Georadar: le proprietà meccaniche della sovrastruttura stradale

L’ indagine preventiva delle caratteristiche prestazionali di una pavimentazione stradale risulta di prioritaria importanza nella corretta implementazione di un efficace sistema di manutenzione programmata delle strade o Pavement Management System (PMS), in quanto la determinazione della soluzione manutentiva più idonea può consentire un notevole contenimento dei costi di intervento, specialmente ove questi siano legati ad operazioni di ripristino e riabilitazione delle condizioni strutturali di origine

"Test-site operations for the health monitoring of railway ballast using Ground-Penetrating Radar"

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An overview of ground-penetrating radar signal processing techniques for road inspections

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

Road foundation detailing using ground penetrating radar systems with different frequencies

This paper reports on the assessment of the underground construction details of a road pavement using different frequency ground penetrating radar (GPR) antenna systems. In addition to this, the possible presence and location of an underground watercourse was investigated in this work. The existence of the latter problem was perceived due to reoccurrence of longitudinal and traversal road surface cracking as well as subsidence at a particular location of the road. Reoccurrence of this damage was interpreted and related to the possible existence of an underground watercourse. The original design and the construction of the road were as such to prevent this movement. Therefore it seemed necessary to perform a GPR survey to investigate and confirm the underground construction details of the road. To this purpose, the identified area was surveyed using high to low frequency antennas with 2000 MHz, 900 MHz, 600 MHz and 200 MHz central frequencies of investigation. The results were conclusive in terms of construction details provided and evidence of subsidence within the road identified. The maximum depth of penetration achieved by the use of the 600 MHz and the 200 MHz antennas (maximum of 3 m) did not allow to identify or confirm the existence of any underground watercourse

Signal processing of GPR data for road surveys

Effective quality assurance and quality control inspections of new roads as well as assessment of remaining service-life of existing assets is taking priority nowadays. Within this context, use of ground penetrating radar (GPR) is well-established in the field, although standards for a correct management of datasets collected on roads are still missing. This paper reports a signal processing method for data acquired on flexible pavements using GPR. To demonstrate the viability of the method, a dataset collected on a real-life flexible pavement was used for processing purposes. An overview of the use of non-destructive testing (NDT) methods in the field, including GPR, is first given. A multi-stage method is then presented including: (i) raw signal correction; (ii) removal of lower frequency harmonics; (iii) removal of antenna ringing; (iv) signal gain; and (v) band-pass filtering. Use of special processing steps such as vertical resolution enhancement, migration and time-to-depth conversion are finally discussed. Key considerations about the effects of each step are given by way of comparison between processed and unprocessed radargrams. Results have proven the viability of the proposed method and provided recommendations on use of specific processing stages depending on survey requirements and quality of the raw dataset

GPR applications across Engineering and Geosciences disciplines in Italy: a review

In this paper, a review of the main ground-penetrating radar (GPR) applications, technologies, and methodologies used in Italy is given. The discussion has been organized in accordance with the field of application, and the use of this technology has been contextualized with cultural and territorial peculiarities, as well as with social, economic, and infrastructure requirements, which make the Italian territory a comprehensive large-scale study case to analyze. First, an overview on the use of GPR worldwide compared to its usage in Italy over the history is provided. Subsequently, the state of the art about the main GPR activities in Italy is deepened and divided according to the field of application. Notwithstanding a slight delay in delivering recognized literature studies with respect to other forefront countries, it has been shown how the Italian contribution is now aligned with the highest world standards of research and innovation in the field of GPR. Finally, possible research perspectives on the usage of GPR in Italy are briefly discussed

GPR data collection and processing strategies for railway ballast evaluation

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)

