Abstract: The underground community-corridor project at Xiamen North Railway Station is situated directly above an operational open-cut tunnel of Xiamen Metro Line 1, with approximately 231 m of parallel overlap and a vertical clear distance of only about 3 m. The corridor excavation reaches a width of 64.5 m, producing a vertical unloading ratio of roughly 70%. To ensure deformation stability and operational safety of the underlying tunnel, it is essential to investigate the tunnel deformation patterns and corresponding control measures during excavation. A numerical simulation is conducted to analyze the deformation behavior of the operational open-cut tunnel under large unloading conditions. Two deformation-mitigation strategies are proposed: an inverted L-shaped anti-floating system and staged excavation with skipping compartments. Their effectiveness is verified through three-dimensional finite-element analysis and field monitoring. The inverted L-shaped anti-floating system—comprising a top-pressing pier, existing subway retaining piles, newly installed uplift piles, and longitudinal beams atop the uplift piles—effectively mitigates rebound deformation of the operational tunnel under ultra-long, close-proximity parallel conditions. During construction, staged excavation with skipping compartments leverages spatial effects to rapidly reconstruct the corridor’s main structure, generating counter-pressure on the underlying tunnel and significantly reducing vertical deformation. Results from numerical simulations and field monitoring confirm that combining the inverted L-shaped anti-floating system with staged excavation and compartment skipping successfully controls tunnel uplift within safe limits, ensuring structural stability and maintaining normal metro operations.

Key words: High Unloading Ratio, Operations, Open Cut Tunnel, Combined Anti Floating System, Interval Excavation