Revisiting the construction of Japan’s now 30 year-old Seikan Tunnel

    An undersea station on the Seikan Tunnel route. Photo: Unmissable Japan.

    The Seikan Tunnel runs beneath the Tsagaru Strait, connecting the Japanese islands of Honshu and Hokkaido.

    Surveying of the geological outlay of the area began in 1946, with construction eventually beginning in September 1971.

    Building a 23km tunnel only 100m beneath the Tsagaru Strait was never going to be an easy task, and in 1976 construction crews hit a patch of soft rock, and water poured into the tunnel at a rate of 80 tons per minute. The leak took two months to fix.

    Construction of the main tunnel’s entrance section began in August 1982, 11 years after initial blasting and drilling had commenced.

    The entrance to the Seikan Tunnel on Honshu Island. Photo: Wikimedia Commons.

    Excavation of the underwater stretch of the tunnel began in 1983, making contact with the Hokkaido end of the tunnel in the same year.

    Construction of the submarine section was completed in March 1985 with an electrified rail system installed in September 1986.

    Four tunnels were dug and constructed during the course of construction: the main tunnel, a service tunnel, a pilot tunnel, and then a connecting gallery between the main tunnel and the service tunnel.

    The tunnel eventually opened on 13 March 1988, having cost a reported ¥1.1 trillion (US$7 billion) to construct, 12 times it original budget.

    The tunnel would run a single gauge track for close to 17 years before it was converted to a double gauge track and connected to Japan’s Shinkansen train network in 2005.

    This formed part of the Hokkaido Shinkansen project which aims to make use of the tunnel to have the Shinkansen network extend to Hokkaido Island.

    On 26 March 2016, the Shinkansen services commenced through the tunnel, with the previous regular narrow gauge passenger services through the tunnel ceasing.

    The electric system in the tunnel was also upgraded from 20kV to 25kV to accommodate the Shinkansen trains.

    A 3D cross-section of the Seikan Tunnel. Image: Blue-eyed Ronin.

    Currently, the maximum speed inside the tunnel is 140km/h.

    The Seikan Tunnel is currently the second longest and second deepest tunnel in the world, but still holds the record for the longest tunnel containing an underwater segment.

    The longest underwater tunnel is the Channel Tunnel, which lies under the English Channel and connects England with continental Europe in France.

    The Hokkaido Shinkansen project aims to connect Tokyo on Honshu Island with Sapporo on Hokkaido Island.

    Currently, the line ends at Hakodate on Hokkaido, which is more than 250km away from Sapporo.

    The completion of the connection of the line with Sapporo is expected to happen in 2030.

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