Subsidence caused by high extraction coal mining in the Sasolburg and Secunda areas : prediction thereof and the mitigation of its effects

[摘要] The thesis describes the results of research which was done overthe period 1985 to 1990 in the Sasolburg and Secunda areas intothe effects of underground high extraction coal mining on thesurface, surface structures and agriculture.Legal restrictions on the undermining of structures potentiallysterilize more than 30% of the coal reserves in the study area.The basic motivation for doing the research was that most of therestrictions could be overcome if methods could be developed toundermine structures safely and economically.For subsidence data analysis, a computerised three dimensionalmethod of analysis, the Surface Element Analysis (SEA) approach,was developed and implemented. Using the results of theanalyses and analytical considerations, a subsidence profileprediction method was developed. The prediction methodincorporates a new approach to the prediction of strain, basedon the shape of the subsidence profile and the thickness ofdeformable layers on surface.The reactions of various commonly occurring structures in thestudy area, namely bituminised roads, gravel roads, pipe linesand conveyor belts, to subsidence were analysed. It was foundthat although no consideration to subsidence was given in thedesign of the structures, most could withstand the effectsthereof safely with only minor and relatively inexpensiveprecautionary and repair measures.With regard to agriculture, it is shown that while there aremining induced effects, they are in general not severe. Thereis, however, reason for concern regarding the long term and notimmediately apparent effects. Further work is thus verynecessary.Overall, it was found that while a very cautious approach tohigh extraction undermining had merits in the past, most of therestrictions can be relaxed in the light of the knowledge whichis now available.The important provision is that careful and detailed priorinvestigations are necessary for each individual case, and thata sound and responsible engineering approach must be followed.Mines can derive substantial economical benefit from themitigation methods which are described.A very important aspect is the administrative handling of theundermining of structures. A coordinated multi disciplinaryapproach, catering for communication and joint planning ofmining and infrastructure, is proposed. It contains theessential elements of the Australian approach with modificationsfor local South African conditions.

[发布机构] University of the Witwatersrand