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Ground configurations are an essential part of rail vehicles during wind tunnel tests. Reasonable reproductions of the infrastructures are of significance for experimental accuracy. In this work, the effects of ballast length were numerically studied via improved delayed detached eddy simulation (IDDES). Three extension lengths of the ballast accompanied by a 1/8th three-unit train model were proposed, with a pseudo infinite scenario as the benchmark. The numerical algorithm was firstly validated through a wind tunnel test in terms of aerodynamic loads and pressure distribution. The results revealed that the extended length of ballast had a significant impact on the leading and tail cars while less affected the middle car, due to the relatively farther distance from ballast ends. Ignored the drag coefficient, the influence of the ballast length on the separate cars was that the aerodynamic coefficients predicted by much longer ballast got closer to the benchmark. The ballast-edge-induced unrealistic flow and the train-nose-tip-induced realistic flow could easily be merged and interacted with each other and reinforced, thus causing a noticeable low-velocity zone at the leeward side. With the increasing ballast length, those two separations gradually moved away from each other, decoupled, and receded. A minimum length of E/H = 2 is recommended considering the aerodynamic performance and practical constraints of wind tunnel width. This study provides potential guidance for the arrangement of ground configurations for rail vehicles during wind tunnel tests. [ABSTRACT FROM AUTHOR]

Geometric description and reconstruction of ballast is the basis of ballasted track bed refinement research. In this paper, Laser scanning is used to establish the ballast contour sample library. The characteristic parameters of ballast contours, such as flattening, rectangularity are analyzed. A reconstruction method is proposed through deconstructing the ballast into the optimal ellipsoid and surface undulation feature by Gaussian projection; the ballast reconstruction function libraries and digital elevation-like model (DEM) are established to realize the regeneration of ballast. The results show that the ballast samples have various parameters of favorable morphological characteristics with no special particles, and the samples are of high quality. The optimal ellipsoid of ballast regenerated by the function libraries conforms to the probability distribution of the sample, and the correlation coefficients of middle-minor axis ratio (E m / E s) and middle-major axis ratio (E m / E l) are 0.9514 and 0.9628, respectively; the optimal ellipsoid generated by the method of equivalent ellipsoid is well fitted, the average overlap rate between the ellipsoid and the ballast reaches 90.62 %; the ballast reconstruction is excellent, all parameters are consistent with the sample distribution. This method can provide an effective way of particle modeling for a more realistic discrete element simulation of ballasted track bed. • The morphological features of ballast are presented by geometric deconstruction. • The ballast surface undulation feature is characterized by Gaussian projection. • A stochastic reconstruction method for 3D contours of ballast is proposed. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the behavior of fresh and recycled Electric Arc Furnace (EAF) slag materials as railway ballast using large-scale cyclic triaxial tests. Recycled slags are materials that were previously subjected to cyclic and monotonic loadings and Los Angeles abrasion. These materials were cleaned and re-grained. Grain size of recycled ballast was similar to fresh ballast, from 19 to 50.8 mm. All the specimens with a diameter of 30 cm and a height of 60 cm were tested in dry conditions. Based on the results, there is no limitation in the use of EAF slag as ballast in terms of quality control criteria. However, the cyclic stress amplitude applied to the EAF slag should be limited to 210 kPa to prevent progressive deformations. An increase in the maximum ballast size and the quantity of recycled ballast can increase the resilient modulus and the ultimate permanent axial deformation. The resilient modulus at the confining pressures of 60 and 30 kPa is at least 400 and 300 MPa, respectively. The resilient modulus reaches less than 300 MPa at the failure stage. [Display omitted] • Cyclic and post-cyclic monotonic behavior of fresh and recycled EAF slag ballast was investigated. • The speed and axial load must be limited in slag-ballasted tracks. • The cyclic stress amplitude applied to the EAF slag should be limited to 210 kPa. • Threshold axial strain of progressive deformations in EAF ballast is 0.025 %. [ABSTRACT FROM AUTHOR]

