围压对红砂岩应力波频谱和频带能量特性的影响

Effect of confining pressure on spectrum and frequency band energy of stress wave in red sandstone

为研究围压对岩石应力波传播衰减特性影响,对具有不同围压的红砂岩试件进行应力波传播试验.通过傅立叶变换得到反射波和透射波频谱数据,分析频谱图形状和主频值随围压的变化规律.对反射波和透射波进行小波包分析,研究不同围压工况下反射波和透射波频带能量分布的变化规律.结果表明,随围压的增加,反射波频谱图的幅值呈"减小—缓慢发展—增加"的趋势,透射波频谱图的幅值逐渐增大后有略微减小,且宽度也越来越窄.透射波主频值随围压的增加呈现"增大—稳定不变—减小"的趋势,围压的两个临界值分别为单轴抗压强度的25%和70%,反射波主频值变化与此相反.随围压的增加,反射波主频带和透射波优势频带所占总能量百分比先增加后减小,围压对低频带能量百分比的影响更大.

To study the effect of confining pressure on stress wave spectrum and frequency band energy of rock, we conducted experiments of stress wave propagation in red sandstone under different confining pressure based on modified Hopkinson pressure bar testing system. The main frequencies and spectrum shapes of reflected and transmitted wave under different confining pressure were analyzed on the basis of fast fourier transform of time domain stress wave. The change laws of frequency band energy of reflected and transmitted wave under different confining pressure were investigated by means of wavelet packet analysis. The results show that, with the increase of confining pressure, the amplitudes of reflected wave spectrum decrease firstly,then change gently, and increase finally. The amplitudes of transmitted wave spectrum increase continuously,and decrease slightly finally, and their widths are getting smaller and smaller with the increase of confining pressure. The main frequency of transmitted wave has the trend of increase-constant-decrease with the increase of confining pressure, and two critical values of confining pressure are equal to 25 % and 70 % of uniaxial compressive strength of red sandstone, and the main frequency of refle cted wave has the opposite trend. With the increase of confining pressure, the energy percentages of main frequency band of reflectedwave and preponderant frequency band of transmitted wave increase firstly, and then decrease. Confining pressure has a bigger impact on low frequency band than high frequency band.