| In recent years,with the development of society,domestic infrastructure projects such as highways and high-speed railways have been greatly developed,and many geophysical detection methods have been applied to the field of geotechnical engineering.However,most of the applications and researches on Rayleigh wave are based on the layered medium model in 2D space.In response to the common local site 3D detection requirements in geotechnical engineering,this paper proposes the study of the lateral inhomogeneous media 3D Rayleigh wave method.In addition,the domestic high-speed rail technology has developed rapidly in recent years,and the high-speed rail seismic source has attracted the interest of many scholars and experts.However,in the field of high-speed rail,both the theoretical research on high-speed trains as seismic sources and the detection research of Rayleigh wave methods are rarely involved.Based on the above situation,this paper uses a combination of numerical simulation and field tests to study the characteristics of the Rayleigh wave field excited by a point source and a high-speed rail mobile source,and the use of Rayleigh wave velocity dispersion and elliptical dispersion.The theory and method of detecting lateral inhomogeneous media in 3D field.This paper mainly includes the following aspects:(1)Numerical simulation of Rayleigh wave field characteristics of single point source.Based on the source load direction,the full wave field numerical simulation is performed in3D space from the shear direction and the compression direction respectively.Research and analyze the 3D Rayleigh wave field characteristics,velocity dispersion and elliptical dispersion characteristics.The characteristics of Rayleigh wave field corresponding to common mixed sources in practical engineering are briefly analyzed.(2)Numerical simulation of 3D Rayleigh wave method with compressed source.Based on the wave field propagation characteristics of the compressed source Rayleigh wave and Huygens principle,a 3D Rayleigh wave exploration method based on the radial survey line network is proposed.Selecting the Ricker wavelet as the compression point source,numerical simulation studies the characteristics of the Rayleigh wave field in a3D uniform and lateral inhomogeneous media.Explore the feasibility and superiority of the proposed three-dimensional Rayleigh wave exploration method.(3)Field test of 3D Rayleigh wave method with compressed source.A site in Southwest Jiaotong University with a known underground drainage channel is selected to conduct a field test study on the 3D Rayleigh wave exploration method proposed in(2).Analyze the existing problems in practical applications,and look forward to possible application areas and prospects.(4)Numerical simulation of 3D wave field characteristics of high-speed railway moving source.Based on the Rayleigh wave field characteristics of the source load direction studied in Chapter 3,a three-dimensional data acquisition network with a matrix arrangement with the survey line perpendicular to the running direction of the high-speed train is proposed.Using the moving compressed Ricker wavelet source and the simulated moving compressed high-speed rail source,the characteristics of the Rayleigh wave field in the 3D uniform and lateral inhomogeneous media are simulated and studied.Research the apparent velocity filtering method and data processing flow of moving seismic source wavefield separation.Study the spatial distribution characteristics of the extracted velocity dispersion and elliptical dispersion data,and explore the feasibility of the 3D Rayleigh wave exploration method for the high-speed rail mobile seismic source.(5)Research on the application of Rayleigh wave in high-speed railway source detection.A section with a simple geological structure of the Chengguan Intercity High-speed Railway was selected to collect seismic records excited by the high-speed train at different speeds and when different load trains passed.The Rayleigh wave velocity dispersion profile and elliptic dispersion profile extracted by the data processing process proposed in(4)are compared with the actual estimated structural characteristics of the engineering site,and the feasibility and credibility of the practical application of the method are explored,and the problems existing in the practical application are analyzed,and the applicability of the method in high-speed railway subgrade disease monitoring is explored and discussed.The main conclusions and results are as follows:(1)The study of source numerical simulation shows that:in the 3D homogeneous half space,the Rayleigh wave excited by compression source can form an omni-directional(360°)stable Rayleigh wave dominated wave field in the far-field region,which should be the main source mode of 3D Rayleigh wave exploration.The far-field Rayleigh wave area excited by shear source is angular domain distribution,and its range is narrow(in each quadrant of rectangular coordinate system,the distribution range is in the angle domain of 30~°-75~°,and there is strong SH wave interference,so this kind of source model is not suitable for 3D Rayleigh wave exploration.In addition,for the mixed source composed of compression and shear components,in the far-field region of the central line perpendicular to the shear component,the Rayleigh wave excited by the compression component dominates and the SH wave excited by the shear component does not exist.In addition,for a mixed source composed of compression and shear components,in the far-field region of the central survey line perpendicular to the direction of the shear component,the Rayleigh wave excited by the compression component and the SH wave excited by the shear component are dominant.,There is no Rayleigh wave excited by the shear component.(2)The Rayleigh wave field excited by multiple compression sources observed by radial line network can be regarded as the Rayleigh wave field excited by a single point virtual source located at the origin of the radial line network.Therefore,there is no multi-source influence of the traditional rectangular 3D observation network in principle.This feature also greatly reduces the amount of calculation of 3D numerical simulation.The numerical simulation results show that:when the Rayleigh wave passes through the transverse inhomogeneous body,the 3D Rayleigh wave records based on the radial survey network,the extracted velocity and the elliptic dispersion can clearly show a circular phenomenon or anomaly similar to the water wave passing through a solid,from which the approximate plane position of the cavity can be judged intuitively It can not be observed in rectangular 3D survey network.(3)The results of field experiments show that:1 The Rayleigh wave field records observed by 3D radial line network,the extracted velocity and elliptical dispersion images can well reflect the horizontal position and buried depth of sewer and well cover.In the actual data acquisition,because it can only be excited at the virtual source location,the multi-point source excitation of traditional 3D exploration can be avoided,can greatly reduce the work cost of 3D exploration measurement.(4)Numerical simulation study of the moving source of the high-speed rail shows:After simplifying the high-speed railway seismic source to a model composed of multiple moving point seismic sources,the Rayleigh wave field excited by the moving seismic source is the superposition of the Rayleigh wave field excited by multiple seismic sources at different locations and at different time points.The three-component recording and minimum apparent velocity filtering method of the rectangular survey network based on the vertical source movement direction of the survey line can well identify the relative position of a single moving compression point source and the survey line,thereby completing the observation of the point source excitation on the survey line.The wave field of the sharp surface wave record is separated from the wave field of the Rayleigh wave record excited by the point source at other locations.The research provides necessary theoretical support for the research and utilization of natural seismic sources of high-speed trains.(5)Research on application of high-speed rail mobile seismic source shows:The seismic records and apparent velocity distribution characteristics of the on-site observations of trains running at different periods and loads are basically consistent with the wavefield seismic records and apparent velocity distributions excited by the simplified model of the high-speed rail moving source proposed in(4),which verifies the feasibility of the simplified model.Therefore,the vibration generated by high-speed train operation can be used as a natural Rayleigh wave source.The Rayleigh wave exploration method using the seismic source of the high-speed train has the advantages of fast,low-consumption,and repeated observations in the lateral non-uniformity detection of the site.At the same time,since it can be regarded as a stable long-term continuous output seismic source,it also has potential application prospects in the field of long-term quality monitoring of high-speed railway subgrades. |
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