ABSTRACT
The Iiyama tunnel is a large-scale tunnel about 22 km long planned at the boundary between Nagano and Niigata prefectures on the Hokuriku Shinkansen Line (between Nagano and Joetsu). The Nabetate-yama tunnel, where pressure generated during excavation from squeezing soil caused serious difficulties in construction, is located thirty kilometers north-east of this project site. The geological conditions in the Iiyama tunneling site were expected to be similar to those in the Nabetate-yama tunneling site.
