Application And Research On Mode Separation In Extracting The Dispersion Curve Of Rayleigh Wave

With the merits of being more simple and useful than traditional exploration ways, instant Rayleigh wave is widely used in actual engineering. In the Rayleigh wave test, extracting the reliable and accurate frequency dispersion curve is the base of the inversion work. At present, phase unwrapping is a difficult problem to solved in the phase difference method for extracting frequency dispersion curve of the double channels signal. In this paper, the problem is studied. By research of the mode of Rayleigh wave which is an important factor of phase unwrapping, it shows that mode separation has an important meaning for the phase difference method for extracting frequency dispersion curve. This paper studies the mode separation method of double channels signal and the method for extracting frequency dispersion curve which is based on mode separation. The primary research work and achievements of this paper are as follows:(1) In this paper, by researching the factors which affect the phase unwrapping, the question of mode separation is introduced. We extracted the fundamental mode signal from the simulate data by mode separation method. From the comparison of unwrapping phase and the theories value, it shows that the high mode is the factor which effects the unwrapping phase of the fundamental mode signal and mode separation has significant effect on the phase unwrapping.(2) The S transformation is introduced to the process of time varying filtering to improve the existing method which separate different modes by filtering (multiple filtering–time varying filtering). We extracted the frequency dispersion curve of fundamental mode after the mode separation for the simulate data and the measure data. Comparing the frequency dispersion curve of the simulate data and the theoretical frequency dispersion curve, the result shows the above method is feasible in theory. Comparing the frequency dispersion curve of the measure data and the frequency dispersion curve which extract by the f ? k method, the result shows the method is practical in the engineering fields.(3) By processing several groups of double channels signal which have different source offsets and processing the simulate data of different geologic models, it is concluded that the best applicable conditions of the above method are the energy of fundamental mode of Rayleigh wave is dominant and the source offsets are long enough in the engineering practices.(4) In this paper, the data processing of the multi-channels Rayleigh wave test are improved by the method which extract frequency dispersion curve for the double channels signal and the theory of the depth of the Rayleigh wave exploration. The method I improves the horizontal resolution of Rayleigh wave test by using the advantages of the method which extract frequency dispersion curve for the double channels signal and the multi-channels Rayleigh wave test. The method II improves the precision of extracting frequency dispersion curve by considering the theory of the depth of the Rayleigh wave exploration. By processing the simulate data and the measure data, it shows that the methods have great applicable value in the engineering practices. For different tests purposes, choosing the different method can achieve the best effect of Rayleigh wave test.