Abstract
A variety of geophysical methods and analytical modeling are applied to determine the rockburst hazard in Polish coal mines. In particularly unfavorable local conditions, seismic profiling, active/passive seismic tomography, as well as analytical state of stress calculating methods are recommended. They are helpful in verifying the reliability of rockburst hazard forecasts. In the article, the combined analysis of the state of stress determined by active seismic tomography and analytical modeling was conducted taking into account the relationship between the location of stress concentration zones and the level of rockburst hazard. A longwall panel in the coal seam 501 at a depth of ca.700 m in one of the hard coal mines operating in the Upper Silesian Coal Basin was a subject of the analysis. The seismic tomography was applied for the reconstruction of P-wave velocity fields. The analytical modeling was used to calculate the vertical stress states basing on classical solutions offered by rock mechanics. The variability of the P-wave velocity field and location of seismic anomaly in the coal seam in relation to the calculated vertical stress field arising in the mined coal seam served to assess of rockburst hazard. The applied methods partially proved their adequacy in practical applications, providing valuable information on the design and performance of mining operations.
Highlights
In addition to measures taken to effectively cope with rockburst hazard, a broadly understood rockburst prevention strategy involves the assessment of hazard levels in relation to specific geological and mining conditions in the area of the planned mining operations (Zorychta 2003)
The main objective of the analysis was to combine the results of seismic surveys with analytical modeling of stress state to examine the rockburst hazard caused by the processes of destruction in the coal seam and/or its immediate rock layers
The experiment was conducted in the longwall panel 09a in section B of coal seam 501, designated for mining operations
Summary
In addition to measures taken to effectively cope with rockburst hazard, a broadly understood rockburst prevention strategy involves the assessment of hazard levels in relation to specific geological and mining conditions in the area of the planned mining operations (Zorychta 2003). In the longwall panel 09a/501, different energy of tremors can be expected in panel sections indicating low and medium rockburst hazard levels associated with structural disruption of the coal seam and of its immediate surroundings rock layers. The calculations indicate that the state of stress within the analyzed longwall panel, between IXa and Xb west headings, in the cut-through and in the panel end sections tends to vary These stress variations can be attributed to the interactions of extensive goafs, the presence of remnants of previous mining operations in the surrounding rock strata as well as by sedimentation and fault disorders. Since the rockburst hazard is a resultant of the state of stress in the coal seam and the predicted seismicity of the rock strata, it should be assumed that the longwall advance should give rise to medium- and locally high-level hazard. It can be assumed that such distribution of tremors can be attributed to the presence of a fault zone with a throw of 17–25 m running along the northern border of the deposit area
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