A study of the behaviour of the rock mass surrounding the Ventersdorp Contact Reef (VCR) at Kloof Gold Mine aiming at improved support design

[摘要] The difference in behaviour of the rock mass surrounding the VCR stopes was believed tobe due largely to the different combinations of hangingwall and footwall rock types. Thedesire to develop a thorough understanding of this behaviour led CSIR, Mining Technologyto identify and define of geotechnical areas on all mines exploiting the VCR by CSIR, MiningTechnology. The results presented in this report were obtained from fie of suchgeotechnical area on Kloof Gold Mine, where the VCR is overlain by soft lava and underlainby quartzite conglomerate.The study was carried out in #3 shaft on both the southern and northern sides of the 33/27longwall at Kloof Gold Mine. The strategies adopted to study the rock mass behaviourincluded laboratory testing of rock samples, convergence and extensometer monitoring,mapping of mining induced stress fractures and geological features, and the use of aconceptual model to investigate the mechanisms which could be responsible for theobserved behaviour. The results obtained from the convergence monitoring indicated thatthe closure rate is generally less than 5 mm/day and could be attributed to the low faceadvance rate. The extensometers did not reveal any appreciable separation of beddingparalleldiscontinuities in both the hangingwall and footwall strata. Detailed mapping ofmining induced stress fractures and geological features showed that the area is highlyfaulted. Extensive rock falls were noted between the composite timber packs.Stereographic projection of the orientation and inclination of the various discontinuities laterrevealed that the observed rock falls between the composite timber packs in the area aredue largely to the unfavourable intersection of mining induced stress fractures andgeological features. Detailed Investigation of the distribution and frequency of bothgeological features and mining induced stress fractures have been seen to be essential foreffective support design studies. A slight reduction in strike spacing between support unitscould help improve the effectiveness of the support system in the northern panels. The testresults obtained from the laboratory have been used as input parameters in a conceptualmodel to understand some of the mechanisms that could account for the observedbehaviour.

[发布机构] University of the Witwatersrand