Construction of an undersea shield driven tunnel under high water pressure from a marine launching base

The Trans-Tokyo Bay Highway is an approximately 15km long automotive highway which has been under construction across Tokyo Bay to connect Kawasaki City in Kanagawa Prefecture on the west side and Kisarazu City in Chiba Prefecture on the east side. The mid-bay section, where the volume of marine traffic is large, is designed as a tunnel structure approximately 10km in length with the Kawasaki Man-Made Island located at its midpoint. This unprecedented project to construct extra-large diameter tunnels by shield driving method under high water pressure involved various difficult problems, the principal ones being measures to avoid the danger of high pressure blowout during shield machine launching, removal of the temporary wall at the launching opening which had a strength of 100N/mm(2) and therefore could not be removed by the conventional method, and high precision connection of the shield driven tunnels within the ground of the bay floor. The connections at all four tunnels were safely completed in May 1997 and the highway was scheduled to be opened to traffic in December 1997. This paper describes the achievements attained in the construction of these tunnels, centered on the Kawasaki Tunnel Kawajin North Contract Section.