Analysis of the underground openings under earthquake induced dynamic loads has been carried out for the three underground openings, which exist at Siahbisheh pump storage project, Iran. Siahbisheh pump-storage project is located in Alborze seismictectonic state which is one of the area that has high risk of earthquake. Therefore dynamic stability analysis should be considered in this project in both dams and Underground facilities. The underground complex consists of three main caverns Placed near each other which are supported with the combination of shotcrete, tendons and rock bolts. Because of huge tectonic activities in the area the proper numerical medium for analysis is one of the major aspects. Analysis in static and dynamic mode carried out in three different circumstances; continuum, semi continuum and discontinuum media. The discontinuum media results in static mode have the best agreement with instrumentation data and the continuum approach was far apart. The main achievement of the static analysis is determining the bedding is the mechanism of instability. The dynamic analysis has been done with the use of UDEC for discontinuum media. The results have shown that the wall between guard gate cavern and power house cavern would be in risk of instability.
Although underground excavations are relatively more resistant to dynamic loading than surface excavations, they are still subject to failure under impulsive loading induced by explosions, earthquakes and mining-induced seismicity . It is accepted that design of an underground excavation for such conditions should also take the probable dynamic loading to be experienced in its functional life into account. Underground power projects play a very important role in meeting the requirements of present day civilization. Several underground structures are being built in regions that are highly seismic and their failure would be disastrous to the human life and property. It is therefore essential that underground structures be designed by checking the anticipated earthquake effects so that they do not undergo any serious damage . The Siahbisheh pump/storage project consists of two concrete face rockfill dams (CFRD), a waterway and a power cavern with a pump/turbine system. The main purpose of the project is to enable a balance in the country's power generation network. The facility has an installed capacity of 1000 MW and represents a vital link during periods of increased power demand. A layout of the project is shown in Fig. 1. The main purpose of the project is to enable a balance in the country's power generation network . The dimension of cavern is presented in table 1. 900 Fig. 1. Siah bishe pump storage project . Table 1. Cavern Dimension .
The existence of three main and active faults named as Mosha-Fasham, Taleghan and Kandovan and according to the seismic history of the region, it is observed that earthquakes with magnitude more than 7 on Richter scale has been occurred in past decades. As the power plant projects have a long life time so the M.D.L criteria are used for hazard analysis.