Selection of Optimal Tunnel Route and Tunneling Method based on AHP Technique.

Selection of optimal tunnel route and tunnelling methods for head raise tunnel of a hydropower project is one of the most critical and complicated steps in its design stage. Since factors involved are highly diversified, the decision making process is quite complicated. In this study, the Analytical Hierarchy Process (AHP), a multi criterion decision making tool was employed to establish the optimal tunnel route and the most appropriate tunnelling method for the established optimal tunnel route. The optimal tunnel route was established by evaluating two tunnel route options with ten factor criterion. Four tunnelling alternatives were evaluated against relevant ten factor criterion in selecting the most suitable tunnelling method for the selected optimal tunnel route. Criterion were limited to geotechnical, geological, geomorphological, safety, technical, economical and socioenvironmental aspects. Analysis reveals that, route B, which is having the overall composite weight of 0.513 (51.30%) is the optimal tunnel route and combination of Drill & Blast method (section III of route B) and New Austrian Tunnelling Method (sections I and II of route B) is the most appropriate tunnelling criteria along the selected tunnel route.