Numerical Simulation Of No.2 Tunnel Construction In Qichong Village,Qianchun Road,Guiyang

At present,the excavation method of shallow-buried,unsymmetrical and large-span tunnel mainly includes the full-section method,step method,ring excavation of core soil method,CD method,CRD method,single side heading method,double side heading method.Different construction methods are adapted to different engineering geological conditions.As the large span tunnel has a large cross section,the rock mass in the tunnel has a large unloading and deformation space during the excavation,local rock mass may be damaged due to excessive deformation,using a reasonable construction method to control the unloading and deformation of the surrounding rock is a effective means to ensure the construction proceeded smoothly.With different construction methods,the size of the excavation section and the degree of disturbance to the surrounding rock are different,the deformation and stress release of the surrounding rock are different.Moreover,for different construction methods,the material cost,labor cost,mechanical cost and time required have a large difference,which directly affects the economic efficiency of enterprises.In this paper,using the finite element software—MIDAS /GTS,this study involves the finite element model of shallow-buried,unsymmetrical and large-span tunnel in 2-qichongcun tunnel in Qianchun road construction project,and also conducted field monitoring tests,to study on the Construction Method in the excavation process of the tunnel.Specific research as follows:(1)According to the test,procedures the monitoring of the earth pressure between the surrounding rock and the initial lining,the pressure between the first lining and the second lining,the displacement of the rock,the strain of the steel arch and the strain of the two monitoring work on the selected three-steps-seven-footwork method excavation section,and organize the monitoring data.The stress characteristics of surrounding rock and supporting structure during the actual excavation are obtained.It shows that the three-step-seven-step method can be applied to the excavation of shallow-buried,unsymmetrical and large-span tunnel.(2)The finite element model of three-steps-seven-footwork method used in the actual excavation were set up,analyze plastic field,top vertical displacement,stress distribution of the surrounding rock,initial lining stress and two lining stress under the tunnel excavation.The characteristics of stress and strain of surrounding rock and supporting structure are obtained.Compare the extracted results of the three-steps-seven-footwork method excavation model with the data obtained from the field monitoring.The above proves that the numerical model can accurately reflect the objective construction process.(3)The finite element excavation model of YK2 + 760 section was set up under the three-steps-seven-footwork method,single side heading method and double side heading method.The stress distribution of surrounding rock,the vertical and horizontal displacement of the surrounding rock,the stress of the first lining and the stress of the lining under the three excavation methods were compared and analyzed.The stress and strain characteristics of the surrounding rock and supporting structures under the three construction methods were obtained,to find the difference between the stress and strain indicators.The above indicates that the three methods can meet the needs of the construction site,the construction process need to select the appropriate excavation method based on specific engineering geological conditions to achieve the purpose of guiding the construction.