Analysis of the Impact of Foundation Pit Construction on the Deformation of Underlying Metro Tunnels

The excavation of a foundation pit will cause soil unloading, resulting in the structural deformation of underlying tunnels, which affects the safety of tunnel operation. Here, the impact of foundation pit excavation on the structural deformation of the metro interval tunnel underlying a foundation pit support project for a storage pond is analyzed through theoretical analysis, numerical simulation, and on-site monitoring, and corresponding safety control measures are proposed. The research shows that simplifying the tunnel into an infinite-length Euler-Bernoulli beam resting on the Kerr foundation model has good rationality and applicability when analyzing the impact of pit construction on the deformation of the interval tunnel. The distance between the foundation pit and the tunnel cross-section significantly affects the deformation of the tunnel structure, and the shorter the straight-line distance from the pit foundation, the more obvious the structural deformation of the interval tunnel. The maximum deformation of the tunnel structure occurs in the upper-left area of the middle of the tunnel near the foundation pit, and the deformation shows a nonlinear decreasing trend toward the two ends of the tunnel. Timely support can effectively inhibit the deformation of the foundation pit, and the spatial and temporal effects of foundation pit excavation on the underlying tunnels should be minimized during construction. The impact on the structural deformation of the underlying tunnels should be mitigated in strict accordance with the three-level control principle: early warning, alarm, and control. The research results provide a reference for guiding foundation pit construction.