Long term stability study of Azad cavern power house using instrumentation data

Feasibility studies of pumped storage power plant in Azad dam has been carried out. This project includes underground spaces such as tunnels, shafts and two big caverns including; power house and transformer. So, in this research long term stability of the powerhouse cavern is studied numerically. To determine the time-dependent behavior of the surrounding rock mass of cavern which includes sandstone layers with phyllite interlayers, was used instrument curves which obtained from one of the access tunnel. To simulate the cavern time dependent behavior, numerical method and Flac3D software have been used. Results of the numerical model showed a good agreement with results of convergent pins of the access tunnel. Long term stability analysis of support system of Azad dam main cavern was objective of research. The study was numerically and Flac3D software was used. Bergar’s time dependent model was considered for rock mass periphery of cavern. Numerical model of cavern was built. Long term stability analysis for 100 years was reviewed. Data which obtained from convergent pins of access tunnel was used for conformity to numerical results. Results of the time dependent analysis showed that the cavern will be stable for a 95-year period with a safety factor of 1. In this research, due to importance of the subject and the sufficient knowledge of conducted studies in similar cases, the long-term behavior of the main cavern in Azad dam pumped storage has been investigated. Hence, identification and description of time-dependent behavior of surrounding rock mass is important, as it is possible to calculate and analyze time dependent deformation and, consequently, long term stability of the cavern. To understand such behavior, creep parameters should be calculated by creep tests or using instrument curves which obtained from installed convergent pins in underground space. Finally, with time-dependent analysis, it can be examined the stability of the cavern for different time periods. In this study time-dependent behavior of rock surrounding cavern which consists of sandstone with interlayer phyllite, have been studied using instrumentation data that were installed in one of access tunnels. Viscoplastic model (CVISC) was selected for the rock mass periphery of cavern. To simulating CVISC model, finite difference software (FLAC3D-V5.01) is applied. Results of numerical method were verified with instrumentation data. Capacity diagrams of support system were drawn. Results of numerical model are in good agreement with the results of convergence pins data which show accuracy of the numerical model. According to long term stability analysis, powerhouse cavern structure will be stable for a period of 95 years with safety factor of one.