TUNNELS IN JAPAN: THE EASTERN WAY

Tunnelling in Japan began in 1619, when a water supply tunnel was constructed in Hiroshima. Notable railway tunnels built in Japan include the 4.6km long Sasago Tunnel (1902), the 7.8km long Tanna Tunnel (1934), the 3.6km long Kanmon Tunnel (1944), and the world's longest underwater tunnel, the 54km long Seikan Tunnel between the islands of Hokkaido and Honshu. Important road tunnels include that in the 15km Trans-Tokyo Bay Aqua line (1997) and the Shimizu No. 3 Tunnel on the New Tomei Meishin Expressway now being constructed. Iwate Tunnel, also being constructed, will be the world's longest on-land tunnel, and has had to be excavated under various geological conditions, using drill-and-blast and mechanical excavation. Tunnelling in Japan has been very extensive, due to very rapid economic growth, very limited land area, extensive mountains, and the need for environment protection. Stimulated by topographical and geological constraints, Japanese tunnelling technology has been advancing continually, and every new tunnel built so far has contributed something new to the technology. The complicated rail and subway network in Japan and the Teito Rapid Transit network have both used many innovations in tunnel construction. Mechanised excavation methods are rapidly replacing drill-and-blast.