Study On Influence And Control Of Coal Pillar In Upper Goaf Of Shi Fengshan Coal Mine On Coal And Rock Stability Of Fully Mechanized Caving Face

Under the condition of coal seam group,the section coal pillar in the upper coal mining will have a great influence on the mining of the lower coal seam under certain conditions,the concentrated stress formed in the floor of the coal pillar in the Goaf becomes the condition of the superposition of the stress produced by the advance mining in the mining process of the lower coal face,the superposition of advance mining stress will increase the probability of spalling and roof fall,which will affect the safe and efficient production of the face.Based on 5302 working face of Shifengshan coal mine,combined with theoretical analysis,numerical calculation and field test analysis,this thesis studies the stress influence range formed in the floor of the remaining coal pillar in the Goaf of the upper adjacent coal seam and the superposition of the leading stress in the working face of the lower coal seam and the law of its influence on the stability of the coal and rock,this thesis analyzes the influence of stress superposition on the relationship between support and surrounding rock,and puts forward the method of using hydraulic fracturing to weaken the key influence zone of stress superposition.The main results are as follows:(1)Based on the geological and mining conditions of Shifengshan coal mine,the load calculation formula of the remaining coal pillar is obtained,this thesis analyzes the influence law of coal body internal friction angle,coal body cohesion,coal pillar width,roof dilatancy coefficient,roof caving residual angle,coal seam and its roof and floor friction coefficient,mining height of working face and coal seam buried depth on the vertical stress distribution of coal pillar.The effects of different width coal pillar on floor stress and plastic failure are obtained.(2)The influence of the pillar in the goaf of No.3 seam on the lead abutment pressure of No.5 thick coal seam is studied.It is found that when the working face advances to the coal pillar influence area,the stress superposition phenomenon occurs between the residual coal pillar floor stress and the advanced abutment pressure.In the coal pillar concentration stress influence degree big position,the work face front stress superposition penetration degree and the scope are biggest.(3)Based on the influence range and degree of stress superposition,the influence area of superposition stress under the influence of coal pillar is divided,and the influence area of coal pillar in horizontal direction is 80 m,the vertical direction can be divided into strong and weak stress superimposition area,in which the fine sandstone layer 10 m thick is the key rock layer.The superimposed stress results in the increase of the plastic failure degree and range of the coal seam in the fully mechanized top-coal caving face,reduces the effective support ability of the coal body to the roof,and increases the actual roof control range of the support to the roof,it is unfavorable to the stability of support and surrounding rock system.(4)Based on the influence of stress superposition on the stability of coal and rock in working face,a method of weakening the key influence of stress superposition of 10 m thick on rock layer by hydraulic fracturing is put forward.The layout and parameters of hydraulic fracturing boreholes are determined,and field fracturing tests are carried out.Field measurements show that the stability of coal and rock and the deformation of roadway have been significantly improved,and good control effect has been achieved.The thesis has 41 figures,9 tables and 55 references.