Research On Strong Mine Earthquakes Mechanism Induced By Fracture Movement Of High Position And Extremely Thick Overlying Strata And Its Risk Assessment

Yanzhou Coalfield is an important coal production base in China.The area is overlying the Jurassic Santai Formation red bed,with frequent occurrences of strong mine earthquakes and rock burst,which seriously threaten the normal and safe production of coal mines.It is urgent to systematically study the geological occurrence characteristics of the red bed,the relationship between strong mine earthquakes and overlying rock movement,and the risk of induced rock burst.Based on the occurrence conditions of coal seams in the sixth mining area of Dongtan Coal Mine,this thesis adopts research methods such as on-site monitoring,theoretical analysis,mechanical model,numerical simulation,and statistical analysis to carry out research on the mechanism and risk assessment of strong mining earthquakes induced by the fracture movement of high and thick overburden rocks.The following research results have been achieved:Summarize the geological occurrence and characteristics of induced strong ore earthquakes of high and thick overlying rocks(lower and upper sub segments of red beds).The conclusions are as follows:(1)The high position and extremely thick overlying strate has the characteristics of large thickness,developed structural fractures,low strength,and strong integrity.(2)The maximum horizontal stress in the mining area will have obvious directionality in the destruction of the overlying strata during the mining process of the working face The high and thick overlying rock in the goaf area is the main active area of strong mining earthquake events.The development height of strong mining earthquake events is about 0～350 m above the coal seam in the first mining face,and about 0～250 m above the coal seam in the single side goaf working face.(4)The front shock frequency band of the strong mining earthquake signal HHT is 0-10 Hz,and the main shock frequency band is 0-50 Hz.According to the formation mechanism,propagation characteristics,and frequency band composition of Rayleigh surface waves,the main shock in the strong mining earthquake signal is induced by the front shock,and the former occurs at a higher level.A two-parameter elastic foundation thick plate mechanical model is established to study the distribution rules of tensile stress,compressive stress,and shear stress of high position and extremely thick overlying strate during the mining process of the working face.It is concluded that in the goaf area,it is mainly upward pressure and downward pressure,while in the surrounding goaf area deep into the coal body area,it is mainly upward pressure and downward pressure,and the central and surrounding boundary positions of the goaf area are subjected to large shear stress effects.By studying the effect of fracture motion parameters on giant thick overburden rock,it is concluded that the evolution mode of fracture motion of high giant thick overburden rock structure is: tensile failure in the central area below the goaf area → shear failure occurs when the shear stress distributed in the giant thick overburden rock reaches its shear strength.The relationship between the mining induced stress field of high and thick overlying rock and strong mining earthquakes is studied.The numerical simulation shows that before the single side goaf is mined,the upper part of the high and thick overlying rock has been partially damaged,and there is a three-dimensional stress concentration phenomenon between the overlying thick and hard rock layer;The maximum horizontal stress in the middle and lower parts of the high and thick overlying rock is always in the state of pressure relief.The vibration field and surface subsidence verify the rule that the upper part of the overlying high and thick overlying rock has undergone partial damage before mining in a single goaf face.The occurrence mechanism of strong mining earthquakes is revealed,which is caused by mining fracture of high and thick overlying rock in the goaf area and connects with the initial fracture formation,inducing the release of elastic energy in the three-dimensional stress concentration area.A safety assessment system for disaster risk caused by strong mining earthquakes in high and thick overlying rocks has been established.The maximum energy value of strong mining earthquakes in the mining area is estimated based on the G-R relationship,and the energy attenuation equation is obtained through statistical analysis of mining earthquake waveform data.The maximum energy value that can be absorbed by the roadway support system in the working face is estimated through the law of energy conservation.Based on the mechanism of mining earthquake induced flooding,the minimum distance of roadway support damage caused by different energy strong mining earthquakes is calculated,Field practice has verified that the existing roadway support in front of the working face can resist the single impact of strong mining earthquakes in most cases.This thesis has 73 diagrams,10 tables,and 105 references.