The Impact of Existing Subway Tunnels on Excavation of Foundation Pits

In order to study the impact of existing subway tunnels on foundation pit excavation, this article takes an actual engineering project as an example and uses the finite element software PLAXIS 3D to simulate the construction status of foundation pit excavation around the existing subway tunnel and the lowering of groundwater outside the pit. The bending stiffness of the foundation pit piles is equivalent, and the soil material of the model is simplified under the action of groundwater, taking into account the connection between tunnel segments, Reduce the stiffness to 75% along its axis and 25% horizontally. At the same time, select boundary constraints that are in line with the actual foundation pit model to reveal the horizontal and vertical displacement changes of the foundation pit. The results show that the horizontal and vertical displacement of the foundation pit under four working conditions of excavation, as well as the horizontal and vertical displacement when the underground water level outside the pit drops by 1.0m and 1.5m, when the foundation pit is excavated to the base, are all within the controllable range of the foundation pit displacement required by the specifications. The research results can provide reference for the safe construction of existing subway tunnel foundation pit excavation.