Study On Deformation Damage And Crack Evolution Law Of Deep Coal-rock Combination

For deep coal mining,it is of great scientific significance to carry out research on the deformation and damage of deep coal-rock combination and crack evolution law under the background of mine impact disaster accidents induced by nonlinear dynamics phenomenon of coal and rock mass.In this paper,we take the 27# coal seam and the roof seam of Xinfa coal mine as the research object,integrate indoor experiments,theoretical analysis and numerical simulation to carry out the study of nonlinear dynamics of deep coal-rock combination.The mechanical properties and damage characteristics of the combination is derived.Based on the absolute energy of acoustic emission to reveal the spatial and temporal evolution of damage of the combination and the numerical simulation to explore the micro and macro mechanical behavior,crack evolution and deformation damage characteristics of combination.The main results are as follows:(1)Physical and mechanical tests and XRD tests of the coal-rock combination are carried out to determine the basic physical and mechanical parameters and mineral composition.Considering the factors of coal-rock thickness ratio and coalrock intersection dip angle,the uniaxial compression coal-rock combination test is carried out.This indicates that the strength and elastic modulus of the combination are between those of the coal and rock mass.And the uniaxial compressive strength and elastic modulus are negatively correlated with the coal thickness and inclination angle,respectively.(2)Analysis of the deformation characteristics and macroscopic rupture pattern of the coal-rock combination shows that the deformation damage of the rock lags behind that of the coal.The hysteresis effect decreases with increasing coal thickness and dip angle.With the increase of coal thickness,the damage mode of the combination shifts from tensile to shear and finally shows coal extrusion damage.With the increase of dip angle,the damage mode of the combination gradually appears slip damage while the compression-shear composite damage.(3)Based on the nonlinear growth characteristics of acoustic emission ringing accumulation to estimate the characteristic strength of different types of combinations,it is concluded that the cracking strength and damage strength of combinations are negatively correlated with coal thickness and dip angle,respectively.The spatiotemporal evolution analysis based on the absolute energy of acoustic emission can describe the damage evolution process inside the uniaxial compression of different types of coal-rock combination more accurately,but the coal occupancy ratio or dip angle is too large to make the acoustic emission signal seriously attenuated,resulting in inaccurate localization.(4)The numerical model of coal-rock combination is established by applying the UDEC-Trigon method based on the indoor mechanical tests and the calibration of block size and contact surface fine view parameters.From the overall and zonal tensile-shear crack extension evolution law in the coal-rock combination,it is concluded that the coal body in the combination is dominated by shear damage,and the upper and lower rock bodies are dominated by tensile damage.For combinations with different coal thicknesses,the combinations exhibit tensile damage when the coal percentage is lower than 40%;when the coal percentage is higher than 40%,the combinations exhibit shear damage.The deformation damage of the combination of different intersection dips belongs to the compression-shear composite damage.When the dip angle is greater than 30°,the slip damage of the upper rock body caused by the shear damage of the coal body appears above the coal-rock interface,and the larger the dip angle is,the more obvious the slip failure is.