Study On Excavation Stability Of Deep Hard Rock Tunnel And The Safety Netting System Rapid Construction Method

As a means of transportation,urban bridges such as overpasses often intersect with the line selection of subways and high-speed railways.The solution for this problem is usually to take the tunnel through the bridge from below,which have caused a large number of bridge and tunnel intersection engineering problems.This article is based on the engineering of Guangtian tunnel which through Huadu bridge from below to study the effect of open cut construction of urban tunnels on adjacent bridge piles,and using FLAC 3D to study the force under 8 working conditions during tunnel excavation: foundation pit stress field and displacement field,Support structure internal force and displacement,Isolated pile internal force and displacement,internal forces and displacements of pile foundations adjacent to bridges.At the same time,the forces of adjacent structures and support systems were analyzed,which can provides optimized solutions for site construction.The main research results are as follows:(1)Summing up the research status and progress at home and abroad of the formation deformation caused by tunnel construction and its effect on the stability of adjacent existing pile foundations.(2)The mechanism of the stability of tunnel adjacent to the bridge pile was analyzed based on three aspects of vertical,horizontal deformation of the stratum and its impact on adjacent bridge piles.(3)Based on the engineering of Guangtian tunnel which through Huadu bridge from below,Using FLAC 3D to simulate tunnel open cut construction and each process.During the numerical simulation,the forces under 8 working conditions during tunnel excavation were researched,including foundation pit stress field and displacement field,Support structure internal force and displacement,Isolated pile internal force and displacement,internal forces and displacements of pile foundations adjacent to bridges.Combining various factors,the effect of open cut tunnel construction on the deformation of stratum and bridge piles was summarized.The time point and process point of maximum axial force and maximum displacement after tunnel excavation under open cut conditions were discussed,which lead to the preliminary conclusions of weather the bridge pile able to maintain stability under open-cut construction of the tunnel.(4)According to the influence mechanism of open cut tunnel construction on the stratum and bridge pier foundation,with the numerical simulation data of foundation pit stress field and displacement field,Support structure internal force and displacement,Isolated pile internal force and displacement,internal forces and displacements of pile foundations adjacent to bridges and structural force calculation,The construction optimization scheme for tunnel under-excavation construction with existing bridge piles was proposed.