Stability Analysis and Support System Design of Intersection of Water Conveyance Tunnel and Surge Tank of Olia Gotvand Dam

This study has been carried out on the stability analysis and the support systems design of the water conveyance tunnel and surge tank of Gotvand dam. The stability analysis of underground openings is one of the most important subjects in rock mechanics principles. There are four different methods for the analysis of underground openings. These are: closed form solutions, numerical methods, empirical methods and physical modelling. Nowadays the numerical and empirical methods are more widely used all over the world. In This research, analyses have been carried out by finite difference method (component of numerical methods) and Q and RMR (component of empirical methods) rock mass classifications. The numerical software used for analyzing the tunnel stability was Flac3D. This software is capable of determining the values of induced stresses and displacements around the underground openings. The results obtained from stability analyses show that the underground excavation is unstable; therefore, installation of a support system is necessary. After installation of support systems, the value of maximum displacement is less than Sakurai’s critical displacement, therefore, the underground excavation will be stable. The recommended support systems are: 1) Installation of systematic grouted bolt by 7m long and spacing 1.5×1.5m with shotcrete by 150mm thick in surge tank 2)) Installation of systematic grouted bolt by 5m long and spacing 2×2 m and with shotcrete by 70mm in conveyance tunnel and box.