Experimental study on the variation of P-wave velocity and waveform characteristics during the whole process of water absorption of coal samples
LI Nan1，2，ZHANG Xin1，2，WANG Daxuan2，ZHAO Xingzhi2，LI Song3
(1. State Key Laboratory of Coal Resources and Safe Mining，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Mines，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；3. School of Safety Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China)
Abstract：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.
李 楠1，2，张 新1，2，王达轩2，赵星智2，李 松3. 煤样吸水全过程纵波波速变化规律及波形特征实验研究[J]. 岩石力学与工程学报, 2017, 36(8): 1921-1929.
LI Nan1，2，ZHANG Xin1，2，WANG Daxuan2，ZHAO Xingzhi2，LI Song3. Experimental study on the variation of P-wave velocity and waveform characteristics during the whole process of water absorption of coal samples. , 2017, 36(8): 1921-1929.
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2017, Vol. 36 
