UNUSUAL FRACTURING ABOVE INTERMEDIATE-TO DEEP-LEVEL BUSHVELD PLATINUM WORKINGS
Severe fracturing is occurring at some distance above the hangingwalls of some excavations. These conditions could affect the long-term sustainability of the South African platinum industry if current horizontal to vertical stress ratios persist to deeper levels. The fracturing is different to that experienced in the South African gold mines, probably owing to the higher horizontal stresses in the shallow-dipping Bushveld strata and the ductile nature of the darker platinum rocks. The severity of the problem appears to be related to the proportion of plagioclase, i.e. lighter coloured rocks. As the immediate hangingwall of the Merensky Reef is usually pyroxenite, which grades upwards into anorthosite, fracturing sometimes occurs in the upper strata whilst the immediate hangingwall remains unfractured. This work was designed to determine if the observed discontinuities were fractures that resulted from mining and, if so what the mechanism of formation was. Our investigations included instrumentation that could monitor the seismicity associated with the fracturing and that could detect the position and persistency of the planes that were formed. Evidence of prominent, persistent shallow-dipping parting planes at heights of between 1.4 m to 2.4 m above the excavation was provided by a ground penetrating radar survey, borehole core and borehole camera surveys. This set of discontinuities extended over at least an area of 20 m × 20 m. The seismicity measured during excavation suggested that these discontinuities were fractures that developed as a result of mining. The micro-seismic network suggested that the fracturing above the excavation occurred near or at the face and little influence of other mining or external seismicity was detected. Stress measurements conducted at a separate site showed high horizontal stress in some anorthositic rocks - so called stress channelling.
BRYAN-PHILIP WATSON ALEX MILEV DAVE ROBERTS
Council for Scientific and Industrial Research Johannesburg, 2006, South Africa
国际会议
The 7th International Symposium on Rockburst and Seismicity in Mines(2009年第七届国际岩爆与微振动性学术研讨会)
大连
英文
817-830
2009-08-21（万方平台首次上网日期，不代表论文的发表时间）