Model Test of Ground Penetrating Radar Detection for High Speed Railway Tunnel Lining with Defects

Based on a tunnel of Yinchuan-Xi'an high-speed railway, the lining model of high-speed railway with defects was established. The detection tests were carried out by using 900 MHz and 400 MHz ground penetrating radar antennas respectively. On the basis of analyzing the forms of radar profile defects, the waveform characteristics and the spectrum characteristics of defects were summarized. In this paper, a method for calculating the thickness of tunnel lining was proposed by using the reflection hyperbola of point object to determine the zero line position of radar wave and to invert the propagation velocity of radar wave. By drilling holes and coring at the corresponding positions in the model, the accuracy of identifying tunnel lining defects and the accuracy of lining thickness calculation method were verified by using the radar wave waveform characteristics and spectrum characteristics. The results show that the waveform characteristics and spectrum characteristics of radar wave can be used to assist in identifying the types of lining defects. Two kinds of antennas have good detection effects on cavity defects and reinforcement distribution in the lining, and even can detect the cavities with an area of less than 0.1 m2. The lining thickness of 8 design defects are calculated. The maximum relative error is 4.11% and the average relative error is 1.53%, indicating that the calculation method for lining thickness has high accuracy. The influence of target buried depth on detection results is much larger than that of target scale. If detecting the targets with larger buried depths, it is necessary to increase the transmitting power of the equipment or reduce the center frequency of the antenna. The defect detection rate is related to the defect scale, line density and other factors, which can be improved by increasing the number of lines. © 2021, Editorial Department of China Railway Science. All right reserved.