子波传过软弱夹层的波形变化规律

Waveform change rule of wavelet propagation across soft interlayer

将软弱夹层抽象为损伤度按照二次曲线规律变化的介质,建立应力波在软弱夹层的传播模型,采用Legendre方程的级数解法计算透射系数,研究子波传过软弱夹层的波形变化规律.结果表明:透射系数实部和虚部对损伤度变化表现出不同的变化规律,损伤度较小时,透射系数实部随损伤度增加几乎不变,当损伤度达到临界值Dcri-r时透射系数快速减小后渐趋于0,透射系数虚部也对应一个损伤度临界值Dcri-i,随损伤度增加,透射系数虚部呈现先增加后减小的变化趋势,随频率和软弱夹层厚度增加,临界值Dcri-i和Dcri-r都减小;波形综合反映了振幅和相位的变化,不同频率的子波传过软弱夹层时,波形变化系数随着主频的增加而增加;随损伤度增加,波形变化系数整体呈现S型增加,对软弱夹层的峰值损伤度变化存在一个敏感区间,随子波峰值频率和软弱夹层厚度增加,敏感区间的宽度增加.现场试验子波波形变化规律与理论Ricker子波波形变化规律一致.

The soft interlayer is assumed as damaged media according to the quadratic curve change rule of damage degree.The propagation model of stress wave across weak interlayer is established.The transmission coefficient is calculated using series solution of Legendre equation.Waveform change rule of wavelet propagation across soft interlayer is studied.The study results indicate that the effects of damage degree to real and imaginary of transmission coefficient are different.Damage degree has no remarkable influence on real of transmission coefficient when damage degree is less.The real of transmission coefficient changes quickly firstly then trends to be zero when damage degree is equal to the critical value Dcri-r.Likewise,there exists the critical value of damage degree Dcri-i.The imaginary of transmission coefficient increases firstly then decreases with the increase of damage degree.The critical values of damage degree Dcri-i and Dcri-r decrease with the increase of frequency and thickness of soft interlayer.Waveform can reflect synthetically the change of amplitude and phase of wavelet.When different frequencies of wavelet across soft interlayer,the coefficient of waveform increases with the increasing of dominant frequency.The coefficient of waveform change increases like＂S＂shape when damage degree increases.The change of peak damage degree of soft interlayer haves a sensitive zone.The breadth of sensitive zone increases with the increase of peak frequency of wavelet and thickness of weak interlayer.The wavefrom change rule of Ricker wavelet is consistent with wavelet which is tested on the scene.