Influence of leading instability in the upper dip coal pillar boundary to the strong strata behaviors during the working face out of the pillar

Aiming at the problem of the strong strata behaviors during the working face out of the upper dip coal pillar in contiguous seams,adopted theoretical analysis,numerical simulation and engineering verification from the view of the instability in the upper coal pillar boundary occurring ahead of the face described the inhibitory mechanism that results in strong strata behavior disasters,and studied the influence law of the leading instability in coal pillar boundary that affected by buried depth of coal pillar,with or without key strata between coal seams,with or without abandoned roadway in coal pillar boundary and others.The results show that when the working face closes to push-out of the upper dip coal pillar,the reverted turning in upper key blocks will take place in advance,which caused by the instability of coal pillar boundary in advance,so weakening the energy generated when key block structure make turning motion on strata between the seams and eventually weakening the possibility and intensity of strong strata behavior disasters.Great depth of the upper dip coal pillar,without key strata between coal seams and abandoned roadway existed in the dip coal pillar boundary are easily led to instability in coal pillar boundary occurring ahead,thus which will play a significant inhibition on the occurrence of strong strata behavior disasters.For the mining conditions of the shallow buried depth of coal seams or only one key strata existing in coal seams which easy to lead the strong strata behavior disasters,we can dig abandoned roadways within the boundary of the coal pillar which is corresponding to the side of the under working face out of the pillar or carry out artificial pre-blasting in this area,which cause the coal pillar boundary occurring instability in advance at the time of working face close to out of the pillar and so as to get the purpose of controlling mine disasters of strong strata behavior.The results are verified with mining engineering projects in four working faces of Huojitu Bulianta Coal Mine in Shendong mining area.