Excavation Timing And Stability Control Of Roadway In Lower Coal Seam During Cooperative Mining Of Shallow-buried Coal Seam Group

There are a large number of shallow-buried coal seam group in Shaanxi and Inner Mongolia regions.In order to achieve the designed production capacity,many coal mines have started to adopt collaborative mining of multiple coal seams.The mining intensity of the working face is high,and the mining and excavation succession is tight.Affected by the mining of upper coal seam,the excavation speed of roadway in lower coal seam is easily restricted,mainly reflected in:（1）It is difficult to grasp the timing of excavation.Early excavation will cause the roadway to bear the greater mining impact caused by the movement of overlying strata in the stope,and late excavation is not conducive to rapid replacement of the working face.（2）The surrounding rock control should not only ensure safety,but also take into account requirements of rapid excavation.It is difficult to determine the unsupported roof distance and rockbolt support parameters.Based on the engineering background of the shallow-buried coal seam group formed by the 4^-2,4^-3 and 4^-4 coal seam in Liangshuijing Coal Mine,this thesis uses a combination of field research,indoor testing,theoretical analysis,numerical calculation and field testing to determine the stability time of overlying strata after mining in the upper coal seam and the reasonable layout of roadway and excavation and support parameters in the lower coal seam.The following results have been achieved:（1）Excavation timing of roadway in lower coal seam.A beam model of high level key layer is established.Based on the rock rheology theory,the mathematical expression of high level key layer displacement with time as the independent variable is derived,providing a theoretical criterion for the stability time of the overlying strata after mining of No.4^-2 and No.4^-3 coal seam.Through theoretical calculation and numerical analysis,it is determined that the overlying strata stability time after mining of No.4^-2 coal seam is 21 months,and that for No.4^-3 coal seam is 15 months,which means the excavation time for the mining roadway of No.4^-4 coal seam should be at least 15 months after the mining of No.4^-3 coal seam.（2）Internal dislocation distance of roadway in lower coal seam.The influence factor of rock and its calculation method are proposed.Through numerical experiments,the distribution rules of the plastic zone,horizontal stress and influence factor of rock after roadway excavation are analyzed.It is concluded that the surrounding rock is in a strong disturbance state when the value of influence factor of rock is less than-0.4.Based on this,supplemented by other criteria,the reasonable internal dislocation distance of roadway in No.4^-4 coal seam is determined to be at least 20m.（3）Width of coal pillar of roadway in lower coal seam.The distribution characteristics of the stress,plastic zone,and cracks in roadway coal pillar with different widths were analyzed,and the stability of the coal pillar under the influence of mining of working face was studied.It was found that when the coal pillar width was 5 m,the internal plastic zone and cracks penetrated After increasing to 10 m,the two sides of the cracks were no longer connected,but the safety factor was low.Finally,the reasonable coal pillar width was determined to be at least 15m.（4）Unsupported roof distance of roadway in lower coal seam.A beam model of the direct roof in unsupported area while roadway excavation is established,and the maximum deflection of the direct roof under different unsupported roof distance is calculated.It is found that there is a nonlinear relationship between unsupported roof distance and the maximum deflection.Through numerical calculation,it is found that separation occurs on the shallow part of direct roof after the unsupported roof distance is greater than 7m.Finally,the maximum unsupported roof distance is determined to be7m.（5）Support scheme of roadway in lower coal seam.Based on the rheological properties of bolted rock and surrounding rock,the parameters of the rockbolt support system in the roadway were optimized.The rockbolt support scheme of（?）20×2100mm at the top,（?）20×1400mm at the side,space and interval distance of 1200×1200mm,HRB335 threaded steel rockbolt was determined.（6）Industrial tests on site.Through the application of the excavation timing and stability control scheme for the roadway of No.4^-4coal seam,the monthly footage was increased from 300m to 412.5m,while the deformation of roadway maintains around10mm.The thesis contains 72 figures,6 tables and 89 references.