Search

Negative outcomes such as noise and vibration generated by railways have become a challenge for both industry and academia in order to guarantee that the railway system can accomplish its purposes and at the same time provide comfort for users and people living in the neighbourhood along the railway corridor. The research interest on this field has been increasing and the advancement in noise and vibration mitigation methodologies can be observed using various engineering techniques that are constantly put into test to solve such effects. In contrast, the life cycle analysis of the mitigation measures has not been thoroughly carried out. There is also a lack of detailed evaluation in the efficiency of various mechanisms for controlling rolling noise and ground-borne vibration. This research is thus focussed on the evaluation of materials used, the total cost associated with the maintenance of such the measures and the carbon footprint left for each type of mechanism. The insight into carbon footprint together with life cycle cost will benefit decision making process for the industry in the selection of optimal and suitable mechanism since the environmental impact is a growing concern around the world., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

With an emphasis on the integrated deterioration of railway track geometry and components, a new hybrid numerical-analytical method is proposed for the predictive analysis of track geometrical vertical levelling loss (VLL). In contrast to previous studies showing a dependency on the number of cycles, this research unprecedentedly incorporates the influence of operational, vehicle and track conditions. The numerical models are carried out using an explicit finite element (FE) package under cyclic loadings, and then, their outcomes are iteratively regressed by an analytical logarithmic function that accumulates permanent deformations in order to quantify VLL over a long term. The results are first compared with other previous studies, indicating a very good agreement with them. Then, field measurements have been used to further verify the results. In this study, parametric simulations are performed varying three key parameters: axle load, train velocity and ballast tangent stiffness. The parametric studies exhibit that the rate of VLL raises about 50% if the axle load increases only from 30 ton to 40 ton for a freight train running at 70 km/h on a stiffer ballast track. In contrast, for a 25-tonnes-axle-load train running from 60 km/h to 100 km/h on a similar track, the vertical levelling degradation reduces by approximately 20%. The main findings suggest that higher axle loads contribute significantly to the VLL due higher contact forces and, on the other hand, a lower train speed does not necessarily imply a low rate of VLL since the influence of train velocities on track geometry (VLL) is associated with the natural frequencies (or wavelengths) of the ballasted railway track. The insight demonstrates that the load frequencies play a key role on the deterioration of VLL. [ABSTRACT FROM AUTHOR]

Investigating the condition of rail track components is important for track maintenance and developing a greater understanding of track design. Railway inspection can be destructive and non-destructive approaches. In the railway industry, the non-destructive approaches are preferred because they retain the track in operation thus significantly reducing the cost of fault testing. One of the non-destructive approaches is using machine learning which is applied in this study. Field measurements and advanced analysis of results are used to extract track properties. This study creates, tunes and examines the validity of different machine learning techniques. The aim is to extract the dynamic track properties from the in-field measurements without needing the intermediary steps, saving both time and effort. Contributions of this study demonstrate that machine learning techniques have the potential to save cost and time for railway inspection. Moreover, the accuracy is satisfied. The following models are produced: Linear Regression, K-Nearest Neighbors, Gradient Boosting and a Convolutional Neural Network. We observe the limitations of linear regression and tune the remainder, producing three models with low errors. [ABSTRACT FROM AUTHOR]

Track quality affects passenger comfort and safety. To maintain the quality of the track, track geometry and track component defects are inspected routinely. Track geometry is inspected using a track geometry car (TGC). Measured values are stored in the machine and processed to evaluate the track quality. However, track component defects require more effort to inspect. Track component defects can be inspected manually which is time- and workload-consuming or using sensors installed at additional cost. This study presents an approach using track geometry obtained by a TGC to detect track component defects, namely, rail, switch and crossing, fastener and rail joint defects. Detection models are developed using several supervised machine learnings. The relationships between track component defects are analysed to gain insights using unsupervised machine learnings. From the study, the best model for detecting track component defects using track geometry is a deep neural network with an accuracy of 94.31% followed by a convolutional neural network with an accuracy of 93.77%. For the exploration of insights, k-means clustering is used to cluster the track components defects, and association rules are used to find the relationships between them. Examples of the insights from applying these two techniques are that switch and crossing defects are usually found where the radius of curvature is less than 2000 m and the gradient is positive, the most common defects when the radius of curvature higher than 4000 m are rail defects, or a worn wing rail will be found when the rail section has failed, ties in switches and worn point blades are found with the confidence of 92.17%. The findings of the study can be applied to detect track component defects using track geometry where additional cost is not required and unsupervised machine learning provides the insights that will be beneficial for railway maintenance. The information obtained from machine learning models will be complementary information to support decision making and improve the maintenance efficiency in the railway industry. [ABSTRACT FROM AUTHOR]

This paper investigates the possibility for implementing machine learning-aided prediction in analyzing the buckling phenomena of ballasted railway tracks induced by extreme temperature. In this study, artificial neural networks (ANNs) have been developed to identify the relationship between various ballasted track conditions and outputs, namely safe temperature and buckling temperature. The variables included in the objective function of the optimization problems are the lateral resistance of ballasted track provided by ballast-sleeper interaction, torsional resistance provided by fastening systems, and misalignment of the track. Due to its complexity in parameter combinations, the objective of this study is to create predictive models with the aim of minimizing the usage of scarce resources. Thus, this paper is the first to develop a novel machine learning-aided prediction of railway track buckling due to extreme temperature. Comprehensively, all 353 datasets of the safe and buckling temperatures derived from previous finite element (FE) simulation results have been collected and trained. Note that the mean squared error (MSE) and the coefficient of determination ( R 2) are considered to quantify the performance of the ANN architectures. The optimal ANN architecture with a very high rate of accuracy has been determined and highlighted. Thus, the suggested neural network model can be applied conveniently to help estimate safe and buckling temperatures of the complex track models in order to improve track conditions and thus prevent track buckling in summer. [ABSTRACT FROM AUTHOR]

Featured Application: The new findings highlight the lifecycle cost and carbon footprint of high-speed railway tunnels, which are usually adopted in real-life practices globally. The in-depth insight incites the systems thinking consideration of rail decarbonisation. The method and field data in the article can be used (not limited to) as an indicative reference for revolutionising design, construction and maintenance to achieve the sustainability of high-speed rail infrastructures. Global warming is a critical issue nowadays. Although the railway system is considered as green transportation, it cannot be denied that railway tunnels have a significant environmental impact during construction and maintenance. At the same time, asset management of a project becomes more popular in project analysis. Therefore, this study aims to analyse life-cycle cost (LCC) and life-cycle assessment (LCA) for the Xikema No. 1 high-speed railway tunnel in China to consider the environmental impact of rail tunnel construction. The initial capital costs of tunnel and rail construction, operation, and maintenance costs have been separately considered in terms of the life-cycle cost analysis and net present value (NPV) with various discount rates. The LCA analysis has presented the CO2 emissions and energy consumption over the construction and operation processes into consideration. The CO2 emissions and energy consumption caused by material production, maintenance, and material transportation have been accounted for. The results show that the materials used during the construction process contribute to about 97.1% of CO2 emissions of the life-cycle while CO2 emissions caused by the operation and maintenance process are relatively small compared with the construction process. Moreover, the maintenance process consumes over 55% of the life-cycle energy. The energy consumption of the tunnel construction process is approximately 44.3%. At the same time, the construction contributes to the main proportion of LCC due to relatively low cost in the operation and maintenance stages. [ABSTRACT FROM AUTHOR]

