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Subway Tunnel under the Han River, Seoul

The 1288 m long Han River tunnel connecting Yoido and Mapo - opened on December 30, 1996 - was constructed as a part of the 52 km long Seoul subway line No. 5, to improve the traffic conditions in Seoul. It lies 15.6-30 m below the riverbed. It is the first sub-aqueous tunnel in Korea. The New Austrian Tunneling Method was adopted as a construction method. A permanent monitoring system was installed to maintain the tunnel effectively. In order to monitor earth pressure, water pressure, and deformation of the tunnel cross section, monitoring pins, reflecting mirrors, electro-resistant type of sensors, and optical fiber sensors were installed for the daily measurement on the construction tunnel.