Study on micro-seismic distribution characteristics of high-position and ultra thick hard overlying strata under repeated mining

Taking No. 3 Coal Seam of No.10 Mining Distict in Baodian Mine as study object,and based on the sOS micro-seismic monitoring data,this paper studied th e micro-seismic activities regularity of high-position ultra thick hard overlying strata when the upper and lower coal seams were repeatedly mined, and analyzed the relation ship between the distribution of strong micro-seismic and the high-position ultra thick hard overlying strata. The study results showed that the high-position ultra thick hard overlying strata before working face and would cause the periodically high energy( 104J) micro-seismic actities and resulted in the chain reaction between the adjacent g ob and strong micro-seismic activities when the advancing distance of upper working face exceeds the length of working face. When the lower coal seam was repeatedly m ined,the total recovery thickness would increase,the secondary broken and migration of the high-position ultra thick hard overlying strata became larger further,the periodic ally strong micro-seismic activities would happen again,but the maximum energy would decrease. The large micro-seismic events mainly took place in the high and ultra thi ck strata and happened peridically in time sequence,and it also had characteristics of large drawing pace type of the strong micro-seismic and migration.