Considerations for stope gully stability in gold and platinum mines in South Africa

Abstract

Gullies have been regarded as the "artery" in mining because they provide the only access route for material, people and ore in stopes. It thus becomes vital to provide the industry with suitable guidelines for gully layouts, geometry and the support required at all depths to keep the gully safe at all times. The research has indicated that best practices for gully layouts have been well recognised, but often poorly applied for many years. To address the issue of best gully practices, research was based on a review of past practices, underground visits, mine standards, codes of practice and the use of numerical modelling as a tool to back- analyse the underground conditions observed. The recommendations provided do not attempt to develop any new techniques for gully protection. They try to provide a guide for best practice under various geotechnical conditions. Based on depth, or stress environment, a broad based recommendation for gully geometry is provided. Using numerical modelling calibrated to underground observations, optimum widths and spans for each mining layout used at different depths are provided as a prescriptive guideline. • Sidings can only be omitted where stress damage does not occur. • A minimum siding width of 2m is recommended wherever sidings are cut. • Lagging sidings should be avoided and used only if absolutely essential. • In high stress areas gullies should be footwall lifted behind the stope faces or within wide headings. • All sidings must be cut on reef. Off reef sidings are not acceptable. • Correct blasting practice is essential to ensure stability of gully shoulders. • Gully width and span between support over gullies should be minimised. • Gullies must be kept straight. Excavation and cleaning of downdip sidings remains problematical from a practical mining point of view and future research is recommended in this area.