Two and three-dimensional analysis of a hydro-electric cavern using back-analysis

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 II) has significant effects on the stability of the powerhouse caverns in phase I. Comparison of the results in two and three dimensional analyses also revealed that these results were considerably different.