Caverns are underground superstructures which their popularity has been increased due to their various and strategic applications, numerous advantages such as low initial and operating costs, and free form designing. The case study in this paper is done on pumped storage cavern in Rudbar, Lorestan, Iran. In this area a power station pumped storage is under construction which has a main cavern with dimensions of 26.8 × 50 × 130.5 meters for width, height and length respectively. The geomechanical data of this cavern was analyzed with empirical method (RMR). Although, implementing this method provides a good outline to the task; but it cannot be an exact method for a definite statement. Therefore, the structural analysis was done through numerical modellings. Comparing empirical and numerical methods implies that numerical results are more reliable. However, proposing a supporting system depends on more factors such as financial issues, construction utilization time and application, etc.
Stress in homogeneous and isotropic rock tunnels and tunnels with specific geometric shape following Kirsh (1898) and after his pioneering research scholars such as Love (1927), Muskelishvili (1953) and Savin (1961) which suggested closed form depending on the drilling of various shapes elastic plates are provided as well known. But most of the underground excavations, have irregular shapes. The first step in designing a space is underground exploratory studies.
Then based on data collected from exploratory studies, project characteristics, including cross-sectional shape, type and number of equipment support and monitoring system, cavern is determined. The most common cross-sectional shape for cavern, arched ceiling and a cross-sectional vertical side walls. But in weaker rocks and high tensions often oval crosssection (horseshoe) can be used. In designing tunnel supports, the RMR rock mass classification system have been employed by many researchers and have gained a universal acceptance (Barton 2002, Ramamurthy 2004, Hoek & Diederichs 2006). In recent years this hypothesis was proposed that in designing of an underground superstructure only numerical studies is not enough to reach a decision, but combination of both numerical and empirical studies could lead to a well decision. Empirical methods do not provide the stress distributions and deformations around the cavern (Gurocak et al. 2007). A power station pumped storage in Rudbar, Lorestan is under construction which has a main cavern with dimensions of 26.8 × 50 × 130.5 meters for width, height and length respectively. The minimum and maximum overburden in the range of cavern are 410 and 460 meters respectively. Due to the problems of water leakage dam reservoir, transformer cavern in the upper level of the power station cavern is allocated. According to the existing plan, the cavern is located lateral about 44 meters and altitudinal about 42 meters away from the power station.