Electrical Time-frequency Characteristics Research Of Coal-rock Mass

Coal mine mining causes rock rupture,and broken rock permeability is much higher than the rock pore permeability,which is the accident source of coal mine gas,water damage.Therefore,studying the time-frequency characteristics of coal-rock mass in time domain and frequency domain,and analyzing the law of electrical change caused by mining destruction,has important application significance for mine water disaster prevention and control caused by mining failure.This subject is based on the physics of the earth,with the basis of different electric properties of coal and rock,based on time domain and principle of electrical prospecting of frequency domain.Through the development of real-time acquisition system of high-precision coal and rock mass parameters,time-frequency field experiment of coal and rock mass,and experiments of nuclear magnetic resonance,liquid nitrogen adsorption and mercury intrusion,the electrical characteristics of coal and rock mass in time domain and frequency domain is studied,and electrical parameters of coal and rock mass(resistivity,self-potential,complex resistivity,phase,etc.)in the time domain and frequency domain are gained,and it was applied to the field engineering test.The main research results are as follows:(1)According to the requirement of high precision and field engineering experiment in indoor experiment,based on the network parallel system,the development of high precision real-time coal rock mass parameter acquisition system is completed.Under the small-scale and high-precision condition of acquisition,the system realizes the obtaining of the four-dimensional dynamic parameters such as self-potential and resistivity of multi-channel coal and rock in real time.(2)Through the uniaxial loading experiment of coal and rock mass,the law of the self-potential parameters of different lithologic rock samples(bituminous coal,anthracite,sandstone and limestone)changing with the uniaxial loading pressure.With the change of uniaxial loading pressure,the self-potential parameters of different lithologic rock samples(bituminous coal,anthracite,sandstone and limestone)are consistent with the pressure.In the initial stage of loading(hardening stage and line elasticity stage),with the gradual increasing trend of uniaxial pressure,it shows the law of a linear increase or linear decrease.Compared with the change of self-potential in the whole process,the self-potential of the loading rock samples is relatively stable.With the gradual increase of the loading pressure(into the softening stage),loading pressure at the first pressure peak of the uniaxial,the self-potential appears change turning point at the corresponding point in time,appearing as a sudden rise or fall,and when the rock is subjected to the maximum load,the fluctuation amplitude of the self-potential reaches the maximum.With the continue of the loading increase,after the maximum load point,anthracite's loading pressure decreased rapidly,and the self-potential showed a rapid decline or rise,while after a number of relatively low pressure peak were appearing at the maximum load point of the bituminous coal,sandstone and limestone,the self-potential is rapidly declining or rising.At the end of the loading,the macroscopic rupture of the rock sample has completed,and the self-potential of all the samples is stable.The magnitude of the change in the self-potential is 10 mv ~ 100 mv before and after the inflection point.(3)Through the electrical experiment in coal field rock frequency domain,the system has firstly obtained the spectral characteristics and response law of different rock nature(bituminous coal,anthracite,sandstone and limestone)in high and low conductivity(simulated mine water)high pressure saturation;the spectral kinetics of coal and rock mass after saturation of high conductivity solution is stronger than that of low conductivity solution.(4)Combined with nuclear magnetic resonance,liquid nitrogen adsorption and mercury intrusion parameters(transverse relaxation time,specific surface area,porosity,etc.),the correlation between spectral parameters and permeability of coal and rock mass was explored.The permeability of bituminous coal and anthracite obtained from mercury intrusion experiments is weakly correlated with the relaxation time of Debye decomposition inversion,but the former is superior to the latter.At the same time,compared with anthracite,NMR parameters-formation factor model and NMR-spectral excitation-formation factor model is more suitable for the prediction of rock sample permeability.(5)Based on the Archie's basic law,the coal field time domain electrical parameters and the frequency domain electrical parameters were fitted to obtain the Archie formula expression of rock samples of different lithologic coal(bituminous,anthracite,sandstone and limestone).(6)In this paper,the response characteristics of the multi-electrical parameters(DC resistivity,quadrature conductivity,total chargeability,relaxation time,etc.)collected in different time and frequency domains of different lithologic coal bodies are analyzed in detail.The time-domain DC resistivity parameter is negatively correlated with its spectral parameters(quadrature conductivity,total chargeability and median relaxation time parameter).The calculation formula of comprehensive response factors of time-frequency electrical characteristics of coal and rock mass are deduced.(7)Based on dynamic monitoring technology of network parallel electricity,through the development of dynamic monitoring examples of coal mine floor mining damage,the response characteristics and laws of the electrical parameters of the coal and rock mass in the bottom of the mine are obtained,and the indoor experimental conclusion is verified.It is proved that the time-frequency parameters of coal rock have the ability to characterize the mining destruction.