ABSTRACT
Shallow-buried sections at tunnel entrances, especially those with large spans and complex cross-sections, present significant construction challenges due to the large excavation areas, complex geometry, and low cover-to-span ratios. This paper focuses on the construction of the Qingdao Jiaozhou Bay Second Subsea Tunnel’s large-span entrance section, proposing a “double pilot side drift and backward core excavation” method. Finite element simulations and on-site monitoring were used to validate the method’s feasibility and effectiveness. Key findings include: (1) the proposed method significantly improved construction efficiency, with deformations and stresses well within safe limits; (2) crown settlement and arch springline convergence stabilized at around 9 mm, with contact pressure of 70 kPa between the initial support and surrounding rock; and (3) the method was successfully applied in practice, offering valuable insights for future large-span tunnel projects.
