Optimization Study on Underground Excavation of a Newly-Built Tunnel Passing Underneath an Existing Subway Station in Zero Distance and the Construction Parameters

With the networked development of subway tunnels, the approaching construction of a newly-built tunnel will bring great threat to the safety of the existing tunnels. In this paper, taking Nanjing Subway Line 5 Passing underneath an Existing Subway Station as an example, the impact of different underpass construction methods on the Project is explored by numerical simulation. As shown in the analysis results, the multi-pilot hole step method has the least impact on the existing station, which can effectively control the progress of vault settlement and surface settlement deformation. The construction would result in large settlement deformation at the center of the existing station, and the closer distance from the central axis of the newly-built tunnel would create a greater settlement value, with the bottom settlement reaching 2.36mm during the excavation of the pilot holes. In the process of excavation, the surface settlement curve changes from the shape “M” to “V”, and the surface settlement due to the removal of temporary support accounts for 66% of the total settlement.