Featured Application: The new findings highlight for the first time the buckling phenomena of interspersed railway tracks, which are usually adopted during railway transformations from timber to concrete sleepered tracks in real-life practices globally. The novel in-depth insight unprecedentedly instigates vulnerability and resilience of traditional and interspersed railway track systems exposed to extreme weather conditions. The method in the article can be used (not limited to) as an indicative reference for innovative design and maintenance for stability and misalignment management of ballasted railway tracks. Nowadays, timber sleepers are still used for ballasted railway tracks to carry passengers and transport goods. However, the process of natural decay causes the problem of timber sleeper degradation over time. A temporary "interspersed" approach is used to replace rotten timbers with concrete sleepers. This implementation has several inadequacies, as interspersed railway tracks have inconsistent stiffness and experience significant deterioration over the years. Increased heat due to the change in the global climate can induce a compression force in the continuous welded rail (CWR), leading to a change in track geometry called "track buckling". A literature review shows that track buckling on plain tracks has been widely studied. However, the buckling of interspersed tracks has not been fully studied. This study presents 3D finite element modelling of interspersed railway tracks subjected to temperature change. The effect of the boundary conditions on the buckling shape is considered. The obtained results show that the interspersed approach may reduce the likelihood of track buckling. This study is the world's first to investigate the buckling behaviour of interspersed railway tracks. The insight into interspersed railway tracks derived from this study will underpin the life cycle design, maintenance, and construction strategies related to the use of concrete sleepers as spot replacement sleepers in ageing railway track systems. The outcome of this study will help track engineers to improve the inspection of the lateral stiffness of interspersed tracks in areas prone to extreme temperature. [ABSTRACT FROM AUTHOR]

Featured Application: The new findings highlight for the first time the nonlinear dynamic phenomena of turnout systems considering unsupported composite and concrete sleepers and bearers. The in-depth insights stemmed from multi-body simulations of dynamic train—turnout interaction demonstrates the influences of unsupported sleepers on dynamic responses, load redistributions, dynamic impact factors and wheel/rail contact forces. The novel insights can be used (not limited to) as a reference for the design, inspection and maintenance of railway switches and crossings. Track settlement is a common problem observed in ballasted railway tracks. The ballast bed and the material layers underneath it, deform under repeated trainloads and create uneven support conditions along the track. In some cases, the ballast settlement could be detrimental and the sleepers lose contact with the ballast bed partially or completely, resulting in higher contact forces and load distributions over the supported sleepers. Numerous studies have been conducted to investigate the phenomenon for normal tracks. Nevertheless, railway turnouts are somehow neglected. As a consequence, this study focuses on the relation between unsupported sleepers/bearers (particular name for turnouts) and a railway turnout system to develop the understanding of the response of turnout system under dynamic loadings. A 3D Finite Element Method (FEM) model is inherited from previous study and adopted to reflect the cases with unsupported bearer configurations. It is noteworthy that inherited model is capable of reflecting the impact forces, which is an inherent and fundamental characteristic of a railway turnout. Model verification is done with the parent model that was verified by field measurements. Three different support conditions (i.e., one, two, three unsupported bearers), five different velocities and six different positions of unsupported bearers are simulated. The results show that the performance of 'fibre-reinforced foamed urethane' (FFU) bearers are promising and more, unsupported bearers carry significant loads at particular locations, which is contrary to the sleepers on normal track that are subjected to insignificant loads. [ABSTRACT FROM AUTHOR]

Steel–concrete composite railway track slabs are a financially viable alternative for the modular construction of railway slab tracks and for the replacement of resilient timber transoms on railway bridges, and design and experiments have been carried out to investigate their technical feasibility. Extended findings based on dynamic eigenvalue analyses of a precast steel–concrete composite slab panel for a track support structure are presented in this paper. The natural frequencies of the railway composite slab were investigated using the finite-element package Abaqus. Dynamic eigenmodes were then extracted using the Lanczos method. Modal cross-over phenomena were clearly observed when the design mass of the track slab was changed. This paper highlights the unprecedented dynamic mode coupling effects on composite track slabs over a railway bridge. This insight can be used to improve practical noise- and vibration-control technologies through composite material design, resulting in quieter railway track slabs. [ABSTRACT FROM AUTHOR]

Each day tens of turnout-related derailment occur across the world. Not only is the prediction of them quite complex and difficult, but this also requires a comprehensive range of applications, and managing a well-designed geographic information system. With the advent of Geographic Information Systems (GIS), and computers-aided solutions, the last two decades have witnessed considerable advances in the field of derailment prediction. Mathematical models with many assumptions and simulations based on fixed algorithms were also introduced to estimate derailment rates. While the former requires a costly investment of time and energy to try and find the most fitting mathematical solution, the latter is sometimes a high hurdle for analysists since the availability and accessibility of geospatial data are limited, in general. As train safety and risk analysis rely on accurate assessment of derailment likelihood, a guide for transportation research is needed to show how each technique can approximate the number of observed derailments. In this study, a new stochastic mathematical prediction model has been established on the basis of a hierarchical Bayesian model (HBM), which can better address unique exposure indicators in segmented large-scale regions. Integration of multiple specialized packages, namely, MATLAB for image processing, R for statistical analysis, and ArcGIS for displaying and manipulating geospatial data, are adopted to unleash complex solutions that will practically benefit the rail industry and transportation researchers. • All estimates seem to be incapable of calculating an estimate for a low number of derailments. • the assumptions seldomly yield a precise estimate of the derailment rates under any uncertainty • Some assumptions which relied on turnout counts, are observed to deviate from the observations • the assumptions regarding turnout counts are a weak spot even when being generated mathematically on the basis of a concrete belief. [ABSTRACT FROM AUTHOR]

