Abstract: The freezing construction of connecting passages in super-large-diameter shield tunnels is challenged by high risk of water and sand gushing during drilling, difficulty in controlling the drilling accuracy, complex tunnel support systems, ambiguous control criteria of frost heave pressure, multiple diameter changes of the connecting passage structure, and low excavation efficiency of frozen soil. To resolve these challenges, a series of innovative technologies and construction techniques have been developed and applied in a renovation project of six frozen connecting passages along the Beijing East Sixth Ring Road. Designed for the geometric characteristics of super-large diameter tunnels and the conditions of high water pressure and water-rich strata, the key technologies are a suspended-basket type lifting drilling platform, a high-precision total station alignment method, an anti-spray device for the pipes of deeply buried freezing holes under high water pressure, three-dimensional visualization of complex multi-section and variable-diameter structure engineering, a rotary drilling rig for rapid frozen soil excavation, and precise sealing and water-stopping of 650 mm segment penetration holes. During the project, it was found that: (1) The proposed key technical system effectively avoided the risk of water and sand gushing during drilling, enabling precise and safe hole-drilling during the construction of connecting passages in super-large diameter shield tunnels via the freezing method. (2) The improved support, cold drainage, pressure relief techniques, and protective doors effectively controlled the freezing risks, thus enhancing the safety and controllability of the freezing process. (3) The three-dimensional modeling visualization successfully assisted five diameter changes of the passage structure, precise reinforcement tying, and precise lining pouring. Moreover, the rotary drilling rig greatly improved the excavation efficiency of frozen soil, reduced the labor intensity of workers, and shortened the construction period.

Key words: super-large-diameter shield tunnel, artificial freezing method, Beijing East Sixth Ring Road renovation project, water-rich stratum, connecting passage, water and sand gushing