World's longest tunnel
to link Honshu and Hokkaido
CONSTRUCTION will begin this fall on what will be the world's longest tunnel (2.7 times the length of Simp- lon Tunnel in Europe) linking the main Japanese island of Honshu with the northern island of Hokkaido.
Scheduled to be completed in 1977, the railway tunnel, named Seikan, will extend 54.2 km (33.6 miles), of which 23.3 km (14.4 miles) will run under the Tsugaru Straits separating Honshu and Hokkaido.
Surveys
Preliminary surveys were begun as early as 1946, and plans began to take shape in 1953, but the recent increase in the volume of passenger and freight traffic between the two islands has made it necessary to complete the tunnels as early as possible.
Boring of the investigation shaft began on the Hokkaido end in 1964 and the Honshu end in 1966. The ob- lique sections of the shaft have been completed on both sides, and excava- tion of the horizontal section of the shaft is currently under way. The in- vestigation shaft will be extended to become a pilot tunnel for the purpose of geological survey. The shaft will be followed up by the service tunnel, for which construction work will begin this fall; the main tunnel will follow some time later.
Seikan Tunnel will run at a maxi- mum depth of 100 m below the sea bed. Though no final decision has been reached, the tunnel will most likely serve a double track line, in which case its inside diameter will be 9.7 m and its concrete wall thickness 0.8 m.
The tunnel will be constructed at a total cost
of ¥200,000 million (US$556 million), using 120,000 tons of steel and 85,000 tons of cement.
Economic impact
It now takes 3 hours and 50 ni- nutes to travel between Aomori at the northern end of Honshu and Hakodate in Hokkaido, using 8,000-ton ferries to cross the Tsugaru Straits. The proposed tunnel will reduce the time to two hours.
In 1967, ferries plying the Tsugaru Straits carried 4.2 million passengers
Far East BUILDER, August 1971
Japan
Sea
Hokkaido
Hakodate
SEIKAN TUNNEL
Hokkaido
Tsugaru Straits
Honshu
Aomori
Honshu
Existing ferry route 113 km (230 min) Future train service 170 km (130 min)
and 6.9 million tons of freight. But these ferries are forced to cancel over 200 trips a year due to storms and typhoons, thereby hampering the development of not only Hokkaido, but the entire country as well.
The tunnel is scheduled to be used by the projected super-express line be- tween Tokyo and Sapporo in Hok- kaido. Once this super-express line is completed (target year: 1978), it will cut to five hours and 50 minutes the present 17 hours and 20 minutes re- quired to travel from Tokyo to Sap- poro by train.
Development of Hokkaido
Development of Hokkaido began over a century ago in 1869. But the island, with its vast tracts of land, still has a great untapped economic poten- tial; a total of ¥8,550,000 million (US$23,750 million) will be spent be- tween 1971 and 1980 in the govern- ment's third ten-year development pro-
Sikoku
Kyushu
gramme. The completion of the under- sea tunnel and the opening of a super- express line will thus undoubtedly have considerable economic impact on Hokkaido and the northeastern parts of Honshu.
Other projects
In addition to the construction of the Seikan Tunnel, the government is working on the construction (now in progress) of an undersea tunnel and a suspension bridge between Honshu and Kyushu, and a plan to connect Shikoku with Honshu by building bridges across the Inland Sea. (Be- tween Honshu and Kyushu, there are already two undersea tunnels, one for trains and another for vehicles.)
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Linking of Japan's four main is- lands-Honshu, Hokkaido, Shikoku and Kyushu – has long been a national goal. Accomplishment of all these projects will serve the requirements of the nation's expanding economy.
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