Railway turnouts or so-called 'switches and crossings' are complex systems by nature of design and construction. Railway turnouts are used to change direction of trains from one to another. They require high-quality construction and maintenance, in order to minimise rapid degradation and component failures that could result in train derailments. Due to the complexity of railway turnouts, the efficiency and effectiveness of maintenance can be improved by integrating existing practice by Building Information Modelling (BIM). This research establishes and analyses the world's first 6D BIM for life cycle management of a railway turnout system. The BIM (Level 3) has integrated 6-dimensions of field data information based on Revit-2018 and Navisworks-2018 platforms. The digital twins of a railway turnout in 3D embrace time schedule, costs and sustainability across the whole life cycle. The use of BIM for railway turnout systems has the potential to improve the overall information flow of the turnout planning and design, manufacturing pre-assembly and logistic, construction and installation, operation and management and demolition, thereby achieving better project performance and quality. Based on integrated information of railway turnout system, the 6D BIM has the ability to assess on economic, management and sustainability, and achieve a balance among them. This is the word first to demonstrate that BIM can fully deliver its essential benefits by information sharing, easing technical communication, improving design quality, reducing of design errors, accelerating implementation, speeding up work, shortening construction duration, reducing construction costs, enhancing carbon efficiency, supporting project management, and providing its owners with higher operational efficiency over the railway turnout system life-cycle. The results reveal that embodied material emission is the main contributor towards carbon footprint, especially produced during the manufacturing stage. The reconstruction stage contributes the most expensive phase of life cycle. The insight will significantly benefit the co-value creation among engineers, project managers, technicians, and senior management team. • Digital twin or BIM (Level 3) of railway switches and crossings is established. • It is the first to highlight sustainability-based life cycle management of railway turnout systems. • The life cycle analyses consider both cost and environmental impacts using field data, design and case studies. • The outcomes highlight best practices for sustainable and cleaner solutions for life cycle management of turnout systems. • The insight will benefit the co-value creation among engineers, project managers, technicians, and senior management team. [ABSTRACT FROM AUTHOR]

As the main component of a ballasted railway system, railway ballast is frequently used by the railway industry to enhance constructability and practicality. Numerous studies into train–track interactions focused on ballast modelling and idealisation in completely dry environments, but recent studies have found that, in extreme weather such as floods, water can clog natural ballast beds and change the initial state of their properties. Ballast models used in multi-body simulations have been mostly developed based on the instrumented impact hammering method considering the ballast as a spring/dashpot. The single degree of freedom (SDOF) idealization for ballast enables a non-destructive field testing technique for monitoring of railway components in practice. In this study, the suitability of the idealization of ballast for dynamic characteristics has been evaluated. A series of experiments have been performed with a variety of ballast conditions in flooding levels from 0 to 40 cm, with a frequency range of 0–500 Hz. The results clearly show that the increase in the flood level will result in increasing dynamic damping of more than 50% of dry natural ballast whilst reducing its stiffness and natural frequency. The novel insights are of great significance for exploring the non-linear dynamic traits of ballast in extreme environments, which can be integrated into the coupled train–track analysis that can better express more realistically the dynamic train–track interaction and load transfer mechanism of flooded railway tracks. [ABSTRACT FROM AUTHOR]

On curved railway tracks, wheel/rail interface can usually cause a traveling source of sound and vibration, which constitutes high-pitch or tonal noise pollution causing considerable concern to rail asset owners, commuters and people living or working along the railway corridor. The sound and vibration can be in various forms and spectra. The undesirable tonal sound on curves caused by excessive lateral wheel/rail dynamics in resonance with falling friction states are often called 'squeal noises'. This paper evaluates the transient effect of curve radii on the possible occurrence of lateral track resonances, which is a principal cause of dynamic wheel/rail mode coupling that could trigger 'curve squeal'. This study is devoted to systems thinking approach and better insight into dynamic phenomena of railway tracks that could resolve the railway curve noise problems. Curved track models in three-dimensional space have been developed using a finite element package, STRAND7. The dynamic responses of curved track have been simulated by applying a moving train load. The transient loading model of a common wheel/rail slip has been adopted. The simulations of railway tracks with different curve radii have been carried out to develop state-of-the-art understanding of lateral track dynamics, including rail dynamics, cant dynamics and overall track responses. Parametric studies have been conducted to evaluate lateral displacements, velocities and accelerations of rail over sleeper and rail at midspan, both in static and dynamic conditions. The study firstly reveals that the lateral resonance of tangent tracks is relatively rare and the mode coupling behavior is unlikely to occur on moderately curved tracks. The lateral vibration responses have been presented in terms of time histories and spectro-temporal responses (also called "Spectogram"). The dynamic lateral responses of the track are found to be sensitive to the change of curved radii. The resonance peak in the lateral direction is related to the agreement of corresponding natural frequencies of rail and the vibration excitation frequencies under an individual rolling velocity. The outcome of this study establishes new insight into the dominant influences of different track parameters to track lateral dynamic behaviors. [ABSTRACT FROM AUTHOR]

The Paris Agreement of December 2015 signifies global unity to limit global warming to well below 2°C (above pre-industrial levels) and to pursue efforts to limit the increase to 1·5°C. The global community now agrees that anthropogenic climate change is unequivocal. According to the Intergovernmental Panel on Climate Change, the global average combined land and surface temperature has increased by 0·78°C. Although the magnitude of change in mean temperatures is relatively small, attendant extreme weather events have been shown to have increased in frequency, and are projected to increase in the future. The potential impacts of climate change on railway infrastructure and operations have not been fully assessed in the literature. The projected urban growth in Kuala Lumpur and Singapore has led to the necessity to establish a high-speed rail (HSR) system between the two. However, the existing railway network in the region has been significantly affected by severe weather conditions such as rainfall, lightning, wind and very high temperatures. This research addresses a knowledge gap regarding the potential impacts of climate change on future rail projects in the region, and points out the vulnerabilities that may lead to impaired operations and system failures. These insights are intended to inform the holistic consideration of climate change impacts in the design stage of HSR systems in Malaysia and beyond. [ABSTRACT FROM AUTHOR]

Inevitably, train and track interaction generates a travelling source of noise and vibration along the railway corridor. Railway noise is generated in various forms and spectra. The undesirable railway sound and vibration include rolling noise, impact noise, curve noise, mechanical noise, airborne noise, wheel/rail noise, structure- and ground-borne noises. The noise that is carried through the vehicle body mainly affects ride quality, customer experience and structural integrity of the rolling stocks, whereas the vibration that is transmitted from the rails to the supporting structure of the track plays a main role in rapid track degradation and potentially affects the surrounding structures. This study highlights the practical guidelines for track vibration isolation resulting from the operation of railways. Its emphases are placed on the contemporary vibration mitigation methods used in existing and ageing railway infrastructures (the so-called ‘brown field project’). Its aim was to provide the overview and lessons learnt for the future development of new vibration isolation strategies in practice. [ABSTRACT FROM PUBLISHER]

