Failure characteristics of retaining coal pillar interval rock formation roof in Shendong mining area
Taking the 2-2 coal seam in Shibitai Coal Mine of Shendong mining area as the engineering background,the breaking law and control technology of the roof of the overlying retaining coal pillar over the working face under the condi-tions of close coal seam were studied.Using theoretical analysis,numerical simulation,field practice etc,the development characteristics of fractures in the lower interval layer of retaining coal pillar were analyzed.The three stages and characteris-tics of the overlying retaining coal pillar over the working face were clarified.The main reasons for the strong mine pressure of the overlying retaining coal pillar over the working face are revealed.The idea of weakening the advanced area of hydrau-lic fracturing in directional long borehole was proposed and applied to field practice.The results of the study show that:Due to the action of the upper"inverted trapezoidal"load structure,the retaining coal pillar will produce stress concentration in the coal seam floor.As a result,the interval rock strata are prone to longitudinal downward fractures along the boundary of the coal pillar.The fracture has a certain influence on the breaking characteristics of the interval key layer.In the process of mining in the lower coal seam,the coal pillar of the working face can be divided into"entering coal pillar stage","coal pil-lar middle stage"and"exiting coal pillar stage".The"exiting coal pillar stage"is the main stage when strong mine pres-sure occurs.Hydraulic fracturing control measures are proposed for this stage.In the treatment area,the weighting step distance of the working face was reduced by 9.8％,the weighting strength was reduced by 13.6％,and the dy-namic load coefficient was reduced by 10.6％.The practice that the hydraulic fracturing control measures are of good effect,providing a reference for the subsequent mining dynamic disaster management of the working face in the mining area.
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