Recent advances in mapping tree roots using ground penetrating radar

Environmental issues and preservation of natural heritage, especially ancient trees and rare plants, are becoming priority objectives to achieve. Unknown pathogens carried along by the wind can lead to epidemic phenomena and often to a quick death of entire forests. To this effect, active and passive methods can be used to reduce the risk of premature death of trees. Passive methods rely on the application of policies for the control and the management of the forestall heritage. These are based on the monitoring of living trees and are aimed at identifying the early-stage symptoms of the disease. Within this context, use of destructive testing methods is increasingly discouraged, and non-destructive testing (NDT) methods are emerging as the only viable solution for a non-intrusive assessment of the disease. The ground penetrating radar (GPR) non-destructive testing method has proved to be one of the most powerful NDT methods, due to a high versatility, rapidity in data collection and the provision of reliable results at relatively limited costs. Applications of GPR in forestry science are related – but not limited to - the effective tree trunk assessment and appraisals, tree roots mapping, soil interaction with tree and plants. This study reports a demonstration of the GPR effectiveness in tracking tree roots. The main objective of the research was to provide an effective and high-resolution mapping of the tree roots. To this purpose, the soils around a fir tree and an oak tree were investigated using a ground-coupled multi-frequency GPR system equipped with 600 MHz and 1600 MHz central frequency antennas. A dedicated data processing algorithm was firstly developed to filter out the data from noise-related information and to highlight deep reflections from attenuated targets. At a later stage, a multi-step algorithm pinpointing the identified targets (i.e., the vertex of the reflection hyperbolas) in a three-dimensional environment was created. Results have proven the viability of GPR in mapping tree roots for different species of trees. The proposed algorithm has allowed to successfully identify both shallow (i.e., within the first 25 cm from the soil surface) and deep (i.e., underneath 25 cm of depth) tree root systems

GPR applications in mapping the subsurface root system of street trees with road safety-critical implications

Street trees are an essential element of urban life. They contribute to the social, economic and environmental development of the community and they form an integral landscaping, cultural and functional element of the infrastructure asset. However, the increasing urbanisation and the lack of resources and methodologies for the sustainable management of road infrastructures are leading to an uncontrolled growth of roots. This occurrence can cause substantial and progressive pavement damage such as cracking and uplifting of pavement surfaces and kerbing, thereby creating potential hazards for drivers, cyclists and pedestrians. In addition, neglecting the decay of the principal roots may cause a tree to fall down with dramatic consequences. Within this context, the use of the ground-penetrating radar (GPR) non-destructive testing (NDT) method ensures a non-intrusive and cost-effective (low acquisition time and use of operators) assessment and monitoring of the subsurface anomalies and decays with minimum disturbance to traffic. This allows to plan strategic maintenance or repairing actions in order to prevent further worsening and, hence, road safety issues. This study reports a demonstration of the GPR potential in mapping the subsurface roots of street trees. To this purpose, the soil around a 70-year-old fir tree was investigated. A ground-coupled GPR system with central frequency antennas of 600 MHz and 1600 MHz was used for testing purposes. A pilot data processing methodology based on the conversion of the collected GPR data (600 MHz central frequency) from Cartesian to polar coordinates and the cross-match of information from several data visualisation modes have proven to identify effectively the three-dimensional path of tree roots

Efficient practices in railway ballast maintenance and quality assessment using GPR

The need for effective and efficient railway maintenance is always more demanded all over the world as the main consequence of aging and degradation of infrastructures. Primarily, the filling of air voids within a railway ballast track-bed by fine-grained materials, coming up from the subballast layers by vibrations and capillarity effects, can heavily affect both the bearing and the draining capacity of the infrastructure with major impacts on safety. This occurrence is typically referred to as “fouling”. When ballast is fouled, especially by clay, its internal friction angle is undermined, with serious lowering of the strength properties and increase of deformation rates of the whole rail track-bed. Thereby, a detailed and up-to-date knowledge of the quality of the railway substructure is mandatory for scheduling proper maintenance, with the final goal of optimizing the productivity while keeping the safety at the highest standard. This paper aims at reviewing a set of maintenance methodologies, spanning from the traditional and most employed ones, up to the most innovative approaches available in the market, with a special focus on the Ground Penetrating Radar (GPR) non-destructive testing (NDT) technique. The breakthrough brought by the application of new processing approaches is also analyzed and a methodological framework is given on some of the most recent and effective maintenance practices