The optimisation of slope angles, that is to say, increasing them, compared to the original design is always the subject of analysis of stability for geotechnical engineers and economic analysis for planning engineers. Questions to be answered include: What is the acceptable risk? What factor of safety? What probability of failure or reliability? The Rosario Open Pit has a history of failure, poor quality rocks and high pore pressures. It was decided to deepen the pit below the programmed design to test the practicality of different design approaches, which if successful, could be used to improve the economics of mining at Collahuasi. The revised slope design has factors of safety in the range of 1.0 to 1.2, probabilities of failure of ten to 38 per cent, and increased slope angles of between 3 and 5 with respect to the original design. The pit deepening with these design slopes will deliver an extra two million tonnes of ore which will have a significant positive impact on mining economics._x000D_
FORMAL CITATION:Santander, E A, Pea, M P and Bonani, A R, 2007. Optimisation of slope angles at Rosario Mine, Collahuasi, in Proceedings Sixth Large Open Pit Mining Conference 2007, pp 129-138 (The Australasian Institute of Mining and Metallurgy: Melbourne).