Numerical Simulation Of Rayleigh Surface Wave Of Subgrade In Qianwei Section Of Chendgui Railway

In recent years,China's high-speed rail industry is booming.High-speed rail has been built and under construction on a huge scale.High-speed railway lines are all over the country,High-speed trains run at the highest speed.High-speed railway subgrade is the track foundation of high-speed railway and one of the principal elements to ensure the operation of high-speed railway.However,the roadbed bears the influence of moving load and static load of the locomotive for a long time and is completely exposed to the natural environment.Therefore,it is hard to avoid various defects,such as cracks and collapses,in the subgrade after a certain period of operation.Therefore,it is necessary to detect roadbed,judge of the harm of roadbed,take timely measures to repair,to ensure the safety of highspeed operation.In the field of the high railway based detection,traditional methods including based on the theory of seismic wave reflection seismic method and based on electromagnetic theory,the geological radar.Both methods can achieve certain results,but there are some shortcomings.Rayleigh surface wave has strong energy,slow attenuation in horizontal direction and dispersion effect in heterogeneous medium.Based on the characteristics of Rayleigh surface wave,Rayleigh surface wave has gradually provided a new method for roadbed,bridge and other engineering detection fields in recent years.Based on the numerical simulation software,this paper establishes the corresponding model for the detection of common defects in the basis of high-speed railway,and analyzes and studies the corresponding model from the four aspects of seismic record,snapshot of wave field,velocity dispersion and elliptical polarizability.The research content is as follows:the basic theories of Rayleigh surface wave elliptical polarizability and Rayleigh surface wave velocity dispersion are studied.The calculation methods of Rayleigh surface wave elliptical polarizability and velocity dispersion are discussed,and the calculation of elliptical polarizability and the extraction of velocity dispersion curve are discussed.By means of finite element simulation software,two-dimensional numerical simulation is carried out for uniform,layered,cavitation-containing and fracture models,and seismic records and snapshots of wave fields of the corresponding models are extracted.The propagation characteristics of seismic waves and the transformation characteristics of seismic waves at the interface are observed intuitively according to the relationship between the energy intensity,velocity and travel time of seismic waves.The velocity dispersion curves of each model were extracted from seismic records,and the corresponding velocity dispersion profile was drawn.At the same time,the elliptical polarizability of the corresponding model is calculated.The response characteristics of the two methods to different models are analyzed,and the resolution and accuracy of the two methods are comparedCombined with practical subgrade engineering,geological radar,velocity dispersion and elliptical polarizability are used for detection.Combined with the construction design data,the three test results are compared.The practicability and accuracy of the three methods in subgrade detection are discussed.Based on the above research,the following conclusions can be drawn:In the active source excitation field,the calculation of the elliptic polarizability of Rayleigh surface wave is obviously affected by the interference wave,which is reflected in the presence of the high and low adjacent elliptic polarizability outliers.The larger the interference,the larger the area of the elliptic polarizability outlier.In order to avoid interference,observation needs to be carried out in the area with a long offset.Velocity dispersion is extracted by using multiple seismic trace data simultaneously,which is also applicable to the near field area near the source.When velocity dispersion is used for detection,a relatively obvious velocity transition zone will appear when the velocity difference interface is encountered,and the velocity will be evenly transferred from one side of the interface to the other side.The existence of velocity transition zone will affect the determination of the actual interface.For the horizontal and transverse media model,velocity dispersion and elliptical polarizability can identify the horizontal interface in the far field.For the detection of abnormal bodies,the velocity dispersion can also identify the location and morphology of abnormal bodies,while the elliptical activation rate can only identify the approximate location of abnormal bodies,and the morphology of abnormal bodies can still be identified.In practical subgrade engineering detection,for the detection of different interfaces of subgrade materials,the detection effect and precision of GPR should be better than velocity dispersion and elliptical polarizability,and the GPR method can accurately identify the location of the interface.The layered interface can also be identified by velocity dispersion and elliptical polarizability,The accuracy needs to be further improved.In this paper,based on the finite element numerical simulation method,models containing common defects in the detection of high-speed railway foundation is established,and the full wave constant simulation of the corresponding model is carried out,which is studied and analyzed from two aspects of Rayleigh surface wave velocity dispersion and elliptical polarization dispersion.It strengthens the theoretical foundation of Rayleigh surface wave detection in non-uniform medium and provides a theoretical foundation for the application of Rayleigh surface wave in subgrade detection and other offline engineering.It is of great significance to promote and perfect Rayleigh surface wave theory and guide practical engineering.