Design parameters and management strategies of soil and rock slopes: Nchanga open pit-Konkola copper mines plc

Rock slope stability is a very important research area for many geo-engineers concerned with civil or mining works. Slope stability of pits, roads, tailings dams and other embankments is very cardinal as it directly impacts on the working or utilisation of these facilities. The Nchanga Open Pit has presented special challenges. This research is directed towards efforts to determine slope design parameters of the Chingola Open Pit F and D (COP F-D) Phase III, which is an important satellite pit of the Nchanga Open Pits. After recent accidents in this mine, attention has been drawn to the need to understand failure mechanisms of the slopes on this site and the need to determine acceptable risks of mining at the designed pit slopes. In addition, further analysis on the management of these slopes is required.COP FD phase II has been operated since 2003 with the slope design parameters projected from phase I (which started in 2001) and as such a need arose to determine specific design parameters for phase III because of variations in geological conditions between Phase I and Phase III. The methodology in this research included reconnaissance surveys, literature review, field work which comprised core logging, mapping, slope monitoring (water table, cracks and slope movements), laboratory testing, data analysis using specialised software and report preparation. In addition, a risk assessment (economic and safety for workers and equipment) was carried out based on Phase II data. Existing slope management strategies were reviewed. Three geotechnical zones based on rock characteristics were established and design parameters (such as cohesion and angles of internal friction) were determined for the zones. Economic risks mainly arose from the costs of repairing ramps and upper benches damaged due to undercutting. Safety risks resulted from the fact that initially the dump (OB 5), was located about a kilometre away from the pit rim but as mining progressed this dump became part of the pit wall on the footwall.Because the upper part of the pit wall was composed of dump material which was unstable, there was a high likelihood of slope failure. Design slope angles have been recommended based on geotechnical zones and a comprehensive rock characterisation. Slope management strategies have been reinforced by recommending better coordination, frequency and effectiveness of monitoring systems. Corrective measures for different rock slope instabilities have also been recommended. Further research work, through numerical modelling, is recommended to give better insight on slope failure mechanisms of the Nchanga Open Pit mining area.