Mitigation of the rockburst risk in deep South African gold mines (original) (raw)
Related papers
2010
Mining-induced earthquakes pose a risk to workers in deep South African mines, while natural earthquakes pose a risk to people living close to plate boundaries. We introduce a 5-year Japanese - South African collaborative project entitled "Observational studies to mitigate seismic risks in mines" that commenced in 2010. The project, which seeks to develop human and instrumental capacity in South Africa, will build on previous studies carried out by Japanese and South African seismologists in deep gold mines. The project has five major work streams: (i) determination of rock properties, (ii) sensitive close monitoring, (iii) seismic hazard assessment methods, (iv) strong ground motion monitoring, and (v) upgrading of the South African National Seismological Network in the mining districts. Some aspects of the study will also cast light on the mechanisms that generate tectonic earthquakes.
11th SAGA Biennial Technical Meeting and Exhibition
Mining-induced earthquakes pose a hazard to workers in deep South African mines, while natural earthquakes pose a hazard to people living close to plate boundaries. We introduce a 5-year Japanese-South African collaborative project entitled "Observational study to mitigate seismic risks in mines". The principal investigators are H. Ogasawara (Japan) and RJ Durrheim (South Africa). The project, which seeks to develop human and instrumental capacity in South Africa, will build on previous studies carried out by Japanese and South African seismologists and rock engineers in deep gold mines. This knowledge will be used in efforts to upgrade seismic hazard assessment schemes and to mitigate the seismic risks in deep mines. The knowledge is also relevant to the study of the mechanisms that generate tectonic earthquakes. The project was conditionally approved in April 2009 by the Japan Science and Technology Agency (JST), an external agency of the Ministry of Education, Culture, Sports, Science and Technology, and the Japan International Cooperation Agency (JICA), an external agency of the Ministry of Foreign Affairs. It is anticipated that the agreement between the Japanese and South African governments will be concluded by the end of the 2009 financial year and that research work will commence in 2010.
Multidisciplinary Monitoring of the Entire Life Span of an Earthquake in South African Gold Mines
2005
deep gold mines. In the second field experiment, the authors successfully monitored the entire strain history within a hundred metres from the hypocentres, associated with a few seismic events with M>2. However, there were no close strong-motion meters available to locate asperities; only a single strainmeter was available, so the authors were not able to locate the strain-change source; no in situ stress measurements were carried out at the site, and no information was available to constrain strength. In order to address these deficiencies, from 2003 to 2004, the authors deployed new experimental instrument arrays at fault bracket/stabilising pillars. Multiple strainmeters, arrays of strong ground-motion meters, sensitive thermometers to monitor seismic heat generation, and fault displacement meters were installed. Successful monitoring began, but the authors learnt that they had to develop instruments for much quicker drilling and installation, especially at highly stressed pil...
Geophysical Prospecting, 2022
Rockbursts pose a significant risk in deep gold mines in the Witwatersrand Basin of South Africa as they may damage the excavation, injure workers, and delay production. We analysed the source mechanisms of 75 large mining-related seismic events (ML 1.5–2.7) that caused damage to stopes in Kloof Gold Mine and used legacy 3D reflection seismic data to delineate the ore body and geological structures that may be correlated with mining-related seismic events. The 75 seismic events took place at depths of 1600–4200 m below surface. Most events were located close to stopes mining the Ventersdorp Contact Reef ore body. The S-to-P-wave energy ratio (Es/Ep) from the analysed seismic events ranged from 1.1 to 19.9. The source mechanisms of mining induced seismic events aid in understanding the dominant modes of failure. Planes of weakness may be the result of mining-induced stresses or pre-existing geological structures such as faults and dykes. The Es/Ep ratio, focal mechanism and moment tensor solutions were correlated to the underground mapped and seismically defined geological structures. Approximately 44% of the events showed strong correlation with the known underground mapped and seismically imaged geological structures (faults and dykes), whereas 56% of the events were related to elements of the mining geometry (dip pillars, abutments and remnants). This information enables mining layouts to be modified to minimize the risk of rockbursting.
