Development Law Of Water Conduction Fissure In Repeated Mining Of Multiple Coal Seams And Its Application In Mine Water Control

Deformation,cracking,crushing,compaction and other phenomena occur in roof overburden rock under the influence of coal seam mining disturbance,especially when multiple coal seams are repeatedly mined,the development of water-conducting cracks in overburden rock is more complicated.A correct understanding of the development law of water-conducting cracks in multiple coal seams repeatedly mined can help develop coal resources more safely,reasonably and efficiently.In this thesis,the Great Wall Minmetals as an example,with multiple coal seam repeated mining water conduction crack development law and overlying rock permeability as the research object,based on the mine geology,hydrogeology and coal seam overlying rock structure characteristics analysis,numerical simulation,theoretical formula calculation and field measurement results as the basis,comprehensive comparative analysis,the development law of multiple coal seam repeated mining water conduction crack;On the basis of repeated mining of multiple coal seams,similar seepage test is carried out on the overburden permeability,and the change of overburden permeability after repeated mining of multiple coal seams is obtained.The main achievements are as follows:(1)By analyzing the hydrogeologic and strata structure features,showed that after repeated mining of coal seam newly flood threat.The coal-bearing stratum is carboniferous ～ Permian system,and the main coal seam has 4 layers in total.The descending mining method is adopted,and the overburden type of the coal seam roof is medium hard type.(2)Using FLAC3 D numerical simulation software to simulate the 3 upper,3,5,9coal seam mining alone,and the repeated mining of coal seam after the changes of stress,displacement and plastic area,analyzed the disturbance of the lower coal after mining the upper coal mining effect and deformation law of destruction of the strata.It is concluded that after coal seam mining,the stress redistributes and reaches the equilibrium state,and the stress lowering zone and stress increasing zone are formed around the working face.The top and bottom of the working face are in the relief zone,and the overlying strata mainly bear the tension pressure,which leads to the tensile failure of the strata above the working face.On both ends of working face in the shear stress,high,where the main roof and floor under shear stress.According to the plastic failure range,the maximum height of the water-conducting fracture zone is obtained after each coal seam is mined separately and repeatedly.(3)Through theoretical calculation and comparative analysis,it is concluded that after repeated mining,the mining of lower coal seam will make the original water-conducting fissure of upper coal seam "activated" and increase the height of water-conducting fissure zone of upper coal seam,and the development height of water-conducting fissure of lower coal seam mining will be affected by overlying rock fissure of goaf of upper coal seam,thus resulting in the effect of overlying rock "weakening" and reducing the height of water-conducting fissure zone of lower coal seam.After repeated mining of multiple coal seams,the mining of upper coal seam causes the roof overburden of lower coal seam working face to be disturbed in different degrees,and the strata structure of goaf is broken.The roof overburden structure of lower coal has changed with the mining of upper coal,and the roof overburden has been "weakened" under the condition of mining disturbance,resulting in the cumulative split mining ratio of multiple coal seams decreased significantly after repeated mining.(4)Through the experimental analysis of the change of overburden permeability after repeated mining of multiple coal seams,it is concluded that the water-conducting cracks of soft overburden rock represented by mudstone show a dynamic process of opening and closing under the disturbance of repeated mining,and the overburden permeability increases to decrease with repeated mining of multiple coal seams.The permeability of medium-hard to hard overburden rock,represented by sandstone,increases with the increase of repeated mining disturbance.This thesis has 64 figures,35 tables and 106 references.