Destress blasting on the border of safety pillars
Abstract
Destress blasting used at the border of safety pillars represents a special kind of destress blasting. The main goal of this type of destress blasting is to separate relatively more deformed mining areas from a non-mined safety pillar area such as shaft pillar or cross-cut pillar and this way to reduce the impact of high stress concentration in areas within the safety pillar.
Destress blasting is carried out in rigid, competent rocks adjacent to hardcoal seams 5 m to 6 m thick at depths ranging from 700 m to 1000 m below surface. Total explosive charge of up to 3450 kg is fired simultaneously in three to seven fan-pattern and line-pattern boreholes drilled from the maingate and the tailgate when the longwall face approaches to within round 100 m of the safety pillar border.
Experiences of this type of destress blasting from hardcoal longwall mining in the Czech part of the Upper Silesian Coal Basin are described here. Natural and mining conditions are described together with the design parameters of destress blasting, registered seismic activity during longwall mining and evaluation of the stress relief effect calculated from the monitored seismological data. Authors present arguments for using this kind of destress blasting as a proactive rockburst prevention measure during mining of thick hardcoal seams. Destress blasting can decrease high stress levels and consequently minimize rockburst hazards on the border regions of the safety pillars.
Keywords: Destress blasting, rockburst protection, stress distribution
References
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