A comparative investigation of the effects of concrete sleepers on the GPR signal for the assessment of railway ballast

This paper reports an investigation into the influence of concrete railway sleepers on the ground-penetrating radar (GPR) signal for the assessment of railway ballast. The main aim was to comprehend the effects of these components on the GPR signal compared to the signal response collected on ballast (clean and fouled conditions) without sleepers. To this purpose, a methacrylate container with dimensions of 1.5 m × 1.5 m × 0.50 m was filled up with limestone railway ballast aggregates. Hence, two concrete sleepers of standard dimensions were laid above the material. GPR tests were carried out using 4 different air-coupled antenna systems with frequencies of 1000 MHz, 1500 MHz and 2000 MHz (in both the standard and low-powered version). Each antenna system was oriented in two different ways, i.e. longitudinally and transversely with respect to the orientation of the tracks. Data interpretation was made by way of comparison between the time-domain and spectral signal responses of the configuration with “ballast material only” and the configuration with “ballast material and sleepers” (longitudinal/transversal orientation of the antenna systems, one/two concrete sleepers and clean/fouled ballast). Results have proven distinctive features of the GPR signal in terms of antenna frequency and orientation, paving the way to enhanced data interpretation in both clean and fouled ballast conditions.