Study On Overlying Strata Movement And The Relationship Between Surrounding Rock In Large Mining Height Fully Mechanized Caving Face

With the rapid development of the coal industry and the continuous improvement of coal mining technology,the mining of extra-thick coal seams with thickness greater than 14 m has been carried out one after another.The mining method is mainly based on the full mining height of the fully mechanized top coal caving mining.The greater the thickness of coal seam mining,the more serious the damage caused by the mining surface pressure and the new broken form.The resistance of the hydraulic support of the stope is increased,the overburden strata of the coal seam are seriously disturbed,and the surface subsidence is deepened.In addition,there is a difference in the law of pressure during the mining of extra-thick coal seams in goafs and non-mined areas.In view of the above problems in the mining of extra-thick coal seams,this paper takes the 13# coal seam mining of Xiegou Coal Mine as the engineering background(the upper multi-region is the 8# coal seam goaf),and uses theoretical analysis,numerical simulation and field test to study.The research contents and conclusions are analyzed as follows:(1)Using the numerical simulation method to explore the evolution law of the pre-supporting stress of the surrounding rock in the 13# coal seam mining face of Xiegou Coal Mine,the research is mainly based on the mining under the goaf.It is found that the influence of the surrounding rock pressure on the 8# coal seam is the smaller the supporting stress in the stratum near the 8# coal seam goaf,and the change law with the working face is not obvious;it is affected by the concentrated stress of 8# coal seam coal pillar The pre-supporting stress of the regional working face is relatively large;at different positions of the working face under the same propulsion,the closer to the middle of the working face,the greater the peak value of the supporting stress in the coal wall.With the increase of the propulsion,the peak stress in the coal stratum is slightly increased.The trend is increased and the peak lead coal wall distance is reduced.The on-site monitoring method was used to monitor the pressure of the hydraulic strut in the working face.It was found that the bearing pressure began to rise slowly at the measuring point 10 m away from the working face,reaching a peak at about 5m.(2)Using the empirical formula calculation and numerical simulation test to study the failure characteristics of post-harvesting overburden in the double-layer coal seam of Xiegou coal mine,the conclusions are as follows: the development height of the overburden strata in the 8# coal seam is 28.9m~30m,and the fissure zone develops.The height is 85m~125m;after the full mining of 8# coal seam and 13# coal seam,the development height of the overburden strata is 95m~102m,and the development height of the fracture zone is 270m~300m.The numerical simulation results show that the topsoil of the 8# coal seam is the largest after sinking.The amount is 1.76 m,and the maximum subsidence height of the surface of the 13# coal seam is about 8.97 m.(3)After theoretical analysis of the overburden structure of 13# coal mining,it is concluded that it is difficult to form a masonry beam structure after the basic top sill,and it is easy to form a cantilever beam structure,which can be regarded as a force analysis of the overhanging beam structure during the rotation.The coupling-surrounding rock coupling relationship suitable for the mining face with large mining height and fully mechanized top coal caving mining face under thinner direct top geological conditions is studied;the bracket suitable for mining under the thin and direct top special thick coal seam under the goaf and non-mining area is derived.—The surrounding rock mechanics model and the empirical formula for the calculation of support resistance.(4)The numerical simulation method is used to determine the working resistance of the hydraulic support on the working face of the 13# coal seam in the inclined trench coal mine in the presence or absence of the overlying goaf.The theoretically derived support-surrounding rock is verified by the field measurement method.The accuracy and applicability of the mechanical model and the calculation formula of the working resistance of the hydraulic support on the working face.(5)The characteristics of the pressure of the large mining height fully mechanized caving mining face in the goaf are different from those in the non-mining area: the basic top cycle is not obvious,and the whole process has a phase change,the first stage(The working face enters the goaf stage)> the third stage(the upper basic top pressing stage)> the fourth stage(the working face out of the goaf stage)> the second stage(the working surface is in the stage of the pressure relief zone).