Study Of Acoustic Emission And Fractal Characteristics Of Coal Samples In The Process Of Rupture

The coal mining depth and mining strength increasing, and the coal mining environment progressive deterioration with gradually reduced of the resources shallow, especially in eastern China. The mine began to appear the phenomenon of increasing the amount of gas emission and gas pressure, soft coal, reducing permeability and homogeneity deterioration, and the possibility of significantly increased of occurrence bottom muster, bumps, cave-power disaster events with increasing the depth of many mines.Inversion of the internal state change in the process of coal and rock instability by using acoustic emission, and detcet the information of the crack formation or extended time during the coal and rock instability by using acoustic emission. The damage degree and failure mechanism can be inversioned, and the the internal structure change of coal and rock can be inferred by analysising and researching of the acoustic emission signal in the failure process of coal and rock. Therefore, the damage dynamic process and crack evolution law during the instability failure of coal and rock can be understanded by studying of the acoustic emission during the instability destruction process. Macroeconomic instability and failure of coal and rock will generally lag behind the precursor of acoustic emission,the mine dynamic disaster of bumps, water bursting, roof collapse and coal and gas outburst can be forecasted by analysising the precursor law.In order to better applied the acoustic emission techniques to engineering practice, focusing on coal samples of Sanjiaohe mine, Tunliu mine and Longshan mine, an experimental study is carried out to investigate the acoustic emission characteristics of different kinds of coal, different loading rates, natural and water coal samples, by using RMT-150 C rock mechanics test system and AE-win E1.86 acoustic emission instrument. In addition, a numerical simulation experimental study is carried out to investigate the acoustic emission characteristics of varying degrees of metamorphism and different loading rates coal samples by using RFPA2 D numerical simulation. Finally, analysis the three laboratory test results by using fractal theory. The mainly test results:(1)The experimental results: Water has a certain influence on the mechanical properties of coal samples, physical characteristics and acoustic emission characteristics. The uniaxial compressive strength decreases 25.71%, the acoustic emission count decreases 39.49%, the peak count rate decreases 46.08%, the peak energy reduced 18.30%. The relationship between uniaxial compressive strength and the loading rate was positively correlated, and the relationship between peak count, peak energy, peak count rate, peak energy rate and the loading rate was positively correlated. The relationship between the acoustic emission peak count, peak count rate and ultrasonic velocity, elastic modulus and density was negatively correlated of coal samples with different pecies in the rupture process.(2)The experimental results: It has a certain regularity of the acoustic emission characteristics in the rupture of the coal samples with different degree heterogrneity. The coal samples, failure mode from the plastic collapse began gradually to brittle fracture with increasing of the degree heterogeneity. It has a certain regularity of the acoustic emission characteristics of coal samples in the rupture process under different loading rate, the relationship between the acoustic emission peak count, peak energy and the loading rate was positively correlated, the relationship between the acoustic emission cumulative counts, cumulative energy and the loading rate was negatively correlated.(3)The fractal analysis test: The three conditions coal samples have fractal character- istics in the rupture process, the trends has a strong consistency of the fractal dimension with time and stress, acoustic emission counts with time of the three conditions coal samples in the rupture process. At the first, the fractal dimension fluctuations rise to a maximum and then decrease, and there will be appear a dump again rising phenonmenon near the peak of the fractal dimension.