Microseismic Monitoring of a Longwall Coal Mine. Volume III - Field Study of Mine Subsidence

摘要

This report is volume 3 of a three-volume report dealing in general with the microseismic monitoring of a longwall coal mine. The research presented was undertaken as part of the overall microseismic project in an effort to relate, if possible, observed microseismic activity with surface subsidence. Field measurements of subsidence carried out at a central Pennsylvania coal mine are described. Comparative analysis of actual field results with data obtained using empirical and finite element techniques was undertaken. Comparison of field results with published National Coal Board data revealed marked differences. The influence of stronger rock beds overlying the coal seam in the current study was assumed to be the main cause. Use of the general Gaussian profile resulted in a satisfactory fit to the field data provided the value of the maximum field subsidence was used in the analysis. In general, when low tensile strengths were assumed for the associated rocks, finite element techniques gave results that compared well with the field data. The study also indicates that at shallow depths there is a marked difference in subsidence over dip and rise sides of the coal face, maximum subsidence shifts more towards the dip side. Finally, time-dependent formations were insignificant shortly after mining operations ceased.