Optimization Analysis And Engineering Application Of Underground Excavation Construction Scheme For Super Large Section Metro Station

Urban metro stations often belong to super-large cross-section tunnels,with shallow burial depth,complicated environment,and difficulty in construction by dark excavation.Especially for the construction of subway stations in the soil-rock combination stratum,the tunnel vault is usually located in the upper soft soil layer,and its arching effect and self-stabilizing ability are poor,and it is easy to induce excessive ground subsidence,which may lead to the cracking,damage and even collapse of ground buildings and underground structures.Therefore,it is of great significance to carry out the optimization analysis and engineering application research of the construction scheme of the underground excavation of the super section metro station for the solution of the practical engineering problems.The Provincial Hospital Station of Guiyang Metro Line No.2 is located in a typical "soil-rock combination" stratum.Taking this as the engineering background,the thesis conducted in-depth research on the optimization and optimization of undermining method and the determination of advanced pre-supporting schemes using numerical simulation and on-site monitoring research methods,mainly achieved the following research results:(1)Summarized and analyzed the major and difficult problems of underground excavation construction of the station,and initially determine the construction plan.The Provincial Hospital Station was summarized in detail from the aspects of design overview,surrounding environment and engineering hydrogeology,and the major anddifficult problems of the underground excavation construction of the station were summarized and analyzed.On this basis,the main construction methods of the single-arch no-pillar excavation station are described,evaluated and selected,the commonly used pre support methods are summarized and optimized according to the characteristics of the project,and the superimposed primary support arch method combined with advanced large pipe shed grouting pre-support excavation construction scheme.(2)Established a three-dimensional excavation geological model of Provincial Hospital Station,explored and compared the mechanical response of surrounding rock and supporting structure under different construction methods,and determined the optimal construction method.Midas GTS NX is used to establish a three-dimensional geological model of the main tunnel excavation of The Provincial Hospital Station,which respectively simulates the whole excavation process of four construction methods,such as the superimposed primary support arch method,double-wall guide method,CRD method and ring excavation core soil method.The mechanical response of surrounding rock and support structure under different construction methods is explored and compared.The comprehensive construction period,construction cost and other factors determined that the superimposed primary support arch method was the optimal construction method.(3)The optimization plan of the construction sequence of the superimposed primary support arch method is proposed,the obvious advantages of the optimization plan are summarized,and the safety and feasibility are explored with the help of finite element software.Based on the core idea of superimposed primary support arch method and the stratum settlement characteristics caused by excavation,the construction sequence optimization plan for the pilot tunnel that is applied in advance to strengthen the initial support and then excavated is proposed and the optimization plan is summarized to ensure construction safety,It has great advantages in shortening construction period and reducing engineering cost,and then further analyzes the optimization plan and the original design plan from the perspective of excavation mechanics response,and clarifies the safety and feasibility of the optimization plan.(4)The method of numerical simulation was used to explore the reinforcementeffect of the pipe shed grouting pre-support and verify its effect.Aiming at the problem that the red clay intrusion in the arch of The Provincial Hospital Station is thick and easy to induce large deformation or even collapse,the effect of the preliminary determined grouting pre-support scheme of the large pipe shed was studied and analyzed by numerical simulation.The settlement control effect,the safety of the supporting structure and the stress characteristics of the pipe shed determine that the pipe shed grouting pre-support system can effectively control the settlement and improve the safety factor of the supporting structure to ensure the construction safety.