Study On The Influence And Countermeasures Of Underground Metro Tunnel Under Expressway Construction

Based on the tunnel project of Chongqing rail transit No.6 branch line passing through Chongqing Ring Expressway,this paper studies the construction influence and control measures of the underground excavation subway tunnel with three pinhole cross section passing through the expressway by the method of numerical simulation and on-site monitoring.The main research contents and conclusions are as follows:(1)This paper analyzes the time-space effect of the formation deformation caused by the tunnel excavation and the mechanism of the subgrade deformation,summarizes the main factors affecting the formation settlement in the process of the construction of the underground excavation tunnel,and summarizes the main countermeasures to control the formation settlement.(2)In this paper,the numerical simulation method is used to study the construction stability of pin shaped three hole cross section tunnel under three different excavation sequences,namely "right tunnel ? left tunnel ? middle tunnel","right tunnel ? middle tunnel ? left tunnel" and "middle tunnel ? right tunnel ? left tunnel".The deformation of surrounding rock and supporting structure,stress of surrounding rock,stress of supporting structure,surface settlement,etc According to the comprehensive comparative analysis of the plastic area of surrounding rock,it is suggested to adopt the sequence of "right tunnel ? left tunnel ? middle tunnel".(3)In view of the problem of large deformation of surrounding rock and surface,the paper puts forward the treatment measures of pre reinforcement of three hole tunnel by small pipe grouting before excavation,and reinforcement of the bottom layer of middle tunnel by concrete-filled steel tube pile.The numerical simulation results show that the reinforcement scheme can effectivelyreduce the deformation of surrounding rock,the stress of support structure and the area of plastic zone,and has significant effect on controlling the surface settlement.(4)Based on the results of numerical simulation,the excavation footage of pin shaped three hole cross section tunnel is optimized.Based on the comprehensive comparative analysis of surrounding rock deformation,support structure stress,surrounding rock stress and plastic area,it is suggested to adopt 1 m excavation footage.(5)Based on the monitoring data of the construction process,the change rules of surface settlement and surrounding rock deformation are analyzed,and the monitoring results are compared with the numerical simulation results to verify the rationality of the determined construction scheme.