Abstract
South Africa is one of the leading producers and exporters of coal globally. A significant amount of the country's production is obtained from previously mined underground bord and pillar workings. This coal is in the form of pillars and remnants on the roof and floor of the old workings. The good quality coal pillars were left behind as primary support during underground bord and pillar mining operations. Due to the depletion of virgin coal reserves, the pillars and remnant coal are now removed using opencast mining rather than underground methods. However, the secondary extraction of pillars and remnant coal from the old workings using opencast methods entails some serious challenges that have a negative impact on the safety and productivity of the operations, affecting both personnel and machinery. If these risk factors and challenges are managed properly, then the opencast mining operations could remove the pillars safely at recoveries competitive with those of virgin coal operations. In this study we review the recurring challenges affecting opencast pillar mining by means of field investigations and consultations with experts at five opencast pillar mining operations, and evaluate the best practices used to combat these challenges. It was found that each mine has its own unique conditions and challenges.
Highlights
Coal was discovered and first mined in South Africa in the 1850s and continues to play a critical role in today’s economy and energy supply (Hanconx and Gotz, 2014)
The size and severity of a sinkhole, and the rate at which it propagates to the surface, depends on a number of factors, including: ➤ T he thickness of the overlying strata: The thickness of the overburden from the old workings to the surface has an influence on the distance of propagation
The flow chart (Figure 14) consolidates the findings from the mine visits and provides a guideline for the selection of the most appropriate blasting technique. This flow chart takes into consideration the risk factors and the possible challenges that can be experienced during operation, which are influenced by the availability of information regarding the old workings
Summary
Coal was discovered and first mined in South Africa in the 1850s and continues to play a critical role in today’s economy and energy supply (Hanconx and Gotz, 2014). According to van der Merwe and Mathey (2013), up to 9.55 Gt of coal has been mined in South Africa, of which approximately 53% came from bord and pillar mines. Moolman and Canbulat (2003) assert that approximately 1.1 Gt of potentially mineable pillar coal remains in the ground in the form of remnant pillars, mostly from mining operations dating to between 1970 and 1997. In 1996, between 100 000 and 150 000 intact pillars were formed during bord and pillar mining operations (Madden, Canbulat, and York, 1998), and this figure has been estimated at 3 million by 2006 (van der Merwe, 2006)
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