Abstract: Using the section where the main line and ramps merge into the super-large span continuous variable cross-section of the Second Qingdao Jiaozhou Bay Subsea Tunnel, this paper proposed a dual guide tunnel advance-central column reverse excavation construction method under specific conditions to ensure the excavation construction stability of shallow-buried, large-span, continuously variable cross-section tunnels. The method's rationality and effectiveness were validated through finite element analysis and field monitoring data. The results showed that maintaining the original design's excavation partitions and using the proposed method could significantly enhance construction efficiency, with deformation and stress on the tunnel support structure within acceptable limits, ensuring structural safety and stability. Numerical simulation analysis showed that the reverse excavation of the central guide tunnel caused a rapid increase in the uplift of the invert, and stress concentration was likely to occur at the side walls of the tunnel, especially in the large-span section. During lateral excavation, the excavation of the lower bench significantly increased the load on the temporary support gantry, and stress concentration was prone to occur at the joints of the steel beams. During lateral expansion construction, the crown settlement and clearance convergence stabilized at approximately 9 mm, the initial support and surrounding rock contact pressure reached up to 70 kPa, and the maximum axial stress on the lining calculated empirically was about 0.354 MPa, with surrounding rock deformation and support stress meeting the standards. The dual guide tunnel advance-central column reverse excavation method had been successfully applied to the entrance section of the second Qingdao Jiaozhou Bay Subsea Tunnel.
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2024, Vol. 6 
