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Linear transport infrastructures, as bridges and viaducts, are exposed to natural hazards or endogenous events, which can affect their operation and structural integrity. Recent unpredicted bridge failures and collapses highlight the need for effective structural monitoring operations, especially for aged concrete structures. Non-Destructive Testing (NDT) methods, such as Ground Penetrating Radar (GPR) and Mobile Laser Scanner (MLS), have been used for the assessing and monitoring of such structures in recent years. Our paper reports on the outcomes of the integrated monitoring method based on the use of GPR and MLS technologies for the structural assessment of bridges and the prevention of damages induced by structural subsidence. The analyses we made aim to assess the structural integrity of the Olivieri Viaduct, located in Salerno, Italy. Designed for this, a GPR inspection was made using multifrequency GPR systems equipped with both ground-coupled and air-launched antennas. In addition, MLS surveys were carried out to analyze and quantify pavement surface irregularities. The surface and structural condition of the pavement as measured by MLS has been integrated with GPR outcomes to identify and classify potential damage sources likely responsible for layer deterioration and surface decay. This study confirms that an integrated nondestructive monitoring approach based on GPR and MLS technologies can be successfully implemented to assess the health-condition of critical assets, clearing the way for integrated approaches in continuous monitoring of transport infrastructure.

Airport apron relates to an airfield area dedicated to the parking, loading/unloading, refueling and boarding of aircrafts. The standard conventional pavement solution in apron areas is a concrete rigid pavement with jointed concrete slabs, which is due to two main reasons. First, use of concrete technology helps to prevent the potential viscous behaviour of the hot-mixed asphalt solution. This is caused by long-term and permanent loads, especially at high temperatures. Secondly, use of concrete blocks avoids the decay of the wearing course due to the contact with fuel. The project of such rigid pavements is a complex process taking into account several factors, spanning from the critical aircrafts that is expected to park in the stand to the subgrade bearing strength. However, issues occurring during the construction phase or overloading of the pavement are likely to reduce the service life with respect to the design expectations. This work presents outcomes from a still on-going non-destructive monitoring activity carried out from 2008 over three park stands located in APRON 800 in Fiumicino Airport of Rome, Italy. In particular, the three stands were subjected over the years to different loadings that produced various rate of damage of the concrete slabs. The area was surveyed, at different time intervals, by visual inspection of the cracking (i.e. calculation of the Pavement Condition Index), Heavy Weight Deflectometer (HWD) testing and Ground Penetrating Radar. By comparing the outcomes from NDTs with the visual evolution of the damages over the area, it was possible to stress out the evolution pattern of the decays and to determine a reliable domain of service life by means of damaging versus time prediction curves.

Railways are important assets requiring continuous and effective monitoring. Within this context, non-destructive testing (NDT) methods are gaining momentum including, amongst others, the ground-penetrating radar (GPR) technique. GPR has proven its viability at providing effective condition-based assessment of railway ballast and identifying several different sources of decay. In this paper, the main challenges related to the data collection and processing stages for railway ballast investigations are reported. In addition, a review of main survey protocols and data processing strategies, including state-of-the-art research in this area of endeavor is presented, in terms of the issues related to the configuration of the track-bed structure (i.e., the effects of rails and sleepers on the signal) and the main inspection targets (i.e., ballast fouling, water content and segregation of the aggregates).

This study reviews research developments in non-destructive assessment of linear transport infrastructures. The main focus will be on the integration between satellite remote sensing and ground-based techniques. Specifically, the potential of using interferometric synthetic aperture radar (InSAR) and high-frequency ground penetrating radar (GPR) techniques as self-standing and integrated survey methodologies will be discussed. To this effect, an overview on data fusion techniques will be given. The last section of the paper reports recent results achieved by using both GPR systems and the permanent scatterers InSAR technique on a real-life railway.

