Underground Trials of Seismic-counter and Goafing Characteristics in Pillar Extraction

Experimental studies tested ways to alleviate compaction on mine soils by combining mechanical treatment with organic material. Survival of 16 pasture species was recorded on mechanically ameliorated compacted soil, dry matter and leaf area were measured for tall fescue and cocksfoot at different levels of organic material, and soil fertility, bulk density and root biomass were tracked under irrigated and dryland grass.

Geophysical logging of boreholes above three Witbank seams identified clay rich matrices, stiffness changes, bedding planes and the principal stress direction, and picked up fractures in 30 to 75 per cent of cases. Core logging found most of the same features faster, so routine use was not recommended unless stiffness and stress direction matter.

Geotechnical factors affecting secondary extraction were identified from interviews with collieries already re-mining pillars and with people experienced in stooping, then quantified and ranked against the different aspects of the work. No single factor governs the outcome. Factors interact, so choosing a method and working safely in old workings depends on managing them together across disciplines.

Aircraft and ground based measurements at Kleinkopje Colliery showed spontaneous combustion to be a significant source of fine particles, with PM2.5 concentrations 91 per cent higher inside a combustion plume than outside it. Sulphur dioxide, nitrogen dioxide and carbon dioxide were also raised in plume, and benzene and toluene were detected. Average particle size was below one micron.