Study On Engineering Geological Characteristics And Hazard Hidden Danger Prediction Of Paleogene Extremely Thick "Red Beds"

“Red Beds”are widely distributed in central,southern,southwestern and northwestern China.They are characterized by low rock strength,weak weathering resistance,strong hydrophilicity,softening of rock mass after immersion and rapid decline in strength,which make the engineering problems of“Red Beds”increasingly prominent.The geological structure of Xinhu Coal Mine of Huaibei Mining Group is complex,and it is generally covered by the thick"Red Beds"of Paleogene.In addition,there are few studies and references on the engineering geology and hydrogeology of"Red Beds",which makes the engineering geological characteristics of"Red Beds"and the possible disasters caused by coal seam mining more and more concerned.Based on the analysis of the hydrogeological and engineering geological conditions of the"Red Beds"in No.82 mining area of Xinhu Coal Mine,Anhui Province,and the information collected during exploration,this paper studies the distribution law and physical and mechanical characteristics of the Paleogene"Red Beds".XRD diffraction analysis and scanning electron microscopy（SEM）were used to analyze the microstructure of the"Red Beds".The stress-strain permeability test（GDS）and disintegration resistance test were carried out to understand the water properties of the"Red Beds"and evaluate its water resistance.At the same time,the unique engineering geological characteristics of Paleogene"Red Beds"in Xinhu Coal Mine are systematically summarized based on the impact tendency test.It is found that the integrity and self-sustainability of"Red Beds"are poor.With the mining of No.8 coal,the extra load of support will increase with the collapse of bedrock under the action of self-weight.Especially at the fault,it is easy to form strong mine pressure.In addition,the bottom of the"Red Beds"often develops a certain thickness of glutenite aquifer.Under the influence of mining,it is easy to be swept by the water fracture zone and cause"Red Beds"water inrush.Therefore,taking 824 working face as an example,combined with FLAC^3Dsimulation software,this paper studies the height of"two zones"（fissure zone,caving zone）,the influence range of faults and the failure law of mining overburden,and determines the height of water flowing fracture zone 113m based on theoretical analysis,numerical simulation and mine analogy under similar conditions.Based on the analysis of the potential hazards of the super-thick"Red Beds"in No.82 mining area,nine main controlling factors of geological hazards are put forward,namely,the distance between"Red Beds"and coal seams,the influence factors of faults,the height of water flowing fracture zone,the thickness of aquifer at the bottom of"Red Beds",RQD at the bottom of"Red Beds",the proportion of mudstone at the bottom of"Red Beds",the thickness of coal seams,the thickness of"Red Beds"and the water inflow per borehole.By using Analytic Hierarchy Process（AHP）,the index system of zoning evaluation of the vulnerability degree of geological hazards is established,and the dangerous degree of adverse geological hazards caused by overlying huge"Red Beds"in the 82 mining area of Xinhu Coal Mine is zoned,which provides basic reference for realizing safe mining of coal seams under extremely thick"Red Beds".The paper contains 79 figures,28 tables and 96 references.