Research On Ground Behavior Law Under Coal Pillar Along Advancing Direction Of 10~# Coal Seam In The Shangyuquan Coal Mine

Close coal seam in China is normal and widely distributed.Longwall mining method is used by most coal mines in our country,which uses the caving method for roof control.And usually the mining sequence is from top to bottom.Many problems of close coal seam under goaf which have got more and more people’s attention have been caused for the above reason,which have got more and more people’s attention.Movement of surrounding rock is increased with the fully mechanized top-coal caving method in close coal seam due to the thickness of coal seam mining is very big compared with the normal mining height.After the coal is extracted,easy caving rock cannot be full of goaf in a short time.So,Basic roof in the traditional sense can’t form a stable "masonry beam structure in this case,transforming into immediate roof strata and forming the cantilever beam structure.When the upper coal is mined,the integrity and strength of Overlaying Strata and Interlayer Roof has been damaged.When the lower coal is mined,surrounding rock stress influenced by second mining will cause a series of new mine ground pressure phenomenon,for example,roof leakage and crushing accidents are more likely to happen in the working face.Influenced by the stress concentration of consequent pillar,support load under coal pillar are usually very big,coal wall spalling is serious,hydraulic support is prone to forward tilt,damage and crushing and the surrounding rock is harder to control.Based on the I031001 working face of 10~# coal seam in the Shangyuquan coal mine,in this paper,Overlaying Strata structure and Mine Pressure Behavior law of working face under goaf and coal pillar are investigated.Comparing the two different conditions,the results show that:(1)According to the occurrence condition of coal seam and the mining method,Overlaying Strata fracture,caving and stable situation have been analysized.It is concluded that the overlying strata around goaf presents the structure of "top coal + direct roof rock + basic roof rock + caving zone and fracture zone",and the the overlying strata around coal pillar presents the structure of “Arch transfer rock beam structure”.(2)There is little difference of weighting step distance between under the Mined-out area and under the coal pillar.Under the influence of the advance pressure relief,the initial load coefficient under coal pillar is 1.51,which is relatively large.Due to the influence of the concentrated stress of the coal pillar,the load of the support under the coal pillar is comparatively large,which is 120% of the load of the support under the goaf,and the dynamic load coefficient under the goaf is 118% under the coal pillar.(3)The theoretical estimation method and the measured method have been used to calculate the support working resistance and the results obtained are more or less the same.The greatest support working resistances under the goaf and coal pillar are obtained by theoretical calculation,respectively,14822 KN,14800KN,and the results are pretty much the same,which is consistent with actual situation.The total average value calculated by theoretical calculation method,mean-variance method and maximum load method is 13078 KN.It can be seen that the rated working resistance of hydraulic support ZFY10200/25/42 D can not meet the actual production requirements.(4)In the process of coal mining,hydraulic support safety valve is often open,coal wall spalling is serious,roof flaking always happens,the support roof and the coal seam are not fully contacted and the support beam is not fully lifted.It can be seen that ZFY10200/25/42 D can not meet the requirements of safe and efficient production.Comparing the advantages and disadvantages of two column and four column type caving support,it is recommended to use four column type fully mechanized caving support shield hydraulic support,whose rated working resistance is not less than 15000 KN.