Propagation Rule And Application Of Wavelet Across The Jointed Rock Mass

It is very important for obtaining accurately rock mass deformation parameters to analyzethe deformation and stability of rock mass engineering. The amplitude spectrum and phasespectrum of seismic across the rock mass change. That is, the waveform of wavelet changes. Thewavelet waveform is more comprehensive and more sensitive to reflect mechanical parametersof rock mass than wave velocity and amplitude and frequency, etc. The propagation rules ofwavelet across viscoelastic stratum and viscoelastic joint and jointed rock mass are studied usingtheory analysis and field test and numerical calculation. The wave test method of joint stiffness isput forward. And the test error and application condition of the method are discussed. The mainstudy results are as follows:(1) The frequency characteristics of wavelet change owing to the absorption optionally ofKelvin medium. The characteristic frequency and band width decreases when propagationdistance increases. The characteristic frequency decreases in the form of negative exponent thentends to a stable value. And wavelet amplitude decreases and oscillation duration increases. Thedistance having relative stable wavelet waveform decreases with increasing glutinousness ofmedium and decreasing elastic modulus.(2) The effect of joint mass on transmission coefficient and reflection coefficient of P waveacross the joint is obvious. The reflection coefficient of P wave and transmission coefficient andreflection coefficient of SV wave are bigger regardless of the joint mass. The deviation increaseswith the increasing joint thickness. The amplitude of transmitted wave decreases because of theabsorption optionally of viscoelastic joint. The main lobe is not obvious and the resolution ratiodecreases. The waveform change of wavelet across joint can be described effectively usingwaveform correlation coefficient and waveform change coefficient. The effect of normalstiffness and normal viscosity coefficient on wavelet waveform change is larger than tangentialstiffness and tangential viscosity coefficient.(3) The elastic layer rock mass has the multiscale comb filter property. The amplitudetransmission coefficient and reflection coefficient change periodically in large scale owing to theintrastratal multiple transmission and reflection. The large scale period=0.5. There exist a bandpass and a band rejection. There have several small large periods in a band pass because of theinterlayer multiple transmission and reflection. The viscoelastic stratified rock mass has thelow-pass filtering property in the whole. And there exist several band-passes and band rejections.(4)The relationship between attenuation coefficient and frequency is remarkable differentfor different frequency stress wave propagation across the rock mass. The intact rock masses show generally the low-pass filtering property. There has non-equidistance low-pass filteringproperty within the scope of low-pass filtering. The attenuation coefficient of stress wavechanges very fast with the frequency in absorption frequency transitional zone. The change ruleof attenuation coefficient of stress wave in intact rock mass can be described effectively usingunstable viscosity coefficient Maxwell model. The more the rock mass broke, the more the filtercapacity is. The smaller the scope of low-pass is, the smaller the gradient parameter is inabsorption frequency transitional zone.(5) The measurement method of joint stiffness is put forward based on the waveformchange of wavelet through joint. This method has good repeatability. The test error is less than15.0%when joint thickness is less than0.1m. The study results indicated that test error decreasesfirstly then increases when the distance increases between measuring point and joint. So, there isa reasonable location having minimal errors. The reasonable distance between measuring pointand joint is10~20cm using numerical calculation and in-situ experiment.