Abstract
Gold mining in the Johannesburg area commenced in the late nineteenth century. The early mines, now abandoned, were at shallow depth and their presence may give rise to subsidence. Consequently, they impose limitations on development in the old reef area which runs east to west through the city of Johannesburg. Indeed, the erection of buildings on the undermined land has been controlled by the Government Mining Engineer. These controls determined whether or not building took place, as well as the permissible heights of buildings in relation to the depth at which mining occurred. More recently, however, due to the pressure on available space in the central business district, the controls have been relaxed when development proposals have been accompanied by sound methods of mine stabilization. The extent and amount of subsidence which occurs varies, and can be difficult to predict, depending on the depth and height of the workings, the number of reefs worked, the local dip, the presence of dykes and faults, the type and extent of any packing, and the age of the stopes. Various types of subsidence have occurred and include the development of sinkholes, and subsidence associated with cavern development and stope closure. Several methods of mine stabilization have been employed from dynamic compaction to concrete dip pillars to provide rigid in-stope support, to plugging stopes and grouting above the plug. Some case histories are provided to illustrate the subsidence problem and how it has been dealt with.
Published Version
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