GPR Laboratory Tests For Railways Materials Dielectric Properties Assessment

Francesca De Chiara,Eduardo Fortunato,Simona Fontul

doi:10.3390/rs6109712

Francesca De Chiara, Eduardo Fortunato + Show 1 more

Open Access

https://doi.org/10.3390/rs6109712

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Abstract

In railways Ground Penetrating Radar (GPR) studies, the evaluation of materials dielectric properties is critical as they are sensitive to water content, to petrographic type of aggregates and to fouling condition of the ballast. Under the load traffic, maintenance actions and climatic effects, ballast condition change due to aggregate breakdown and to subgrade soils pumping, mainly on existing lines with no sub ballast layer. The main purpose of this study was to validate, under controlled conditions, the dielectric values of materials used in Portuguese railways, in order to improve the GPR interpretation using commercial software and consequently the management maintenance planning. Different materials were tested and a broad range of in situ conditions were simulated in laboratory, in physical models. GPR tests were performed with five antennas with frequencies between 400 and 1800 MHz. The variation of the dielectric properties was measured, and the range of values that can be obtained for different material condition was defined. Additionally, in situ GPR measurements and test pits were performed for validation of the dielectric constant of clean ballast. The results obtained are analyzed and the main conclusions are presented herein.

Highlights

In the last decades, railways have been subjected to a fast development in terms of traffic speeds and axle loads
Engineering (LNEC) is ongoing aiming at improving the data interpretation process and the calibration of the default values, generally used for Ground Penetrating Radar (GPR) interpretation in commercial software, to realistic values of materials used in Portuguese railways, in different in situ condition
For GPR railways studies, the knowledge of dielectric constant represents a crucial aspect for obtaining good results in terms of ballast thickness and high quality surveys

Summary

Introduction

Railways have been subjected to a fast development in terms of traffic speeds and axle loads. Monitoring actions are usually performed by using track inspection vehicles [2,3] They enable the evaluation of track condition and the detection of geometric defects, which are corrected later on, if needed. They present the main advantages of inducing the similar dynamic loads as regular trains, measuring at the traffic speed and of performing the track assessment in a continuous way, without traffic interdictions. In Portugal, railway monitoring is performed by using Plasser and Theurer EM-120 track inspection This equipment is able to assess track performance by detecting geometric defects, among other parameters, but does not enable the identification of their causes. The aim was to determine their dielectric properties and their sensitivity to water content and fouling level

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Conclusion