2012
Mining-induced earthquakes pose a risk to workers in deep mines, while natural earthquakes pose a risk to everywhere, but especially near plate boundaries. A five year Japanese-South African collaborative project entitled 'Observational studies to mitigate seismic risks in mines' commenced in August 2010. Here we report on the achievements of the first 18 months of the project. Faults at Ezulwini, Moab-Khotsong and Driefontein gold mines considered likely to become seismically active during mining activity were modelled using pre-existing geological information supplemented by cores and camera images from new boreholes. As of 30 January 2012, about 90% of about 70 planned boreholes totalling more than 2 km in length had been drilled at project sites to locate fault zones accurately and to deploy sensors. Acoustic emission sensors, geophones, accelerometers, strain-and tilt meters, and controlled seismic sources were installed to monitor the deformation of the rock mass, the accumulation of damage during the earthquake preparation phase, and changes in stress produced by the propagation of the rupture front. The suite of sensors has greater sensitivity and dynamic range than those typically used in civil or mining engineering applications, making it possible to record very small changes in stress and strain as well as violent rock mass deformation associated with large seismic events. These data sets will be integrated with measurements of stope closure, strong ground motion in stopes, and seismic data recorded by the mine-wide network.
Japanese-South African collaboration to mitigate seismic risks in deep gold mines
2009
Mining-induced seismicity poses a hazard to workers in deep South African mines, while natural earthquakes pose a hazard to people living in Japan and other regions of the world that are close to plate boundaries. We introduce a 5-year Japanese-South African collaborative project entitled "Observational study to mitigate seismic risks in mines". The principal investigators are H. Ogasawara (Japan) and RJ Durrheim (South Africa). The project will build on previous studies carried out by Japanese seismologists in South African mines, and will develop human and instrumental capacity in South Africa. This knowledge will contribute to efforts to upgrade schemes to assess seismic hazard and to mitigate the seismic risks in deep mines. The knowledge is also relevant to the study of the mechanisms that generate tectonic earthquakes. The project was conditionally approved in April 2009 by the Japan Science and Technology Agency (JST), an external agency of the Ministry of Education, Culture, Sports, Science and Technology, and the Japan International Cooperation Agency (JICA), an external agency of the Ministry of Foreign Affairs. It is anticipated that the agreement between the Japanese and South African governments will be concluded by the end of the 2009 financial year and that research work will commence in 2010.
A magnitude 5.3 seismic event occurred on 9 March 2005 in the Klerksdorp district of South Africa. The event and aftershocks shook the nearby town of Stilfontein, causing serious damage to several buildings and minor injuries to 58 people. At a nearby deep gold mine, two mineworkers lost their lives and 3200 mineworkers were evacuated under difficult circumstances. The Chief Inspector of Mines initiated an investigation into the risks to miners, mines and the public arising from seismicity in gold mining districts. It was found that the seismic event on 9 March 2005 could be ascribed to past mining, and that seismic events will continue to occur in the gold mining districts as long as deep-level mining takes place and are likely to persist for some time even after mine closure. Placement of slimes in old mining workings is unlikely to reduce risks significantly. Seismic monitoring should continue after mine closure, and the seismic hazard should be taken into account when the future use of mining land is considered. Seismic events are likely to be triggered as mines are allowed to flood. It is possible that a seismic event could cause movement on a fault transecting a water plug and/or water barrier pillar, open up a fluid pathway, and allow flow of water into populated mine workings. While it is unlikely that such an occurrence would become an uncontrollable inrush, the consequences could be disastrous and the risk must be seriously addressed. However, the risk of a seismic event on one mine causing serious damage in a neighbouring mine is considered small because major infrastructure such as shafts are usually located at least a kilometre from mine boundaries, and there is generally good cooperation between neighbouring mines with respect to mine planning and blasting schedules. The national and local monitoring networks,operated by the Council for Geoscience and mining companies, respectively, are on a par with those installed in seismically active mining districts elsewhere in the world. However, steps should be taken to improve the quality of seismic monitoring and to ensure continuity, especially as mines change hands. A range of technologies is available to mitigate the risks of underground damage resulting from large seismic events. However, if there has already been extensive mining near geological features that could host large seismic events, any further mining adjacent to the structure must be carefully planned. The Klerksdorp and Free State gold mining districts are incorporating the risks of seismicity in their disaster management plans, and Johannesburg is urged to do likewise. Some buildings are considered vulnerable to damage by large seismic events, posing safety and financial risks. It is recommended that an earthquake engineer inspect the building stock and review the content and enforcement of building codes. Appropriate training should be provided to all members of emergency services, and drills should be practised regularly at public buildings to avoid panic should a large seismic event occur.