Bakhtiari Dam and Power Plant is located at a distance of 100 km from the city of Khorramabad. The dam's water delivery system includes two tunnels with a diameter of 12 meters. Rock mass of water flow is varied from a geological view. The study area has medium to thick limestone, shale and marn. In tunneling the most important action after drilling, is supporting the structure. In order to increase efficiency and expanding construction and mining operations in the country, the improvement of the underground excavations support system as one of the important technical and economic parameters, is necessary. The main objective of this project is to evaluate the performance of Permanent support system in Bakhtiari Dam’s water tunnel by using numerical modeling. Therefore, in this project, given the characteristics support system and the geomechanical parameters using numerical methods, the performance of this support system is studied. In addition, this project studies the sensitivity analysis on mechanical parameters such as E, C and ? as well as the effect of the shotcrete thickness on the amount of displacement, have been studied and present the results. In the present study FLAC 3D software is used to model water delivery tunnel of Bakhtiari Dam. After modeling it became obvious that the maximum displacement is of the roof of the tunnel which is 2.66 cm. After the installation of suppoet system, the amount of displacement is reduced to 1.41 cm which is an acceptable amount. In the following, sensitivity analysis performed on the mentioned parameters, shows the importance and influence of the elastic modulus in decreasing the amount of displacement before and after the installation of support system. In fact, it was shown that the rock mass with elastic modulus of 7 GPa, is a Strong mass of rock. It was also found that the cohesion of C = 0.2 MPa for a rock mass discontinuities with expanding more than 20 meters is acceptable.This amount of cohesion is because of discontinuities in the rock mass. The increase of cohesion to the amount of C = 5 MP is more related to intact rock. With increasing the angle of friction and keeping other parameters fix the amount of displacement is reduced by almost 25%. Using sensitivity analysis indicated that Variation of the thickness of shotcrete for weak rocks and rocks of good quality, has no significant impact on the rate of displacement change. In this study, using the JMP statistical software, the graph of displacement changes to the elastic modulus, cohesion and angle of internal friction are plotted. In fact, this diagram is a factor (multiple) of the graph obtained from FLAC3D software information. As a result, with these two graphs, the rate of displacement for different values of the elastic modulus, cohesion and internal angle of friction of the rock can be predicted. Keywords: water delivery tunnel, Bakhtiari Dam, support of underground excavations, geomechanical parameters, elastic modulus, cohesion, internal friction angle, sensitivity analysis, statistical analysis, numerical modeling, FLAC3D, JMP statistical software.
