Roof failures in underground coal mines remain a major threat to safe working conditions and can lead to devastating consequences such as a significant impact on the production of coal. The Magdalena Colliery in Dundee, South Africa currently mines two seams; the upper Alfred seam and the lower Gus seam of the Vryheid Formation. These seams are separated by a planar cross-laminated sandstone, here referred to as the parting, which ranges in thickness from 2 cm to 11 m. The parting forms the floor of the upper Alfred seam and the roof of the lower Gus seam. Roof failures are a major cause for concern where the parting forms the roof of the mine. A study of the mineralogy and geotechnical properties of the parting has been undertaken in order to investigate its contribution to the frequent occurrence of roof failures. Thin sections of the parting were subjected to detailed petrographic analysis and X-ray diffraction analysis was undertaken in order to investigate the presence of any clay minerals within the parting. The geotechnical test work includes an impact splitting test, point load test, and Schmidt hammer rebound test on representative samples of the parting. The results classify the parting as a medium- to high-strength rock. However, water and the anisotropic nature of the parting were found to significantly affect its strength. High horizontal stresses associated with the mining method may be of great concern with respect to roof failures in areas where they are concentrated parallel to the laminations.

INTRODUCTION

Coal mining has played a vital role in the development of energy production in South Africa as coal accounts for 73% of the country's primary energy. In spite of advances in renewable energy technologies, coal will remain the major energy source in the near future due to its abundance and low cost (Jeffrey, 2005). Buffalo Coal currently operates two collieries in Dundee, South Africa; the Magdalena Colliery and the Aviemore Colliery, which are hosted within the Klip River coalfield. The Aviemore Colliery extracts high-grade anthracite coal while the Magdalena Colliery extracts high-grade bituminous coal (Muller et al., 2013). The focus of this study was the Magdalena Colliery, which has been mining bituminous coal since 2005.

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