Development of sandwich-structure Submerged tunnel tube production method

Since 1988, Nippon Steel Corporation has developed a new submerged tunnel tube production method consisting of prefabrication method which does not required graving docks, composite structure, and reliable flexible joint. The Kobe Minatojima Submerged Tunnel, the first steel-concrete sandwich tunnel tube, was produced in the graving dock. This development has been completed with the first tube completion of The Naha Submerged Tunnel, which the double-skin steel tube shell body including a bellows joint was towed to Okinawa from Kitakyusyu and was placed high fluidity concrete while afloat early spring in 2001.