Towards the Failure Probability of Coal Pillars: a Review of Intact and Failed Cases in South Africa

No operating full scale frictional ignition test facility was found anywhere in the world, and building one was judged expensive, impractical and unlikely to justify its cost against laboratory scale testing. Effort should instead go to small scale laboratory equipment using South African rocks, and to expanding geological data such as silica distribution and petrographic analysis.

Heat exchanger material governs how fast ice scale forms during eutectic freeze crystallisation of dilute brine. Induction time fell as thermal conductivity rose, so copper scaled first, while aluminium gave the lowest scaling rate because its low surface energy pushed ice crystallisation into the bulk. Stainless steel delayed onset but scaled heavily once nucleation started.

No surface geophysical method can map individual bords and pillars at the depths typical of the Witbank coalfield, a limit the review attributed to physics rather than to technology, since the targets are small relative to their depth and conductive layers often lie above the seam. Borehole laser scanning remains the workable option, with sonar suited to flooded workings.