Determination of slope angle is one of the most important parameters in open pit mine design. With low slope angles, stripping is considerably increased. On the other hand, selection of high slope angles may reduce safety and causes failure. Therefore, to prevent slope failure and high stripping, a compromise is necessary to select an optimum slope angle. There are several methods of analyzing the stability of open pit slopes such as limit equilibrium methods, empirical methods and numerical methods. In this paper, FLAC software has been applied to determine the overall slope angles in the different parts of Sungun copper mine. For analyzing the slope, five vertical sections with a proper coverage of all parts of the mine, were considered. For the aforesaid sections on the static loading, stability analysis was performed for different slope angles and then with the help of regression analysis a relationship was developed between safety factor and angle of slope for each of the sections separately. In this research work, on the basis of geo-mechanical characteristics of rock mass, a factor of safety of 1.2 was selected. On the basis of obtained results, mine slope in the south and south-west was detected to be critical. Based on this analysis, slope angle of the mine, in the south and south-west parts and for the north and north-east part, was considered to be 25 and 37 degrees respectively.
Sensitivity analysis was fulfilled for each section to study the role of cohesive strength and internal friction angle. It was considered that section 4800 (west) and section 4800 (east) respectively have the highest and lowest sensitivity to variations of cohesion. Also it was seen that section 4800(east) and section NE-SW respectively have the highest and lowest sensitivity to variations of internal friction angle.
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