Advances in the nondestructive condition assessment of railway ballast: A focus on GPR

This paper addresses the use of nondestructive Ground Penetrating Radar (GPR) methodology in the investigation of railway ballast under a diverse set of fouling and moisture conditions through comprehensive laboratory experiments and field track surveys. Granite ballast and three fouling agents; sand, gravel, and the mixture of these two materials were used in the laboratory tests. Numerous estimation methods were employed to attain the Relative Dielectric Permittivity (RDP) of the ballast using 2 GHz air-coupled antenna for the laboratory tests. Experimentally obtained RDP values were verified by the theory-based mixing model. Field track GPR surveys using miscellaneous frequencies (400, 900, and 2000 MHz) were undertaken, where the same type of granite ballast used in the laboratory tests, were laid along a track section composed of metal, wooden and concrete sleepers. Using the laboratory-measured RDP values, the data from field track surveys and ground-truth data were in good agreement. The results of this paper confirm the efficiency and the eligibility of the GPR technique in condition assessment of railway granite ballast using various frequencies and orientations of antennas.