| As an important means of short distance physical exploration,ground penetrating radar(GPR)has been widely used in engineering field.In highway tunnel detection,the reflection wave of GPR is characterized by "weak signal and strong interference",which brings great difficulties to data processing and interpretation.In this paper,the main interference sources in highway tunnel detection are studied.Based on several highway tunnels under construction in guangxi,the characteristics of interference signals are analyzed and summarized from physical model test data,field detection test data and actual engineering case data.Subsequently,Shearlet transform and wavelet transform combined denoising method is proposed based on the theory of Shearlet transform algorithm and the processing effect of ground penetrating radar simulated data.The method is successfully applied to interference suppression of measured data to verify the applicability and effectiveness of the proposed method.The research results of this paper can effectively suppress the interference signals containing both abnormal energy and abnormal frequency in the data of the highway tunnel GPR,so that the weak target signals hidden by the interference signals can be shown,which is of great significance for improving the accuracy of data interpretation.The main research results of this paper are as follows:(1)In view of the possible interference source of GPR in highway tunnel,the indoor physical model test was carried out to study the influence of intercom,metal mesh and water on the detection data under ideal conditions.Then,on the basis of the le’ao tunnel under construction in guangxi,the field detection test was carried out to study the influence of power cable,construction trolley,steel arch,anchor bolt and cable on the detection data.Finally,the interference data of the actual geological prediction of the tunnel was collected.The characteristics of the above interference data were compared and analyzed,and the characteristics of the interference waveform were summarized and identified.(2)Shearlet transform is introduced into GPR signal processing based on wavelet transform and Shearlet transform theory.The threshold function of interference suppression in the algorithm is improved.Shearlet transform and wavelet transform combined denoising method are proposed according to the characteristics of interference signals and the processing effect of GPR forward data.Shearlet transform is sensitive to signal energy and wavelet transform is sensitive to signal frequency.It can effectively suppress the abnormal energy interference signals generated by the power cable,construction trolley,steel arch and other interference sources,as well as the abnormal frequency interference generated by the presence of geological interfaces such as water and mud clamping in the detection medium.(3)The proposed denoising method is applied to the measured data case,select the tunnel advance geological forecast rich water fracture zon,bare cavity field test and tunnel lining detection of three typical road tunnel detection data,success to identify and suppress the interference signal of the data.After processing,the data image is clearer,the feature of the same phase axis is more obvious,and the hidden weak signal is also visible,which is of great significance for improving the interpretation accuracy of GPR data. |
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