Evalution of Railway Track Substructure using Ground Penetrating Radar Coupled with Time Domain Reflectometry

Ballast fouling in railway substructure leads to a reduction in bearing capacity, a decrease in the drainage capacity, and an increase in track deformation. As a consequence of these detrimental effects, riding comfort, speed, and capacity are reduced and, if the problem is not addressed, track misalignment may lead to derailment. This problem is costly; thus, optimizing the maintenance operation is required to reduce the overall cost of freight and passenger transportation. This study presents a methodology to identify depth of fouling and fouling type in railway track substructure using Ground Penetrating Radar (GPR) coupled with Time Domain Reflectometry (TDR). This investigation was conducted on a mainline track section that has been underperforming with continuing maintenance operations. TDR measurements were conducted to determine the relative dielectric permittivity to thus calibrate and interpret the results obtained by 200-MHz-GPR profiles. Ballast specimens were obtained and tested in addition to Dynamic Cone Penetration (DCP) testing in the field to validate the geophysical results. Results show that TDR applications can be beneficial to the interpretation of GPR profiles and to quantify the level of fouling in larger scale maintenance operations.