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The Cuajone porphyry copper deposit is located on the western slopes of Cordillera Occidental, the southern Andes of Peru. The current pit measures about 2.5 km east–west, 3.0 km north–south, and at the end of 2012, had a maximum depth of 950 m. Mining by open pit methods commenced in 1976 and has continued since that time. Ore production is 80 ktpd.
As part of the slope design program and slope optimisation, the past and present performance of the pit slopes was evaluated to provide information on the potential behaviour of future pit expansion. A geomechanical assessment is being carried out to evaluate the stability of the walls of the next expansion. To evaluate the stability of the open pit, a series of geotechnical studies have been performed. These studies involve, among others, slope stability analyses based on limit equilibrium methods and finite element numerical models. In addition, a detailed back-analysis of a five million ton failure (DSE42) was performed to calibrate rock mass properties and to understand slope behaviour in poor rock mass quality.
This paper describes the back-analysis of the DSE42 failure and the slope design process for the current pit and next pushback.
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