Study On Repeated Mining Technology Of The Layer Under Thick Coal Seam No.3 In Jushan Mine

In the past,there was a technology of top mining-bottom abandoning applied to the thick coal seams of many mines for unadvanced mining technology and equipment,leading to a large amount of coal resources waste.Therefore,recovering remaining coal resources has become a great significance for improving the recovery rate of these resources and extending the length of service.Based on the typical No.3thick coal seam geological characteristics of Jushan coal mine,from the overall perspective of the complex structural condition about gobs which was remained by upper slice pillar mining,adopting some measures(the theoretical analysis,filed and laboratory testing,numerical simulation,etc.)has been studied for the repeated mining technology of underlying seam of No.3 thick coal seam in Jushan Coal Mine.The specific research results are as follows:(1)The characteristics of the pillar mining method,namely for Jushan Coal Mine,was analyzed in the upper seam of No.3 thick coal seam.Through taking a set of samples from the roof,floor and underlying coal seam,the physical and mechanical parameters of coal and rock were tested that included tensile strength,compressive strength,shear strength,density,as well as poisson’s ratio,etc.Thus,these could give basic parameters to develop the research.(2)The stress distribution of remaining coal pillars in upper seam under different conditions of mined-out and factors affecting the addition stress at any point in underlying seam were analyzed.Besides,a mechanical model of the failure depth between the upper and underlying seams was established,implying that the failure depth of the underlying seam is 0.36 m after its calculation.Therefore,the coal seam roof should be left to prevent the accident of roof caving.(3)The deformation-failure characteristics and stress distribution of surrounding rock in the old gob of upper seam were analyzed,revealing three results:(i)the false roof and immediate roof were caved,as well as the main roof was broken firstly when the width of a coal pillar was less than 8 m and the depth of roof cutting was more than 3 m.However,the failure depth of roof cutting was shallow,especially being up to 2 m,and the main roof was unbroken when the width of a coal pillar was more than8 m.(ii)The shorter the width of a coal pillar,the stress concentration was more serious.When there were coal pillars with less than 8 m wide,the concentrated stress of coal pillars was up to 10 MPa.And the influence areas of vertical stress on theunderlying seam was widely large that greater than the thickness of the underlying seam.So with the exploitation of the underlying coal seam,the effect of concentrated stress was focused on.(iii)the failure depth of the upper coal seam acting on the underlying coal seam was 0.35 m that in accordance with calculation results.(4)The layout mode of the coal pillar across the repeated mining face was determined,and the fully mechanized for top coal mining was selected as the recovery method of the underlying coal seam,and the layout position of the roadway used for repeated mining was ensured.On this basis,the UDEC numerical calculation model was established,determining the width of the reserved reasonable coal pillar of 5 m in underlying mining.(5)With the mining engineering process of the underlying in No.3 thick coal seam,the comprehensive control technologies of surrounding rock in thick mining face that included high foam cement grouting reinforcement materials controlling broken the roof,the compound mining face left a deep hole directional blasting in coal pillar unloading,as well as the compound mining face of main haulage,return air roadway and end of roof control was put forward as a core control system.Moreover,the law of mining pressure in F203 mining face was analyzed,implying that the average working resistance of hydraulic support was 31.6 MPa when the mining face passed through the area of stress concentration.Therefore,the ZZS3800-1550/2500 chock-shield support with rated working pressure of 37.5 MPa was applied,and this selection was reasonable.The dissertation contains 56 pieces of figures,6 pieces of tables and 86 pieces of references.