Study On The Influence Of The Residual Coal Pillar In The Room And Pillar Mining Goaf On The Law Of Strata Pressure Behavior In The Downward Coal Seam Mining

In the past,some backward mining methods used in our country,that have formed the room-and-pillar mining goaf,and in recent years,the problem of coal seam mining under room and pillar goaf has been encountered.A large number of coal pillars remained in the goaf after the room-and-pillar mining was adopted in the upper coal seam.When the lower coal seam is exploited,the stress of the residual coal pillar is transferred downward on the roof of the lower coal searm,which makes the law of mining pressure for working face different from the ordinary single coal seam mining.By means of theoretical analysis,field measured data,numerical simulation and other methods,this paper studies the influence of the concentrated stress of residual coal pillar on the e mine pressure in the lower coal seam mining in the shallow buried coal seam room-and-pillar mining goaf.The main contents and conclusions are as follows:(1)The upper load is acting on the coal pillar and passing through the coal pillar to the lower rock mass,and the mechanics model is established by the semi plane body theory to obtain the stress transfer law of single room type coal pillar and multiple room type coal pillar in the floor,and to determine the influence range of the coal pillar down transfer.The mechanical model of the stress of the isolated coal pillar gets its downward stress transfer law,which will have a great influence on the working face when the isolated coal pillar is mined under the isolated coal pillar.(2)Consider the stress of the upper goaf pillar pass down to residue on the key stratum of in the lower coal seam,the first weighting step and periodic weighting step are obtained by establishing the elastic solid supported beam and the cantilever beam mechanics model.Due to the influence of the residual pillar stress,make the load set on the key stratum increasing so that the weighting step become smaller.Through the analysis of the basic roof structure,the change of the structure into "single rotating rock mass" structure,the working resistance of the support is obtained.(3)Based on the engineering example,the periodic weighting step and the working resistance of the suppor are obtained through theoretical calculation,and the results show that it is close to the field data.When the isolated coal pillar is over the section,the sudden release of the concentrated stress of the coal pillar and the rotation of the key blocks of the overlying strata will cause the accident.The numerical simulation method is used to simulate the pressure phenomenon in the mining process,which shows that the upper samll room-and-pillar has less influence on the lower coal seam mining,and through the isolation coal pillar has a larger influence.when the working face through the isolated coal pillar are prone to dynamic load crushing,put forward the roof control technology of pre-splitting blasting loose coal pillar in advance,to ensure safety mining of working face.