Australian railway networks suffer a large fluctuation of extreme heats each year due to their wide variety of geographical conditions. Depending on climatic, cloud and radiation conditions, an ambient temperature of 20 °C could induce an equivalent thermal load absorption of track components as much as 30 °C to 35 °C or even more. As such, relatively high turnover of timber sleepers (crossties in a plain track), bearers (skeleton ties in a turnout), and transoms (bridge cross beams) can often be observed due to their unstable deformation and rapid deterioration. This paper investigates an application for the replacement of ageing timber transoms mounted on existing railway bridges using fibre reinforced foamed urethane (FFU) transom beams, which are proven to provide environmental, safety and financial benefits. Clear benefits of the FFU material are the maintainability and constructability, especially for existing railway bridges. In this study, numerical simulations using finite element package ABAQUS have been carried out to illustrate the effect of thermal loads on the structural behaviour of a railway transom bridge. The model was developed using a case study of an actual railway bridge in Kiama, Australia and it has been validated by field data measurements. It is found that nonlinear structural behaviour of the bridge components exists at highly elevated temperatures. The better insight into the thermal load responses will lead to safer and more reliable rail stress adjustment practice, preventing rail misalignment or buckling. [ABSTRACT FROM AUTHOR]

Prestressed concrete sleepers (or railroad ties) are designed to carry and transfer the wheel loads from the rails to the track foundation. Over a period of time, a railway track could experience various types of static and dynamic loading conditions, which are attributable to commercial train operations. Previous studies have established two main limit states for the design consideration of concrete sleepers: ultimate limit states under extreme impact and fatigue limit states under repeated probabilistic impact loads. Prestressed concrete has played a significant role in maintaining the high endurance of the sleepers under low to moderate repeated impact loads. Despite the most common use of the prestressed concrete sleepers in railway tracks, their remaining lives are not deeply appreciated nor taken into account for track maintenance and renewal. The present experimental investigation was aimed at determining the residual prestressing force of railway concrete sleepers after revenue services using the dynamic relaxation technique. Fifteen sleepers were extracted from a heavy-haul rail network for testing using experimental facilities at the University of Wollongong in Australia. The structural evaluation program included quasi-static bending tests, dynamic impact tests, and tests to establish the current level of prestress in the steel wires using the dynamic relaxation technique. Two of the sleepers were evaluated for the level of prestressing forces in accordance with Australian standards. It was found that the level of prestress determined using the dynamic relaxation technique was significantly lower than that expected from the theoretical analysis of time-dependent prestressing losses for the concrete sleepers. [ABSTRACT FROM AUTHOR]

Statistically, the actual loading conditions for railway tracks are rather dynamic and transient. The dynamic loadings due to train and track interactions redistribute from the rails to the rail pad, from the rail pad to the railway sleeper, and from the railway sleeper to the underlying ground. Commonly, railway sleeper in track systems is modeled as a beam on elastic foundation. This study makes use of a calibrated finite element model of railway sleepers in a track system, in order to investigate the resonant frequencies and associated mode shapes of railway components in interspersed track systems. The numerical model takes into account the tensionless characteristic of the elastic support as well as the more realistic partial support condition. Using a finite element package STRAND7, the dynamic finite element model of the railway concrete sleeper was precisely established. The dynamic model has then been extended to demonstrate free vibration behaviours of the railway tracks. The effect of interspersed patterns (1 in 2; 1 in 3; and 1 in 4) on railway track dynamics has been firstly investigated and presented herein. [ABSTRACT FROM AUTHOR]

New knowledge has raised a concern about the cost-ineffective design methods and the true performance of railroad prestressed concrete ties. Because of previous knowledge deficiencies, railway civil and track engineers have been aware of the conservative design methods for structural components in any railway track that rely on allowable stresses and material strength reductions. In particular, railway sleeper (or railroad tie) is an important component of railway tracks and is commonly made of prestressed concrete. The existing code for designing such components makes use of the permissible stress design concept, whereas the fiber stresses over cross sections at initial and final stages are limited by some empirical values. It is believed that the concrete ties complying with the permissible stress concept possess unduly untapped fracture toughness, based on a number of proven experiments and field data. Collaborative research run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail CRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete ties that were designed using the existing design code. The findings have led to the development of a new limit-states design concept. This paper highlights the conventional and the new limit-states design philosophies and their implication to both the railway community and the public. [ABSTRACT FROM AUTHOR]

Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated impact cycles. In spite of the most common use of the prestressed concrete sleepers, their impact behavior and capacity under the repetitions of severe impact loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated impact loading. The impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Railway sleepers in a track system are usually utilised to transfer any loading from the rails to the ground support. A wide range of loading conditions has been observed but the critical loading condition is the wheel impact force, which is often due to the wheel or rail irregularities. The railway industry has been aware of a high potential that an out-of-round, single-sided wheel defect may occur and cause cracking in the railway concrete sleepers. This paper presents the dynamic effects on the railway concrete sleeper in a track system due to a single wheel impact. In this study, the railway concrete sleeper is modeled using the beam on elastic foundation theory. The dynamic finite model makes use of the elements coupling with shear and bending deformations to represent the concrete sleeper, and features the use of the tensionless elastic support as the nature of ballast. The parametric investigations focus on the influences of both magnitude and duration of the transient loading. Using the robust finite element software STRAND7, the finite element model of the railway concrete sleeper was previously established and validated against experimental data by the authors. The numerical simulations present the dynamic flexural moment magnification factor of the railway concrete sleeper under the asymmetrical wheel load patterns. [Copyright &y& Elsevier]

There has been a considerable increase in derailment investigations, in particular at railway turnouts (RTs), as the majority of derailments lead to lengthy disruptions to the appropriate rail operation and catastrophic consequences, being potentially severely hazardous to human safety and health, as well as rail equipment. This paper investigates the impact of climates with different features across the US on the derailments to light up a scientific way for understanding importance of climatic impact. To achieve this, official derailment reports over the last five years are examined in detail. By means of geographic segmentation associated with spatial analysis, different exposure levels of various regions have been identified and implemented into a Bayesian hierarchical model using samples by the M–H algorithm. As a result, the paper reaches interesting scientific findings of climate behaviour on turnout-related component failures resulting in derailments. The findings show extreme climate patterns impact considerably the component failures of rail turnouts. Therefore, it is indicated that turnout-related failure estimates on a large-scale region with extreme cold and hot zones could be investigated when the suggested methodology of this paper is considered. • The climate effects causing derailments at turnouts have been identified and classified. • A novel methodology dealing with the climate effects on derailments is proposed. • The relationship between turnout component failures and climate impact is assessed. • The suggested model is validated through actual derailment cases in the US. [ABSTRACT FROM AUTHOR]

