| With the accelerating urbanization process,there's a growing number of disasters such as road surface subsidence take places in the urban road and underground space(For example: the underground garage,basement,etc.)Ground Penetrating Radar(GPR)as a kind of nondestructive testing technology can be used to determine the condition of underground medium by launching high frequency electromagnetic wave underground through transmitting antenna.The receiving antenna will receive the reflected signal of different mediums and then start data processing analysis.Therefore,it has a broad application prospect in defectdetection.However,Ground Penetrating Radar(GPR)is very subjective to data interpretation based on experiences.It is still lack of the systematic research in corresponded underground engineering defect at present stage.Hence,this article is trying to apply the Ground Penetrating Radar to city underground engineering detection and provide reference to the city underground engineering detection.The main research contents and conclusions are as follows:(1)In view of the influencing factors of GPR detection of geological defects,based on the finite-difference time-domain method,the model of soil voiding-out defect and voiding-out defects under mass concrete in urban underground space is established,Gprmax software programming contributes to simulating the GPR values and research the radar characteristic images of mass concrete underground voids in different center frequency,different depth,different shapes of voids,different moisture content of soil media and different filling materials.According to the research,the characteristic images of circular cavities defects approach to hyperbola,rectangular and triangular cavities defects approach to hyperbola.And the detection resolution with the influence of antenna frequency is constrained by the detected maximum depth.However,the soil moisture rate has a great influence on the detection effect.The analysis of image formation could contribute to the interpretation of the measured radar image of urban mass concrete underground defects and the application of ground penetrating radar in urban underground space.(2)The Hilbert transform program written by Matlab is used for further process of the numerical simulation signal,extract the three instantaneous parameters of the analog signal,namely,the instantaneous amplitude,the instantaneous phase and the instantaneous frequency.Additionally,it can also analyze and determine the abnormal signal in the forward simulation from multiple perspectives.The results show that the application of Hilbert transform to forward modeling data can amplify the effective characteristic signals of deep soil,which is more conducive to the quantitative analysis of diseases or abnormal bodies by using wavelet.In addition,the previous judgment of shallow soil can be verified,and the accuracy of the judgment of abnormal signals can be improved comprehensively.(3)The ground penetrating radar was used to detect the mass concrete foundation floor of the square in front of a high-speed railway station,and the original radar data was obtained.A better radar image was obtained and was compared with the previous forward modeling after processing the original data.(e.g.improve the data quality and reduce the noise.)Research results shows that the actual measured data in the project are more complicated compared with forward modeling due to geological conditions.The obtained abnormal body resulting from processing may not be obvious or may overlap with other information.However,after co-analyzing forward modeling,it is helpful to identify defects characteristic image,which reflect that the forward modeling results have great significance in guiding the actual measurement data.Figure [51] table [4] reference [60]... |
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