Influence of overburden on subsidence development over room and pillar coal mines

Abstract

Abstract The magnitude and extent of the subsidence that occurs over coal mines may be estimated reasonably accurately by current empirical and numerical/physical prediction modelling. There are, however, few effective procedures for predicting the duration of time that elapses between the advent of mining and the initial surfacial expression of subsidence. This is particularly so with respect to subsidence over mines in which the coal was extracted by room and pillar (pillar and board) mining methods. This undefined time delay may be a critical concern in areas above old or abandoned room and pillar mines where the uncertainty of potential subsidence affects property values and urban development. The relationship between time and subsidence development was evaluated in this study by comparing data on mining systems, overburden and floor characteristics, physical properties of the coal seam, and the delay that occurred between coal extraction and initiation of surface deformation. The data was collected essentially from the Illinois Basin coal field with additional data from other coal-producing regions in the United States. Reasonably complete data sets from over 80 subsidence events were evaluated. Multiple-variable statistical analysis techniques, including regionalized variables theory and trend surface analysis were used to identify those parameters that most significantly influenced the time lapse between mining and the onset of surface deformation. The results of the study indicated that the behaviour of material in the lower half of the overburden is critical to the ultimate expression of subsidence at the surface. In addition, it was shown that an algorithm can be developed to predict the type of subsidence and also that there is a correlation between time lapse and, not only such anticipated factors as depth of mining and pillar size, but also between the relative position of competent strata in the overburden.