Back of envelope mining subsidence estimation

Surface grounds undermined by coal mines are potentially susceptible to large amounts of differential surface subsidence and horizontal movements causing substantial impacts on our environment and economy. There are a number of methods available to predict or estimate subsidence. At CSIRO we normally use such rigorous, rational numerical methods as finite, boundary, discrete element methods to analyse mining induced subsidence using advanced constitutive laws of material behaviour. However, the requirement that only highly specialised engineers should develop and use such rigorous and rational models of analyses, seems to have prevented non-specialised mining students and engineers from the understanding the basics of ground subsidence analysis from simple irrational models. There is certainly a gap between these two extreme approaches for an engineer who is looking for a simple practical analytical tool. Based on a triangular zone of major caving, beyond which arching and within which caving is dominant, this technical note presents a simple model for estimating potential maximum ground surface subsidence caused by underground coal mines and the required volume of remedial fill or grout (materials) for either its reduction or prevention.