Tunnelling difficulties under squeezing and flowing conditions at Ayas tunnel

Squeezing ground condition frequently results in excessive rock pressure and large deformation when it is encountered in tunnel excavation through the mountains. Flowing of loose and saturated deposits into opening is another problem in tunnel engineering. Both cases require special precautions or heavy support systems. The stabilization process may be difficult where the cross section is large. Consequently, in such a tunnel some repair and reshaping works become time consuming and high cost can not be avoided. This paper discusses two different problems which were caused by special ground conditions in the Ayas Tunnel, the longest tunnel on the route of Istanbul-Ankara Speed Railway Project in Turkey. The precautions and methods of tunnelling to tackle with these problems are also discussed.