This work proposes an experimental-based model for the assessment of the stiffness of a road flexible pavement using ground-penetrating radar (GPR – 2 GHz horn antenna) and light falling weight deflectometer (LFWD) non-destructive testing (NDT) methods. It is known that the identification of early decay and loss of bearing capacity is a major challenge for effective maintenance of roads and the implementation of pavement management systems (PMSs). To this effect, a time-efficient methodology based on quantitative and qualitative modelling of road stiffness is developed. The viability of using a GPR system in combination with LFWD equipment is also proven.

Ground-penetrating radar (GPR) was firstly used in traffic infrastructure surveys during the first half of the Seventies for testing in tunnel applications. From that time onwards, such non-destructive testing (NDT) technique has found exactly in the field of road engineering one of the application areas of major interest for its capability in performing accurate continuous profiles of pavement layers and detecting major causes of structural failure at traffic speed. This work provides an overview on the main signal processing techniques employed in road engineering, and theoretical insights and instructions on the proper use of the processing in relation to the quality of the data acquired and the purposes of the surveys. GPR is an increasingly used NDT technique in pavement applicationsProper choice of the signal processing techniques according to the GPR data sourceOverview of signal processing techniques to use prior to any post-processing stepOverview of signal processing techniques to perform after the GPR data collection

Ground Penetrating Radar (GPR) has proved to provide a high reliability in detecting several subsurface features such as water and gas pipes, energy and telecommunication supplies, water reservoirs or air voids. The present work uses a comparison between different central frequencies of investigation to reconstruct the network of utilities located underneath a paved surface and to understand the best strategy of analysis to undertake. To this purpose, a 757 m2 paved carpark situated in London was used as test site and divided into three smaller areas. Central frequencies of investigation of 250 MHz, 400 MHz, 500 MHz, 1000 MHz, 2000 MHz, and 4000 MHz were selectively employed over these areas, and the outcomes from the 250 MHz, 500 MHz, and 1000 MHz are here analyzed. The analysis of the data has detected the presence of several utility lines with placements different from those represented within the design charts. Useful insights about the performances of different central frequencies of investigation are here discussed, as well as the usefulness of GPR in validating information collected by visual inspections and available from cartographic maps. Ground Penetrating Radar (GPR) has proved to provide a high reliability in detecting several subsurface features such as water and gas pipes, energy and telecommunication supplies, water reservoirs or air voids. The present work uses a comparison between different central frequencies of investigation to reconstruct the network of utilities located underneath a paved surface and to understand the best strategy of analysis to undertake. To this purpose, a 757 m2 paved carpark situated in London was used as test site and divided into three smaller areas. Central frequencies of investigation of 250 MHz, 400 MHz, 500 MHz, 1000 MHz, 2000 MHz, and 4000 MHz were selectively employed over these areas, and the outcomes from the 250 MHz, 500 MHz, and 1000 MHz are here analyzed. The analysis of the data has detected the presence of several utility lines with placements different from those represented within the design charts. Useful insights about the performances of different central frequencies of investigation are here discussed, as well as the usefulness of GPR in validating information collected by visual inspections and available from cartographic maps.

In this work a numerical model capable to predict the electromagnetic response of railway ballast aggregates under different physical conditions has been calibrated and validated by a simulation-based approach. The ballast model is based on the main physical and geometrical properties of its constituent material and it is generated by means of a random-sequential absorption (RSA) approach. A finite-difference time-domain (FDTD) simulator is then employed to calculate the ground-penetrating radar (GPR) signal response to the scenario. The calibration of the model has been performed by taking into account the main physical properties and the grain size characteristics of both the reference ballast material and a fine-grained pollutant material, namely, an A4 soil type material, according to the AASHTO soil classification. The synthetic GPR response has been generated by using the gprMax freeware simulator. Several scenarios have been considered, which in turn were reproduced in laboratory environment and used for the validation of the model. Promising results have demonstrated the high potential of such approach in characterizing the simulated response of complex coarse-grained heterogeneous materials.