Railroad ballast plays an important role in supporting heavy rail loading, preventing the
deformation of track, and providing drainage of water from the track structure. However,
over time, ballast is fouled by the breakdown of ballast aggregate and=or the infiltration
of fines, which undermine ballast functions. This may result in damage to the rail system,
such as track settlement. Ground penetrating radar (GPR), a nondestructive method, can
be used to rapidly, effectively, and continuously assess railroad track substructure conditions.
Ballast under various fouling conditions generates various electromagnetic (EM)
scattering patterns. In this study, air-coupled 2GHz antenna was found to be sensitive to
the scattering pattern change. Appropriate data processing was used to remove the effects
of ties and rails to obtain clear GPR images of the subsurface layers. Then, the amplitude
envelope and time-frequency approaches were implemented to characterize the signal in
time and frequency domains simultaneously. Using these techniques, non-fouled ballast
thickness can be assessed and trapped water can be detected, along the track.
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