Significance of three-dimensional analyses on static and seismic stability analyses of fractured open-pit mine slopes

Abstract

Most studies on open-pit mine stability have been performed in the two-dimensional (2-D) mode which neglected the effect of the circular shape and thus the effect of third direction boundary conditions. This paper aims to study the effect of the third dimension in static and dynamic stability analyses of pit slopes, comparing results from 2-D and 3-D numerical and limit equilibrium analyses. The geomechanical data from Choghart open pit mine located in the seismically active area in central Iran is considered, under a historical earthquake (Mw=6.4). Kinematic analyses showed that two tectonic blocks of the mine namely, BL1 and BL2 are susceptive to wedge and planar failures, respectively. From the 2-D and 3-D static analyses, both blocks are stable with higher safety factors for numerical 3-D analyses. For dynamic analyses, unlike BL1 where both 2-D and 3-D analyses showed wedge instability, for BL2 the 2-D numerical analyses showed instability, whereas the 3-D numerical and pseudo-static analyses indicated the block stability. The results revealed that the 3-D safety factors are generally 20 to 40 percent greater than the ones from 2-D analyses. This can be explained by the consideration of the third direction effect, verifying the importance of 3-D analysis.