Abstract: The double-arch tunnel has the advantages of reducing the spacing between two tunnels, having high space utilization rate, and effectively saving the investment cost, but there are disadvantages such as complicated construction process, potentially disturbance of the surrounding rock, difficult to construct, and long construction schedule. How to optimize the construction sequence, to control the deformation of the surrounding rock, and to ensure the construction quality are the current challenges in the design and construction of double-arch tunnels. This paper presents a case history of a double arch tunnel project of Maozhutang Station Storage Line of Changsha Rail Transit Line 5. The design utilized “five-pilot hole + stepped excavation” method, which could continuously perform the construct operations, effectively shorten the construction period, and thus reduce the construction cost. To explore the influence of the excavation on the stress and ground subsidence of the initial shielded structure, the feasibility and safety of the proposed method are validated by the numerical analysis and the on-site construction monitoring data. This information can provide a reference for the similar projects in the future.

Key words: Argillaceous Siltstone formation, Double-Arch Tunnel, Ultra-Shallow Burial, New Construction method, Numerical Analysis