Relationship between geological structures and shortwall mining at Matla Colleries, Mpumalanga

Abstract

In the Matla coal mining area, coal occurs in a palaeo-channel trending northeast-southwest. Three upward-coarsening cycles are each capped by a coal seam. A study of boreholes and the rocks exposed during underground mining reveal the presence of large sinuous sills called flow rolls that run at right angles to the strike of the palaeo-channel and also at right angles to the high-energy fluvial current direction. Studies underground revealed that joints formed by compaction occur in the vicinity of the floor rolls. These joints referred to as slips, cause roof failures during the mining operation resulting that the short-wall mining operation in the No. 2 Coal Seam has to stop. This phenomenon can also be explained by referring to the roof rocks e.g. those underlying the No. 4 Coal seam to act as a cantilever during mining operations. When mining is terminated as a result of floor rolls, the cantilever extends and roof failure occurs. The most important result of the study is that the size, geometry, orientation and distribution of floor rolls must be determined before mining and development operations commence.