The Study On The Law Of Strata Behaviors And Strata Movement In Close Coal-seams Mining Under Goaf

The short-distance coal seams group is distributed extensively in our country, thethiekness of coal seams varies from less than one meter to hundreds of meters; the number ofuseful coal seams ranges from one to ten, the domestic method of coal seam group is mainlyfor exploitation. with the raise of the mining intensity, More and more mine start mining thelower seams.The goaf made by up coal seam exploited inexorablely has a great influence onlaw of strata behaviors of down coal seam working face in its stoping when the distancebetween coal seams is very close, and cause the difficulties in roof management of lower coalworking face, mine pressure behavior remarkably, which may cause the water, dust and gas inupper goaf influx into lower coal working face and result in water and sand inrush, gasoutburst and other problems that greatly threaten the safety of personnel and equipment,restrict the safety and efficient production of the mine.As we all know, all of these problems are closely related to the roof rock movement.Grasp the law of roof rock movement under goaf is a key to solve such problems. On thisbasis,the paper builds the Loading Layer theory based on the original principle about rockstrata movement. The paper proposes the concept of load-bearing layer and judging method ofmain load-bearing layer. The paper derives the expression of caving step length whenconsidering the upper coal bottom failure depth. The paper analyzes the influence of theprocess of load-bearing layer rupturing and collapsing on the law of strata behaviors of coalseam working face. The results indicate that fracture form and motion feature of load-bearinglayer plays a decisive role on the law of strata behaviors and landmark movement.Interlaminar fracture of load-bearing layer causing different strength and incidence roofweighting different strength and incidence superposes in working faces and causes the lawworking face weighting confusing. The working face under goaf surface movementparameters are quite different compared with the Regular working face. Basing on the loading layer theory, considering the factors of the bearing layer thicknessand lower coal seam mining face height, divided the coal seams into extremely close distancecoal seams, close distance coal seams, non-close distance coal seam. The failure regularity ofcoal seam roof of the three respectively is introduced respectively. The paper analyzes theinfluence of the process of load-bearing layer rupturing and collapsing on the law of stratabehaviors of coal seam working face, and the formation mechanism of surface movement lawwhich is different with conventional working face.Finally, basing on the project of Ningtiaota N1200working face, combining with thepractical work and numerical simulation analysis, verified the results of theory analysis arelogicality and have an extensive application.