An innovative vehicle-mounted GPR technique for fast and efficient monitoring of tunnel lining structural conditions

- Full-section: Vehicle-mounted GPR with 6 channels.
- Non-contact NDT far from the tunnel lining: The distance from antenna to tunnel wall is 0.93 m-2.25 m.
- High speed and No interference: Maximum inspecting speed 175 km/h; Normal railway operation not affected.
- Higher resolution and deeper detection: The minimum thickness of tunnel linings 0.091 m; 2.0 m depth.
- Fully automated data collection: Nearly a thousand kilometers a day can be detected on the line.

The health status of a railway tunnel should be regularly inspected during its service period to ensure safe operation. Ground-penetrating radar (GPR) has been used as a key technique for tunnel detection; however, so far, the measurements of GPR are only obtainable in contact mode. Such methods cannot meet the requirements of the operational tunnel disease census and regular inspections. Therefore, a new method-vehicle-mounted GPR with long-range detection-has been developed. It consists of six channels. The distance from its air-launched antenna to the tunnel lining is approximately 0.93 m-2.25 m. The scanning rate of each channel is 976 1/s. When the sampling point interval is 5 cm, the maximum speed can reach up to 175 km/h. With its speed and air-launched antenna, this system has a significant advantage over existing methods. That is, for an electrified railway, there is no need for power outages. Indeed, the proposed system will not interrupt normal railway operation. Running tests were carried out on the Baoji-Zhongwei and Xiangfan-Chongqing railway lines, and very good results were obtained.