Research On Rock Strata Between Coal Seams Movement And Deformation In Pillar Ascending Mining Of The Left-over Coal In Jinhuagong Mine

Under the background of resources integration, it has a certain practical meaning on construction of conservation-minded society and a promotion of sustainable development of coal industry to recycle the abundantly reserved mineable coal seams above the mine goaf through ascending mining.In order to avoid serious lost of resources, prolong mine life and improve recovery rate of the limited mineral resources, Jinhuagong coalmine of Datong Coal Group Company is ready to use the method of ascending mining to excavate 9# coal seam which lies above 12# coal seam in the minitype coal mine destructive area of Jurassic Period. However, the present study about ascending mining mainly focuses on the influential factor of lower seams mining with interlayer space and hasn't made systematic study on the movement and deformation of the rock strata between coal seams. Therefore, the paper conducted the movement and deformation of the rock strata between coal seams with the initial point of its mechanical properties in view of the ascending mining of 9# coal seam above 12# coal seam goaf in the destructive area of No.402 minitype coal mine in Jinhuagong coalmine. With reference to"three-zone"theory of overlying rocks, considering the mechanical properties of the rock strata between coal seams with the method of ascending mining, the paper built the mechanical structural zones with control layer as the main subject of the rock strata between coal seams:plastic deformation zone in the control layer and tension and fracture zone under the control layer, elastic deformation zone above the control layer. Considering non-uniform and discontinuous deformation characteristics of the rock strata between coal seams, applying numerical analysis method, mathematical models of different working face advancement were built according to three schemes of the rock strata between coal seams with different thickness and properties. The simulation result includes:ascending mining causes the result that stress concentrates between the rock strata between coal seams and moves to the goaf and coal pillars with working face advancement, which forms pressure relief arch and pressure increasing arch. While the control layer forms larger stress arch and the strata movement and deformation inside the stress arch remains stable. Besides, through monitoring points data drawing, the rock strata between coal seams descending trend caused by ascending mining during advancement in different working face was put forward. Combining the key layer theory, the paper determined that the control layer which has a static balanced structure can keep continuous movement and deformation of the entire rock strata between coal seams from macrocosmic perspective.Based on the mathematical model which had been established in the thesis, a conclusion could be reached from the Jinhuagong coal mine that when there are control layers in both the floor of 9# coal seam and the roof of 12# coal seam, the coal pillar possesses enough supporting capacity, besides, the rock strata between coal seams is stable and the whole subsidence is stable. When there is only one control layer in the floor of No.12 coal seam, the coal pillar reaches its fractured limits, however, it could also provide efficient support and the rock strata between coal seams reaches its limit stability, too. The subsidence value increases but it can still sustain the integrity. When there is no control layer between 9# and 12# coal seams, the rock strata between coal seams become instable and show a waving subsidence, under which circumstance the ascending mining does not work.The paper used comprehensive aero geophysical techniques to verify the stability of goaf and coal pillars and the wholeness of the rock strata between coal seams. The result reveals that radon value and the simulated visual resistivity value in 9# and 12# coal seams increase abnormally and the simulated visual resistivity value of the rock strata between coal seams is comparatively lower, which indicates that the rock strata between coal seams has a good wholeness and the goal and coal pillars keep stable, which has identical results with numerical simulation.Above all, the movement and deformation of control layer in the rock strata between coal seams plays a critical role on the feasibility of the pillar ascending mining method in the left-over coal as well as the movement and deformation of the surrounding rock, which would provide theoretical guidance and technical assistance to the safety control of the pillar ascending mining in the left-over coal.