| At present,China's coal mining is still in the form of underground mining,and the mining depth continues to increase.The geological structure,high geostress,high gas and low permeability of deep mining areas and other factors make coal and rock dynamic disasters become one of the main mine disasters.Because coal and rock dynamic disasters are sudden,harmful and complex,the reliable monitoring and early warning technology has become an important means of effective prevention and control.Although these traditional and modern monitoring and early warning technologies,including acoustic emission,direct current resistivity and electromagnetic radiation,have been widely used in coal and rock dynamic disasters mines,they have their own advantages and disadvantages.The regional and local integration,combination of multiple information,less interference from environment and human factors,high automation integration and continuous comprehensive monitoring technology will be possible to become the development direction of monitoring and early warning.Due to the heterogeneous structure of coal and rock,the mechanism of acoustic,electrical and optical phenomena during the fracture process of loaded coal and rock has not been comprehensively explained by the researchers at home and abroad.But in terms of whether the microcosmic or macroscopic mechanism,the fracture process of coal and rock is inseparable from the crack propagation.The research contents of this dissertation mainly include five parts:the basic research on heterogeneous structure of coal,the research on experiment parameter characteristics of acoustic-electro physical effects and surface crack propagation of loaded coal,the research on regularity,mechanisms and models of acoustic-electro physical effects and surface crack propagation,and the field application of acoustic-electro physical effects.Firstly,the heterogeneous structure characteristics of coal were studied,and the heterogeneous characteristics of composition and structure were obtained.Through the establishment of a high-speed acquisition experimental system for acoustic-electrical-crack observation of loaded coal,the simultaneous monitoring of acoustic emission signal,electromagnetic radiation signal,electrical parameters and surface crack propagation was carried out during the uniaxial compression failure and short-term creep process,and the distribution characteristics and regularity of relevant parameters were obtained and analyzed.In order to further study the surface crack propagation velocity,the distribution characteristics of longitudinal and shear wave velocities with loaded stress were analyzed by measuring the acoustic wave velocities of coal samples during the process of uniaxial compression failure,and the regularity of stress and longitudinal wave velocities was obtained.The processing method and program of crack image based on CPTM(a coal particle tracking method)and crack calculation and recognition based on Matlab were proposed and developed.The surface crack propagation images of coal under uniaxial compression were analyzed and calculated,and the change characteristics and regularity of surface crack propagation speed and quantity based on pixels were studied.Based on the experimental study and the feasibility of caustics experiment for the determination of dynamic stress intensity factor,the surface crack propagation velocity and electromagnetic radiation model of mode I dynamic stress intensity factor under uniaxial compression were constructed theoretically.Based on the experimental datas,the influence factors of dynamic stress intensity were calculated by the surface crack propagation velocity model.It was found that the tre1d of Kld was similar to that of crack propagation velocity,which verified the validity of model calculation.In the field application,on the basis of electromagnetic radiation monitoring system and microseismic monitoring system,the field working face was monitored,the double differential velocity field image testing model of working face and geological anomaly area was adopted,and the evolution regularity of velocity field in working face and geological anomaly area during the coal mining process were analyzed.By comparing the electromagnetic magnetic radiation monitoring datas with the pressure sensor monitoring datas,the variation regularity was studied between the electromagnetic radiation intensity signal and hydraulic support resistance in the working face during the period of periodic roof weighting,and the variation rules of electromagnetic radiation intensity signal near the coal side of inlet and return air roadway were also studied.The research work in this dissertation are of great significance to provide a certain experimental and technical basis for the comprehensive monitoring of coal and rock dynamic disasters in China.The main contents and innovative achievements of this dissertation are as follows:(1)The heterogeneous structure of coal was studied from the aspects of industrial analysis,macerals,rock and clay mineral components,pore mechanism of coal,and the characteristics were obtained.(2)The distribution characteristics and rules of acoustic emission signal,electromagnetic radiation signal,electrical parameters and surface crack propagation were obtained at each stage of uniaxial compression failure and short-term creep.For the brittle-ductile failure of loaded coal during the uniaxial compression process,the Boltzmann function relation between cumulative ringing counts and time was established,while the exponential function relation was established for the ductile failure,and the Weibull parameters were obtained by the well-fitted datas.For the acoustic characteristics of coal under uniaxial compression,the power function relationship between loading stress and longitudinal wave velocity was established,and the experimental parameters were obtained.Based on the matlab program of wavelet and FFt transform,the distribution regularity of electromagnetic radiation spectrum during the short-term creep process was obtained and analyzed.The frequency range was 0-200 KHz during the initial and intermediate stages of creep deformation under step loading,and 0-400 KHz during the later stage of accelerated creep phase under step loading.The amplitude of frequency showed a trend of first increasing,decreasing and then increasing before the main rupture occured.(3)Based on the CPTM crack image processing method and Matlab crack calculation and identification program,the crack propagation images of coal under uniaxial compression were analyzed and calculated.It was found that the crack propagation of coal under uniaxial compression was mainly caused by the tensile crack failure with partial shear crack failure.The crack propagation length was compared with the measured values based on pixels,the crack propagation speed was compared with the related research,and the validity was verified.Based on the experimental study and the mechanism summary analysis of crack propagation and electromagnetic radiation,combined with the feasibility of caustics experiment for the determination of dynamic stress intensity factor,the crack propagation velocity and electromagnetic radiation model of mode I dynamic stress intensity factor under uniaxial compression were theoretically constructed.Based on the experimental datas,the influence factors of dynamic stress intensity were calculated by the surface crack propagation velocity model.It was found that the trend of Kld was similar to that of crack propagation velocity,which verified the validity of the model calculation.(4)Through the field test of EME-HF mine intrinsically safe electromagnetic radiation monitoring system and ESG microseismic monitoring system,156 days of effective monitoring was carried out on the N1202 isolated working face of Yuwu coal mine.The distribution regularity of microseismic events,energy and space-time evolution of microseismic events in N1202 working face was obtained.By the imaging model of double differential velocity field,the velocity field distribution regularity during the coal mining process and geological anomaly area were analyzed.By comparing the electromagnetic magnetic radiation monitoring datas with the pressure sensor monitoring datas,the variation regularity was studied between the electromagnetic radiation signal intensity and hydraulic support resistance in the working face during the period of periodic roof weighting,and the variation rules of electromagnetic radiation signal intensity near the coal side of inlet and return air roadway were also studied.Through the discriminant analysis,the electromagnetic radiation monitoring signal can realize the early warning of roof weighting. |
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