Research On Propagation Law In Coal And Rock Strata Of Infrasonic Wave Of Fracture Of Coal And Rock

In recent years,with the development of coal resources into deep mining,coupled with the complex geological conditions of coal seam in China,the geostress and gas pressure of coal seams increase,the phenomenon of coal-rock dynamic disasters,which are dominated by coal and gas outbursts,appears frequently.The research results show that the infrasound signal can be generated during the fracturing process of coal and rock.The infrasonic wave technology may become one of the most promising monitoring and early warning methods for coal and rock dynamic disasters in coal mines.The propagation medium of infrasonic waves in coal mines is mainly coal and rock strata.The complexity of coal and rock causes the attenuation of infrasonic waves in the propagation process,reducing the accuracy of infrasonic monitoring applications,and the effective distance of infrasound propagation is still to be verified.Therefore,it is very necessary to carry out the study on the propagation of infrasonic wave in coal and rock fracture.In this dissertation,the research on the propagation of infrasonic waves of coal and rock rupture is carried out by the combination of laboratory experiments and numerical simulation.Through the uniaxial compression test on coal samples,the infrasonic signal monitoring system was used to collect the signals generated during the deformation and rupture of coal samples in real time.The energy distribution characteristics of signal were analyzed by wavelet packet transform signal analysis method.The frequency distribution of infrasonic signal of coal sample was analyzed to determine the dominant frequency of the wave source.With the low frequency rock test system based on stress-strain method,the infrasound velocity and attenuation parameters of coal samples under different frequencies are measured to determine the theoretical model parameters of the actual coal rock formation.Considering the viscoelasticity of coal,the wave equation of viscoelastic medium was derived.The MATLAB program was programmed by staggered grid finite difference method.The propagation of coal-rock rupture infrasound in the real coal bed was numerically simulated and the attenuation law was analyzed.The main research results are as follows:(1)The coal sample rupture process can produce obvious infrasonic signals,and has a good correspondence with the stress in time.Wavelet packet transform can finely divide the signal into various frequency bands,which can play the role of filtering.The frequency of the infrasound of the coal sample is distributed at 0~20Hz,but it mainly concentrates at 3.125Hz~12.5Hz and 18.75Hz~21.875 Hz.(2)The variation trend of longitudinal wave velocity,shear wave velocity and attenuation 1/Q of coal samples are no frequency dependence.Among them,Young's modulus is about 9.7 GPa;Poisson's ratio is about 0.28;longitudinal wave velocity is about 2882 m/s;shear wave velocity is about 1576 m/s;attenuation 1/Q is about 0.05.(4)The PML boundary can well absorb the energy reaching the boundary wave and avoid the reflection caused by human boundary.Elastic wave equation has only spherical attenuation,viscoelastic attenuation compared with the viscoelastic wave equation,more in line with the actual coal and rock mass.(5)The attenuation of infrasound in the coal seam is mainly divided into spherical wave attenuation and viscoelastic attenuation,and the relationship with the propagation distance is a power function.In addition to the attenuation of the spherical acoustic wave and the viscoelastic attenuation,the attenuation of the infrasound in the coal seam also includes the interfacial attenuation of the coal seam and stratification.Infrasound technology can be used for long distance monitoring of underground and uphole coal mines.