Tunnel design and construction process in difficult ground conditions with Analysis of Controlled Deformations (ADECO) approach; a Case Study

The 10.6 km long Sabzkuh water conveyance tunnel is currently under construction in High Zagros structural zone, located in western Iran, has used conventional (in section T1) and mechanized (in section T2) methods. The section T1 of the tunnel driven through alluvial geological units with great complexity in an area high potential for sliding and water-bearing fault which has made the excavation operation encounter many challenges. After excavation 35 m of the tunnel using conventional methods, geological problems and inappropriate method of tunnel excavation resulted in the tunnel collapse and failure in the tunnel inlet portal. After the incidence of the collapse, the Design and Construction Process (DCP) of tunnels was revised by using Analysis of Controlled Deformations in Rocks and Soils (ADECO-RS) in conjunction with the Sequential Excavation Method (SEM). The ground improvement in the portal and tunnel excavation continued in five phases including survey, diagnosis, therapy, operation, and monitoring. The application of this approach into construction of Part T1 of the tunnel increased the safety and minimized risks and costs despite geological complexities and hazards. Moreover, the excavation process with appropriate daily advance rate of 1 to 1.5 meters was achieved according to the predicted schedule.