• Nonlinear FE model of sleepers has been presented. • Full-scale experiments have been conducted for validation. • Crack propagations are monitored and presented. • It is the first time that crack propagations are predicted. • Prestress forces play a significant role on the crack propagation. The prestressed concrete sleeper is a primary type of sleeper for railway systems around the world. Compared with wooden and composite sleepers, concrete sleepers are of good elasticity and sufficient longitudinal and lateral resistance to ensure the stability of the track. As the railway system is developing to a heavier load and higher speed system, the cracking of concrete sleepers under dynamic load and long-term service is becoming more and more critical. It is essential to evaluate the crack behaviour of prestressed concrete sleepers. In this paper, three-dimensional FEM models have been established using Abaqus based on the brittle cracking model. After the validation by experimental results, the numerical research is performed to evaluate the crack propagation behaviours of prestressed concrete sleepers with different concrete compressive strength, different prestressing force magnitudes, and different loading rates. The results reveal that the cracking resistance of a concrete sleeper turns enhanced by improving the compressive strength of concrete and the initial prestressing force of tendons. It is also observed that the cracking becomes more progressive as the loading rate increases. [ABSTRACT FROM AUTHOR]

Railway sleepers in a track system are usually subjected to a wide range of loading conditions. A critical type of loading condition that causes cracking in the railway concrete sleepers is the dynamic transient wheel force. The transient wheel forces are often due to wheel or rail abnormalities. This paper presents a dynamic finite element model of a railway concrete sleeper in a track system, aimed at raising the consideration of dynamic effects in sleeper design. The railway concrete sleeper is modeled using the beam-on-elastic-foundation theory. Since in the actual tracks the ballast underneath does not provide any tensile resistance, the finite beam elements employed in this investigation take into account the bending and shear deformations, together with the tensionless nature of the elastic support. This paper places emphasis on the effect of the transient periods on the flexural responses of railway sleepers in track systems. Using the robust finite element software STRAND7, the finite element model of the railway concrete sleeper was previously established and validated against experimental data by the authors. The numerical analyses present the ratio between the dynamic and the static bending moment resultants, the dynamic magnification factor, of the railway concrete sleeper under different sinusoidal pulse durations. [ABSTRACT FROM AUTHOR]

Abstract: Assessment of condition of railway track is crucial for track design, repair, and effective maintenance operations. In-field dynamic testing in combination with track modelling represents an efficient strategy for identification of the current condition of railway track structure and its components. Field investigations for the dynamic characteristics of a railway track and its components were carried out and are presented in this paper. A non-destructive technique using impact excitation, so-called ‘modal testing’, was utilized in these trials. Integrated approach combining field measurements, experimental modal analysis, and finite element modelling to evaluate the dynamic parameters of the in situ railway track components are appended. A ballasted railway track site in Central Queensland managed by Queensland Rail (QR) was selected to perform the field tests. Six sleeper-fastening-rail assemblies were selected for dynamic testing. The frequency response functions (FRFs) were recorded by using Bruel & Kjaer PULSE vibration analyser in a frequency domain between 0 and 1600Hz. The data obtained were best fitted using the least-square technique to determine the dynamic stiffness and damping constants of the tested track components. In addition, the experimentally determined resonance frequencies along with the dynamic properties of the track components can provide an important input for determining the maximum speed and axle load for the future track upgrades. This paper also points out on how to judge the dynamic responses (e.g. FRFs) together with the visual inspection of existing conditions from the field experience. Examples of testing results representing the deficient integrity are additionally highlighted. Based on the results, the impact excitation technique is an efficient method susceptible to the structural integrity of railway track structures. [Copyright &y& Elsevier]

Ballasted railway tracks are impaired due to either normal or abnormal operations. One of the problems is the differential settlements along the track. Clearly, there is the need to maintain periodically the track substructures by means of ballast packing/tamping. Inappropriate conducts result in the nonlinear distributions of support stiffness. This study firstly demonstrates the effects of improper ballast packing/tamping on the free vibration behaviors of in situ railway concrete sleepers. The two-dimensional finite element modeling of an in situ concrete sleeper was employed in the parametric studies. This model takes into account the coupled flexural-and-shear deformations of concrete sleepers, elastic displacements of fastening system, and nonlinear dynamic interaction between the sleeper and ballast support. Dynamic interaction between sleepers and ballast was investigated based on the nonlinear distribution of ballast support stiffness underneath the sleeper. Effects of both symmetrical and asymmetrical stiffness distributions on dynamic behaviors of the local in situ concrete sleeper were also highlighted. [ABSTRACT FROM AUTHOR]

Abstract: The vibration of in situ concrete sleepers in a railway track structure is a major factor causing cracking of prestressed concrete sleepers and excessive railway track maintenance cost. Not only does the ballast interact with the sleepers, but the rail pads also take part in affecting their free vibration characteristics. This paper presents a sensitivity analysis of free vibration behaviors of an in situ railway concrete sleeper (standard gauge sleeper), incorporating sleeper/ballast interaction, subjected to the variations of rail pad properties. Through finite element analysis, Timoshenko-beam and spring elements were used in the in situ railway concrete sleeper modeling. This model highlights the influence of rail pad parameters on the free vibration characteristics of in situ sleepers. In addition, information on the first five flexural vibration modes indicates the dynamic performance of railway track when using different types of rail pads, as it plays a vital role in the cracking deterioration of concrete sleepers. [Copyright &y& Elsevier]

• 3D FE model of interspersed tracks has been developed. • Vulnerability of interspersed tracks has been assessed. • This study is the first to assess the failure of interspersed tracks exposed to flood damage conditions. • The new insights will help track engineers to define operational restrictions in order to improve resilience capability of interspersed railway tracks. In traditional railway networks globally, timber sleepers have been widely adopted since the advent of railway systems. After a certain period of time, timbers tend to degrade and it becomes more and more difficult to seek cost-effective replacement hardwood sleepers. To provide a short-term solution, many rail infrastructure managers use an interspersing method of track maintenance. The interspersed sleeper of railway tracks, which is a spot replacement of old timber sleeper with concrete or composite counterparts, is often utilised as a temporary maintenance measure for secondary railway tracks such as low-traffic lines, yards, balloon loops or siding. Reportedly, the performance of railway lines including the interspersed tracks can quickly deteriorate when the tracks are exposed to heavy rains and floods. In many cases, ballast washaway can be often seen. This study is the world first to demonstrate the effects of ballast washaway on the vulnerability assessment of interspersed railway tracks using nonlinear finite element simulations, STRAND7. Two sets of moving point loads representing a bogie along the rails have been established to investigate the worst-case, potential actions for impaired performance of sleepers and differential settlements of the track. In this study, the emphasis is placed on the effects of ballast washaway on the maximum displacement of rails and the relative track geometries (i.e. top and twist). The maximum bending actions causing the failures of the track components are also investigated. The new insights will help track engineers develop appropriate climate change adaptation methods and policies for operations of interspersed railway tracks facing extreme rainfall and flooding conditions. [ABSTRACT FROM AUTHOR]

