| Along with for a long time dependence on coal in china,coal production increased year by year, more and more coal mines entered a period of great mining depth. With the increase of the mine deep, coal and rock dynamic disasters occur frequently, it has caused great threat to the coal mine production. The prediction work of coal and rock dynamic disasters is important. In recent years, the use of physical signal(such as acoustic emission,seismic and electromagnetic radiation signals) to predict dynamic disasters became the new trend. These geophysical indexes compared with other existing methods, they have much advantages: a continuous monitoring, non-contact and small impact on the job. However the current index of the geophysical prediction method were put forward on the basis of researches in signal characteristics in the process of coal and rock compression strength(uniaxial and multiaxial compression, dynamic impact) burst. They lack of mechanism and characteristics researches of magnetic and seismic in the process of coal and rock tensile stress rupture. And the tensile stress has a significant influence on the occurrence of coal and rock dynamic disasters.Based on the mechanism analysis of electromagnetic and microseismic in the process of material fracture, the association response mechanisms and change characteristics of electromagnetic and microseismic signals in the static tensile rupture blasting process of coal or rock are studied by experimental research. We validate the conclusion with field test results in the dissertation. According to material damage and fracture mechanics theory, static tensile crack propagation characteristics of coal or rock are analyzed. According to the correlation theory of electromagnetic and seismic, the association response mechanisms and change characteristics of electromagnetic and microseismic signals in the static tensile rupture blasting process of coal or rock are studied. And further analysis of correlation between electromagnetic, seismic and strain characteristics. The change rule of intermolecular hydrogen bond in the process of coal or rock damage was studied with the theory of spectroscopy. The research conclusion made up for the research blank of electromagnetic and microseismic signals in the static tensile rupture blasting process of coal or rock.It is significant to improve electromagnetic and microseismic index method to predict signals coal and rock dynamic. The main research contents and results are as follows:(1) Static tensile mechanism of coal or rock, and mechanism of soundless broken agentOn the basis of previous studies, the expansion mechanism of soundless broken agent are analyzed. Static tensile mechanism of coal or rock was studied with material damage and fracture mechanics theory. And the static tensile fracture process of coal or rock was divided into three parts: micro crack stage, expansion stress transfer stage and cleavage stage. Soundless broken agent expansion stress change curve over time were tested when hole diameter are 20 mm and 40 mm by designing expansion stress testing experiment. They Provide strong guidance for experiment design and numerical simulation. Static tensile mechanism of coal or rock was numerically simulated by Abaqus finite element analysis software. According to the results of the simulation experiment, we decorated two strain gauges on the specimen to determine tensile stage of static explosion.(2) Characteristics of electromagnetic signals in static cracking process of coalWe set up the monitoring experiment system to test low-frequency electromagnetic signal in static cracking process of coal and cement mortar specimens with ZDKT-1 coal and rock dynamic disasters experimental simulation system. By using ofSTA/LTA algorithm, effective electromagnetic signals were automatically identified and extracted. Through the Ensemble Empirical Mode Decomposition(EEMD) and wavelet threshold denoising method, the low frequency electromagnetic were denoising. Then we analyse change rule of electromagnetic signal amplitude, frequency spectrum and energy. FT-IR has been applied to the characterization study of the hydrogen bonds of Dongpang coals, which were under drop weight impact. The results show that:? The static tensile fracture process of coal or rock was divided into three parts: micro crack stage, expansion stress transfer stage and cleavage stage. Only M40 coal set had significant electromagnetic signals in micro crack stage. There are more electromagnetic signals generated by the static blasting coal material than cement mortar. While the same material, there are more electromagnetic signals in large static explosion rate. In the same group experiments, the electromagnetic signals in cleavage stage had high amplitudes and energies than the first two stages, and the frequencies increased too.?The static cracking process of coal is a combination of longitudinal and transverse crack, the numbers of macroscopic crack were differences. Cement mortar only