煤样吸水全过程纵波波速变化规律及波形特征实验研究

 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。

Experimental study on the variation of P-wave velocity and waveform characteristics during the whole process of water absorption of coal samples

The measurement of P-wave velocity and the waveform analysis of coal samples during the whole process of water absorption were performed to study the variation of P-wave velocity and the characteristics of waveforms. The variation of P-wave velocity with the water saturation and porosity were studied. The amplitude-frequency and time-frequency characteristics of the waveforms under the different water saturations were researched based on the FFT and HHT methods. The results show that the P-wave velocity is influenced by the water saturation and porosity at the same time. The P-wave velocity increases nonlinearly as the water saturation increases. The increasing rate of the P-wave velocity increases significantly when the water saturation reaches about 70%. The properties of water and the uniform existence of pore water in the porous structure of coal are the main causes of the increase of the P-wave velocity. The P-wave velocity decreases linearly with the increasing of the porosity of coal. The higher the water saturation，the less affected the P-wave velocity by porosities. It indicates that the water in the coal samples weakens the influence of coal porosity on the P-wave velocity. The waveform frequency distributions differ dramatically during the whole process of water absorption of coal samples. The main frequency moves towards the low frequency nonlinearly with the increase of water saturation. The higher the water saturation and the porosities of coal，the smaller the maximum amplitudes of waveforms are. The energy distribution of wave frequency bands and the temporal changing characteristics of the waveform signals can be revealed by the three-dimensional Hilbert spectrums of energy. With the increase of the water saturation，the proportion of the high frequency component reduces gradually，and the frequency bands with the high energy move to the low frequency. It means that the pore water in the porous coal structure not only speeds up the energy attenuation of all frequency bands，but also makes the attenuation of high frequency components greater than the low-frequency components.