Numerical Study Of Surface Wave Detection Method For Shallow Heterogeneity In Layered Media

In practical engineering,the underground working conditions are all layered media,and the common phenomenon of heterogeneity under layered media is also encountered.The existence of heterogeneity can seriously affect the quality of engineering,endanger property and personal safety.Therefore,it is crucial for engineering construction to determine whether there are harmful heterogeneous materials underground.Rayleigh wave is a kind of elastic wave propagating along the free surface of semi infinite elastic medium.The energy is mainly concentrated in a wavelength range,and with the increase of detection depth,the energy of Rayleigh wave decays faster.Therefore,Rayleigh wave is used to detect underground heterogeneity.In view of the reflection,transmission and scattering effects of Rayleigh wave wave when encountering heterogeneous objects,it will have a corresponding disturbance effect on the surface wave field.This article will use numerical simulation for research,using quantitative analysis and experimental methods to verify the accuracy and feasibility of the results.Based on the two-dimensional axisymmetric model,the calculation results are studied and analyzed,and the propagation law of Rayleigh wave wave in layered media and the propagation characteristics when encountering different heterogeneous bodies are obtained.Quantitatively study the position,shape,and burial depth of heterogeneity in layered media through time-domain and frequency-domain analysis.The main content and conclusions of this study are as follows :(1)Numerical simulation of the propagation law in a uniform semi infinite body to verify the feasibility and rationality of model parameter settings.Based on the wave field snapshot cloud image analysis of the propagation law of elastic waves,the frequency domain spectrum analysis shows that the horizontal particle velocity response has a greater impact on the receptor wave,and the vertical particle velocity response analysis has less interference.Through the frequency phase velocity spectrum analysis,whether the basic mode is distributed in a straight line and the degree of influence by the higher-order mode,we can distinguish whether the site has stratification.(2)Since the energy of Rayleigh wave wave will decrease when encountering the heterogeneity,the size of the heterogeneity can be determined quantitatively.Based on the change of Rayleigh wave wave energy in the time history curve and offset wavelength spectrum,the horizontal size of the heterogeneous body is judged.Based on the relationship between Rayleigh wave and the wavelength corresponding to the dominant frequency,the effective amplitude ratio method is used to estimate the buried depth of underground heterogeneity,and an analysis method and identification method for shallow heterogeneity detection in layered media are proposed.(3)For layered media with soft upper layer and hard lower layer,Rayleigh wave mainly propagates in softer media.According to the change of energy when Rayleigh wave encounters heterogeneity,the geometry of underground heterogeneity can be judged.For layered media with hard upper and soft lower layers,the surface is mainly dominated by leakage plate waves,with relatively small energy.Most of the energy propagates in the form of body waves in a semi infinite body,with relatively small layer energy.In view of the dispersion characteristics of Rayleigh wave encountering a heterogeneous body,it can be seen that the reflected wave energy generated by Rayleigh wave encountering a heterogeneous body’s smooth surface is weak.For a heterogeneous body with inflection points,the reflection path of its reflective surface is different,resulting in the existence of different forms of reflected waves.(4)According to the analysis of the degree of hardness and frequency spectrum characteristics of the heterogeneous body,the disturbance of the hard body is obviously stronger than that of the soft body in the spectrum,and the wavelength range of the Rayleigh wave wave will become smaller when encountering the soft body,and the opposite is true when encountering the hard body.By studying the lining around the hole of special heterogeneity,it can be seen that Rayleigh wave has the strongest reflection ability to this heterogeneity,and the energy dissipation of Rayleigh wave is significantly higher than that of hole heterogeneity and hard body,which can judge the existence form of underground heterogeneity.(5)The transient Rayleigh wave wave method is used to test the sewage pipeline site under construction,collect and analyze the field test data,verify the accuracy of the numerical simulation results and the feasibility of data analysis,and obtain the method to judge the parameters of underground heterogeneity in layered media.In view of this,the results indicate that this method can provide guidance and reference significance for the detection of underground heterogeneity in practical engineering.