A train-mounted GPR system for fast and efficient monitoring of tunnel health conditions

The health status of a railway tunnel should be regularly inspected during its service period for safe operation. The frequency of periodic inspection should be increased when the tunnel has become aged. For the coverage tunnels, health assessment is more essential. Ground penetrating radar (GPR) has been used as a key tunnel health detecting technique; however, so far, such (GPR) techniques are in contact mode. Such methods cannot meet the requirements for tunnel disease prospection and regular inspections across the whole operational network. Therefore, a new method has been developed that uses long-range detection with the train-mounted GPR. It consists of six channels, whose air-launched antenna distance to the sidewall is about 0.93m~1.5m, and the distance to the vault is 1.7m~ 2.25m. The scanning rate of each channel is 976 scans/second. When the sampling point interval is 5cm, the maximum test speed can reach up to 175km/hr. With such a speed and air-launched antenna, this system has a big advantage over existing methods. That is, for electrified railways, there is no need for power outages and for inspections to occupy time during maintenance periods. Indeed, they will not interrupt normal railway operation. The running tests with this system have been carried out on the Baoji-Zhongwei and Xiangfan-Chongqing railway lines and very good test results have been obtained.