Study On Surrounding Rock Deformation Law And Processing Parameters In Extra-thick Seam Of Fully Mechanized Caving Mining With Great Mining Height

For mining of super thick coal seam,increase of coal cutting height brings about increase of coal holding space behind the hydraulic supports on the one hand,which helps strengthen top coal caving peoperty and promote the overall recovery rate,and on the other hand it causes increased rate of coal wall caving of mining face.In view of the storage condition of coal seam 13 in Xiegou Coalmine,based on analysis of the exsisting researching results of predecessors,with the combined methods of theoretical analysis and numerical simulation,the paper made a more systematical study on the yielding and fracturing characteristics of the top coal, movement and transformation of top coal in different layers, the stability of the long wall coal face.the behavior law of underground pressure as well as the reasonable processing parameters of the working face in super thick coal seam with the thinckness of 14 to 20 meters with fully mechanized top coal caving mining technology of great mining height and with the increase of both coal cutting height and overall coal seam thickness.The conclusions are as follows.1. Movement and transformation charateristics of top coal with fully mechanized top coal caving mining technology of great mining height are in accord with the macroscopic damage mechanics principle.With the application of damage theory,the range of elastic zone in top coal is:S(?)ΔS=Hmεmax=ΔS1, the range of plastic zone isΔS1,(?)S(?)ΔS2=Hmε,and the range of granular media zone is S(?)ΔS2.Damage constitutive equation of coal seam 13 was given according to the detailed conditions and parameters of Xiegou Coalmine:σ=Ecε=E(1-D)ε=E(1+0.00501ε-1.641)ε2. The damage characteristics of the top coal and the vertical and horizontal displacements of the base point at different layers of the front and back of the big mining height shield controlling area were analyzed by using the finite numerical simulation software FLAC3D.Before caving and drawing,most units of top coal show shear damage.The overall amount of the completely damaged units increases with the increase of mining height.So does the accumulative amount of top coal displacement.The vertical displacements in the upper top coal are always larger than the lower ones.While, the horizontal displacements in the middle of the top coal are larger than both the upper and lower ones.According to the displacement changing data of the top coal,caving of the upper parts of top coal is lagged. All in all,with the specific coal seam thickness,increase of mining height helps fragmentation of top coal and can improve the recovery rate.3. Theoretical research and calculation of rib spalling theory of the coal wall and the width of the plastic zone in fully mechanized top coal caving mining technology with great mining height were conducted and the analytic formula of the width of plastic zone in front of the coal wall was put forward.The yield and damage depth of the great mining height coal face, the horizontal movement of measuring point at different heights on the coal face and the bearing force distribution at the front of the working face were analyzed by FLAC3D with the following results:as the mining height increases bring about increase of the vertical stress peak value in front of the coal wall,decrease of the space between the peak value points and linear increase of the horizontal displacement peak value of call wall,which indicates the increase of both coal cutting height and overall coal seam thickness would give rise to rib spalling rate.4.According to the storage state of coal seam 13 in the first working area of Xiegou Coalmine,the related technological parameters were worked out through numerical analysis.When the thickness of coal seam is 15 meters,the comparativiy reasonable parameters can be dertermined as follows:coal cutting height is 4.0 meters;roof controlling distance is 4.8 meters; working resistance of each hydraulic support is 12000kN; drawing interval is 0.6 meters;the distance between the action point of resultant force of hydraulic support and coal wall is 1.4 meters.