FOSSA MAGNA AND LONG RAILWAY TUNNEL

摘要

The great fault, which is called The Itoigawa-Shizuoka Geological Structural Line separates Japan into Northeast and Southeast parts. This line is also the south-edge fault of the Fossa Magna, which means the great graben and is said the tangent between the Amur Plate and the North American Plate based on the plate tectonics theory. The long railway tunnels of the Hokuriku-Shinkansen (the New Trunk Line) near Itoigawa through the northwest region of the Fossa Magna. The tunnels came across many faults. Especially, the Asahi-East-Tunnel came across approximately 500 m fracture zone. In this area, the tunnel suffered great ground pressure. Then, squeezing of the ground, deformation of steel support and shearing of rock bolts had occurred. A maximum horizontal convergence measured 554 mm. These phenomena required replacing of steel support and made slow progress in excavation. This paper describes excavation works in the fracture zone, analyses of the characteristics of tunnel deformation, the horizontal borings aimed at obtaining geological information and measures against tunnel deformation such as double steel supports and so forth.