Safety and financial value created by good slope management strategies and tactics

Anglo Platinum's Potgietersrust Platinums (PPRust) operates three open pits and plans to excavate 90 Mt of rock in 2007. With pit slopes expected to reach a height of 400 in, the geotechnical department has a key role to play. Over the last four years PPRust has successfully implemented new geotechnical strategies and tactics to reduce risk, improve safety and maximise profitability. A large database of core logging, face mapping and rock testing data has been assembled and used for failure analysis, geotechnical zoning and rock mass ratings. The data has also been used for optimising blast designs on a daily basis through the use of a geotechnical block model. This greatly improves blast fragmentation and therefore loading and milling efficiencies. The slope design process involves limit equilibrium analysis, numerical modelling, rock fall analysis and block modelling. Slope management includes comprehensive limit blasting and visual inspections, and state-of-the-art slope monitoring equipment, namely the GroundProbe radar, Riegl lasers and GcoMoS automated prism monitoring. The risk-consequence approach has been used in slope optimisation, where all the slope analyses, operational controls, costs of failure, economic analyses of various slope designs and fault tree analyses are used to determine the ideal slope designs. These activities added over $25 million of value to the operation and also ensured compliance with Anglo American's acceptable risk level. The successful mining of the optimised slopes is to due to the greatly improved geotechnical knowledge and slope management. PPRust's geotechnical work is used as a benchmark for Anglo American open pit operations. The focus of the paper will be on the value added to the operation by all aspects associated with slope management.