子波在节理岩体中的传播规律及其应用

发布时间：2018-10-13 10:09

【摘要】：准确获取岩体变形参数对于分析岩体工程的变形和稳定性具有重要意义。子波在岩体中传播时振幅谱和相位谱发生变化，综合体现为波形变化，因而子波波形变化比波速、振幅和频率等参数能更全面灵敏反映岩体力学参数。本文采用理论分析、现场试验和数值计算等多种研究手段，研究子波在黏弹性岩层、黏弹性节理、层状岩体和节理岩体的传播规律，提出了节理刚度的波动测试方法，并讨论了该方法的测试误差和适用条件，研究的主要结论如下。（1）Kelvin介质的选择性吸收引起子波的频谱特性发生变化，随传播距离增加，子波的特征频率和带宽减小，特征频率呈负指数规律减小，并趋于稳定值，，进而引起子波振幅减小和振动持时增加；随着弹性模量减小或者介质的黏滞性增加，形成子波波形相对稳定的距离减小。（2）节理质量对P波在节理的透射系数和反射系数有重要影响，不考虑节理质量时，采用位移不连续模型计算得到的P波反射系数、SV波透射系数和反射系数都偏大，而P波透射系数明显偏小，随节理厚度增加，偏差增加；黏弹性节理的选择性吸收引起透射波振幅减小，主瓣不突出，分辨率减小，波形相关系数和波形变化系数能够有效反映子波传过节理的波形变化，相对切向刚度和切向黏性系数，节理的法向刚度和法向黏性系数对子波波形变化影响更大。（3）弹性层状岩体具有多尺度梳状滤波器的特性，随岩层厚度与波长之比增加，由层内多重透、反射引起振幅透射系数和反射系数成大尺度周期性变化，大尺度周期为=0.5，在一个大尺度周期内存在一个带通和一个带阻，在带通内又存在多个小尺度周期，是由层间多重透、反射形成的，黏弹性层状岩体总体表现为低通滤波，在低通滤波范围内存在多个带通和带阻。（4）不同频率范围内的应力波在岩体的传播过程中，衰减系数对频率的依赖性具有显著差异，完整岩体总体上表现为低通滤波，在低通滤波范围内具有非等间距带通滤波特性，在吸收频率过渡带，应力波衰减系数随频率变化非常快，黏性系数非定常Maxwell模型能够有效描述应力波在完整岩体中的衰减系数变化规律；岩体越破碎，滤波能力越强，低通范围越小，吸收频率过渡带陡度参数越小。（5）根据子波传过节理的波形变化规律提出节理刚度测试方法，该方法具有很好的重复性，当节理厚度小于0.1m，测试误差小于15.0%，研究结果表明，随测点与节理间的距离增加，测试误差先减小后增加，存在一个合理测点布置位置，通过数值计算和现场试验确定测点与节理间的合理距离为10~20cm。
[Abstract]:It is very important to obtain the deformation parameters of rock mass accurately for analyzing the deformation and stability of rock mass engineering. When wavelet propagates in rock mass, the amplitude spectrum and phase spectrum change, which is reflected by waveform change. Therefore, wavelet waveform can reflect more fully and sensitively the mechanical parameters of rock mass than the parameters of wave velocity, amplitude and frequency. In this paper, the propagation law of wavelet in viscoelastic strata, viscoelastic joints, layered rock mass and jointed rock mass is studied by means of theoretical analysis, field test and numerical calculation. The main conclusions are as follows: (1) selective absorption of Kelvin medium causes the variation of wavelet spectrum characteristics, and the characteristic frequency and bandwidth decrease with the increase of propagation distance. The characteristic frequency decreases exponentially and tends to be stable, which leads to the decrease of wavelet amplitude and the increase of vibration duration, with the decrease of elastic modulus or the increase of the viscosity of the medium. (2) the mass of joint has an important effect on the transmission coefficient and reflection coefficient of P wave in joint, and when the mass of joint is not considered, The reflection coefficient of P wave calculated by discontinuous displacement model, the transmission coefficient and reflection coefficient of SV wave are larger, but the transmission coefficient of P wave is obviously smaller, and the deviation increases with the increase of joint thickness. The selective absorption of viscoelastic joints causes the amplitude of transmission wave to decrease, the main lobe is not prominent, and the resolution decreases. The correlation coefficient and variation coefficient of waveform can effectively reflect the waveform changes of wavelet transmitted joints. Relative to tangential stiffness and tangential viscosity coefficient, normal stiffness and normal viscosity coefficient of joints have more influence on wavelet waveform change. (3) Elastic layered rock mass has the characteristics of multi-scale comb filter. With the increase of the ratio of rock thickness to wavelength, the amplitude, transmission coefficient and reflection coefficient change periodically on a large scale with a large scale period = 0.5. There is a bandpass and a band barrier in a large scale period. There are many small scale periods in the bandpass, which are formed by interlayer multiple permeation and reflection. The viscoelastic layered rock mass is characterized by low pass filtering. There are many bandpass and band-stop in the low pass filtering range. (4) in the propagation process of stress wave in different frequency range, there are significant differences in the dependence of attenuation coefficient on frequency, and the whole rock mass is characterized by low pass filter. In the range of low-pass filtering, it has the characteristic of non-equal-spacing band-pass filtering. In the transition zone of absorption frequency, the attenuation coefficient of stress wave changes very quickly with the frequency. The unsteady Maxwell model of viscosity coefficient can effectively describe the attenuation coefficient of stress wave in intact rock mass, the more broken rock mass, the stronger the filtering ability and the smaller the low pass range. The steepness parameter of the transition band of absorption frequency is smaller. (5) according to the variation law of wavelet transmitted joint waveform, the method of joint stiffness measurement is presented, which has good repeatability. When the thickness of joints is less than 0.1 m and the measurement error is less than 15.0, the results show that with the increase of the distance between the measured points and joints, the measurement errors decrease first and then increase, and there is a reasonable location of measuring points. The reasonable distance between the measured point and the joint is determined to be 10 ~ 20 cm by numerical calculation and field test.
【学位授予单位】：中国地质大学（北京）
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU452

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