Popping of Cavities in the Near-Surface Coal-Bearing Strata of the Donets Basin

Long-term research has proved the connection between old mine workings preserved at the outcrops of coal seams and land subsidence, and sinkhole collapse. Now the causes and types of such disturbances are determined, the most dangerous of which are caves, over various types of the abandoned mine workings. In addition to it, a method has been developed and improved for assessing the hazard rate of any abandoned working (cavity) with relation to sinkholes for mining and geological conditions of the Donets Basin. At the same time, a number of cases are known when cavities wiped out due to the failure of the overlying rocks reappeared on the upper levels, threatening to generate surface depression. Thus, the former, but already liquidated cavity seemed to pop in the overlying rocks. The understudied process of cavities moving in the subsurface coal-bearing strata from the places of their original location towards the surface in the Donets Basin is described. The computation of stage-by-stage popping of relatively undestroyed mine opening (cavity) in coalbearing strata of different strength is made. The conditions and factors contributing to the popping of the remaining cavities towards the overlying levels are determined. An assumption (hypothesis) on the inevitability of popping of any abandoned working or cavity preserved on the upper levels, with a favorable combination of the affecting factors is made. The necessity for this process to be taken into account in assessing the hazard rate of the surface areas undermined by the abandoned mine workings at shallow depths due to their potential capability of making sinkholes is demonstrated. The effective reference documents regulating the procedure for assessing the hazard rate of abandoned mine workings (cavities) at shallow depths do not take into account popping of cavities that hurts correctness of the results obtained for them.