Railway ballast condition assessment using ground-penetrating radar – An experimental, numerical simulation and modelling development

Abstract

This paper reports on the GPR-based assessment of railway ballast which was progressively "polluted" with a fine-grained silty soil material. It is known how the proper operation of a ballast track bed may be undermined by the presence of fine-grained material which can fill progressively the voids between the ballast aggregates and affect the original strength mechanisms. This occurrence is typically defined as "fouling". To this effect, a square-based methacrylate tank was filled with ballast aggregates in the laboratory environment and then silty soil (pollutant) was added in different quantities. In order to simulate a real-life scenario within the context of railway structures, a total of four different ballast/pollutant mixes were introduced from 100% ballast (clean) to highly-fouled (24 %). Ground-penetrating radar (GPR) systems equipped with different air-coupled antennas and central frequencies of 1000 MHz and 2000 MHz were used for testing purposes. Several processing methods were applied in order to obtain the dielectric permittivity of the ballast system under investigation. The results were validated using the "volumetric mixing approach" (available within the literature) as well as by performing a numerical simulation on the physical models used in the laboratory. It is important to emphasize the significance of the random-sequential absorption (RSA) paradigm coupled with the finite-difference time-domain (FDTD) technique used during the data processing. This was proved to be crucial and effective for the simulation of the GPR signal as well as in generating synthetic GPR responses close to the experimental data.

Railway Track Condition Assessment at Network Level by Frequency Domain Analysis of GPR Data

“…Some experimental studies have analysed the influence of different fouling levels in the electromagnetic waves. In [35], four different levels were simulated (from 0% to 76% fouling) and two different air-coupled antennas were used with frequencies of 1 GHz and 2 GHz. Regarding the assessment of the moisture content in the ballast, this parameter was easily evaluated by GPR as the dielectric value of the ballast increases with the presence of water [36].…”

“…The first step was to establish a range, in the time and frequency domains, that corresponds to segments of each acquired trace of the GPR signals that are considered to better reflect the changes in the track condition at subsurface layers level [15,35,40,63].…”

A Computer‐Aided Model for the Simulation of Railway Ballast by Random Sequential Adsorption Process

“…Hence, a simulation domain with dimensions complying with the above real‐life conditions is realized. This proves to be effective for model validation purposes (comparison between simulated and measured scenarios) (Benedetto et al., ; Benedetto et al., ), as will be discussed in Section . Nevertheless, if higher resolutions are required for the simulation of the real object (e.g., fine or microscale investigations), it is worth noting that the size and the shape of the elementary components must be reproduced consistently.…”

“…The above two approaches have shown some limitations that are discussed in Benedetto et al. (). In more detail, one of the restrictions of the “clump logic” approach is that the model ignores the internal contacts between the overlapping spheres (Ferellec and McDowell, ; Indraratna et al., ).…”

Suppression of Ground Borne Vibration Induced by High-Speed Lines

“…Benedetto et al [12] investigated the response of a rubber mixed ballast which would have low stiffness and the results should increase in vibration in low frequency bands of 10 -30 Hz. Zhang et al [13] found that the increase in thickness, decreases particle velocity.…”