Railroad Ballast Inspection
3d-Radar Ground Penetrating Radar on Railways Provides High-Speed, Full Track Width Coverage
Ground penetrating radar has proven to be an effective way to assess the quality and thickness of railroad ballast as well as to detect the presence of moisture. However, to be able to fully assess ballast conditions using ground penetrating radar, it is important to collect an entire railroad tie width’s worth of data. Collecting less data opens up the possibility of missing problem areas. However the job is challenging using traditional methods. Impulse based radars and antennas require multiple antennas tuned to different frequencies to capture data at different depths. When using individual impulse based antennas, there is no way to collect data directly underneath metal rails. To complicate things further, after data is collected, the engineer is then faced with the difficult task of stitching the 2D imagery together for visualization in three dimensions.
By employing a 3d-Radar Mk IV GeoScope™ and the appropriate 3d-Radar VX-Series antenna, a track width of data is collected in three dimensions at maximum speeds in a single pass, while maintaining high resolution and good depth penetration. Step frequency GPR makes this possible by collecting both data at low frequencies and then stepping up to very high frequencies which captures the entire subsurface with a single radar and multi-channel antenna array in one pass. A single pass with the GeoScope Mk IV provides imagery of near surface ballast fouling and much deeper and potentially dangerous voids.
To overcome the issue of data collection directly underneath steel rails, the GeoScope and antenna array can be programmed to transmit energy into the ground from an antenna element adjacent to the rail, and capture the response with an antenna element on the other side of the rail, enabling all data to be collected along the track width.
Different scan patterns are shown in the figure to the left: Top) standard scan pattern; Center) common mid point (CMP); Bottom) custom pattern. Standard scan patterns provide full coverage of the subsurface. CMP enables accurate depth calculations without requiring excavation. The custom scan pattern on the bottom of the figure facilitates the “look under rail” capability of the GPR.
Survey speeds vary depending on the specific objectives of the railway survey and also the amount of track time available. The shorter the distance between scans, the slower the system needs to travel in order to guarantee full coverage. That being said, a 2.4 meter wide antenna attached to a GeoScope Mk IV provides an effective coverage area of 2.1meters, or 82.5in. With 21 of 29 antenna elements active, the maximum speed with sampling every 2.5cm is 54kph/33mph. Doubling the distance between samples to 5cm also doubles speeds to 108kph/67mph while sacrificing only a small amount of data quality.
Once collected, this data can be quickly analyzed in the field using 3dr-Examiner, 3d-Radar’s processing and display software suite. This enables visual assessments to be done on the spot and in high-definition while the equipment and high-rail vehicle is in the area or stored, ready for export into tools like Railway Doctor for further analysis, interrogation and reporting.
- Track width coverage and beyond in a single pass – 100% coverage and analysis provides greater confidence in the survey
- High detail and high speed surveys – Less time in the field while collecting more data and minimizing track closures
- Deeper depths without compromise in resolution – Near surface and with deeper coverage data collection provides the entire picture in a single pass
- Interleaved Common Midpoint(CMP) scan pattern – Accurately calculate depths and layer thicknesses
- Different width antennas are available – Narrower antennas can be used in tight areas such as nearby 3rd rails
- Fully customizable scan patterns – Provides “look under rail” capability
- Advanced data processing and visualization software – Quickly look through captured data with full access to 3d GPR data
- Full export capabilities to Railway Doctor from RoadScanners and other packages -Enables 3rd party railway specific analysis and reporting software to be utilized for ballast assessment, ballast depths, moisture intrusions and more