from the related functions of shield machine and soil,the main contents of this paper were studied on the main factors affecting the surface subsidence and the trend of change.In this paper,the constitutive model of tunnel excavation from the Bell Tower Station to Yongning Gate Station in Xian metro line 2 was established by using numerical analysis method.Through the simulation calculation of FLAC3D finite difference program,the influence of the covering soil thickness,shield tail,grouting intensity,tunneling pressure and segment rigidity on the deformation of the strata was studied under different construction schemes,and the law of the change of the surface subsidence was obtained.Provide reference for similar project shield construction,reduce and avoid engineering accidents.The research was carried out from the following aspects:1)Through collecting and reading relevant documents and materials,the basic principle and main technical links of shield tunneling construction were introduced in detail.Based on the theory of space-time effect of stratum movement,the cause and mechanism of surface subsidence caused by shield tunneling were expounded,and the main influencing factors of formation deformation and surface subsidence were summarized.2)The engineering hydrogeology and the monitoring of surface subsidence data from the Bell Tower Station to Yongning Gate Station in Xian metro line 2 were analyzed and sorted out.The existing Peck formula was corrected by using existing monitoring data of subway excavation.And the lateral subsidence analysis of the data collected from the monitoring section of the tunnel section was carried out.3)According to the background of shield driven tunnel project from the Bell Tower Station to Yongning Gate Station in Xian metro line 2,with the help of ANSYS finite element software,the variables which are not easy to be quantified were generalized as homogeneous and equal thickness,and a simplified three-dimensional numerical simulation model was established.According to the normal tunnel shield construction procedure,the surface subsidence law during the earth pressure balance shield construction was studied by using FLAC3D finite difference software.Finally,by comparing and analyzing the simulation results and the actual monitoring results,it was verified whether the software simulation was reasonable.4)The surface subsidence curves of different covering soil thickness,shield tail grouting intensity,tunneling pressure and segment rigidity were simulated and calculated.By comparing the characteristics of subsidence curves of the same group,the influence rule of above factors on surface subsidence was analyzed and judged.It provides some reference and reference value for reducing the formation disturbance of similar project background.