Ground Penetrating Radar (GPR) is a non-destructive inspection method used since the 1970s for the inspection of roadways, concrete structures and bedrock among a dozen other applications. However, its application in the railway industry remains fairly uncommon.

Conventional track inspection methods require the inspector to perform destructive testing of the sub-surface to properly investigate and understand the condition of the track-bed. Additionally, the bulk of the analysis is completed on site, which limits the speed of the inspection and increases the number of spot excavations required.

In contrast, a properly calibrated GPR system can inspect at speeds of up to and above 70 km/h. This represents a considerable advantage for segments of track with limited inspection window availability. Changes in media, voids, cracks, and various materials are detected using electromagnetic waves and their dielectric properties. When used effectively, it can detect the conditions of the track sub-structure, including the ballast and sub-ballast thicknesses, uneven settlement, perched water tables, sinkholes, and other irregularities. All this at speeds unmatched by conventional inspections.

CANARAIL has developed a distinct railway inspection expertise through previous projects by implementing new methods of integrated visual and GPR inspections.

The righthand picture shows that three coupled antennas are used to inspect the railway's sub-surface conditions. Below is an illustration of the analysis produced by the GPR system.