抄録
Iiyama tunnel has bored into Tertiary sandstone, mudstone and tuffbreccia which include inflammable gas like methane gas, at boundary of Nagano and Niigata prefecture. For methane gas is very combustible and explode easily, investigation and monitoring of inflammable gas is very important for safety construction of the tunnel. It was reported that horizontal exploratory boring, automated monitoring system and ventilation system for dilution of the gas were applied effectively on this tunneling.
