Geotechnical Factors Affecting High- and Low-wall Stability in Opencast Coal Mines

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.

Ion exchange applied to brine from a three stage reverse osmosis plant at eMalahleni converted the brine entirely into saleable fertiliser and explosives feedstock, and recovered close to half of the water the reverse osmosis stage leaves behind. On this basis the existing brine pond and the two planned for the plant expansion would not be needed.

Watercourses on post mined land near Kriel showed deterioration in manganese, calcium, magnesium, sodium, total dissolved salts and sulphate, while other parameters stayed within drinking water standards. Aquatic invertebrate communities had suffered significant losses and two sites were classified as eutrophic. The water is not fit for human consumption or recreation, and a minimum 32 m buffer from wetland boundaries is recommended after earthworks.