Occurrence patterns and zonal control of rockburst in deep mining of steeply inclined extra-thick coal seam groups under varying rock pillar thickness
Sui-lin Zhang , Jun-wen Zhang , Feng Cui
Journal of Central South University ›› : 1 -32.
The occurrence of rockburst disasters is closely associated with spatial structures. Taking the complex geological setting of steeply inclined extra-thick coal seam groups as the research background, this study focuses on three key factors: mining depth, rock pillar thickness, and coal seam characteristics. Through an integrated approach combining mechanical analysis, numerical simulation, and microseismic monitoring, the mechanisms of rockburst under complex geological conditions were elucidated. The evolution of stress was characterized, the patterns of microseismic activity were clarified, the rockburst hazard was assessed, and zonal prevention and control measures were proposed and their effectiveness evaluated. Results show that: (1) The rock pillar acts as the primary disaster-inducing structure. The bending deformation and energy accumulation effects of the rock pillar are positively correlated with mining depth and inversely correlated with rock pillar thickness. The superposition of static and dynamic loads triggers rockburst events, where static loads store energy and dynamic loads initiate bursts. The greater the mining depth and the narrower the rock pillar thickness, the higher the rockburst risk. (2) The rock pillar stress exceeds that of the roof, and the roof stress exceeds that of the floor. The degree of stress concentration is proportional to mining depth and inversely proportional to rock-pillar thickness. With increasing mining depth, both the intensity and spatial extent of rockburst hazards increase. The rock pillar and surrounding strata stresses during B3+6 coal seam extraction are significantly higher than those of the B1+2 seam, and the mining of B3+6 leads to stress relief in B1+2. (3) In regions where the rock pillar is narrower, microseismic events occur more frequently and release higher energy, exhibiting stronger spatiotemporal activity and resulting in a higher probability and intensity of rockburst occurrence. Compared with the mining of the B1+2 coal seam, extraction of the B3+6 seam produces more frequent and energetic microseismic events with enhanced spatiotemporal activity, thereby increasing the likelihood of rockburst. (4) Zonal prevention and control measures were proposed and implemented at the +425 level. Microseismic monitoring indicated that, following the implementation of these measures, the energy of microseismic events significantly decreased while their frequency notably increased. Borehole observations revealed extensive fracture development within the rock pillars, reducing their structural integrity. No rockburst occurred during the extraction of the B3+6 coal seam at the +425 level. Comprehensive assessment demonstrated that, after the implementation of the measures, the coal–rock mass stored less energy, dissipated energy more efficiently, and released energy in a controlled and distributed manner, thereby substantially reducing the risk of rockburst. These findings provide a scientific basis for safe mining in other mines with similar geological conditions.
steeply inclined extra-thick coal seam groups / varying rock pillar thickness / mining depth / rockburst / stress evolution / microseismic monitoring
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Central South University
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