Non-destructive tests for railway evaluation: detection of fouling and joint interpretation of GPR data and track geometric parameters
Mercedes Solla and Simona Fontul
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Abstract: This paper deals with railway assessment by using Ground Penetrating Radar, eventually combined with Falling Weight Deflectometer and Light Falling Weight Deflectometer. All measurements were performed during a Short-Term Scientific Mission (STSM) funded by the COST (European Cooperation in Science and Technology) Action TU1208 “Civil engineering applications of Ground Penetrating Radar.” In particular, the tasks addressed were: 1. Detection of track defects at infrastructure level (voids and cracking); 2. Measurement of layer thickness; and, 3. Evaluation of the fouling level of ballast.
Keywords: Ground Penetrating Radar (GPR); railways; detection of track defects; measurement of layer thickness; fouling evaluation; Falling Weight Deflectometer (FWD).
A Short-Term Scientific-Mission (STMS) entitled “Non-destructive tests for railway evaluation: detection of fouling and joint interpretation of GPR data and track geometric parameters” was funded in 2015 by COST (European Cooperation in Science and Technology), in the framework of the COST Action TU1208 “Civil engineering applications of Ground Penetrating Radar” activities. Mercedes Solla visited Simona Fontul in Lisbon, Portugal, from June 1st to June 30th, 2017, and they jointly carried out a series of experiments concerned with the non-destructive assessment of railways. The objective of this paper is to present the results obtained during the STSM.
Railways, as all infrastructures, have to behave properly during their life cycle. A regular maintenance policy has to be established, to guarantee high safety standards . At the same time, costs and traffic interruptions have to be limited. Nowadays, track monitoring mainly consists in measuring parameters related to the track layout and rail wearing. During maintenance operations, some track components are replaced while others can remain the same, such as the substructure [2, 3]. The customary monitoring procedure does not detect the real causes of rail deficiency, which may be due to the presence of ballast pockets, fouled ballast, poor drainage, subgrade settlements or transitions problems [4-6]. A more thorough analysis of the conditions of both the railway platform and substructure is crucial to reduce maintenance costs and increase operational safety levels.
Non-destructive testing techniques can be effectively employed for railway assessment. The main purpose of the STSM was to study how Ground Penetrating Radar (GPR) can be used to inspect the infra- and super-structure of railways. In particular, the tasks addressed were: 1. Detection of track defects at infrastructure level (voids and cracking); 2. Measurement of layer thickness; and, 3. Evaluation of the fouling level of ballast.
Two different GPR systems were used and compared, in terms of their capability to detect defects in the subgrade (at platform level) and estimate the dielectric permittivity of concrete asphalt for sub-ballast. In particular, the available equipment included: a ground-coupled GPR manufactured by MALÅ (brought to Lisbon from the University of Vigo, Spain) and an air-coupled system manufactured by GSSI (available at the National Laboratory For Civil Engineering, in Lisbon). The MALÅ system was a ProEx control unit equipped with 1-GHz and 2.3-GHz antennas. The GSSI system was a SIR-20 control unit equipped with 1-GHz and 1.8-GHz antennas. The accuracy of different inspection procedures was evaluated, to determine the best way to proceed for assessing railways with GPR.
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Unrestricted use, distribution, and reproduction in any medium of this article is permitted, provided the original article is properly cited. Please cite this article as follows: M. Solla and S. Fontul, "Non-destructive tests for railway evaluation: detection of fouling and joint interpretation of GPR data and track geometric parameters," Ground Penetrating Radar, Volume 1, No. 1, Article ID GPR-1-1-4, pp. 75-103, January 2018, doi: 10.26376/GPR2018004.
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