Characteristics of T-type overburden structure and tremor activity in isolated face mining under thick-hard strata.

To study the influence of isolated coal face mining on rock burst or strong tremor, the structure characteristics of thick-hard strata above 10305 isolated face were analyzed in this paper, and the seismic activity and burst risk were also monitored and analyzed. The results show that the strata structure above 10305 isolated face is an unsymmetrical isolated "T" structure, with the main key strata fractured on the short-arm side and non-fractured on the long-arm side, that is, the long-arm main key strata will fractrure and move in large-scale after face mining, and the risk of strong tremor or rock burst is relatively high. In addition, the inferior key strata can only form "O" fracturing structures, and the super-thick main key strata will form layered "O-X" structures, while the fracturing and movement of main and inferior key strata are the main sources of seismic activities. According to seismic monitoring, seismic events manily located on the long-arm side of "T" structure, especially the strong tremors occurred almost within the super-thick main key strata above 10305 and 10306. Moreover, the stong tremors present high ratios of S-wave to P-wave energy, which means they are mainly the results of shear fracturing or slip movement of main and inferior key strata. The burst risks caused by unsymmetrical "T" structure were evaluated by volocity gradient inversion, and the evaluation results are satisfactory. The big-diameter pressure-relief boreholes in coal seam and pre-blastings in main roof were implemented respectively in advance, and the burst effects of strong tremors were greatly reduced. [ABSTRACT FROM AUTHOR]