Theoretical analysis of bump and airblast events associated with coal mining under strong roofs

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Virginia Tech


This investigation was conducted to study the bump and airblast problems associated with delayed caving of competent longwall roofs. The roofs were modeled as elastic beams on continuous elastic foundations subject to exponentially distributed abutment stress. Elastic beam theory was applied to develop analytical solutions for deflection of single-layer roof models. Methods for analyzing double-layer roof and double-layer foundation models are discussed. Formulae for evaluating critical spans of the roof beds and strain energy storage in the roof and foundation are developed. The factors affecting roof caveability and energy accumulation are identified and analyzed. A comprehensive parametric analysis reveals that mechanical characteristics of roof beds, “foundation properties, abutment stress concentrations, and roof configurations may interact to influence roof caveability and energy storage. Based on estimation of local Richter magnitude, criterion for pressure and shock bump events are suggested. Five case studies of bump events show that the theoretical predictions agree well with field data. The developed model solutions were implemented in a Windows-based software package CBPEP. This package facilitates determination of roof spans, stored strain energy in the roof and foundation, and the coal bump potential caused by delayed caving of strong roofs. The increases in air pressure and temperature associated with sudden roof collapse in a large area was also investigated using an adiabatic air compression model. The presence of fragmented gob materials on the floor greatly influences the pressure and temperature variations after the recompaction of fragmented material commences. Three case studies of airblasts were analyzed, one of which was associated with a mine explosion. The investigation indicates that when a sufficiently large collapse is anticipated in a mine where flammable gas or dust may be present, it should be assumed that there exists a possibility that the high air pressure and temperature induced could trigger an explosion.



roof, energy, span