Resumen

NGWENYAMA, P.L.  y  DE GRAAF, WW.. Risks and challenges affecting opencast pillar mining in previously mined underground bord and pillar workings. J. S. Afr. Inst. Min. Metall. [online]. 2021, vol.121, n.12, pp.623-631. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/1675/2021.

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.

Palabras clave : opencast pillar mining; spontaneous combustion; bord collapse; bord and pillar collapse; bord voids; sinkholes.

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