• A lightweight RGB-based model for predicting railway ballast's Fouling Index (FI). • The minimum subsample size was determined experimentally and analytically. • Achieved the same prediction accuracy using just 1% of the data compared to the previous model. • The ability to quantify local fouling conditions effectively. Ballasted track is the major form of freight railroads. Despite various requirements for material selection, ballast will degrade due to wear and the infiltration of fine materials. These fine particles will cause ballast fouling and degraded track performance. The fouling condition is directly related to both ballast performance and track maintenance planning. It can be quantitatively assessed using the Fouling Index (FI), calculated as the sum of the percentages of materials passing through No. 4 (4.75 mm) and No. 200 (75 µm) sieves. Traditional fouling assessment methods rely on labor-intensive sieve analysis. While non-destructive techniques such as Ground Penetration Radar, Impulse Response, Surface Wave, and SmartRock offer alternatives, they require specialized equipment and skilled technicians for accurate interpretation. Deep learning models have also been employed, trying to assess ballast fouling conditions by segmenting particles. However, these models struggle to account for fine materials. Recently, the FI was found to be linearly correlated with the variance of RGB (Red, Green, Blue) intensities in fouled ballast images, and this correlation could be used to assess ballast fouling conditions. Improving upon the previously developed FI prediction model and making it more practical, this study proposes an enhanced and lite RGB-based model that predicts the FI through a simple random subsampling approach. The optimal subsample size is determined both experimentally and analytically. Based on the results obtained from this study, the correlation between FI and the variance of RGB intensities in fouled ballast images is further confirmed. The proposed lite model can achieve the same accuracy in FI prediction but requires fewer than 1 % of the data points needed by previous methods, which demonstrates its promising potential for ballast fouling condition assessment practice. [ABSTRACT FROM AUTHOR]

The coastal plain of West Sussex and south-east Hampshire preserves a succession of Pleistocene raised beaches, periglacial deposits, and estuarine channels. These incorporate numerous 'erratics' or 'exotic' rocks, here described as enigmatic rocks, and sarsen stones. The enigmatic rocks include large boulders of non-local igneous, metamorphic, and sedimentary rocks, which have attracted interest since the early 19th century. Many suggestions have been made regarding their origins, transport, and date of emplacement. More recently, it has been realised that these rocks may have important implications for understanding the Quaternary history of southern Britain and the palaeogeography of the English Channel region during the Pleistocene. This paper presents a literature review, supported by details of historic and extant boulders, distribution, and dimensions. In agreement with previous authors, it is concluded that the enigmatic rocks were likely transported within ice floes or icebergs, but further studies are required to identify possible sources. Suggestions have included northern Britain, Scotland, Scandinavia, Greenland and Laurentia. There are doubts concerning an adequate build-up of periglacial sea-ice to accept the historic consensus for a source in Brittany, the Cotentin Peninsula, and the Channel Islands. The date of emplacement is suggested to be MIS 13, but multiple phases of emplacement cannot be excluded. In contrast, the sarsen stones are considered to be relic of pre-MIS 7 periglacial erosion of weathered Lambeth Group in a regolith of Clay-with-flints formerly capping the local Chalk outcrop. Many questions remain unanswered, particularly regarding the enigmatic rocks, so aspects for future study are identified. [ABSTRACT FROM AUTHOR]

