Study On Longitudinal Deformation Of Existing Metro Tunnel Caused By Undercrossing Construction And Engineering Measures

With the increasing of metro and various municipal tunnel projects, there are more and more crossing constructions. In crossing construction, the new tunnel casts great effects upon the existing ones. So it becomes a great urgent to study the evaluation of the influence that the undercrossing construction upon the existing tunnels and the corresponding measures. This paper is based on a full understanding of the deformation patterns of the surrounding soil caused by tunnel excavation and the mechanical principles of undercrossing construction and the influencing factors. Through theoretical analysis, numerical simulation and in-situ experiments, this research studies the influence of undercrossing construction upon the performance of longitudinal structure of the existing tunnels. The main conclusion is as following:(1)The curves of stratum settlement trough caused by the Tunnel excavation can be showed through Gaussian curves. Stratum settlement causes the deformation of existing tunnels. At the same time, the existing tunnels retroact on the stratum which makes the deformation of the existing tunnels differs from the deformation of the free stratum.(2)Based on the theory of beam on elastic foundation, the calculation method of longitudinal deformation of existing tunnel caused by undercrossing construction is established. Further, the longitudinal internal forces and the longitudinal vertical limit deformation of the existing tunnels are studied. Through the calculation of longitudinal internal forces, a reasonable evaluation of the longitudinal performance of existing tunnel can be achieved.(3)To make up for the shortcomings of analytical methods, through numerical simulation, this research analyzed the functions and the effects of a variety of reinforcement measures in reducing the influence of undercrossing construction upon the existing tunnels.(4)By in-situ experiments, research is made on the feasibility of the application of deep-hole subsection back-grouting with concentric tubes in the sand and gravel stratum. The research results are applied to a South-to-North water diversion project, in which the water-deliver tunnel undercrosses the Wukesong subway station, and results achieved are quite positive.