Research On Key Technology Of Undercut Construction Of Loess Metro Section Tunnel Under Complex Engineering Conditions

With the extensive construction of subway in various cities,different cities will have different geological conditions due to different geographical location,which will also bring different construction problems.Based on the Tianwang Hongqing tunnel project of Xi’an Metro Line 9(Lintong line),this paper carries out the construction technology of crossover section,section conversion technology,air duct construction technology,and the construction of hidden ground fissures under earthquake load Dynamic response and so on.(1)This paper analyzes the different construction methods used in different sections of the crossover line,analyzes the section conversion forms of section e(middle tunnel method)and Section D(double side heading method),Section C(double side heading method)and section B(CRD method),Section B(CRD method)and section a(bench reserved core soil method)by numerical simulation method,and analyzes the surface settlement,structural deformation and stress distribution in the process of different construction methods conversion To determine the key control parts.(2)The construction technology of piston duct is analyzed,and the ground settlement,deformation and stress of main line tunnel and duct structure under different construction sequence are studied.At the same time,the paper puts forward the reinforcement measures for the optimization scheme,analyzes the deformation of the opening position of the main line tunnel,and determines the optimization reinforcement scheme.(3)This paper studies the expansion of buried ground fissures in X direction and Y direction under the action of earthquake load,analyzes the deformation of main line tunnel under three conditions of section size,double line tunnel spacing and ground fissure buried depth,and explores the weak position of tunnel structure under stress.(4)The structural stress and deformation monitoring of e section(middle tunnel method)and D section(double side heading method)of crossover section is carried out,and the variation law of structural stress and deformation with construction engineering is analyzed,so as to timely feed back and guide tunnel construction.In this paper,the reasonable cross-section conversion form of crossover section was proposed,the construction scheme of air duct was optimized,the propagation law of hidden ground fissures under seismic load was studied,the stress and deformation law of tunnel structure with middle tunnel method and double side heading method was mastered,and the key technology research of Loess subway tunnel excavation construction under complex engineering conditions was formed.It provides technical support for ensuring tunnel construction safety and engineering quality.