Investigations into the effect of size and width to height ratio on the strength of the laboratory sized coal specimens

[摘要] The design of bord and pillar working in SouthAfrican collieries is based on the pillar strengthformula developed by Salamon and Munro1967 andwhich has been used widely since then for designingpillars. This formula is based on the statisticalanalysis of 27 collapsed and 98 intact coal pillarcases from collieries located in the Transvaal andthe Free state.The main objective of this study is to establish thedifference in the strength of the coal material inditferent seams by means of laboratory testing. Inthis manner, some 753 coal samples from 10collieries from 4 seams were tested.The size and width to height ratio effects onstrength were analysed. The size effect showed thatthe difference between the seams was obvious, with adifference of 59,4 per cent between the strongestand weakest coal.The statistical re-analysis showed that the strengthof the six blocks from the No 2 seam, WitbankCoalfield occurred in a fairly tight strength range;and that laboratory coal strengths from individualseams or mines could deviate to a significantalthough relatively small extent from the overallaverage.

[发布机构] University of the Witwatersrand