Influence of Local Leakage in a Shield Tunnel on Stratum Deformation

Local leakage from a shield tunnel significantly impacts the surrounding strata, leading to surface subsidence and potential collapse. This study develops a discrete-element program and adopts the FEM-discrete-element method coupling model to accurately simulate the entire process of stratum deformation caused by shield tunnel leakage. The variation rules of stratum deformation, leakage rate, and leakage area around a locally leaking tunnel are analyzed under varying leakage position (θ), gauge height (HW) and opening size (C), considering both stratum properties and local tunnel deterioration. Based on the simulation results, the deformation area of the stratum is categorized into severe, moderate, and mild leakage zones, and the leakage process is divided into four Stages A–D. The research findings indicate that the stratum leakage characteristics are positively correlated with the opening size, while the leakage location significantly impacts the integrity of the stratum leakage process, with only the leakage located on the vault and arch shoulder resulting in noticeable surface settlement. Additionally, as the leakage position shifts downward, both the final area of leakage and the leakage rate for each stage decrease, with the maximum settlement point shifting correspondingly. Furthermore, an increase in gauge height leads to an initial rise, followed by a subsequent decline in the stratum leakage parameters. Ultimately, the quantitative relationship between the area of moderate leakage and the leakage angle is established, along with an equation for the maximum leakage rate. A rapid evaluation method for the leakage stage is proposed based on the maximum leakage rate. This study offers valuable insights for mitigating tunnel leakage disasters in a water-rich sandy stratum.