Numerical Simulation Of Rayleigh Wave Dispersion Characteristics Based On FLAC3D

Dispersion characteristic is the theoretical basis of Rayleigh wavedetection method. The presence of dipping layer has significant influence onthe Rayleigh wave propagation. Researches on the dispersion characteristic onsites with dipping layer can expand the application of the Rayleigh wavemethod to those complex sites, and have important theoretical significanceand application value on the propagation theory and reconnaissance means ofRayleigh wave.In this paper, FLAC3D is used to set up dynamic models of double layer,the data acquisition and analysis process of Steady-state Rayleigh method aresimulated, and dispersion curves of Rayleigh wave are extracted. Studies arefocused on the dispersion characteristic of Rayleigh wave in the medium withdipping layer. The main results and accomplishments are as follows:1. Flat double-layer models are setup and the steady-state Rayleigh wavetest is simulated by FLAC3D. The dispersion curves obtained by crosscorrelation method are close to the theoretical value, and there is nosignificant difference between the dispersion curves observed at differentlocation but with same span, which verifies that the Rayleigh dispersioncurves in flat-layered medium are irrelevant to the observation location. So itis applicable and accurate enough to simulate steady-state Rayleigh wave testby FLAC3D.2. Three double-layered models with different dipping slopes of5%,10%and15%are setup. The test and analysis of steady-state Rayleigh wavemethod excited at uphill and recorded at downhill are simulated. Dispersioncurves corresponding to23pairs of observation locations are extracted, andthe dispersion characteristic of Rayleigh wave is studied.3. Study on the models with dipping layer shows that the presence ofdipping layer has significant influence on the Rayleigh wave dispersioncharacteristic, the observed dispersion curves are different from the theoreticalones in centre position, shallow observation point or deep observation point.The deviations are much bigger than those caused only by the difference ofthe thickness below the two observation stations, and the deviations increasewith the increase of dipping slpoes.4. Analysis also shows that even with the same observation spacing,dispersion curves also alternated at different locations relative to the dippinglayer, indicating that the extracted dispersion curves of Rayleigh wave arerelevant to observation locations.5. It is discussed that the way to obtain the average velocity of dippinglayer sites under observation stations by correcting the results of the observation and analysis. Finally, further researches are also suggested.