抄録
The areas around the Kamisunagawa tunnel were dotted with many cavities from of old coal mines. Furthermore, as this tunnel was planned to pass Gm beneath a very decrepit existing tunnel, there was a fear that the two would interfere with each other.
The main results obtained through this construction method are as follows.
(a) Under complex ground conditions, as in the case of this tunnel, “urethane-injected rock-bolts” are an effective reinforcing measure, as they do not require special equipment.
(b) When excavating the new tunnel beneath the existing one, a distorted settlement phenomenon occurred in the existing tunnel, due to weak strata. When weak strata exist, natural ground reinforcement is required in wide areas.
