Research On Detection Of Tunnel Lining Thickness With Railway Train-Mounted Ground Penetrating Radar

Train-mounted Ground Penetrating Radar detects the lining state away from the tunnel lining by air-launched antenna, as an advanced Non-destructive Testing technology, due to the advantage of its unique rapidness, continuity and high-resolution, it will be the primary means of tunnel quality detecting. Lining serves as the important part of tunnel structure, its status is related to the safety and service life of the tunnel, in which secondary lining thickness is an important indicator of the quality and health status of the tunnel lining. Therefore, it is of important application value to research on the lining layer identification of the Train-mounted GPR image.This paper summarizes the research status of the layer picking methods, especially proposes the Hilbert instantaneous amplitude envelope maximum method to identify the lining layer. In view of the problem that the interface between the secondary lining and the initial lining is weak, and then the lining layer of the original sectional view is difficult to be identified, the Hilbert envelope maxima method is adopted. The real GPR signal is processed by Hilbert transform, its imaginary and real signal together to compose a complex signal is defined as the instantaneous amplitude, made the width between the maximum reflection wave envelope of bottom and maximum envelope of surface in the secondary lining to be the secondary lining thickness, then identifies the lining interface.According to the Finite Difference Time Domain, the GPRMAX software is chosen to simulate the electromagnetic wave propagation in the medium with different dielectric constant and different thickness, after that analyze the waveform of reflected wave and the position of the lining interface. Through using Hilbert envelope maximum method to process analog data to identify the lining layer, the validity of the Hilbert maximum method is verified, which provides a theoretical basis for applying Hilbert envelope maximum method to process the Train-mounted GPR detected data.Combined with the typical tunnels in Xiang-Yu railway, the Hilbert instantaneous amplitude envelope maximum method is applied to identify the lining thickness. The result shows that, from the real waveform of Train-mounted GPR, using the reflection wave envelope of bottom surface in the secondary lining can identify the weak reflection interface between the initial lining and the secondary lining, which obtains satisfactory tracking results, the interface is intuitively visible, and greatly improves the ability to identify the layer. Furthermore, it provides higher precision for measuring the lining thickness, and avoids the subjective error of the artificial interpretation effectively. Consequently, it is reliable that applying Hilbert envelope maxima Method to analyze the layer, which can evaluate the changes of the effective thickness of the lining when estimates the quality of the tunnel lining.