Showing papers by "Fabio Tosti published in 2018"

An investigation into the railway ballast dielectric properties using different GPR antennas and frequency systems

Abstract: This paper presents an investigation into the relative dielectric permittivity of railway ballast using ground-penetrating radar (GPR). To this effect, the experimental tests are carried out using a container (methacrylate material) of dimensions 1.5 × 1.5 × 0.5 m. GPR systems equipped with different ground-coupled and air-coupled antennas and central frequencies of 600 MH, 1000 MHz, 1600 MHz and 2000 MHz (standard and low-powered antenna systems) are used for testing purposes. Several processing methods are applied to assess and compare the dielectric permittivity of the ballast system under investigation. A comparison of the results identifies critical factors as well as antennas and central frequencies most suitable for the purpose.

A comparative investigation of the effects of concrete sleepers on the GPR signal for the assessment of railway ballast

Abstract: This paper reports an investigation into the influence of concrete railway sleepers on the ground-penetrating radar (GPR) signal for the assessment of railway ballast. The main aim was to comprehend the effects of these components on the GPR signal compared to the signal response collected on ballast (clean and fouled conditions) without sleepers. To this purpose, a methacrylate container with dimensions of 1.5 m × 1.5 m × 0.50 m was filled up with limestone railway ballast aggregates. Hence, two concrete sleepers of standard dimensions were laid above the material. GPR tests were carried out using 4 different air-coupled antenna systems with frequencies of 1000 MHz, 1500 MHz and 2000 MHz (in both the standard and low-powered version). Each antenna system was oriented in two different ways, i.e. longitudinally and transversely with respect to the orientation of the tracks. Data interpretation was made by way of comparison between the time-domain and spectral signal responses of the configuration with “ballast material only” and the configuration with “ballast material and sleepers” (longitudinal/transversal orientation of the antenna systems, one/two concrete sleepers and clean/fouled ballast). Results have proven distinctive features of the GPR signal in terms of antenna frequency and orientation, paving the way to enhanced data interpretation in both clean and fouled ballast conditions.

Mapping the root system of matured trees using ground penetrating radar

Abstract: This study reports a demonstration of the ground penetrating radar (GPR) potential in health monitoring of tree roots. The main aim of the research was to provide effective and high-resolution mapping of tree root systems. To this purpose, a dedicated data processing methodology, based on two main chronological stages, was developed. First, an algorithm was proposed to filter out the data from noise-related information and to enhance deep reflections from attenuated targets. At a later stage, a multi-step algorithm connecting the identified targets (i.e. the vertices of the reflection hyperbolas) in a three-dimensional environment was created. To demonstrate the viability of the proposed methodology, the soils around two different tree species (i.e. fir and oak trees) were investigated using a ground-coupled multi-frequency GPR system equipped with 600 MHz and 1600 MHz central frequency antennas. The method has allowed to identify distinctive features in terms of shallow (i.e. within the first 25 em from the soil surface) and deep (i.e. lower than 25 cm from the soil surface) tree root systems for different species of trees.

A computer-aided model for the simulation of railway ballast by random sequential adsorption process

Abstract: This paper presents a computer-aided multi-stage methodology for the simulation of railway ballasts using the Random Sequential Adsorption (RSA – 2D domain) paradigm. The primary stage in this endeavour is the numerical generation of a synthetic sample by a "particle sizing and positioning" process followed by a "compaction" process. The synthetic samples of ballast are then visualised in the Computer-Aided Design (CAD) environment. The outcomes of the simulation are analysed by comparison with the results of an experimental investigation carried out using a methacrylate container in which real samples of railway ballast are formed. A test of model reliability is carried out between the aggregates number and the grading curves of the synthetic sample and the real one. A validation is therefore performed using the ground-penetrating radar (GPR) non-destructive testing (NDT) method and the finite-difference time-domain (FDTD) simulation developed in a computer-aided environment. The results prove the viability and the applicability of the proposed modelling for the assessment of railway ballast conditions.

Use of Ground Penetrating Radar for Assessing Interconnections between Root Systems of Different Matured Tree Species

Abstract: This study presents recent advances achieved in the use of ground penetrating radar (GPR) for the assessment of tree root systems. The primary objectives of the study were to provide a valid and high-resolution mapping of the root systems belonging to different species of matured trees, as well as to investigate areas of roots interconnection. To this effect, a data processing methodology based on three main stages was developed. A pre-processing algorithm was first proposed to remove noise-related information from the raw data and to improve deep reflections from attenuated targets. Afterwards, an algorithm was developed for target identification (i.e. the vertices of the reflection hyperbolas) and their automatic tracking in a three-dimensional environment. A third stage was focused on estimating tree root density with emphasis on the interconnection area. To test the feasibility of the proposed method, the soil around two different tree species (i.e. maple and ash trees) was surveyed using a ground-coupled GPR system equipped with a 700 MHz central frequency antenna. The approach has proven to identify peculiar characteristics of both trees, in terms of surface (i.e. within the first 25 cm from the soil surface) and deep (i.e. deeper than 25 cm from the soil surface) root systems. In addition, results have allowed to assess how different root systems interact with each other.

