I am highly honored to have this opportunity to deliver a special lecture to the many experts from all over the world on the occasion of the Opening Ceremony of Tokyo Symposium of International Society for Rock Mechanics.

Tokyo Symposium on weak rocks is mostly significant to Japanese expertises who are engaging in many intractable tunnelling and underground works which are caused by unfavorable conditions of our topography and geology.

The Setting

First, I would like to say a few words on the setting of Japanese lands and the Seikan Undersea Railway Tunnel. The Japanese lands comprises four islands of Hokkaido, Honshu, Shikoku and Kyushu as represented in the Figure 1.

Japan has a population of about 115 million in the land area of 370 thousand square kilometers. But, figured on the basis of a higher ratio of people to the habitable land, Japan is said to be one of the top crowded countries in the world thus making the effective utilization of the lands imperative and requisite.

The projects of direct links among the four islands by links of bridges and undersea tunnels have been conceived for a long time.

The southern island of Kyushu is separated from the main island of Honshu by the 800 meter-wide Kanmon Straits where the four links have already been completed; they are the two systems of undersea double track railway tunnels-Shinkansen and conventional the undersea road tunnel, and the Suspension bridge over the Straits for the expressway. The four links are providing valuable transportation sevices of passengers and cargoes.

To the east of Kyushu, lies the island of Shikoku. The three big bridge projects are under construction between Honshu and Shikoku. Of the three, two projects are the combined railway and road bridges, and the rest is for exclusive road usage. All the projects are composed of long spanned suspension bridges and cable stayed bridges, and the construction works are now in the stage of full swing. The northern island of Hokkaido is the less developed part of our country, but is expected to have a great potentiality of development in future.

The Technical Investigation of the Project

The Seikan Undersea Railway Tunnel is to connect promissing Hokkaido with Honshu across the Tsugaru Straits by means of efficient railway networks.

At present, the Japanese National. Railways' ferry boats are carrying passengers and cargoes across the Straits in 3 hours and 50 minutes over the distance of 113 km.

The car ferry boats of private companies are also providing vehicle transportation services. As the Figure 2 shows, the alignment of the Seikan Undersea Tunnel crosses the western capes of the two islands.

The original planning aimed at providing the conventional railway system of narrow gauge, but the Project has been modified to afford both the conventional and the high speed Shinkansen with the maximam speed of 260 km per hour.

How has been the Tunnel Project promoted and the studies begun?

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