DIFFICULTIES ARISING IN SILVEH DIVERSION TUNNEL DUE TO COMPLEX GEOLOGY

Silveh damsite, an 89m high embankment dam is located in Northwest of Iran. The construction of its diversion tunnel, 800m long and 5m diameters has already started. Area has undergone a high tectonic activity and low metamorphism. Heavy mechanical erosion has formed thick overburden on the hills and hill slopes. Therefore, the exact location of some faults remained unknown despite extensive geotechnical and geophysical investigations. Consequently, many failures occurred during tunneling where fault planes were encountered. , This fact caused serious challenges to the work. This paper deals with the problems encountered during tunnel excavation and appropriate remedial measures undertaken to remove and control the defects such as failures. Now the situation is getting better and excavation is proceeding safer.