Research On Support Crushing Mechanism And Control Of Fully Mechanized Caving Face In Close Distance Coal Seam Under Goaf

Long wall mining technology has become the most important method ofunderground mining in China, full caving method has become China mostimportant goaf treatment method;For the close distance coal seam groupmining,the most conventional mining sequence is downward mining.And thismethod will produce problems in fully mechanized caving face in close distancecoal seam under goaf.In fully mechanized caving face in close distance coal seam under goaf,dueto the increase of coal thickness and the affected overburden thickness, the stresssecondary distribution by the upper coal seam goaf terrane static load and theoverburden structural instability,and the stable coal thickness,strength betweenthe upper and lower layers, the initial caving distance and the cycle cavingdistance always changed,makes mining pressure complex.Therefore,thecrushing accindents of fully mechanized caving face in close distance coal seamunder goaf has become a practical engineering prlblem to be solved ofunderground mining. Currently the researches focused on avoiding the pillar stress concentrationof fully mechanized caving face in close distance coal seam under goaf,thispaper argues that under the goaf of close distance coal seam mining,overlyinggoaf without coal pillars overlying caving zone,fractured zone stress of lowercoal will also affect the pressure fuame,and we can control the support crushingwith the water of overlying goaf.Therefore,with Shanxi Xishan Xiegou CoalMine13#coal as the research object,through theoretical analysis,laboratory testsand numerical simulation methods, support crushing mechanism,control methodand control effect of13#coal were studied.Research contents are as follows:(1)When we caving on fully mechanized caving face in close distance coalseam under goaf,the fault zone may be directly through the overlying goaf,thebroken rock in goaf passed directly down load,lead roof strata of static is largerthan ordinary mechanized mining face,the top plate is difficult to form a stablestructure,crushing accident is easy to happen when roof pressure,face causingstagnation to effect production.In considering of the weight of rock of fracturedafter the upper layer has caved,the mechanical model is established to analyzethe relationship between support and surrounding rocks,giving the theoreticalrelationship between support and caving distance of fully mechanized cavingface in close distance coal seam under goaf and the calculation formula of thetensile strength of collapse section.(2)Using the overlying goaf hydrops to weaken thecoal seamroof,according to the mechanical characteristics of roof rock,drilling from work face to overlying goaf,given the weakening process and parameters,leading theoverlying goaf water into drilling,by using the water self weight perssuer andphysical and chemical properties to make a further development ofcracks,reduce the mechanical strength of rock,artificially formed a weaksurface,control of the caving distance of roof,control of the crushing,the coalmining safety is guaranteed.(3)The crushing control effect of fully mechanized caving face in closedistance coal seam under goaf is verified by numerical simulation, the numericalcalculation model were establishment before and after the weakening,dynamicanalysis the displacement distribution and destructive characteristics during coalmining on lverlying strata and working face.From the displacement distributionand destructive characteristics on lverlying strata,after the weakening control byusing the overlying goaf water,the peak value of pressure decreased by anaverage of2000KN than before,the top coal subsidence peak reduced by anaverage of10mm~15mm,that proposed that the crushing control method in thispaper in feasible.