ABSTRACT
In smaller tunnel projects for construction of, for example, headrace tunnels for hydropower plants or pilot bores of large-section tunnels, use of tunnel boring machines (TBM), which enables safer, faster tunneling than in conventional methods, has grown recently. When applied to complex ground conditions in Japan or to small-section tunnels, however, the TBM approach poses problems concerning supports, hauling and excavation, and an efficient and systematic method has not yet been established. Before headrace tunneling at the Shin-Onagatani No. 1 Hydropower Plant, problems likely to hamper expeditious TBM excavation were identified, and the Combined Boring and Lining TBM Method, an automatic shotcreting system, a double-track mucking system and a new ground evaluation system using TBM machine data were developed and adopted. As a result, an average monthly advance of 381 m and a maximum monthly advance of 785 m, both of which are a new record in Japan, were achieved.
