Research On Comprehensive Design And Construction Technology Of Bifurcation Tunnel In Complex Urban Environment

Urban development in China has long followed the extensive mode of extension and centrifugation.With the rapid increase of urban population,the existing transportation facilities and roads in cities are far behind the needs of development,resulting in a series of "urban diseases" such as space congestion,traffic congestion and environmental deterioration.Especially in some urban core areas and old urban areas,the urban ground level road construction has no great potential to dig,so the urban underground road system emerges as a result.The underground interchange project is the key point of the underground road system,which can make the traffic flow in the underground space to achieve "quiet" conversion and diversion.The design,construction and operation technology of the long-span bifurcation tunnels for entrances and exits has become one of the most critical technologies in the construction of the underground road system.Taking the underground interchange bifurcation tunnel of Chongqing Yuzhong connection tunnel as the research background,and combined with the monitoring data of the construction site,this paper studies and summarizes the mechanical morphology of the bifurcation tunnel construction,the influence of the surface buildings on the safety of the bifurcation tunnel structure,and the influence of the construction of the bifurcation tunnel on the safety of the surface buildings.We hope to provide reference for similar domestic projects.Firstly,this paper reviews and introduces the current research status of bifurcation tunnel,tunnel adjacent buildings,and tunnel numerical analysis,etc.Secondly,it studies the rules of surface buildings’ influence on the structure of asymmetric small clear distance tunnel.It includes the influence of surface buildings on the distribution of tunnel support load,the influence of surface buildings on the safety factor of tunnel support,and the influence of the position relationship between the buildings and underpass tunnel on the settlement of tunnel vault,etc.Thirdly,in the case of the asymmetric small clear distance tunnel,double-arch tunnel,triple-arch tunnel and tunnel sections,this paper obtains how the internal force of different tunnel lining varies with working step through calculation and analysis.It determines the working step with maximum internal force and minimum safety factor(the worst working step),and the working step with the greatest change of internal force and the sharpest reduction of safety factor(key working step),and has evaluated its safety accordingly.Fourthly,by mathematical method and based on the existing research results,considering the influence of the surface buildings on the surface settlement deformation,this paper puts forward the stiffness correction method of the building settlement prediction.Finally,through numerical calculation and theoretical analysis,the safety of the bifurcation tunnel roof is analyzed and evaluated combining with the monitoring data.The main conclusions of this paper are as follows:(1)For asymmetric small clear distance tunnels,surface building load above large section tunnels or between two tunnels has a greater influence on the support load of two holes,while small surface building load above section tunnel has a smaller influence on the support load of two holes.The influence of the surface building load of left hole on the safety factor of the supporting structure of right hole is greater than that of left hole(the same is true of right hole).The influence of the surface building load between left and right holes on the safety factor of the supporting structure of both holes is both relatively big;(2)For asymmetric small clear distance tunnel and asymmetric double-arch tunnel,the excavation of the rock wall in the left hole will have a great negative influence on the secondary lining of the right hole and the initial support of the left hole.For triple-arch tunnel,the excavation of the right guide hole upper step of the connecting passage has a great negative influence on the initial support of the left hole,the secondary lining and the initial support of the connecting passage.(3)Based on the existing research results,considering the influence of surface buildings on the surface settlement deformation,this paper puts forward the stiffness correction method of building settlement prediction,and the calculated surface settlement by this method is relatively consistent with the numerical results.(4)Through numerical calculation and theoretical analysis,the safety of the tunnel roof of the bifurcation tunnel is analyzed and evaluated conbined with the monitoring and measurement data of the construction site.