Underground power plant projects play very important roles in meeting the requirements of present electricity requirements. Several underground structures are being built in regions that are highly prone to sheared and fault zones where their failures could cause severe damages to underground spaces. It is therefore essential to analyze and design underground structures for preventing any serious damages in these regions. Siah-Bisheh Dam and Underground Power Plan is one of the significant and important projects in Iran which is under construction. The project consists of two main parallel tunnels crossing the Alborz Structural Zone containing the Shale, Limestone and Sandstone in major parts. Because of the main role of these tunnels for conveying the water, studding and monitoring of the main fault and sheared zones and their effects on the stability of the parallel tunnels are essential. On account of these facts, at the first stage, practical methods were chosen to provide proper and reasonable supporting systems to meet the stability of the tunnels. At the second stage, two-dimensional static distinct and finite element methods were collected to perform static analysis of parallel tunnels. In this stage, with the use of the field monitoring results, the stability analysis was examined and provided supporting systems were optimized. The results of analysis were presented as displacement and strain curves and contours along the main fault, sheared zones and surrounding medium of the tunnels before and after the installing the provided supported systems [1].


Siah-Bisheh Dam and Underground Power Plan project consists of two main parallel headrace tunnels. In this part of the project, a bigger chamber is located which is called Displacement Chamber Headrace (DCH). In DCH, there is a main fault connects Shemshak and Elika zones which are some parts of Alborz Structural Zone. There are also some shear zones besides. Stability analysis of these tunnels has been taken in account by using numerical Distinct and Finite elements methods separately [1]. Inputs of analysis have been gathered and determined from laboratory tests. In fact, at first stage, with use of GSI value, the strength parameters of rock mass were determined and equivalent medium which is consisting intact rock and joint sets has obtained and modeled. These parameters were examined with Rocdata software according to the latest Hock and Brown's failure criteria. The results of the analysis were compared with the monitoring data and the models were calibrated. Finally, appropriate supporting systems were determined with use of practical methods parallel to numerical analysis.

Statement of The Problem

Siah-Bisheh Dam and Underground Power Plan is located in 155 Km of Chalous – Karaj road. It is planned to make balance the electricity power in the network [1]. In this research, the effects of shear zones and faults on the stability of DCH were examined. The dimensions of this structure are 10 × 10 × 37.5 m in width, height and length correspondingly.

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