Study On Roof And Floor Failure Law Of Fully-mechanized Caving Mining Under The Extra-thick Coal Seam

The fully-mechanized caving mining of extra-thick coal seam has the problems of large mining space,large range of rock caving,coal wall spalling,support crushing and instability accidents,which seriously affect the safe and efficient production of coal mine.Therefore,it is of great practical significance and theoretical value to study the structural characteristics and failure law of the roof and floor of the fully-mechanized mining face in the extra-thick coal seam,which is of great practical significance and theoretical value for the safe and efficient production under the condition of fully-mechanized caving mining in the extra-thick coal seam.On the basis of collecting and consulting a large number of documents and hydrogeological engineering geological conditions of the study area,this paper adopts the research method of combining theoretical calculation,numerical simulation and comparative analysis of field monitoring data,some research results have been achieved as follows:（1）FLAC^3D numerical simulation software is used to analyze the dynamic evolution characteristics of plastic zone,stress field and displacement field of roof and floor under different advancing distances of working face.The results show that the maximum value of roof failure height is 153.2 m and the maximum value of floor failure depth is 12.1 m.Since then,with the continuous advancement of working face,the failure height of coal seam roof and the failure depth of floor remain stable without obvious change,while the failure range further increases.（2）Based on the theoretical analysis of the roof failure based on the overall mechanical model of the support-surrounding rock,combined with the roof failure form of the extra-thick coal seam,the“three-zone”theory and the balance structure of the main roof strata,a direct roof mechanical model was established.Then,by analyzing the balance structure of the main roof strata,the energy variational method was used to solve the model.It was concluded that the subsidence of the direct roof strata was negatively correlated with the resistance of the hydraulic support on the working face,and positively correlated with its elastic modulus and the rotation angle of the main roof.（3）The stress function is used to analyze the floor stress field and failure depth by elastic theory.The results show that the stress concentration degree in the surrounding rock near the stope is positively correlated with the dip width.The maximum failure depth of floor is positively correlated with the dip width of working face and the stress of surrounding rock,and negatively correlated with the compressive strength of rock mass.In addition,the elastic theory formula calculates that the maximum failure depth of the floor rock stratum is 16.4 m and the maximum horizontal distance from the two ends of the working face is 4.4 m.Based on the semi-infinite body theory in elastic mechanics,the stress field and failure depth of the floor are analyzed by plastic theory.The maximum depth of the floor rock failure zone is 11.84 m,the maximum horizontal distance from the coal wall is 7.11 m and the maximum plastic failure length of the floor rock mass in the horizontal direction is 22.315 m.（4）Combined with the empirical formula of“two zones”,the height of water flowing fractured zone is 190.75 m,and the height of caving zone is 75.89 m.According to the floor failure empirical formula developed by different scholars,the floor failure depth range is 26.53～34.78m;in addition,the on-site microseismic monitoring results show that the fracture development range of the roof water-conducting fracture zone is142～195m and the failure depth of the strong fracture development section of the floor is14m.（5）Comprehensive numerical simulation,theoretical analysis and calculation,empirical formula results and on-site monitoring results are compared and analyzed.From the perspective of mine safety production,it is finally determined that the height of water-conducting fracture zone in 61605 working face is 195 m,the ratio of fracture to mining is 8.44,and the depth of floor failure is 14 m.In summary,the research results obtained in this paper can provide a certain theoretical basis for mine safety production,and can also enrich the research content of comprehensive safety mining thick coal seam in China at present.Figure[28]Table[14]Reference[83]...