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

Abstract: 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.

A GPR Spectral-Based Processing Method for Minimisation of Concrete Sleepers Effects in Railway Ballast Investigations

Abstract: This paper investigates the influence of concrete railway sleepers on the ground-penetrating radar (GPR) signal for the assessment of railway ballast conditions. The main aim of this study is to propose a data processing scheme capable to filter out the effects of concrete sleepers on GPR signals with compound information (ie., containing multiple reflections from the concrete sleepers and the underlying ballast material). The method relies on spectral-based processing, i.e., it is based on the minimisation of the difference between i) the frequency spectra of the GPR traces collected along the scanning line at the abscissae of the sleepers and ii) the spectra of the traces acquired at the abscissae of the material between two consecutive sleepers. To this purpose, a stretch of 9.8 km of railway line was investigated using two horn antenna systems with operating frequencies of 1000 and 2000 MHz. Each system was oriented in two different ways, i.e. longitudinally and transversely with respect to the orientation of the tracks. Results have proven the viability of the proposed data processing scheme and spectral-based processing method to reduce the effects exerted by the sleepers on the signal.

A Sampling Investigation of GPR Wave Propagation Velocity Data to Improve Migration Processing of Concrete Rebars

Abstract: In this study, a demonstration of the potential of ground-penetrating radar (GPR) for improving location of rebars is given. To this purpose, a high-frequency GPR system with a 2000 MHz dual-polarised antenna (HH/VV polarisations) has been used to collect data on a reinforced concrete floor of dimensions 1m × 0.80m (longitudinal and transversal acquisitions). The high-dense grid mesh of rebars and the use of the hyperbola fitting method allowed for the acquisition of a dataset of wave propagation velocity values. Hence, an analysis of the statistic distribution of propagation velocity values was carried out to assess the data dispersion throughout the area. A data sampling approach was then proposed and velocity values were sampled at different percentages and in an evenly-distributed manner throughout the inspected area. Corresponding values of velocity were therefore used for data migration purposes and C-scan maps were produced as a combination of longitudinal/transversal acquisitions and HH/VV polarisations. The optimum sampling rate of wave propagation velocity was then assessed by way of comparison of the migrated maps.

The ArchaeoTrack Project: Use of Ground-Penetrating Radar for Preventive Conservation of Buried Archaeology Towards the Development of a Virtual Museum

Abstract: This paper reports the main activities planned within the context of the ArchaeoTrack research project. The project aims at creating a new ground-penetrating radar (GPR)-based methodology producing information for use of communities and local administrations within a preventive archaeology perspective. To this aim, the project provides i) identification of the most suitable GPR system for archaeological prospections, ii) development of a virtual “buried” museum and iii) data storage and visualisation in a freeware dissemination digital platform. An overview of GPR applications in archaeology is reported, followed by a description of the main structure of the project and the expected results.

Evaluation of the impact of pavement degradation on driving comfort and safety using a dynamic simulation model

Abstract: The dynamic effects exerted by the vehicles on the road pavement have been thoroughly investigated over years. The main reason for this investigation is the major influence on the propagation and worsening of the pavement damages exerted by the dynamic loads rather than the static ones. To date, the modelling theories of systems have evolved, along with the computational capability of the modern calculators. To this effect, three-dimensional simulations of the tire-surface interaction are commonly used. These simulations take into account the dynamics of the load and the consequent deformation of the pavement. However, previous studies aimed at analyzing the above interaction for the optimisation strategies of the maintenance activities within the context of effective road asset management. On the contrary, this work focuses on the safety-related issues linked with the dynamic effects suffered by the vehicle, when passing on different road defects. The goal of this study is to analyse numerically the kinematic and the dynamic effects of the pavement degradations (and in particular rutting) on the driving safety. The simulation of the main characteristics and the evolution of the pavement damages over the time (e.g., the simulation of the tire-pavement contacts and the dynamic response on the vehicles) is a useful method for the development of safe and comprehensive rehabilitation programs. These are of paramount importance to limit the accident rates. The effects on the driving safety was analysed using a simulation model for the vehicles behaviour in the case of damaged pavements. Different road geometries and vehicle types were considered to evaluate the rutting effects on safety, as a function of the evolution stage of this type of pavement damage. In more detail, the performance characteristics of the vehicles, the dynamic and kinematic parameters (e.g., the vehicle trajectory and the vertical acceleration), were collected for pavement conditions with progressively high levels of rutting. The study proposes a theoretical model of qualitative relationships between differing stages and location of rutting, and the consequent effects on driving safety for different types of vehicles (passenger cars and powered two wheelers). It is worth to emphasize the relevance of this research for maintenance prioritization purposes at the road network level. Priority is based on the level of risk associated with the pavement degradations and with different types of vehicle.

