Tokyo's Dainikoro Underwater Tube-Tunnel

The Tokyokou Dainikoro Tube-Tunnel is a four-lane highway tunnel which, when completed in 1980, will provide direct access to manmade islands in the Bay. The estimated cost is about 30 billion yen ($130,000,000). The overall project length is 1,782 m (5,847 ft), of which 744 m (2,441 ft) between two ventilation buildings is the submerged tube-tunnel, consisting of six section each 124m (407 ft) long. Approaches and ventilation buildings are contructed on deep-pile foundations, while the tube sections are placed in a dredged trench that is later backfilled. Interesting methods described include: (1)Construction of tubes from reinforced concrete rather than fabricated steel. (2)construction in a dry dock that was subsequently flooded: (3)a two-point temporary landing on adjustable jacks rather than on a precisely leveld bedding: and (4)subsequent pumped backfill with bentonite mortar grout under the tubes.