Influence And Control Research On Super Large Section Tunnel Undercrossing Closely Subway Bridge In Beijing

Urban rail transit is one of the most important infrastructures of a city. Beijing urban rail transit construction is still in the stage of rapid expansion, thus there has been a number of projects of super-large cross-section tunnels undercrossing existing bridges. Obviously, the construction of these projects is quite difficult and with high risks. While research on a tunnel undercrossing the existing rail transit bridges research is very few. Therefore, this paper compared and analyzed the effects of different excavation methods and grouting measures for this kind of projects.It is crucial for the healthy development of underground engineering.This paper analyzed the impacts of different influence factors for these projects by numerical simulations, and then selected the reasonable tunnel excavation method combined with bridge protection measures by comparisons. Furthermore, the project of a super-large cross-section tunnel closely undercrossing the existing subway bridge in Beijing was taken as the research object.The main research contents are as follows:(1)The basic principle of super-large cross-section tunnel construction was inductived. Summed up the advantage of the overall analysis method-the finite element method under the condition of the complicated factors.(2) The stratigraphic-structure three-dimensional entity models has been established by ANSYS. Effects of different excavation methods, grouting measures and horizontal distance were simulated under the conditions of super-large cross-section tunnels undercrossing existing subway bridge in short distance, and the reasonable tunnel excavation method combined with bridge protection measures was selected.(3) The exanpling project adopts the selected double guide holes method and the whole section grouting for protection. By the numinical analysis and monitoring data analysis in the construction process, the structure deformation law of the bridge crossed by the tunnel and the track were studied. And the pile foundation bearing capacity was calculated.(4) Some reasonable protection measures was put forward for the construction process, in the case of super-large cross-section tunnels closely crossing metro bridges, providing guidance to protect the safety of metro operation for similar construction projects.