Ranking the Risk of Mechanized Tunnel construction in Large Cross Section by Fuzzy Multi Criteria Decision Making Methods in Western Alborz Tunnel

Mechanized excavation of the large cross section tunnels in rock condition has some hazards. Machine purchasing costs, fault zones, water inflows, squeezing, face instability, and etc. are some of the hazards which may cause excavation stop for a long time. In addition to mechanized excavation advantages, machine inflexibility in the complex geological conditions, high investment costs, technical, geometrical and political risks are the major disadvantages. Due to the high investment costs in this method, assessment and ranking the mentioned hazards are of a great importance. In this study, the tunneling risks of Alborz Western Tunnel (AWT) has been investigated using the fuzzy multi criteria decision making methods. The AWT in Tehran Shomal Highway is one of the major country project that considered to be excavated by an EPB shield machine. By analyzing geological condition and survey of some specialist's point of view, in this study, 17 possible hazards have been identified, and assessed by fuzzy TOPSIS and ELECTRE methods. Results shown that insufficient experience in mechanized tunneling of the large diameter tunnel and gas emission in the tunnel and investment and purchasing the machine are the most important risks in the project.