Research Of Rayleigh Wave In Seismic Wave Field And Its Application In Engineering Construction

Although the frequency dispersion of Rayleigh wave has been known early and has made great progresses in solving the geological problems as a physical prospecting method, there exists many problems need to be solved when it is applied to synthetic evaluation subtly and quantitatively in geotechnical engineering. In the thesis, we mainly discussed the application of the multi-channel transient Ralyleigh wave in the geotechnical prospecting and ground evaluation; studied the testing technology and the theoretical calculation of frequency dispersion curve in stratified media, inversion based on data acquisition and the Rayleigh wave testing, the interpretation of the frequency dispersion curve, and the evaluation and the influence of the high modes Rayleigh wave to the frequency dispersion characteristics; analyzed the existing frequency dispersion curve extraction method in f-k domain in theory deeply and studied its advantages and its shortcomings; further analyzed the energy distribution of the Rayleigh wave patterns under the transient excited vibration source on the surface. In theory, we analyzed the corresponding relationship between the extracted dispersion curve in f-k domain and multi-mode dispersion curve; conducted a comparative study on forward modeling of multi-modes dispersion curve, and proposed the programme on the extraction and the inversion of the dispersion curve, then verified the effectiveness of the programme by numerical simulation, and after the necessary programme adjustment, further verified the effectiveness of the programme by the measured data processing; at last proposed the Max-mode dispersion concept and constructed a stable Max-mode forward modeling method. This study realized the extraction of the frequency dispersion curve of the max-mode Rayleigh wave in f-k domain using the actual signal; analyzed the wave velocity and layer characteristics of several fields based on the extracted frequency dispersion curves and forward modeling of the max-mode Rayleigh wave. Inversion of max-mode dispersion curves of the actual signal can be realized by combination of manual and automatic inversion, although it is difficult to conduct automatic inversion directly by Quasi-Newton method. The results after combined with the manual and automatic inversion show that the Max-mode inversion reflect the layered structure better, and it can solve zigzag dispersion curve which cannot be solved by the fundamental mode.The frequency dispersion of the Rayleigh wave has been used widely in seismic exploration and engineering exploration. Through the study of the theories and summarization of the experiments, the research in the thesis contributes as follows:⑴It is a systemic study and summarization in theory and engineering application to apply the multi-channel transient Ralyleigh wave to the geotechnical engineering investigation and to evaluate the intensity and uniformity of the ground. In the thesis, the optimized combination principle of acquisition parameters were discussed systemically, such as the excited vibration source, offset, time and space sampling rate, and the length of testing. Then the procedures were constructed including data collection, processing and interpretation for the rapid acquisition of high-quality data and information, for providing the basis for effective application, and for the promotion of Rayleigh wave technology applications in geotechnical engineering;⑵The calculation of Rayleigh wave dispersion based on fundamental mode is improved to multi-modes by using a fast scalar-transfer algorithm successfully for numerical stability of the forward modeling and for the requirements of computational speed in engineering applications. In order to effectively identify and separate fundamental mode and high modes of Rayleigh wave, as well as a reliable calculation of the dispersion curve, an energy calculation method for all kinds of modes was provided in f-k domain;⑶According to the multi-mode Rayleigh wave propagation, we analyzed the representation and the identification of fundamental mode and high modes, such as the waveforms and energy distribution, in time domain and frequency domain. Using f-k spectrum multi-channel data-processing technology combined with multi-channel data acquisition technology, the discussion was conducted on the feasibility of an effective identification and separation of the Rayleigh wave and noise such as body-wave, and the fundamental mode and high modes, as well as ways to extract dispersion curve effectively, and the integrated design principles of the testing parameters from data processing;⑷In theory, it makes the fast scalar-transfer algorithm as the tool to calculate the multi-mode frequency dispersion curves to improve the computational speed; on this basis, a formula was proposed to calculate the received signals energy of all kinds of modes under the vertical transient excited vibration source on the surface; In the dispersion curve inversion, the global optimization of Quasi-Newton method was applied to dispersion curve automatic inversion of Rayleigh wave. The numerical simulation of the different stratum models shows that the established Quasi-Newton method in the thesis worked much effectively in dispersion stratum and inverse dispersion stratum compared to other methods used at home and abroad, such as Least-squares algorithm. It opened up a new way and means for the fast and effective inversion of Rayleigh wave dispersion curve;⑸According to the numerical simulation results and the experiment results in different stratum structure fields, we discussed the formation mechanism of the multi-mode Rayleigh wave and its influence to the Rayleigh wave propagation; the settings of the related acquisition parameters combination, representation, identification, and separation of fundamental mode and multi-mode and its significance in engineering. We proposed an idea that the composite mode or Max-mode dispersion curves should be used to inversion and stratum interpretation based on the stratum structures of the fields and energy distribution and contribution of each mode. At the same time, we analyzed and discussed the characteristics, formation, and meaning of the zigzag dispersion curve;⑹We discussed the uncertainties of the frequency dispersion curve of Rayleigh wave and the inversion from some aspects, such as the identification and extraction of the Rayleigh wave, high modes influence, the relation between the inversion results and the distribution and the density of the dispersion points. It will be useful to improve the precision of the Rayleigh wave testing and analysis;⑺A preliminary discussion was conducted on the influence of the inhomogeneity of the layer structure and the subsurface anomaly to the Rayleigh wave propagation, frequency dispersion curves, and their representation. These discussions will help extend the application fields of the Rayleigh wave.In brief, it is the essential purpose to apply the results of Rayleigh wave test to geotechnical engineering investigation, evaluation of ground quality and mechanics. Therefore, we have conducted the thorough systemic research on the basis of combination with a large number of practical projects. The thesis summarized several methods based on Rayleigh wave testing technique, such as different methods on stratigraphy, evaluation of ground bearing capacity (rigidity), and investigation of influence depth and uniformity of ground treatment. We conducted geotechnical engineering investigations effectively by the Rayleigh wave testing technique combined with other geophysical methods. The thesis used a lot of drilling data and in-situ tests (static, wave speed and drilling tests) and construction data of the local practical projects. Therefore, we may think that the conclusions in the thesis are reliable and have the prospect of spreading. Moreover, the remarkable innovation of the thesis is to transform the achievement of Rayleigh wave research into practical techniques, ultimately the productive forces, which is based on the tight combination with the conventional geotechnical engineering analysis methods and exploration of the general laws through the induction and summarization of case studies.