In this research the stability of the diversion tunnel for the Namroud dam, Tehran, Iran, is investigated. Using finite element method (FEM) and the Schleiss technique, a detailed study on the design of a pressure tunnel lining in a real construction situation with different conditions is performed. From the FEM model, in addition to determining the general condition of the lining, the rock mass conditions around the tunnel, including tension and plastic zones, are determined. Using a numerical model including the Schleiss method, it seems that an efficient solution for the optimum and economical design of lining for water and pressure tunnels is achieved.
Pressure tunnels are among the most complicated of tunnels, both in design and construction. Therefore, any shortcoming in the design and construction of these tunnels may result in great damage. The Namroud dam is a clay-core embankment dam, which is currently under construction, located about 100 km east of Tehran. It will be used for controlling water, 130 million m3, for several purposes. The height from foundation level is 83.5 m with 680 m length of crown. The diversion tunnel is located in the left side of the dam. The level of the tunnel floor at inlet is 1,946 m above sea level, 1,941 m at the outlet. The length of tunnel is 754 m with a 4.5- m excavation diameter and 3.5-m effective diameter. Classification of the rock mass was carried out according to RMR and Q, showing a weak rock mass. Considering this fact and the variability of the ground water table, the tunnel was studied, both for dry and saturated (for maximum ground water table) conditions. Both analytical and numerical methods were used for the tunnel stability analysis.