Assessment of Railway Track Substructure Condition using Ground Penetrating Radar’, AREMA

Ground penetrating radar (GPR) has been employed to assess railway track substructure (ballast, subballast, and subgrade) conditions. GPR involves transmitting radar pulses into the substructure and measuring return signals that have reflected off boundaries between substructure layers with different electromagnetic properties. The principle electromagnetic property of the layers is the dielectric permittivity, which is a function of the density, water content, and type of material. For railroad applications, the GPR equipment is mounted on a hy-rail vehicle with clearance between the antennas and the track surface, which permits continuous measurements to be made from above the top-of-rail at normal vehicle speeds. The antenna configuration and surveying procedures are optimized to account for the influence of ties and rail. Antennas are located at both ends of the ties as well as in the center of the track, so the variations of conditions laterally across the track are seen. Studies have demonstrated the ability of GPR to distinguish between the different substructure layers as well as areas of trapped water and fouled ballast. Images from fiel