Abstract

VAN DER MERWE, J.N.. The development of a time-based probabilistic sinkhole prediction method for coal mining in the Witbank and Highveld coalfields. J. S. Afr. Inst. Min. Metall. [online]. 2020, vol.120, n.6, pp.393-398. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/752/2020.

There is a growing need for a method to predict sinkhole occurrence. The paper describes the development of a method to predict the occurrence of sinkholes due to mining, caused by the progressive collapse of underground openings. The shape of the collapse cavity is assumed to be conical. If the top of the cavity reaches or extends beyond the base of weathering, sinkhole development is likely. Progression of the collapse may be terminated by wedging out of the cavity, choking by bulking of the collapsed material, or the presence of a strong layer between the mining horizon and the base of the weathered material. The likelihood of failure of the strong layers is evaluated as a probability of failure based on the frequency distribution of tensile strength derived from more than 800 tests on sandstone samples from the industry. Time is brought into the equation by including the rate at which bord widths increase. As the bords increase, the probability of failure of the strong layers increases. The end result is a method on which to base the probability of sinkhole occurrence with respect to time.

Keywords : sinkhole; collapse cavity; time; bulking; wedging; probability of failure.

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