Design of stable slopes for Songun copper mine

Slope angle is a critical parameter in the design of open pit mines. With low slope angles stripping ratio is increased considerably, adversely affecting the economics. Steep slope angles may reduce safety and cause failure. Therefore, a compromise is necessary to optimise the slope angle. Methods to analyse the stability of open pit slopes include limit equilibrium methods, empirical methods, physical and numerical methods. In the present work the fast Lagrangian analysis of continua (FLAC) software package was applied to determine overall slope angles in different parts of the proposed Songun copper mine, Iran. Five vertical sections with a proper coverage of all parts of the mine were considered. Stability analysis was performed with a safety factor of 1·2 to determine stable angles for each section. On the basis of analysis, slope angles of 25 and 37° were selected for the southern and south western parts and for the north and north eastern parts of the mine respectively. Sensitivity analyses showed sections 4800 (west) and 4800 (east) have the highest and lowest sensitivity to the variation of cohesion respectively, whereas sections 4800 (east) and NE-SW showed the highest and lowest sensitivity to the variation of internal friction angle.