Using Time Domain Reflectometry to Determine Depth of Fouling and Fouling Type in Railway Track Substructure

This study documents the development of a procedure for the identification of the depth and type of ballast fouling using the time domain reflectometry (TDR) technique. Ballast fouling leads to a reduction in the bearing capacity of the railway substructure, a decrease in the drainage capacity, and an increase in track deformation. As a consequence of these detrimental effects, rail tracks lose load capacity, ride comfort deteriorates, and trains may ultimately derail. The determination of type and extent of ballast fouling may be used to assess the expected life of rail track and to plan maintenance operations. TDR waveforms of variably fouled ballast and subballast layers were evaluated in the lab to yield relative dielectric permittivity and electrical conductivity and to thus characterize the effect of ballast gradation, mineralogy, and water content on electromagnetic response. Strong relationships between depth of fouling, volumetric water content, and relative dielectric permittivity were developed. These results were then expanded to the interpretation of ground penetrating radar (GPR) inspection and to quantify the level of fouling in larger-scale maintenance operations. The proposed technique can be complementary to GPR as it reduces the uncertainty in determining the depth and type of fouling when using GPR alone.