Concentration gradient batteries (CGBs) use electrodialysis and reverse electrodialysis to charge and discharge, respectively. An important factor hindering CGB efficiency is osmosis through ion exchange membranes (IEMs); however, adding an osmotic ballast to the dilute compartment reduces osmosis and improves CGB efficiency. Despite the importance of osmosis in CGB performance, there has been no evaluation of the effects of CGB parameters on performance with and without an osmotic ballast. Accordingly, our goal was to evaluate the effects of selected CGB parameters on various CGB performance metrics to inform future optimization of CGB designs. Results showed ballast addition improved current and round-trip energy efficiency and stabilized CGB performance across multi-cycle operation. However, ballast addition caused lower average (net) power densities due to its impact on IEM stack resistance and solution viscosity. Increasing the flowrate and decreasing the spacer thickness led to decreases in average net power densities. Importantly, the effect of IEM properties on CGB performance varied with ballast addition: low water permeability IEMs had greater and lower round-trip energy efficiencies without and with ballast, respectively, compared to low resistance IEMs. This work informs CGB parameter selection, demonstrates tradeoffs associated with osmotic ballast addition, and shows multi-cycle CGB operation is feasible. • Ballast addition substantially improved CGB current and round-trip energy efficiency • Ballast addition enabled stabilized CGB operation across multiple battery cycles • Thin spacers and high flowrates weakened CGB performance due to high pressure drops • Effects of altering parameters on RED performance do not directly translate to CGBs • Impacts of IEM properties on CGB performance varied with ballast addition [ABSTRACT FROM AUTHOR]

The shear strength of geogrid-reinforced ballast is often dependent on the aperture size of geogrids and the nominal size of ballast. This paper presents a theoretical analysis based on probabilistic mechanics of how aperture size affects the interaction between particles and geogrid. Unlike past literature, in this study, the properties of the particle size distribution is analysed using a Weibull distribution. The probability of grain interlock is proposed to describe the interactive mechanisms between particles and geogrids based on the relative particle size, which is defined as the ratio of particle size to aperture size. The mathematical model is calibrated by a set of large-scale direct shear tests with almost single-size (highly uniform) ballast aggregates, and then validated by independent set of data taken from both literature and current study. The study concludes that more uniform particle size distribution increases the probability of grain interlock at the optimum aperture size but decreases it at non-optimum aperture sizes. • This research proposed a novel analytical model to capture the size effect of geogrid aperture on ballast-geogrid interaction. • The concept of probability of grain interlock was developed to uncover how the relative ballast sizes, defined as the ratio of particle size to aperture size, determine different interaction mechanisms. • The interaction behaviors between each particle and geogrid have been integrated through particle size distribution curve, hence evaluating the overall ballast/geogrid interface behaviour. • A set of direct shear tests have been conducted between highly uniformed ballast and geogrids to calibrate the parameters of this model. • Then, model predictions have been validated by two independent sets of direct shear tests conducted from literature and current study. [ABSTRACT FROM AUTHOR]

Vertical stiffness and shear strength of ballasts are significantly degraded when contaminated with sands. There is a lack of solutions/studies related to strengthening ballast against sand contamination. Addressing this limitation, a comprehensive laboratory investigation was made on effectiveness of geogrid reinforcement for improvement of mechanical properties of sand-contaminated ballast. To this end, large-scale direct shear tests as well as plate load tests were conducted on geogrid-reinforced ballast samples prepared with different levels of sand contamination. The obtained results indicate that geogrid reinforcement considerably improves shear strength and vertical stiffness of contaminated ballast. A bandwidth was obtained for contamination levels in which ballast reinforcement is effective. Through examining geogrid with different aperture sizes and locations in the ballast layer, the best performance conditions of geogrid reinforcement were derived. The results were used to propose an effective method of ballast reinforcement and an efficient ballast maintenance approach in sandy areas. [ABSTRACT FROM AUTHOR]

Rail tracks continue to deform due to degradation of ballast under the application of heavy train traffic. The resulting track deformations often lead to drainage impairment as well as loss of resiliency. For track replenishment, deep screening of ballast is usually adopted by Indian Railway (IR) either after 10 years or passage of 500 MGT traffic, whichever is earlier. To study the effectiveness of geotextile on track stability and assess possible reductions in maintenance costs, a layer of woven geotextile was installed at the ballast-subgrade interface in Bhusawal-Akola central railway section of IR which is the present study area. The results show that the amount of degradation and fouling are different in UP and DN tracks due to inherent variation in traffic characteristics. This study also shows that the placement of geotextile in the track has led to prolonged maintenance cycle with favorable implications on cost and track shutdown periods. The findings of the present case study results will be useful for IR to reduce the ballast procurement and reuse of discarded material during deep screening in future. [ABSTRACT FROM AUTHOR]

