Study And Application On Characteristics Of Overburden Failure In Close Distance Thick Coal Seam Group Mining Under Thick Unconsolidated Layer And Thin Bedrock

Taking the shallow close distance thick coal seam group in Xisan mining area of Gaozhuang coal mine as engineering background,a variety of research methods including on-site investigation,data collection and statistical analysis,theoretical analysis,laboratory tests,numerical simulations,and field tests were applied to research and analysis the spatial distribution of the bedrock and the quaternary bottom strata and the characteristics of their combined sedimentary structures in the study area.The characteristics of lithological characteristics and water resistance performance are analyzed,the characteristics of the structure of the coal seam group and the characteristics of the overlying rock failure under different storage conditions are analyzed and studied.The main work and conclusions are as follows:1)Through field investigation,statistical analysis and field test,it was found that the lower Quaternary Group near the study area was formed by the alternating deposition of clayey and sandy layers,and that the lower part of the lower section of the Quaternary lower section had a large thickness.In the stable clay layer,the lower aquifer and bottom of the lower Quaternary Formation are all weak aquifers;the bedrock is thin and the upper part has a oxidized zone,which is a weak aquifer.2)According to the field coring and laboratory test results of drilling hole,it is shown that the clay in the lower Quaternary system has good water resistance,the sandy grain size in the sand layer is small and the permeability is poor,and the bedrock is medium hard and soft rock,and the permeability of the clay in the sand layer is small and the permeability is poor.The bedrock pillar has the structure of"upper soft and lower hard".The strength of the rock in the oxidized zone of bedrock wind decreases obviously and the composition of clay increases,which can effectively restrain the development of mining fracture.3)Analysis of overburden damage characteristics of close thick coal seam group,on this basis,the failure characteristics of overlying rocks in mining coal seams with different thickness of bedrock,spacing of coal seams and thickness of seams are simulated by UDEC software.According to the simulation results,the influence of various factors on the bad characteristics of overlying rock in coal seam mining is analyzed.4)By means of numerical simulation and theoretical calculation,the height of coal pillars for sand-proff should be retained when the coal seam group working face is fully mechanized mining,and the reasonable mining scheme is determined and exploited.At the same time,example verification and application are carried out.The research results have certain reference significance for the mining of the near-thick coal seam group under the thick loose bed and thin bedrock in Gaozhuang coal mine and similar geological conditions.