Asymmetrical distribution of roof microseismicity and its application to roof control of a deep longwall panel

Abstract

Deep mining is widely carried out across the world. Due to large cover depth, both stress magnitude and fracture development are greatly enlarged, increasing the complexity in mining conditions. Correspondingly, a series of ground control problems emerge in deep coal mines, such as face collapsing, roof falling and support jamming. This study mainly focusses on the variation in roof activity along face length direction, which helps to strengthen roof control of a deep longwall panel. Geological radar detection reveals that the development of mining-induced fractures present an increasing trend from the maingate to tailgate side, implying the variation in roof activity along face length direction. Microseismic (MS) monitoring is moreover conducted, with which both spatial distribution and dynamic evolution of MS events in roof strata are thoroughly analyzed. Due to stronger influence provided by fault structures, the concentration of MS number mainly occurs to the tailgate section. Thus, roof microseismicity is brisker in the referred section, accounting for 63.7% of the total events. The sensitivity of MS energy to fault structures is weaker than that of MS number. Energy concentration can be observed in the whole panel width. In the maingate section, the energy proportion reaches 44.1%, indicating stronger roof microseismicity. Such asymmetrical distribution in roof microseismicity is sensitive to fault activation, fracture influence and mining disturbance. The location of fault structures, spatial variation in fracture parameters and the difference in stress rotation characteristics contribute to asymmetrical distribution in roof microseismicity on two sides of the target panel. Based on MS characteristics, a coordinative movement method is innovatively proposed for hydraulic supports, which weakens cyclic disturbance of support movement on roof strata at the face area. The method is proved to be effective by the improvement in roof stability and mining efficiency.