Characterizing Railroad Ballast Using GPR: Recent Experiences in the United States

Recent work has been conducted in the United States with 2 GHz horn antennas to characterize railroad ballast. There were a number observations made during the course of the project that derive from gaining a more thorough understanding of ballast and the interaction of GPR with the ballast matrix. The major observations from over 238 km of track data at four different geographical locations include: (1) it cannot be assumed that there will be a reflection from the bottom of clean ballast or that there will be a reflection from the ballast-subballast interface; (2) the presence of a strong reflection in the data generally, but not always, infers moderately-fouled to clean ballast above the reflecting boundary; and (3) no observable ballast-subballast interface reflections are generally, but not always, associated with gradational fouling or a fully-fouled ballast section.