| The emergence of the current integrated mechanized roof release mining method has improved the mining efficiency of extra-thick coal seams,while this mining method may cause the workings to show intense mine pressure.In the case where the two effects of coal seam thickness and hard top plate exist simultaneously,the phenomenon of mine pressure appearing will also be more prominent.Take Guobei Coal Mine 8205 working face as an example,8 groups of coal total 10.8 meters,the basic roof is 22 meters thick sandstone,so it is very important to master its overburden breaking law for working face back.Based on Guobei Coal Mine 8205 working face,this paper adopts a combination of field research,laboratory experiments,theoretical analysis,similar simulation,numerical simulation and field data acquisition to study the law of basic roof breaking of thick sandstone in header mining of extra-thick coal seams.The main findings of this paper are as follows:(1)By analyzing the overlying rock layers on the working face and calculating the load borne by each rock layer,the location of the key layer was determined.Fault-related elements are introduced,and when fault-influencing factors exist,the analysis yields that the top plate equilibrium structure is affected,and when the working face advances from the lower plate to the fault,the top plate rock is more likely to be destabilized using the fracture structure surface.(2)With the advancement of working face,the overburden rock as a whole is more stable before the basic top breakage of thick sandstone in key layer,after the basic top breakage of thick sandstone,the soft rock layer above the key layer starts to destabilize in a wide range,the basic top rock block broken in the cycle is more integral,the closer the overburden rock is to the coal seam,the larger the displacement is.The top collapse in the middle of the mining area is obtained by distributed fiber optic monitoring,the fiber optic closer to the retrieved coal seam suddenly appears tensile strain,the fiber optic strain sudden increase position corresponds to the left and right breakage line position formed by the overburden collapse,the model collapse height reaches the maximum,the fiber optic strain also reaches the maximum,the strain change characteristics of the fiber optic correlates with the overburden collapse width.(3)The evolution of mining fracture field of coal seam under thick hard basic top of extra thick coal seam is closely related to the breakage of thick hard basic top,the overlying rock fracture development is not obvious when the basic top is not collapsed in the early stage of back mining,but due to the large free space of coal seam thickness and the complete rock block of basic top collapse,the collapsed rock will have strong impact on the collapsed rock,which leads to the fracture of the rock body itself.Thick hard basic top as a key layer,its broken destabilization will also lead to its upper soft follower layer also widely destabilized,which also promotes the further evolution of mining fissure field.(4)Under the influence of the fault,the initial incoming pressure step of the working face is ahead,the mining of the coal seam will lead to the activation of the fault,the low overburden rock near the fault slides along the fault in a wide range,the high top plate appears to be off-layer fissures,the damage height becomes significantly larger in comparison,the initial advance appears stress concentration and unloading area,and the law is basically the same as when there is no fault,the overburden rock damage range is larger,and the damage of the rock layer with weaker stress strength at the fault is more serious.Subsequently,as the working face advances away from the fault location,the back side continues to collapse and compaction occurs,and the whole is no longer affected by the fault,and the incoming pressure is gradually stabilized.(5)According to the analysis of mine pressure monitoring data,it is determined that the average initial pressure step is 33.8m,and the average periodic pressure step is21.48 m,there is no large overhanging roof phenomenon,the distance between the fault and the working face has obvious influence on the mine pressure appearance,because the fault causes the overburden rock to break,the overburden rock near the fault is more prone to instability,the closer the distance to the fault,the more intense the mine pressure appearance.The frequency of fluctuation and the peak of fluctuation of working surface brace resistance curve in the non-pressure stage under the influence of fault are larger,and become smaller as the distance from the fault location becomes farther.According to the strain distribution characteristics of the sensing fiber,the change process and the peak strain of the fiber,combined with the advancing situation of the working face,it can be judged that the influence range of over-support pressure is about 59.3m.Figure [38] Table [12] Reference [82]... |
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