Geological Risk Reduction Management Ahead of Tunnel Face

In construction of the mountain tunneling in Japan, the accident resulting from face collapse accounts for about 65% of the total. Therefore, in order to perform tunnel construction safely, it is important to grasp the situation of geology, bedrock and groundwater of an unexcavated part in detail before construction. This paper reports the risk management example which reduced geological risks and performed suitable construction by various geological investigations during construction stage in deteriorated ground that was predicted to be in the mountain tunnel. In these sections of ground, while geological survey had been inadequate in a prior stage, tunnel The recent trend of tunneling is toward larger and longer tunnels. From the viewpoint of safety and efficiency of operation, it is highly advantageous to grasp geological conditions before tunneling. Geological evaluation ahead of tunnel face and face stability are especially an important issue to make effective use of the TBM was started, and face collapse accident was encountered. Since this tunnel has long length and high overburden, suitable and more effective investigation technique which can be performed in a short time is needed during construction. Test for physical properties and consistency of soil applied the concrete slump test was carried out in altered sandy Granite ground. Moreover, fractured and altered zone are distributed repeatedly in Rhyolitic welded tuff ground, it analyzed by the seismic imaging method using three-component geophone. These investigation results were analyzed synthetically, drainage drift and advanced drainage boring were performed, the geological risk was reduced and tunnel construction was continued more safely and economically