ABSTRACT
The lithological units surrounding the tunnel consists of disintegrated schist and metavolcanics taking part as blocks in the matrix material. The complex structure indicates a medium permeability. However, the permeability level increases due to existence of dense cracks and fractures in limestone. The water-table is about 8-14 meters below the tunnel floor and it is located at the top of an alluvial strata. It is probable that this water table located on the alluvial strata triggers the tunnel to be displaced from the mountain side towards the creek side. On the other hand, the water precipitation leaking into the rock-mass around the tunnel has always given rise to instability (Ergun et al., 2002).
