Thursday, October 2, 2008
Seikan Tunnel (Seikan Tonneru)
After two decades of planning and construction, the 33.5-mile-long (53.85-kilometer) Seikan submarine tunnel was opened to traffic on 13 March 1988. Part of a railroad between Aomori City and Hakodate City, it links Honshu, the main Japanese island, with Hokkaido to the north, passing under the 459-foot-deep (140-meter) Tsugaru Strait. The tunnel runs 328 feet (100 meters) beneath the ocean bed for 14.5 miles (23.35 kilometers); thus, at 787 feet (240 meters) below sea level, it is the deepest railroad line in the world. The journey between the terminals takes two and a half hours. It has been called “one of the most formidable engineering feats of the twentieth century.”
Before the tunnel was built, ferries provided transport between Honshu and Hokkaido. After a typhoon sank a ferry boat in the Tsugaru Strait in September 1954, killing 1,430 people, public pressure for the construction of a safer crossing increased. Plans were already under way: geological studies of the area had been started as early as 1946, and the Tsugaru line among those planned in Japan’s Railway Construction Act of August 1953. In April 1964, almost immediately after the newly established Japan Railway Construction Corporation took over research operations from Japan National Railways, a basic plan was called for, and exploratory inclined shafts were sunk on either side of the strait by early 1966. Five and a half years passed before the minister of transport approved the final plan, allowing construction to commence.
Excavation began on the underwater section of the tunnel first, with a 16.35-foot-diameter (5-meter) pilot tunnel, which was started from both ends, meeting in the middle in January 1983. Next followed a service tunnel of similar size. The latter, about 100 feet (30 meters) from the rail tunnel and connected by regularly spaced junctions, now serves as a maintenance and escape route. The main tunnel’s entrance section was commenced in August 1982.
The main tunnel, with an internal width of 32 feet (9.7 meters) and a clear height in the center of almost 26 feet (7.85 meters), was slowly constructed through the seismically unpredictable seabed by drilling and blasting (nearly 3,300 tons, or 3,000 tonnes, of explosives were used); the nature of the geology made the use of a tunnel-boring machine impracticable. The submarine section of the tunnel was completed in March 1985, and eighteen months later the two-track electrified rail system was in place. Commercial rail services for passengers and freight began in March 1988. There are two stations in the tunnel: Tappi Kaitei on Honshu and Yoshioka Kaitei on Hokkaido, just on the respective coasts.
Because the Seikan Tunnel’s signal system is based on an uninsulated rail circuit, rails were welded together to form a single rail—the longest in the world—running nearly the length of the tunnel. This provides a much smoother ride for commuters. The tunnel was designed with high-strength rails, large-radius curves, and minimal gradients to enable possible future use by Japan’s famous Shinkansen (bullet trains). For the time being, the cost of extending the Shinkansen has proved prohibitive. Moreover, the Seikan Tunnel had cost 1.1 trillion yen (U.S.$7 billion) to build—almost twelve times the original estimate. Much of the budget blowout was attributable to inflation, because the ten-year estimated construction time had, through accidents and other circumstances, extended to twenty-five. The delays had another effect: ironically, the convenience offered to travelers by the Seikan Tunnel has now been rivaled by quicker and cheaper air travel between Honshu and Hokkaido.