A GPR spectral-based filtering for minimisation of concrete sleepers effects in railway ballast investigations

Abstract: This paper investigates the influence of concrete railway sleepers on the ground-penetrating radar (GPR) signal for the assessment of railway ballast conditions. The main aim of this study is to propose a data processing scheme capable to filter out the effects of concrete sleepers on GPR signals with compound information (i.e., containing multiple reflections from the concrete sleepers and the underlying ballast material). The method relies on spectral-based filtering, i.e., it is based on the minimisation of the difference between i) the frequency spectra of the GPR traces collected along the scanning line at the abscissae of the sleepers and ii) the spectra of the traces acquired at the abscissae of the material between two consecutive sleepers. To this purpose, a stretch of 9.8 km of railway line was investigated using two horn antenna systems with operating frequencies of 1000 and 2000 MHz. Each system was oriented in two different ways, i.e. longitudinally and transversely with respect to the orientation of the tracks. Results have proven the viability of the proposed data processing scheme and spectral-based filtering to reduce the effects exerted by the sleepers on the signal.

A GPR signal processing procedure for detecting rail ballast conditions by an entropy-based approach

Abstract: Ballasted railroads are among the most common construction types in railway engineering due to the effective drainage capability and load-bearing capacity achieved at relatively low construction costs Rail ballast is usually made of uniformly-graded coarse aggregates derived from crushed rocks of differing geological nature, mostly granite, basalt and limestone According to Selig and Waters [1], several categories can be identified as principal source mechanisms of fouling, namely, the breakdown of ballast, the infiltration from ballast surface (downward migration of coal dust from commercial trains) and the upward migration of clay fines from the subgrade, are the major causes of fouling Notwithstanding the increased costs of maintenance, fouling occurrence may dramatically impact on the safety and operation of railways [2] In view of this, effective health monitoring and early-stage detection of fouling is mandatory to allow significant reduction of both unsafe events and maintenance costs Within this context, non-destructive testing (NDT) techniques are becoming more important in the health monitoring of railways

A high-resolution velocity analysis to improve GPR data migration for rebars investigation

Abstract: Investigation of rebars in reinforced concrete is a matter of high interest in civil engineering. Reinforced concrete has been widely used for over a century as a high-performance construction material, although it is subject to damage and deterioration for a variety of different and complex reasons. Hence, a large number of tests and routine assessments are usually required for this material. To these purposes, destructive and non-destructive testing methods have been used specifically to identify particular features of rebars. Non-destructive testing methods are gaining momentum in this area of research. Ultrasonic sensors are used to assess dimensions of the rebars as well as for damage location purposes (e.g., voids and cracks); location of reinforcement and assessment of corrosion have been carried out using electromagnetic methods, such as radiography, eddy current sensors and impedance tomography. Chemical-based techniques, thermography and impedance tomography are widely used methods for detection of moisture. Within this scenario, it is worth to mention that the ground-penetrating radar (GPR) non-destructive testing method has proved to be suitable to the largest spectrum of the above application areas. In more detail, GPR systems with high-frequency antennas are extensively used on concrete structures, and several GPR-based algorithms for effective assessment of corrosion and moisture infiltration have been developed in the literature. Research is nowadays being oriented towards the assessment of the size of rebars. One of the most common applications of GPR in reinforced concrete relates with the rebars location and the estimation of the concrete cover depth. Accuracy of the above estimations is improved using dedicated data processing algorithms, e.g. migration. Within this context, although a good degree of accuracy can be reached by the available commercial software, a higher precision can be required for quality control and health monitoring purposes. In this study, a demonstration of the potential of GPR for improving location of rebars and estimation of the concrete cover depth is given. To this purpose, a high-frequency GPR system with a dual-polarised antenna has been used to collect data in a reinforced concrete pavement. Hence, a high-resolution velocity analysis has been proposed to improve data migration and locate rebars with a higher accuracy. Results demonstrated the viability of the high-frequency GPR system coupled with the proposed velocity analysis for rebars investigation purposes.