Research On Disease Detection Technology Of Subway Integral Track Bed Based On GPR

As an important part of the civil structure of subway,the integral track bed of subway is prone to empty and hollow diseases in the process of service,and such diseases are not easy to detect.To solve these problems,ground-penetrating radar technology can detect the internal diseases of the whole track bed.However,due to the interference of the reinforcement inside the track bed,the thickness of the track bed and other factors,the accuracy of the detection results of radar is low,and the identification is difficult.This thesis takes the integral track bed of a city subway as the research object and uses ground penetrating radar to study the nondestructive detection technology of the integral track bed disease.The main research work is as follows.(1)Investigate the existing integrated track bed and analyze the causes of hidden diseases of the integrated track bed.According to the detection mechanism of ground penetrating radar,the reflection,transmission and scattering characteristics of electromagnetic wave in different media of the integral track bed are analyzed.Through the comparison of radar detection methods,it is determined that the section method is more suitable for the detection of the whole tunnel bed disease.The B-can data acquisition method is selected and the location of the survey line is determined.The center frequency of 900 MHz antenna and the time window size of 20 ns were selected considering the dielectric characteristics and detection conditions of the integral bed.(2)According to the conductivity,permeability and relative permittivity of the medium of the integral ballast bed,the forward modeling model of the integral ballast bed was designed,and three kinds of diseases including cavity,uncompacting and void were added.On the basis of the designed detection scheme,the forward simulation study of cavity,compaction and void under different filling types,sizes and buried depths is carried out to judge the rationality of the detection scheme,and the propagation law,wavelength characteristics,amplitude energy and clutter quantity of radar wave are analyzed.(3)Ground penetrating radar was used to detect the overall track bed disease of a subway line on site,and drilling method was used to determine the specific condition of the disease,thus verifying the rationality of the radar detection scheme.Background removal,FIR bandpass filtering and K-L filtering were performed on the radar data successively.The results showed that the three preprocessing methods could effectively enhance the radar reflection characteristics of the disease.The radar reflection characteristics of cavity,compact and void disease bodies were analyzed,and the disease bodies containing different media(air,water and ice)were identified from the Angle of electromagnetic wave waveform characteristics.This thesis designs a disease detection scheme suitable for the whole ballast bed,and uses forward simulation and field detection to verify the rationality of the scheme.Through forward modeling,the influence of different conditions on disease identification was analyzed,which improved the accuracy of disease identification.The forward simulation results and radar images were preprocessed appropriately,which enhanced the reflection characteristics of the disease,and realized the recognition of the typical disease with different filling types from the aspect of electromagnetic wave waveform characteristics.