Determination of the Installation Time of Secondary Liner during Excavation of Large Cross-Section Double-Arch Tunnels

Double-arch tunnel construction involves in high risk due to its large span and special structural shape. In order to explore the proper installation time for the secondary liner during the excavation of large cross-sectional double-arch tunnels supported by three layers of the liner, this paper optimizes the distribution of the stress release ratio based on the analysis of surrounding rock deformation and structural stress. Proper installation time for the secondary liner is determined according to the optimization results and regressive analysis of monitoring data of initial support crown settlement. The results show that the reasonable distribution of stress release ratio is 30% during tunnel excavation, 30% after initial support installation, and 40% after secondary liner installation. After installing the initial support, the total crown settlement at three monitored sections is 51.5, 52.0, and 49.8 mm, respectively. When the initial support crown settlement reaches 65–75% of the final value, the secondary liner should be installed, and the crown settlement is 14.4–19.5 mm, 15.3–20.5 mm, and 14.4–19.4 mm, respectively, at three monitored sections. Findings from this paper can provide reference for design and construction of similar projects.

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