Primary Lining Timing and Mechanical Response in Bedding Rock During Arch Construction Using the Arch Cover Method
摘要
Arch construction is a critical step in the excavation process of the arch cover method for station excavation. However, there is a lack of mature experience in mechanical response and construction parameters for bedding rock masses. Relying on the Qingniwaqiao Station project of Dalian Metro Line 5, this study establishes a transversely isotropic elastoplastic model and further proposes the Zone State Index (ZSIsu) applicable to bedding rock masses. Based on this model and the ZSIsu, the mechanical response analysis of arch construction under bedding surrounding rock conditions is realized. Integrating the convergence-confinement principle, a methodology is proposed for identifying the optimal support installation time for large-section pilot tunnels in station construction using the arch cover method under bedded rock conditions. Research findings reveal that surface settlement occurring during the arch construction phase is mainly attributable to the excavation of the middle pilot tunnel and the dismantling of temporary support structures. The smaller ZSIsu values at the right side of the vault and the arch feet indicate the weakest stability in these regions. Based on displacement growth rates and the ZSIsu, the optimal support timing for primary lining of the middle large-section pilot tunnel at this station is determined to commence 2.5 m behind the tunnel face. Based on ZSIsu and the convergence constraint method, the timing of primary lining for bedding rock mass can be determined more accurately. As a quantitative method for evaluating bedding surrounding rock stability, ZSIsu compensates for the limitations of relying solely on displacement rates to assess stability, thereby enhancing the reliability of tunnel support timing selection.