Study On Strong Ground Pressure Mechanism Of Gob-side Roadway And Its Control In Extra Thick Coal Seam With Hard Roof

At present,in the process of fully-mechanized top coal caving of extra thick coal seam with hard roof in China,the strong ground pressure of gob-side roadway is unusually prominent,which is characterized by intensified deformation of roadway surrounding rock,serious damage to support,and increased advanced influence range of working face,which seriously affects the safe and efficient production of working face.Therefore,based on the engineering background of gob-side roadway of fully-mechanized top coal caving in extra-thick coal seam with hard roof in Datong mining area,research methods such as field observation,numerical calculation,theoretical analysis and field industrial test are adopted,the characteristics of strong ground pressure,the stress distribution and deformation law of gob-side rock strata under the influence of mining,and the mechanical mechanism of strong ground pressure of gob-side roadway in extra-thick coal seam with hard roof are studied in depth.The main results are as follows:(1)The gob-side roadway of extra-thick coal seam with hard roof has the characteristics of large advanced influence range,serious overall damage of surrounding rock,large number of failure and damage of bolt and cable.These characteristics of strong ground pressure are related to the increase of active range and strength of rock strata in fully-mechanized top coal caving of extra-thick coal seam,the formation of broken structure in lateral direction of multi-layer thick and hard strata in roof,and the degree of action of intensified activation and instability of the structure on gob-side roadway under the influence of mining.(2)The mining of working face has an activation effect on the lateral gob-side rock strata.Under the influence of mining,the stress of the lateral gob-side rock strata in the working face increases with the increase of the rock layer within a certain range,and the subsidence deformation increases with the closer to the coal pillar.Moreover,the stress and displacement of the lateral gob-side rock strata increase significantly with the closer to the working face.This indicates that the activation degree of adjacent rock is enhanced.(3)The distribution conditions of key strata and the range of collapse zone of gob-side rock strata in ultra-thick coal seam with hard roof were determined,and the structural model of ’ low combined cantilever beam + high multi-story masonry beam’ was constructed.(4)The mechanical model of lateral overburden structure of the gob-side roadway in extra-thick coal seam with hard roof was established.According to the influence range of overburden structure on the stress of the gob-side roadway and coal pillar,the mechanical model was divided into the obvious indigenous moving deformation zone A and the elastic stable small deformation zone B.Through mechanical analysis,the expression of additional stress generated by the lateral overburden structure on the coal and rock mass below it was obtained,and the stress transfer mechanism of lateral overburden structure was revealed.(5)The results show that with the increase of the mining influence of the working face,the additional stress generated by the lateral overburden structure activation in the lower coal body increases,in which the high additional stress generated by the low key layer mainly affects the shallow coal body on the goaf side,and the influence range is small,while the high additional stress generated by the high key layer has a large influence range,reaching the deep part of the coal body,revealing the mechanism of the strong rock pressure of the gob-side roadway caused by the lateral overburden structure mechanical effect.(6)The multi-direction roof cutting and pressure relief control method of gob-side roadway in extra thick coal seam with hard roof is proposed,and the calculation formulas of roof cutting height and fracturing borehole angle are given based on the control of key layer activation of gob-side overburden.Field application and observation show that remarkable control effect has been achieved.There are 85 pictures,17 tables and 141 references in the dissertation.