The mechanical vibrations caused by underground operations can easily lead to coal and gas outbursts in coal mines. Using the MVGAD-I experimental platform that we designed, the raw coal (0 Hz) was treated with vibration frequencies of 25, 50, 75, and 100 Hz, and the coal samples with different frequency vibrations were obtained. The total pore volume (TPV), specific surface area (SSA), pore size distribution, and the pore fractal dimension (PFD) of five coal samples were analyzed by mercury intrusion porosimetry and low-pressure nitrogen adsorption data. We found that the TPV, SSA, and PFD of the coal samples fluctuate with the increase of vibration frequency. The changes of the TPV and SSA of coal samples treated with 25 and 75 Hz vibrations were significantly greater than those subjected to vibrations of 50 and 100 Hz. Compared with the raw coal (0 Hz), the TPV and SSA of macropores, mesopores, and micropores increased the most in 75 Hz vibration coal sample. Therefore, the 75 Hz vibration excitation can improve the permeability of a body of coal mass and is conducive to the diffusion and seepage of coalbed methane and its production.. The influence of 25 Hz vibration on the TPV and SSA of macropores and mesopores is not obvious, but the TPV and SSA of minipores and micropores decrease significantly, which is not conducive to gas diffusion and adsorption. In addition, 25 and 75 Hz vibrations obviously damaged the fractal characteristics of both mesopores and micropores, resulting in the change of gas adsorption and diffusion ability. The rational use of a 75 Hz vibration is beneficial to both the production of gas and the prevention of outbursts, while a 25 Hz vibration should be avoided. The results are expected to reveal the microscopic mechanism of a vibration-induced outburst and provide theoretical guidance for employing the appropriate frequency of vibration to improve the rate of gas drainage and reduce the risk of outbursts.

中文翻译：

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不同频率机械振动对贫煤孔隙结构和分形特征的影响

井下作业引起的机械振动很容易导致煤矿瓦斯突出。利用我们设计的MVGAD-I实验平台，对原煤（0Hz）进行25、50、75、100Hz振动频率处理，得到不同频率振动的煤样。通过压汞孔隙率法和低压氮气吸附数据分析了五个煤样的总孔容（TPV）、比表面积（SSA）、孔径分布和孔隙分形维数（PFD）。我们发现煤样的 TPV、SSA 和 PFD 随振动频率的增加而波动。25 和 75 Hz 振动处理的煤样的 TPV 和 SSA 变化显着大于 50 和 100 Hz 振动处理的煤样。与原煤（0 Hz）相比，75 Hz振动煤样中大孔、中孔和微孔的TPV和SSA增加最多。因此，75Hz振动激发可以提高煤体的渗透率，有利于煤层气的扩散渗流及其产生。25Hz振动对大孔和中孔的TPV和SSA的影响不大。明显，但微孔和微孔的 TPV 和 SSA 显着降低，不利于气体扩散和吸附。此外，25Hz和75Hz的振动明显破坏了介孔和微孔的分形特征，导致气体吸附扩散能力发生变化。合理使用75赫兹的振动，有利于产气和防止爆裂，而应避免 25 Hz 的振动。研究结果有望揭示振动诱发突出的微观机制，为采用适当的振动频率提高瓦斯抽采率、降低突出风险提供理论指导。