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为了研究含水煤体的纵波波速变化规律及波形特征,开展原煤试样吸水全过程的纵波测试实验;研究煤体纵波波速与孔隙率、含水饱和度之间的变化规律;基于FFT和HHT研究不同含水饱和度煤样波形幅频和时频特征。结果表明:煤体纵波波速同时受孔隙率和含水饱和度的影响;波速随含水饱和度的增加总体呈现非线性增加趋势,当含水饱和度达到70%左右时,波速增加速率明显提高;水自身性质及煤体内部孔隙水均匀存在形式是导致含水煤波速增加的主要原因。纵波波速随孔隙率的增加总体呈现线性降低趋势,含水饱和度越高波速受孔隙率影响越小,表明水的存在降低了煤体孔隙率对波速的影响。煤样在吸水过程中的波形频率分布存在显著性差异,波形主频随含水饱和度的增加呈现向低频非线性移动的“频移”现象;含水饱和度越大、孔隙率越大,波形最大幅值越小。Hilbert三维能量谱能够反应波形的频带能量分布及随时间的变化特征;随着煤样含水饱和度的增加,波形高频成分所占比例逐渐降低,且高能量频带范围不断向低频移动,表明煤体中孔隙水不但加快了波形中所有频带能量的衰减速度,而且对高频信号的吸收损耗大于低频信号。
In order to study the variation law of longitudinal wave velocity and waveform characteristics of water-bearing coal, a longitudinal wave experiment was carried out in the whole process of water absorption of coal sample. The variation law of longitudinal wave velocity, porosity and water saturation of coal was studied. Amplitude and frequency characteristics of water sample with water saturation. The results show that the longitudinal wave velocity of coal is affected by the porosity and water saturation at the same time. The wave velocity increases nonlinearly with the increase of water saturation. When the water saturation reaches about 70%, the wave velocity increases obviously. The nature and the uniform existence of pore water inside the coal are the main reasons leading to the increase of the velocity of water containing coal. The longitudinal wave velocity decreases linearly with the increase of porosity. The higher the water saturation is, the smaller the wave velocity is and the smaller the porosity is, indicating that the presence of water reduces the influence of porosity on the velocity. There was a significant difference in the frequency distribution of the waveform of the coal sample during the water absorption process. The dominant frequency of the waveform presented a “frequency shift ” phenomenon with the increase of water saturation, and the larger the water saturation, the larger the porosity. The maximum amplitude of the waveform is smaller. Hilbert three-dimensional energy spectrum can reflect the frequency band energy distribution of the waveform and changes with time; with the increase of water sample saturation, the proportion of high-frequency components of the waveform gradually decreases and the high-energy frequency band continuously moves to the low frequency, Body pore water not only speeds up the attenuation of the energy in all the frequency bands in the waveform, but also absorbs the high-frequency signal more than the low-frequency signal.