• Nonlinear FEM of a prestressed concrete sleeper is presented. • Field measurements are used for validations of the time-dependent simulations. • Creep and shrinkage properties are taken fully into account. • It is the first time that the time-dependent effects are considered throughout the models. • Flexural stress resultants of the prestressed concrete sleepers are underestimated by design. The main functions of railway sleepers are: (i) to safely transfer loads from wheel axles to foundation; (ii) to secure both rails ensuring correct track gauge at all time; and, (iii) to restrain movements of rails to control longitudinal creeps. In reality, railway industry can experience costly problems of railseat twists and tight gauges, for instance, due to time-dependent actions and poor workmanship. These problems prevent trains to navigate over tracks safely, effectively and quietly. They require additional, expensive maintenance activities much more frequently over time such as rail renewal, rail reprofiling/grinding, rail pad replacement, curve lubrication adjustment, etc. On this ground, it is very important to maintain the geometry and topological/dimensional stability of railway sleepers. The long-term geometric performance of sleepers can be significantly influenced by time-dependent actions and behaviours. The creep and shrinkage in prestressed concrete sleepers result in internal actions that is led to geometric deformation, which change the rail gauge and influence the safety and reliability of track components. Time-dependent behaviours also lead to increased complex internal stresses, which can cause cracking on prestressed concrete railway sleepers. The cracks stemming from creep and shrinkage can be observed in real life, at a certain time after construction, along the sleepers and near the fasteners such as anchorage, bolt holes, and web openings. In this study, unprecedented experimental and numerical investigations are conducted to evaluate time-dependent behaviours of full-scale prestressed concrete sleepers. An empirical calculation method is also introduced and the empirical results are compared with both experimental and numerical results. Insights into creep and shrinkage effects are highlighted in order to essentially aid predictive and preventative track maintenance, supporting the effective and efficient decision making of both (i) engineers and manufacturers and (ii) infrastructure managers and owners. [ABSTRACT FROM AUTHOR]

• Unprecedented effects of unconstrained length of railway tracks are highlighted. • Physical nature of track buckling is studied using nonlinear FEM models. • Interspersed approach can shift failure from progressive to snap-through buckling. • Buckling of timber sleepered tracks can be prevented by interspersed approach. • Track lateral resistance plays a significant role in track buckling prevention. In a conventional railway system, timber sleepers have been widely used for ballasted railway tracks to carry passengers and transport goods. However, due to the limited availability of reliable and high-quality timbers, and restrictions on deforestation, the "interspersed" approach is adopted to replace ageing timbers with concrete sleepers. The replacement of ageing timber sleepers is frequently done over old and soft existing formations, which have been in service for so long, by installing new stiff concrete sleepers in their place. This method provides a cost-effective and quick solution for the second and third track classes to maintain track quality. Presently, railway track buckling, caused by extreme temperature, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. According to the buckling evidences seen around the world, buckling usually occurs in ballasted track with timber sleepers and thus there is a clear need to improve the buckling resistance of railway tracks. However, the buckling of interspersed tracks has not been fully studied. This unprecedented study highlights 3D finite element modelling of interspersed railway tracks subjected to temperature change. The effect of the boundary conditions on the buckling shape is investigated. The results show that the interspersed approach may reduce the likelihood of track buckling. The results can be used to predict the buckling temperature and to inspect the conditions of interspersed railway tracks. The new findings highlight the buckling phenomena of interspersed railway tracks, which are usually adopted during railway transformations from timber to concrete sleepered tracks in real-life practices globally. The insight into interspersed railway tracks derived from this study will underpin the life cycle design, maintenance, and construction strategies related to the use of concrete sleepers as spot replacement sleepers in ageing railway track systems. [ABSTRACT FROM AUTHOR]

• Nonlinear 3D track-ballast interaction model is firstly presented. • Field measurements are used for the validation of the model. • It is the first time that the balllast degradation effects are considered in track bucklings. • Ballast fouling play a significant role in undermining lateral track stability. • Lateral track resistance can reduce by half when fully fouled ballast incurs. Presently, railway track buckling, caused by extreme heat, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. It is important to ensure the lateral stability of railway track in order to tackle the extreme temperature. However, in fact, railway track can be progressively degraded over time resulting in poorer track stability. This includes the larger lateral track misalignment and component deteriorations. This unprecedented study highlights 3D Finite Element Modelling (FEM) of ballasted railway tracks subjected to temperature change considering different ballast fouling conditions. The buckling analysis of ballasted railway tracks considering ballast fouling conditions has been investigated previously. This paper adopts the lateral resistance obtained from the previous single sleeper (tie) push test simulations to the lateral spring model. The influences of the boundary conditions and rail misalignment on the buckling temperature are also investigated. The results clearly show that the ballast fouling may increase the likelihood of track buckling even if the fouled ballast is accumulated at the bottom of the ballast layer. More importantly, the allowable temperature can be reduced up to 50% when the ballast is completely fouled. The results can be used to predict the buckling temperature and to inspect the conditions of ballast. The new findings highlight the buckling phenomena of interspersed railway tracks and help improve the inspection regime of ballast conditions especially in summer to encounter the extreme heat. [ABSTRACT FROM AUTHOR]

To minimize the maintenance frequency as well as the environmental impact caused by the growing number of railway materials reaching the end of their lives, appropriate sustainable management is inevitable prior to either turning them into wastes or leaving them in landfill sites. This paper presents the recent developments of Fibre-reinforced Foamed Urethane (FFU) sleepers installed in the railway turnouts. It determines the recycling and recovering processes of this infrastructure system. The results of recyclability (R cyc) and recoverability (R cov) rates for the railway turnout system are subject to assumptions associated with data which are taken from relevant sources (e.g. UNIFE). The result presents a value of 92.23% and 93.50%, respectively. A sensitivity analysis demonstrates that Mass Recovery Factor (MRF) has superior effect on R cyc and R cov values compared to Energy Recovery Factor (ERF). In addition, this study evaluates environmental life-cycle impacts based on the calculation of carbon emissions and energy consumption over 75 year's lifespan. Comparison of the life-cycle sensitivity for the whole railway turnout system is conducted between FFU sleepers and concrete sleepers. The results show that concrete sleeper emitted almost the same carbon emission as the FFU material, but with much more maintenance and replacement frequency over the mentioned lifespan. • Sustainability analysis of composite materials for railway switches and crossings is established. • It is the world's first to highlight life cycle cost and sustainability of railway turnout systems. • Life cycle evaluations have been carried out using designs, case studies, and field data. • The outcomes highlight best practices for sustainable and cleaner solutions for composite materials. • The insight will vastly improve recyclability and sustainability of composite materials for railway turnouts. [ABSTRACT FROM AUTHOR]

