Seikan Tunnel (undersea tunnel)  Japan

The Seikan Tunnel is an undersea railroad tunnel 53.85 km long (100 m and 240 m below the seabed) connecting Honshu and Hokkaido in Japan. Mining construction was difficult due to water runoff. New leakage prevention measures were implemented, and new seawater-resistant spraying materials and Microfine Cement were developed for this construction. After 27 years of construction, the tunnel was opened to traffic, and bullet trains and freight trains are still operating safely every day.

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