The selection of the most suitable excavation method of Beheshtabad water conveyance tunnel

Beheshtabad water conveyance tunnel, which is 65 kilometers in length and 6 m in final diameter, is studied to convey water from Karun river to central part of Iran. In this study the first 17 km of the tunnel is examined to select the most efficient excavation method. This interval of the tunnel was divided into three zones based on geological and geomechanical conditions, these three zones are from 0 to 5450, 5450to7800 and 7800 to17000 meters.
Selection of the optimal excavation method was a complicated decision to make since it required many factors to take into account. In this paper, a model was first constructed using Fuzzy Analytical Hierarchy Process (FAHP). Three excavation methods of drill and blast, road header and TBM were investigated based on the foregoing model, in which geological, geomechanical, economical, operational and environmental conditions as well as geometry of the tunnel and management factors were considered. Results showed that TBM scored the most point in all three zones. It is therefore, recommended a TBM to be used.