• Three-dimensional FE models have been developed and validated by full-scale tests of prestressed concrete sleepers. • It is the first to identify the impact responses of railway concrete sleepers with under sleeper pads exposed to impact loading. • Increase in insertion losses and decrease of contact pressures from impulse moderation have been highlighted. • It is the first to reveal the effectiveness of USP in impact load response of railway sleepers. • Insights will help track engineers to make decision on the design and usage of USP. Exposed to operational uncertainties, the investment in railway infrastructure is increasing to improve track resilience, to mitigate long-term consequences, to prolong the track service life, and to reduce unplanned maintenance costs and carbon footprint. Under sleeper pads (USPs) have been widely used in several countries as a resilient component placed underneath concrete sleepers. However, it is well-known that, with any imperfection of either wheel or rail, railway tracks usually are incited by impact loading conditions. Accordingly, the application of USPs to mitigate the detrimental impact load consequences on track structure is unprecedentedly highlighted in this paper. Despite the common uses of USPs in various countries in Europe, the dynamic behaviour of the USPs under high-intensity impact loading conditions has not been fully investigated. Note that not only does this study focus on serviceability condition but it also instigates an extreme condition, which can occur when there are coupled effects of short and long wavelength defects (e.g. dipped rail joint coupled with track settlement, switches and crossings, etc.). This paper thus establishes a 3D finite element model of prestressed concrete sleepers with USPs, using LS-Dyna. This study has confirmed field measurement data that the sleepers with USPs tend to have lesser flexures, contact force and impact energy. However, this study is the world's first to reveal that the vibration of sleeper with USPs could be amplified by the large amplitude impact force, which can be induced especially when excited by a high-speed train travelling over short-pitch rail defects, rail joints, coupled defects or crossings. It is also noteworthy that a very stiff pad with a bedding modulus of 1 N/mm3 can be alternatively used as USPs as recommended by the results obtained. Based on both numerical and field measurement results, it demonstrates that the applications of USPs should be very carefully considered since the USPs could trade off the desired benefits by aggravating dynamic behaviours of sleepers with USPs. The new insights will help track engineers to make appropriate decision on the design and usage of USP. [ABSTRACT FROM AUTHOR]

• Interspersed track systems are simulated using nonlinear finite element method. • Ballast model using tensionless stiffness has been adopted to reflect the real-world physical behaviour. • 600 nonlinear simulations varying various time-dependent parameters have been carried out. • Dynamic uplifts are the source of rapid track deterioration over life cycle. • More routine ballast tamping is recommended to resolve any track geometry problem. Presently, timber-sleepered tracks are still being adopted in railway networks transporting goods and passengers. However, the deterioration of timber sleepers is evident after years of service due to natural decay; and it is difficult to seek cost-effective hardwood sleepers to replace the aging sleepers. An impermanent "interspersed" approach is an alternative method used to substitute rotten timbers with concrete sleepers. Although the interspersed tracks offer a cost-effective short-term solution for certain track classes, there are some drawbacks to this practice, since the interspersed track has inconsistent stiffness problems, and the different track decay rate can cause uneven settlement and foundation failure, which can lead to significant track deterioration over time. The emphasis of this study is placed on the long-term behaviour of interspersed track components under repeated train loading. Interspersed track models in three-dimensional space have been developed and validated using a finite element method. The effects of deteriorated railway components (timber, rail pads, ballast) are taken into account to examine the dynamic performance of the interspersed tracks under moving train loads. This study will help rail track engineers better understand the time-dependent behaviour of interspersed tracks, enable a truly predictive track maintenance and improve the reliability of infrastructure asset maintenance and life cycle management. [ABSTRACT FROM AUTHOR]

This unprecedented study aims to demonstrate the potential to locate crack damage and severity in full-scale railway prestressed concrete sleepers. The dynamic mode shape curvature squares method has been utilised. This approach adopts structural deflection shapes extracted from experimental modal analysis using an impact excitation. The railway concrete sleepers are exposed to the first crack and 1.5 times above the first-crack loads using experimental setup in accordance with the British Standard (for benchmarking purpose). It is found that the first cracking of the sleepers has caused non-significant stiffness reduction of the structural component evidenced from the fact that the natural frequency shifts are only few percent and no visible differences in deflection mode shapes are observed. In addition, the mode shape curvature alone cannot indicate the crack establishment in the railway sleepers. However, a relatively sparse wireframe for deflection shapes enable the plausible density of sensor grids that can be further analysed for damage detection. In this paper, the curvature square approach has been developed to quantify and locate the damage in the railway sleepers. The standardized damage index distributions and subsequent thresholding with different levels of confidence of damage localization have been firstly developed to enhance the accuracy of crack localization. It is found that accurate locations of cracks mostly in the mid span of the sleepers can be reasonably detected in accordance with the actual crack measurements from the experimental data. The novel insight into this approach can enhance the new development of on-board technology for railway sleeper crack detection using operational modal signals. • Dynamic mode shapes of cracked railway concrete sleepers are extracted. • Mode shape curvature square method is used to identify cracks in railway sleepers. • Polynomial smoothing of mode shape curvature eliminates the need for baseline data. • Initial and further cracks in railway concrete sleepers are accurately detected. [ABSTRACT FROM AUTHOR]

• 3D FE model coupled with multi-body simulation has been developed. • Vulnerability of railway turnout systems has been assessed. • This study is the first to assess train-turnout interactions exposed to flood damage conditions. • The new insights will help track engineers to define operational restrictions building resilience capability. Track twists used in modern railways indicate the warpage of a particular track plane to identify track quality. In some cases, a twist is intentionally introduced on tracks to facilitate motions in curves. Nevertheless, twists can exceed above certain thresholds resulting in twist faults, which impose direct risk to safety and a potential cause for derailments. Twist faults are commonly observed in ballasted tracks, which consists of crushed rock particles and have low endurance to resist against dynamic track forces. In general, the deterioration in ballast structure progresses slowly. However, in reality, there are some catalysts such as extreme events that can speed up the deterioration of the ballast bed. Extreme events have rare occurrences but a high potential to damage structures and environment in a short duration. Even though the term 'rare' is still used to define extreme events, a consensus among the environmental scientists on the increased frequency of extreme events could be found in open literatures. In this study, the impacts of flooding, one of the most common extreme events, on the dynamic phenomena of a turnout structure is investigated in terms of dynamic twists. The emphasis is placed on railway turnouts of which the asymmetrical structure is expected to amplify twist responses. A 3-dimensional finite element method (FEM) model has been developed and many hypothetical scenarios ranging from various materials to vehicle speeds have been tested in virtual environments. It should be noted that the developed model is the modified version of a previously validated model and therefore, validation of the model is done by a comparison with the parent model. This study is the world's first to demonstrate that the dynamic performance of composite and plastic bearers is relatively poor in comparison to concrete bearers when considering dynamic twist phenomena. Our new results also exhibit that partially damaged turnout structures in the case of flooding is the most critical and vulnerable situation, which could result in detrimental train derailments. This vulnerability cannot practically be inspected by naked and untrained eyes. On this ground, when exposed to flooding conditions, it is recommended to halt any railway operations over vulnerable switches and crossings, and to avoid the approach of 'reach the station first' in emergency cases. [ABSTRACT FROM AUTHOR]

