Large cross-section shield tunnel passing right under the Jyoban and Hibiya railway lines: Minowa Tunnel of the Tsukuba Express line

摘要

The Minowa Tunnel, constructed by the slurry shield method with an outer shield diameter of 10.2 mm, passed obliquely right under railway lines in service (Tokyo Metro Hibiya, JR freight, and JR Jyoban lines) for a length of about 300 m. The construction conditions were severe because the overburden of the tunnel in the intersection area is thin (1.2 to 0.4 times the tunnel diameter), an alluvial clay layer with N-values of 0 to 6 is prevalent in the area, and a sandy soil susceptible to collapse is present in the upper part of the tunnel. To ensure the integrity and safety of the railway facilities while operating the existing railway lines on usual schedule, the tunnel was constructed by preventing slurry eruption during shield advancement and suppressing abrupt settlement of the railway tracks.