Abstract
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.
Highlights
Double-arch tunnels are composed of two side-by-side parallel tunnels with their adjacent liners supporting on a central pillar to form an “M” shape. e double-arch tunnels require smaller construction space, and its alignment selection is more flexible compared with two separate parallel tunnels
Part of the earth load will be released as the deformation energy, and the remaining will be undertaken by supporting structures, i.e., tunnel liners. e portion of load depends on the installation time of the tunnel liner
Based on optimal distribution of stress release ratio, proper installation time for the secondary liner is determined through regressive analysis of monitoring data of the initial support crown settlement. e research results can provide reference for the design and construction of similar projects worldwide
Summary
Double-arch tunnels are composed of two side-by-side parallel tunnels with their adjacent liners supporting on a central pillar to form an “M” shape. e double-arch tunnels require smaller construction space, and its alignment selection is more flexible compared with two separate parallel tunnels. Erefore, it is important to accurately determine the reasonable installation time for the secondary liner to ensure the structural safety and control the deformation of the surrounding rock. Is paper analyses the proper installation time for the secondary liner of the Haicang double-arch tunnels in the Xiamen western passage project. E double-arch tunnels are mostly buried in completely weathered to moderately weathered rock mass, except at the east end of the alignment where the tunnel is buried in mixed ground. E local groundwater table is about 2 m below the ground surface and is connected with the West Xiamen Sea. e fill material (stratum 1), residual soil (stratum 3), completely weathered rock mass (stratum 5–1), and heavily weathered rock mass (stratum 5–2) have a high permeability ranging from 10–4 to 10–2 cm/sec, and it is important to control the groundwater intrusion during excavation The upper part of the tunnel face is buried in residual soils classified as gravelly clay (stratum 2) and completely weathered rock mass (stratum 5–1), and the lower part of the tunnel face is buried in heavily weathered rock mass (stratum 5–2). e local groundwater table is about 2 m below the ground surface and is connected with the West Xiamen Sea. e fill material (stratum 1), residual soil (stratum 3), completely weathered rock mass (stratum 5–1), and heavily weathered rock mass (stratum 5–2) have a high permeability ranging from 10–4 to 10–2 cm/sec, and it is important to control the groundwater intrusion during excavation
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