Dept. of Civil and Environmental System Engineering, Konkuk University, Seoul, KoreaA.T.
Most conventional 2-arch tunnels have been constructed with pilot excavation of center tunnel utilized 3-step excavation. However, such method has low constructability due to the confined space of the center tunnel and is exposed to various issues, including leakage from the required complex waterproofing drainage system. Accordingly, this research studied designing an improved 2-stage 2-arch tunnel excavation method in which the proceeding tunnel is constructed after establishing structural stability of preceding tunnel through reinforcement shotcrete or concrete. First, a scaled model test using plaster was conducted to validate the improved 2-arch tunnel construction method. Based on the experimental test results, various parametric studies were conducted through numerical analysis. Findings from those studies yielded a standard cross section with the central support thickness at 40 to 60cm.The suitable amount of support and a standard supporting pattern were then suggested through converted breadth estimation. Bench cut and/or CD cut excavation sequences were suggested for excavation of the proceeding tunnel."