• This the world's first to establish a probabilistic Bayesian model for railway operations. • Model verifications against the long-term FRA's data exhibit excellent accuracy >95%. • Both of decision tree and Petri-nets models are embedded for risk assessment. • Both DT and PT models can be practically used by any railway authorities. • Railway accident reduction and reliability can be achieved by model adoption. Not only has the railway accidental prevention been a prime focus, but it has also become a key challenge for the industry in recent years. For many decades, rail authorities have attempted to significantly improve rail safety, whilst facing various passengers' risks and uncertainties. The overarching goal of this study is to develop a new posterior probability model to quantify uncertainties for benchmarking. This is the world's first to establish new insights from the benchmarking of risk and safety across different rail networks. The insights will point out the advantages and practicability of launching safety policies and reducing railway accidents for other rail networks. The new model has been developed using unparalleled long-term accidental data sets, including 'a trailer an accident' and 'causes of the accident'. The investigation adopts a Bayesian approach (via Python) to codify the novel model. The new findings lead to the better understanding into the uncertainty of railway accidents. Five notable rail networks have been selected as case studies. This study has also compared the effectiveness of the decision tree and Petri-net models using the posterior probability and number of injuries and fatalities. Based on the benchmarking outcomes, Chinese and Japanese railway systems denote the lowest risk over other networks, followed by Spanish, French and South Korean rail networks. The study also demonstrates that the novel benchmarking criteria can effectively measure and compare any rail networks' risk and uncertainties. Its adoption will lead to performance improvement in terms of safety, reliability and maintenance policies of railway networks globally. [ABSTRACT FROM AUTHOR]

• Fouled ballast modelings have been conducted using DEM. • Progressive degradation of ballast has been evaluated and modelled. • Effect of ballast degradation on lateral stability is highlighted. • Lateral resistance of railway sleepers largely depends on ballast conditions. • Contamination in ballast can reduce the lateral resistance of sleepers by more than half. • Highlighted is the necessity for ballast inspection for predictive track maintenance. Track lateral stability is one of the most critical considerations for safe and reliable railway infrastructures. With increasing exposures to high temperatures globally, a greater expansion in continuous welded rails can induce a higher risk of track buckling, especially when track defects exist. In ballasted track structures, ballast layer holds sleepers in place and provides lateral support and stiffness to the track. Note that there are several factors influencing the lateral resistance of ballasted railway tracks. However, the effects of the progressive degradation of the ballast on the track's lateral resistance have thus far never been fully investigated. Note that the fouling conditions can be due to the accumulation of ballast breakage or external contamination, such as subgrade intrusion or coal dust, and difficult to inspect in the field. It is evidenced that track buckling can incur even if the railway track and ballast seem to be in a good condition by visual inspection. Therefore, this paper presents a more realistic model to study Single Sleeper (Tie) Push Test (STPT) conditions using the Discrete Element Method (DEM) with the objective to evaluate ballasted track lateral resistance considering different fouling scenarios. Note that coal dust, acting as a lubricant, is considered as a fouling agent. The lateral force–displacement curves of sleepers are analysed. The lateral force is derived from the sleeper-ballast contact forces obtained from three main components: sleeper bottom friction, sleeper side friction, and sleeper end force. The fouling conditions are employed by adapting appropriate model parameters to the ballast layer that represents the fouled ballast condition by coal dust in the DEM simulations. Note that the fouling layer is considered to start from the bottom of the ballast layer and is applied all the way to the top to represent the completely fouled ballast layer condition. The results indicate that fouled ballast can significantly undermine the lateral stability of ballasted tracks by more than about 50%. Track lateral stiffness may be reduced significantly due to fouled ballast layer conditions that cannot be inspected visually in the field. This may reduce track restraint and increase the likelihood of track buckling even though the degraded ballast does not have direct contact with the sleeper. Finally, the study will enrich the development of inspection criteria for ballast lateral resistance and support conditions, improve safety and reliability of rail network, and mitigate the risk of delays due to track buckling leading to unplanned maintenance. [ABSTRACT FROM AUTHOR]

• Three-dimensional FE models of railway track transition have been developed. • Baseplate fastening system can help reduce the differential settlement at transition zone. • The new insights will improve the design of baseplate fastening systems at the transition zone. In railway industry, significant attention has been spent to solve stiffness transition zone problems since the railway tracks at these zones, especially at the transition between bridge and embankment, are prone to the significant degradation and they need extra maintenance activities and cost to ensure the safety and comfort of passengers. A variety of applications to solve the transition zone problems have been widely investigated. However, never has the application of baseplate fastening systems to fix the transition zone problem been fully investigated. The study proposed herein is the world's first investigation to fill the knowledge gap by using numerical models to investigate the effect of baseplate pad stiffness and baseplate weight on the dynamic behaviours of the transition zone between slab track and ballasted track. The numerical models have been simulated using LS-DYNA software and validated by comparing with field measurements and other simulation results. The obtained results present that soft baseplate pads can intensify the rail displacements and increase an uneven track profile at transition zone. The results also show that the effect of baseplate weight play a slight role in reducing the differential settlement. The 400 MN/m/m2 pad stiffness provides the best solution as the slab track stiffness can be equalised to the stiffness of ballasted track. Overall, the optimal stiffness of baseplate can significantly reduce the differential settlement leading to reduce track degradation. However, the uses of heavier baseplates and softer baseplate pads together may cause negative effect by increasing the rail displacements leading to higher differential settlements. Hence, baseplate fastening systems should be carefully selected to maximise the benefit of baseplate fastening systems. The new insights will help track engineers to make an appropriate decision on the design and usage of baseplate fastening systems at the stiffness transition zone to mitigate the risk of accelerated track degradation. [ABSTRACT FROM AUTHOR]