Application of 'casting support tunneling system using TBM' to unconsolidated soil with high groundwater level

The Sambongihara Tunnel on the Tohoku Shinkansen Line, located between Hachinohe and Shin-Aomori stations, is a double-track tunnel 4,280 meters long. The geology of this tunneling site mainly consists of alternating layers of unconsolidated sandy soil under high hydraulic pressures and cohesive soil. Excavation of this tunnel began in August 2001 using the NATM from the Shin-Aomori side, but the tunnel face collapsed twice, preventing the tunnel construction from advancing as scheduled. We therefore conducted an in-depth study to develop a new tunneling technique, aimed at improving efficiency and safety of the work. The new tunneling method uses a standard earth and mud pressure shield to maintain face stability and ensure good excavating capability. The technique developed will significantly improve the efficiency and safety of the work. This paper outlines the construction and design of the linings selected for this tunneling practice.