HIGH-TECH TUNNELS

The article reports on Japan's most expensive highway project, the construction of a 15km road link across Tokyo Bay. This complex project will involve the construction of new 10km long twin tube tunnels and a 4.4km long bridge. Each tunnel will have 13.9m diameter, and be lined with rings of 10t precast concrete segments. Each tunnel face is using the largest tunnelling machines yet built, which are also totally automated and move forward about 45m per week. The two engineers, who operate a clean control room inside each shield, equipped with television and computer screens, are only there to monitor a computerised operation of excavation, shield advance, and lining erection. Special procedures have been designed for the operation of joining the two sections of one of the tunnels, due by the end of July 1996. During construction, the tunnels pass through the large artificial Kawasaki Island, which houses a central ventilation shaft. They emerge onto the large artificial Kisarazu Island, from whose other end the already completed 42-span steel box girder bridge to the eastern shore emerges. Both artificial islands are almost complete, and construction activity focuses on the eight tunnel faces converging on each other. Special precautions are being taken against seismic shocks.