Numerical Study on the Fully Mechanized Rapid Construction Method for Subsea Tunnel

ABSTRACT This paper presents a case study of a super‐long subsea tunnel in Jiaozhou Bay, Qingdao, China. To address key technical challenges in the fully mechanized rapid construction of super‐long subsea tunnels, this study systematically investigates the optimization of excavation methods and support installation distance across different rock grades by integrated numerical simulation and field monitoring. A numerical model was developed to analyze deformation response and stability under classes III, IV, and V surrounding rock conditions using both bench method and full‐face methods, supplemented by multi‐scenario construction step tests. Results indicate that the full‐face method is suitable for class III rock without strict support distance requirements, where lining can be applied based on monitoring data and construction plans; For class IV rock, the full‐face method is recommended in stable sections, while the bench method should be used in fractured zones, with initial support closure limited to ≤70 m and secondary lining to ≤250 m from the excavation face; For class V rock, the bench method is advised, with initial support closure within ≤60 m and secondary lining within ≤240 m from the excavation face. Field monitoring confirmed that surrounding rock deformation remained within design limits, and initial support performed effectively, validating the proposed methods and distance criteria. This study provides theoretical and practical guidance for fully mechanized construction in similar subsea tunnel projects.