had longitudinal cracks. Electromagnetic signal numbers were related to the macro crack area. The large macro crack area had more electromagnetic signals.?The Ensemble Empirical Mode Decomposition(EEMD) and wavelet threshold denoising method had a very good effect to remove the electromagnetic background noise in the process of experiment.?The electromagnetic signals generally appeared in the period of strain change sharply and the microseismic mass.?Electromagnetic mechanism in static cracking process of coal may be: the emission of electrons and charged particles from fracture surfaces, micro-fracture electrification, hydrogen bonds rupture.?Absorption intensities of intermolecular hydrogen bonds markedly declined after impact. Free OH groups mechanical-power chemical reacted in drop weight impact testing. The infrared spectrum were curve-resolved into their component bands. The absorption intensities of various hydrogen bonds decreased with the increasing of impact energy, but the trend was slowing. By statistical relationship between two, we find the twice complying with power function relationship. By comparing the exponents of fitted equations, we concluded that failure sensitivity sequence of hydrogen bonds to the impact: OH…N > free OH groups > cyclic OH tetramers > OH…p > OH…OH.(3)Characteristics of microseismic signals in static cracking process of coalWe set up the monitoring experiment system to test microseismic signals in static cracking process of coal and cement mortar specimens with ZDKT-1 coal and rock dynamic disasters experimental simulation system. By using of STA/LTA algorithm, effective microseismic signals were automatically identified and extracted. Through the Ensemble Empirical Mode Decomposition(EEMD) and wavelet threshold denoising method, the microseismic signals were denoising. Then we analyse change rule of microseismic signals amplitude, frequency spectrum and energy, and briefly analysis the influence factors of microseismic signals in this process. The results show that:?Microseismic signal numbers were related to the macro crack area. The large macro crack area had more microseismic signals.? While the same material, there are more electromagnetic signals in large static explosion rate. The average amplitude of microseismic signals accompany this period was greater.?The total energies of microseismic signals were related to the macro crack area. The larger of macro crack area, the higher of total energy.?The amplitudes and energies of micro-seismic signals in the static cracking process did not change monotonically but changed between weak and strong. The microseisms signals were paroxysmal.?The characteristics of microseismic signals in static cracking process of coal is not only related to static explosion rate, but also associated with the composition and structure of materials.(4) The association response characteristics of electromagnetic and microseismic signals in static cracking process of coalWe analyse the relation of electromagnetic and microseismic signals in staticcracking process of coal, and researched the association characteristics of amplitude and energies of the two types of signals. The results show that: ? The emergence of microseismic signals were related to the strain of the specimens, the change trend of both is consistent with the overall. Electromagneticand microseismic signals were paroxysmal. The electromagnetic signals generally appeared in the period of microseismic mass. ?Electromagnetic and microseismic signals showed good synchronicity in time.? The amplitudes of electromagnetic and microseismic signals at the same time point conform to the linear relationship.The fitting parameters of each groups are difference(from 0.778 to 0.877).? The energies of electromagnetic and microseismic signals at the same time point conform to the linear relationship.The fitting parameters of each groups are difference(all were greater than 0.88).(5) The association response characteristics of electromagnetic and microseismic signalsin the dissertationBased on similarity effect mechanism between blasting excavationin the disse rtation and static cracking process of coal in the laboratory. We monitored electr omagnetic and microseismic signals of blasting excavationin the dissertation with coal and rock dynamic disasters experimental simulation system. We analyse the characteristics of electromagnetic and microseismic signalsin the dissertation, and explore association response characteristics of them in amplitude and energy.The results show that: ?The background noise of electromagnetic and microseismic signalsin the dissertation are not strictly in accordance with 50 Hz frequency or it s doubling.? Electromagnetic and microseismic signals in the dissertation showe d good synchronicity in time.?The energies of electromagnetic and microseismic signals in the dissertation conform to the linear relationship. The fitting paramete rs were greater than 0.966. |
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