Monitoring and analysis of newly-built subway over-passing through existing shield tunnels in soft soil areas

Currently, many control and protection technologies have been applied in the construction of cross-passing projects. However, their implementation effects are dynamic and influenced by multiple factors. Therefore, further research is still needed to optimize the selection and implementation effect of these technologies, so as to adapt to increasingly complex underground engineering problems. This article carries out relevant monitoring data analysis based on the engineering project of Ningbo Metro Line 5 crossing over the existing Line 2. The results show that the vertical deformation of the existing tunnel is significantly affected by the superimposed construction of the new shield tunnel, with obvious spatial and superimposed effects. The vertical deformation of the existing tunnel generally manifests as bulging with a unilateral influence range of 6~7 times the outer diameter of the tunnel. The transverse deformation manifests as "vertical duck egg" shaped elliptical deformation with horizontal contraction and vertical expansion. More importantly, when constructing a new subway tunnel over-passing through the existing shield tunnel, a combination of several control and protection technologies used in this project has proved to be effective, including controlling construction parameters, weighting measurements, reinforcement of existing tunnel segments, soil reinforcement, intensifying monitoring and informationized construction. This paper can be used as a reference for similar projects.