Masjed Solayman hydroelectric power plant is one of the largest underground projects in Iran. This project is divided into two phases; Phase I has been constructed and phase II is planning to be constructed as an extension plan. Monitoring system was used in the phase I caverns to control the rock mass response and check the validation of the assumed properties of rock mass used in design. Back analysis of the data obtained through the instrumentation of phase I revealed that the rock mass parameters used in the analysis have been appropriate. In order to analyze the caverns in phase II, a computer model was prepared with considering excavation sequences. An equivalent medium was defined for the rock mass surrounding the caverns and its geomechanical parameters were obtained by both rock mass classification systems and back analysis method. Three and two dimensional analyses showed that excavation of the caverns in the extension plan (phase If) has significant effects on the stability of the powerhouse caverns in phase 1. Comparison of the results in two and three dimensional analyses also revealed that these results were considerably different.
Masjed Solayman (or Godar-e-Landar) dam and the corresponding hydroelectric power plant is one of the greatest national projects in Iran, which is located in Khoozestan in the south-west of Iran. This dam has been constructed on the Karoun River at 25 km north-west of Masjed Solayman city. The underground hydroelectric power plant consists of two phases; phase I, which include one half of the hydroelectric plant, has been constructed and the second half of the plant will be constructed in phase II as an extension plan. Four units with capacity of 250 MW were constructed in phase 1. The extension plan will added a capacity of 1000 MW. This phase consists of a hydroelectric cavern (154.5 m length, 50 m height, and 30 m width), a transformer cavern (100 m length, 21 m height, and 13.6m width), and the related tunnels and openings such as access invert tunnels, shafts, pressure tunnels and tailraces (Niponcoe, Moshanir, Lamayer 1994).
The side walls of the caverns are flat and perpendicular to floor. The roof consists of three circular curves. The cavern axis is parallel to the bedding planes which have an azimuth of 340°.This will lead to the situation where the weak rocks such as siltstone and claystone do not intersect the roof of the cavern. The upper part of the cavern at the roof consists of coarse grain clastic sediments (Niponcoe, Moshanir, Lamayer 2000).
In this paper, the caverns in phase II have been analyzed in two and three dimension, using ANSYS computer program. Supporting systems in the caverns consist of shotcrete with wire mesh, grouted rockbolts and anchored-grouted rockbolts as primary and permanent support.
Monitoring system was used in phase I caverns to control the rock mass response and also check the validation of the assumptions and rock mass parameters used in the design.
