Mechanism of abnormal strata pressure of mining under coal pillar in close distance shallow coal seams

In terms of the strong dynamic pressure hazard occurred in mining out boundary pillar of 22307 working face in Bulianta Coal Mine, with the theoretical analysis, field testing and other methods applied, the authors studied the mechanism of abnormal strata pressure when the ultra-high face mining under boundary pillar in close distance shallow coal seams.Research results show the strong dynamic pressure hazard occurs when the working face of lower coal seam reaches the entering coal pillar stage, and the descending amount of piston reached 1 000 mm.During working face advancing, the key stratum structure between the two coal seams changes constantly.In the stage of repeat mining, there is an inferior key strata structure between the two coal seams, there is a main key strata structure between the two coal seams at the entering coal pillar stage.At the entering coal pillar stage, the reverse rotary motion will occur for the hinged structure of key block above the coal pillar.