Study On The Evolution Of Overburden Structure And Ground Pressure Control Of Multiple Coal Seams

Coal seam group mining is common in many mining areas in China,such as Xinwen mining area,Pingdingshan mining area,Xishan mining area,Huainan mining area,Datong mining area,Jingxing mining area.The roof damages for many times after upper coal seam mining,the roof structure and the rupture range is different from single coal mining.The breaking roof strata stress will transfer downwards through the residual coal pillar,causing the stress field changed near the mining face in the lower coal seam.Therefore,the stress in some regions will increase when mining the lower coal seam,leading to support break-off,falling and rock burst.Many coal mines in Datong mining area belongs to the Jurassic seam mining.The number of minable coal seam is large,and the distance between the Jurassic coal seam groups is small.The coal seam roof is generally hard sandstone or sand conglomerate,which is a typical coal seam group mining condition under hard roof.In this dissertation,using the Datong mining area of Jurassic coal mining as an example,theoretical analysis,laboratory test,numerical simulation and field test and other research methods are used,the evolution of overburden structure and ground pressure control of multiple coal seams is studied.The main research content and the innovative achievements include:(1)By uniaxial compression,triaxial compression and acoustic emission test,the Hoek-Brown strength criterion is modified based on the fractal feature of rock fracture distribution,and the fractal dimension of rock specimen under different crack condition is obtained which lays a foundation to study the mechanical mechanism of crack evolution of the overburden in mining multiple coal seams.(2)The similar material simulation and modified Hoek-Brown criteria are used,and the evolution and breaking roof structure of multiple coal seams mining and the influence of different mining height and interval layer thickness of the lower coal seam on the evolution of upper hard rock break is studied,and the newly increased range of breaking roof structure and evolution of stress transfer of residual coal pillar are revealed under different mining conditions.(3)According to the mining characteristics of coal seam group in Jinhuagong mine,the evolution model of breaking roof group structure of multi coal seams is established firstly.Based on the analysis of the disaster causing mechanism of the lower coal seam with strong pressure,the development and extension height of breaking roof group when mining successive coal seams are derived,and the formula of mining face support strength is given under the interaction of“residual coal pillar and breaking roof group structure",and reasonable working resistance of support is obtained.(4)Based on the monitoring of ground pressure of the coal face and abutment pressure in advance in 14#coal seam,the concentrated stress caused by the residual coal pillar of the upper coal seams to the lower mining face was analyzed.(5)The corresponding schemes of coal pillar and the floor blasting were proposed and the reasonable blasting parameters were designed.The floor blasting scheme was applied in the field and it was proved valid according to the results of electromagnetic radiation and ground pressure observation.