Study On Regularity And Mechanism Of Low-frequency Electromagnetic Signals In Deformation And Fracture Of Coal And Rock Under Load

With the increase of the devastating coal and rock dynamic desaraster such as rock burst, to predict and forecast it accurately has become a problem to be solved. Currently, electromagnetic radiation(EMR) technology has been accepted as an effective method for coal and rock dynamic disasters forecasting, and coal and rock low-frequency(LF) electromagnetic signals with the advantage of long distance transmittion and strong capacity of anti-interference has the potential to become a promissing developing direction of EMR technology.This thesis establishes LF electromagnetic signal(0—5kHz) of coal and rock under laoding experiment system, which innovatively studies the rule of LF electromagnetic signals (300kHz) of coal and rock under different ways of loading including uniaxial compression, shearing, spitting and stretching. The study results are compared with stress, acoustic emission(AE) and conventional electromagnetic signals. The influential factors of LF electromagnetic signal of coal and rock under loading are analyzed. The conclusion shows that coal and rock under different conditions of loading could produce LF electromagnetic signals, which have close relativity with stress and AE. And under different ways of fractuer, the relativity between LF electromagnetic signal of coal and rock and the stress and AE is better than with the LF signal, and the LF signal of concrete is much stronger. In the coal and rock experiment, the component parameter, loading rate and sample size could affect the rules and production of the LF electromagnetic signals. The coal and rock with stronger strength shows better LF electromagnetic signals when its brittleness changes, and the rule of LF electromagnetic signals are better when the materials with worse building feature such as concrete materials. And the faster and greater of the loading rate, the greater the speed changes of the LF electromagnetic signal will be when fracturing.By applying the mathematic methods such as wavelet transform, relativity calculation and Fourier spectrum analysis, the time domain and frequency domain features of the LF electromagnetic signal in the destroying process of coal and rock are extracted and analyzed. By calculating the relation coefficient between the LF electromagnetic signal part and the stress, it is found that these two factors are highly correlated, and the frequency spectrum analyzing result shows that under different stress loading level, the LF electric signals are concentrated below 20Hz.The production mechanism of free charge of coal and rock under deformation and fracture are analyzed from the micro angle, according to the calculation and analyzing of electromagnetic signals produced by the movement of electricity. Combined with the fracture mechanics theory, numerical simulation software, the thesis studies the wrecking extending trend when the coal and rock body under shearing, spitting and stretching conditions, and it is testified and concluded that the LF EMR signals reach its maximum value while shearing destroying face are parallel with it when shearing and vertical when spitting and stretching. Thus, the statistics destroying calculation model of LF EMR signals of coal and rock is established.The spot test studies the time and space variation regulations of the LF EMR signals of coal and rock. The result shows that the distribution between the space and the front coal body's stress in work face are basically identical, and the signal is well correlated with the period pressure in time distribution.The test of the dynamic phenomenons such as shows that LF EMR signals'regularity reflect well with the coal and rock dynamic disaster.By studying the EMR direction orientation and positioning technology, the result shows that EMR are mainly concentrated on the deep coal body and workface directionThis thesis studies LF signals when loading coal and rock are wrecking and expands the research scope of the coal and rock EMR technology. The study has profound and important application value on realizing wide scope, long distance predition ,improve the testing anti-interference capacity and eventually achieving the position and quantity prediction on the coal and rock dynamic disasters with the EMR technology.