| The Longwall mining with split-level gateroads(LMSG)in the thick coal seam,the roadway layout of panel is different from the traditional two-dimensional layout,and the three-dimensional(3D)"high and low roadway" layout is adopted.However,there is still a lack of understanding in the study of the migration and evolution law of the overburden structure and the characteristics of the combined support structure caused by the goaf and the surrounding rock mass after the LMSG.For the traditional mining method of thick coal seam,wide pillar is set between sections,resulting in a low recovery rate of coal resources.While the technology of gob-side entry is also accompanied by the problems of weak supporting capacity of narrow coal pillar,high support cost and large workload of roadway maintenance.At the same time,the occurrence of thick coal seam in China is relatively large,and the main advanced production capacity is concentrated here.Therefore,how to increase the energy efficiency ratio of thick coal seam mining becomes more meaningful,which has a huge impact on the development of the coal industry and even the development of China’s overall energy market.The thesis combines theoretical analysis,numerical simulation and laboratory test to analyze the migration and evolution law of the overburden structure under LMSG and the research on surrounding rock control technology of gob-side entry in continuous panel.The main contents and conclusions are as follows:(1)Based on the LMSG,the characteristics of the migration and evolution of the spatial overburden structure between the goaf and the surrounding rock are studied.Through theoretical analysis,it can be seen that the interaction relationship between the "gangue + triangular bottom coal body below the air-return entry(TBCBHE)" coal-rock synergetic system and the main roof.At the same time,the elastic foundation beam theory is used to determine the position of the maximum bending moment of the main roof.The main factors affecting the fracture position of the main roof include: the thickness,the foundation coefficient,the elastic modulus and so on.According to the influence of different factors on the distribution law of the bending moment of the main roof,the variation law of the position of the maximum bending moment of the main roof under this factor is obtained.Then,the instability sensitive factors affecting the key block B of the main roof are analyzed,including the filling situation of gangue in goaf,related parameters and characteristics of the main roof itself.(2)The stress-strain relationship of gangue with different particle sizes and intact gangue was analyzed by laboratory test.The final results show that the strain values of gangue under different particle sizes in confined-side uniaxial compression test are dozens of times higher than that of intact mudstone specimens.At the same time,the energy consumption of gangue compression deformation and bearing buffering effect of gangue under different particle sizes are studied.Based on the analysis of three stages of main roof rotation subsidence,the mutual feed-mechanics model relationship between gangue and main roof block is studied.The change of the supporting force of the gangue on the main roof in the goaf is mainly related to the thickness of the coal seam,the thickness of the immediate roof and the gangue expansion coefficient.In the method of LMSG,the mining height of the panel is equivalently reduced due to the triangular coal body under the high-level roadway of the panel that has been mined,thereby reducing the space-to-top distance above the gangue,and effectively reducing the sinking angle of the main roof.Finally,it can reduce the impact and slow down the rotary motion of the main roof,and the extrusion effect of the high stress on the coal(body)column,and provide a good surrounding rock environment for the gob-side entry of the continuous panel.(3)The stability of the triangular coal body is analyzed by the Janbu method,and the mechanical model of triangular coal body can be built based on limit equilibrium method.It can be concluded that with the increase of width and height of triangular coal body,internal friction angle and overburden pressure,the corresponding lateral pressure shows an increasing trend,which has a confined support effect on solid coal side.Through numerical simulation analysis of vertical stress distribution in transverse and longitudinal directions of LMSG,it can be seen that the roadway of 2207 panel is the most reasonable and favorable when roadway along the floor and closer to the goaf of 2205 panel,which provides a basis for roadway layout of 2207 panel.Therefore,combined with the mechanical model and numerical simulation analysis,it is determined that the reasonable size of the horizontal coal pillar in the roadway of the2207 continuous panel is 3m.(4)Considering that the support systems of adjacent roadways between panels are independent of each other in conventional fully mechanized caving mining,the layout of "high and low" roadways under the three-dimensional system of adjacent roadways between panels is adopted in the LMSG,and the three-dimensional combined support system of adjacent roadways is proposed.Give full play to the support effect of the high-level roadway in the panel that has been mined and the active support of the integral bolt(cable),thereby forming a triple support structure of "arch-beam-arch" for the gob-side entry under the LMSG.Theoretical analysis and orthogonal test scheme are used to jointly determine the roadway support parameters,and based on the numerical simulation analysis under two different support scheme,the gob-side entry of 2207 continuous panel supporting stress field and plastic zone distribution in the mining process and the situation of the relative deformation rate of surrounding rock,and then determine a reasonable roadway support plan for the 2207 continuous panel. |
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