Research On Ground Penetrating Radar Signal Analysis And Localization Method For Underground Pipeline Leakage

According to the 2020 Urban and Rural Construction Statistical Yearbook,China’s urban public water supply network has a leakage rate of 13.4 %,which is high compared to developed countries.Leakage of urban water supply network not only causes waste of water resources,but also causes soil erosion,ground collapse,and endangers public safety.The existing pipeline leakage detection methods have disadvantages such as low efficiency and limited applicability,which are insufficient to cope with the current complex situation.Ground Penetrating Radar(GPR)method,as a non-destructive and efficient geophysical detection method,also has good prospects for application in pipeline leakage detection.However,the relevant research is still mainly concentrated in the laboratory,and there is a lack of research on the detection mechanism and the conditions for mature application.However,the related research is mainly concentrated in the laboratory,and there is still a lack of research on the detection mechanism and difficult to apply in the actual detection.Based on the existing research,this paper has carried out the following work :(1)Water leakage from a pipeline can significantly change the dielectric constant of the surrounding soil,which in turn affects ground-penetrating radar image characteristics.In this paper,we simulated the change process of leakage zone after the leakage of underground pipeline by model box test,and measured the shape of leakage zone under different leakage volume by using 3D ground-penetrating radar.After the leakage of underground water pipe occurs,the leakage area expands spherically in all directions with the leakage point as the center,while water seeps down in the soil,so that the leakage area gradually develops into a mushroom-like shape.Disturbed by the leakage area,the pipeline reflection disappears in the ground-penetrating radar image collected parallel to the pipe.(2)In order to obtain ground-penetrating radar images after underground pipeline leakage close to the real situation and to study the influence of pipeline material on the characteristics of ground-penetrating radar images before and after leakage,an outdoor sand test was conducted.It was found that in the ground-penetrating radar images collected perpendicular to the pipe before the leakage,the metal pipe could only see the reflection from the top of the pipe,while the PVC pipe could see the reflection from the top and bottom of the pipe,and there were multiple waves.After the underground pipeline leakage,the reflection representing the boundary of the leakage area appear in the radar image,and the reflection at the top of the pipe is shifted down and a complex oscillation signal appears below.The oscillation signal below the top of PVC pipe is more complex than that of metal pipe.(3)In order to investigate the formation mechanism of oscillation signals in groundpenetrating radar images of pipeline leakage,this paper first simulates the seepage field of underground pipeline leakage,then establishes an electromagnetic field simulation model based on the results of the seepage field simulation,and finally simulates ground-penetrating radar images before and after the leakage of underground water pipes using the finite difference method in the time domain.By analyzing the wave field snapshot of electromagnetic field,comparing the simulation results of seepage field-EM field coupling of water pipe leakage with the radar images of the actual test,the propagation path of electromagnetic waves is analyzed,and the causes of oscillatory signals and the role played by creeping waves are explained.(4)By comparing and analyzing the radar image features before and after leakage in model box test and sand field test,a pipeline leakage location algorithm based on wavelet entropy is proposed.Through the wavelet entropy analysis and calculation of the data representing the reflection range of the pipeline in the GPR signal,it is found that there is a high entropy phenomenon in the area of pipeline leakage,and the effectiveness of the algorithm is proved by the measurement data.