<title>Ground-penetrating radar evaluation of railway track substructure conditions</title>

Abstract

railroad track substructure condition on a continuous top-ofrail nondestructive basis. In this study, 1 GHz radar data were acquired between concrete and wood ties as well as from the ballast shoulders beyond the ends of the ties, and with multiple antenna orientations and polarizations. Automatic processing of the data was developed to quickly generate hard copy sections of radar images and for input into railroad track performance monitoring software such as ORIM. Substructure conditions were observed such as thickness of the ballast and sub ballast layers, variations in layer thickness along the track, pockets of water trapped in the ballast, and soft subgrade from high water content. In addition, locations and depths of subsurface drainage pipes, trenches, and utilities were quickly and continuously mapped. GPR data were acquired and processed from a hirail vehicle moving continuously at 10 miles per hour with radar resolution of a few inches horizontally and a fraction of an inch vertically to depths of more than six feet. The largest errors resulted from the positioning system used to locate the antennas along and across the track. Automatic modeling to determine density and water content is being developed but the uneven and rough (at radar wavelengths) air-ballast interface is a major problem in modeling the data.