Research On Evolution Rule Of Overlying Strata Structure In Repeat Mining Of Shallow Close Distance Seams

In view of the current urgent need to solve the impact of repeated mining of short-distance coal seams and the hazards caused by overlying strata,it takes the short-distance coal seam mining of Longde Coal Mine as the research background,and uses similar material physical simulation,numerical calculation,theoretical analysis and engineering field practice,to analyze the damage evolution characteristics of the overlying strata under repeated mining conditions,explore the mechanics evolution law of the overlying strata under repeated mining conditions in the short-distance coal seam mining,and study the mechanical behavior of stope overburden under the repeated mining conditions in the close-distance coal seam mining,the influence of its mining failure deformation.It establishes a failure criterion for the failure of the stope overlying water-resistant layer under the condition of repeated mining,and then proposes the control strategy of the overlying rock stability of the stope under the condition of repeated mining of the short distance coal seam.The main results of this article are as follows:(1)Under the condition of repeated mining in short-distance coal seam mining,the greater the thickness of the coal seam,the more severe the impact of overburden mining cracks;the closer the distance between the coal seams,the more affected the impact of overburden mining cracks will be obvious.(2)Based on three aspects of stress field,displacement field,and mining damage distribution,it reveals that repeated mining of short-distance coal seams causes the overlying water-proof layer of the stope to show the mechanics behavioral characteristics of "slab structure with three sides fixed and one unstable support".(3)Regarding the repeated mining conditions of short-distance coal seam mining,the key points for judging whether the overburden water-resistant layer of the stope "slab structure with three sides fixed and one unstable support" is damaged by mining is as follows: the side boundary of the solid coal along the strike of the first mining face and the continuation face,followed by the advance mining of the front coal wall perpendicular to the strike and the rear off-cut at the first mining face and the continuation face,which affects the short boundary.(4)it constructs a mechanical model for the failure of the overburden water-resistant layer of the stope under repeated mining conditions,and obtains the three sides of the overlying rock slab structure under the condition of "given deformation" under repeated mining conditions.The deflection function of a rectangular slab of an unstable supporting water-resistant rock layer when it is bent:,and the moment equations and stress equations are given;(5)The failure criterion for the failure of the overlying water-resistant layer of the stope under repeated mining conditions is proposed,the height of the water-conducting crack zone of the overlying rock of the stope is used as the spatial influence criterion,the final settlement deformation of the overlying rock of the stope is the isolation mechanical influence criterion for the failure of the water rock formation,the unstable settlement of the coal pillar fixed side is attributed to the mechanical influence criterion for the failure of the water-proof rock layer,the bending stiffness and thickness of the water-proof rock layer belong to its own attribute criterion,the size of the goaf,the size of the mined-out area,the distance between the water barrier and the underlying coal seam,and the deformation and movement angle of the overlying rock in the stope are all spatial influence criteria;(6)Aiming at the engineering geological conditions of the short-distance coal seams in Longde Coal Mine,based on the research results in the article,a control plan for NO.2-2 coal seam to preferentially select limited-thickness mining during downward repeated mining is proposed.The limited-thickness mining thickness is 4.0m.Based on the results of on-site observations Comprehensive analysis shows that the proposed limited-thickness mining plan is successful and effective,and the repeated safe mining of the short-distance coal seam in Longde Coal Mine has been realized.