The location, hazard assessment and sealing of unsafe mine openings in the Central Witwatersrand Gold Mining Basin

摘要

One of the most unfortunate legacies of more than 100 years of mining in the Central WitwatersrandudMining Basin is the presence of many unsafe mine related openings such as shafts and subsidencesudthat are present in the southern part of the city of Johannesburg. Using available mine plans andudknowledge of the manner in which these holes were formed, a search was undertaken and a total ofud244 openings were located.udA literature survey revealed that perimeter walls, concrete seals and plugs have most often been usedudto prevent human access to these unsafe mine openings. Locally mine openings have most oftenudbeen backfilled with available materials though concrete plugs or seals, walls and fences have alsoudcommonly been used. In order to assess which holes should be considered for sealing, a simple “holeudrisk rating system” was developed, which considered the depth of the hole and its proximity toudsettlements or thoroughfares. During a Department of Minerals and Energy project led by the author,udit was concluded that concrete plugs were probably the most effective method of sealing such unsafeudmine openings. Eighty holes were thus sealed using unreinforced, concrete plugs. PolyurethaneudFoam (PUF) has been used as an alternative method to seal mine openings in the United States forudnearly 25 years and was used here to seal two abandoned mine openings. This method requiresudminimal design, engineering supervision and offers a quick, simple, cost effective and environmentallyudfriendly method of sealing such openings.udThe documentation of the mine openings, the openings plugged, the methods of plugging and theudlocations of the plugged holes ia a valuable practical and historical record. The plugging of manyudholes is a significant contribution to public safety.