: The first part of the paper deals with the development of a three-dimensional mine visualization model for a section of the mine. Discontinuity orientation, location, including the three-dimensional co-ordinates of start and ending points were taken directly from this visualization model for use in slope stability analyses. The results of the laboratory tests performed on samples obtained from the mine to estimate shear strength properties of discontinuities and properties of intact rock are discussed in the second part of the paper. The third part of the paper is focused on the results obtained for maximum safe slope angles for the section considered of the mine based on the kinematic and block theory analyses conducted under only the gravitational forces using the mapped discontinuities at the mine. The effects of water that exist in the rock mass, a tension crack, slope face inclination, overall wedge height and double benching on factor of safety of wedge stability are illustrated through limit equilibrium slope stability analyses conducted on a single tetrahedral wedge belonging to “potential key block ” category that exist in the investigated area of the mine.


The Phelps Dodge Sierrita-Esperanza open pit copper mine is located 40 km south-southwest of Tucson, Arizona, on the southeast flank of the Sierrita Mountain Range. Figure 1 shows the investigated area that is on the north side of the Esperanza pit. The area under investigation includes eleven benches each about 50 feet high and approximately 1,000 feet in length, encompassing two different rock types namely, Esperanza Quartz Monzonite Porphyry (EQMP) and the Triassic Oxframe Andesite (TrOA). This area is very much affected by the Cooper fault (Fig. 1), better described as a fault zone. This fault strikes NE-SW and dips towards NW. The main trace of this fault is the apparent contact of the EQMP and the TrOA. As material has raveled down the pit slope, the trace of the fault has been obscured, but at depth it is clear that the main trace of the Cooper Fault zone is not the contact between the rock types. This paper covers the studies performed to investigate the slope stability of the selected area of the mine.

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