A new method to model the abrasion of granular particles using the discrete element method is demonstrated in this paper. This new, simple method is based on a classical theory of abrasive wear, relating the volume of solid lost to the frictional work at particle contacts. The modelling technique is demonstrated in simulations of railway ballast using realistically-shaped particles, which are compared to experimental data. The new abrasion model correctly introduces stress-dependent behaviour at small strains into the simulations, which is essential for any realistic discrete element model. [ABSTRACT FROM AUTHOR]

Background: Walking on railroad ballast is a unique challenge for railroad workers and contributes to a large number of falls and slips. However, the characteristics of ground reaction force (GRF) when walking on ballast combined with a cross-slope condition are poorly understood.Research Question: How does the magnitude and temporal distribution of GRF change during walking on railroad ballast combined with a cross-slope condition?Methods: Eight experienced railroad workers walked with their self-selected speed on three surfaces (mainline ballast, walking ballast and no ballast) in both a level and cross-slope (7°) condition. The magnitude and time of occurrence of selected key features of the GRF were extracted from the force plate. A two-factor repeated measures ANOVA was used to determine the effect of surface and cross-slope condition.Results: The minimum anteroposterior GRF and the first peak of the normal GRF occurred earlier on mainline ballast and walking ballast than no ballast. The maximum anteroposterior GRF was smaller, but the first peak of the normal GRF was larger on walking ballast compared with no ballast. Additionally, the asymmetrically mediolateral GRFs were observed between upslope limb and downslope limb in the cross-slope condition, which were also significantly different from the level condition.Significance: Ballast combined with a cross-slope condition posed a higher requirement for dynamic control to prevent downslope slippage and body instability, which could increase the fall risk for railroad workers. Future studies should investigate interventions to improve dynamic balance and reduce foot slippage on ballast. [ABSTRACT FROM AUTHOR]

• The features of ballast silhouettes based on optimal ellipses and stretch curves are presented. • The suitable number of sampling points based on the optimal ellipses is presented. • A random batch generation method of ballast silhouettes is established. Research on the topological rule and random generation method of a ballast silhouette can realize different batch generations of ballast 2D topology under the condition of definite gradation, which can lay a foundation for the microscopic simulation and performance research of a railway ballast bed. Based on the analysis of ballast particle silhouette samples collected by digital image processing technology (DIPT), this paper presents a method of characterizing ballast silhouette features based on an optimal ellipse and surface stretch curve and achieves random batch generation of ballast silhouette 2D topology by establishing ballast particle reconstruction function libraries. The results show that the optimal ellipse processed by the least squares method can represent the holistic shape of ballast particles; the silhouette surface stretch curve based on the optimal ellipse can reflect the fluctuation degree of the silhouette; the function libraries can effectively support the reconstruction and random generation of ballast 2D topology; and the reconstructed ballast database passes the particle size gradation curve test and the main morphological characteristic parameter test, which shows that the method can be used in batch generation of ballast 2D silhouettes and related simulation. [ABSTRACT FROM AUTHOR]

• New bonding schemes were proposed for mitigating ballast flight with polyurethane. • Single sleeper pull-out tests were performed on polyurethane-reinforced ballast. • DEM simulations with realistic particle shapes and parallel bonds were presented. • Mechanisms of ballast resistance improvement due to polyurethane were analyzed. To mitigate the ballast flight risk in the high-speed railway, this paper presents three new polyurethane bonding schemes which have negligible influence to tamping operations. With the application of these bonding schemes, a series of laboratory tests indicated that the polyurethane-reinforced ballast exhibited much larger lateral resistance than the ordinary ballast by 31% at least. Discrete element simulation results further demonstrated that the polyurethane improved the load-bearing capacity of the ballast at the particle scale through effectively restraining the particle movement. Therefore, the proposed bonding schemes ensure adequate lateral ballast resistance and are effective measures for improving the ballast performance. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) has become a widely used trackbed inspection tool for railroad maintenance engineers. The method is attractive, due to the ability to autonomously collect continuous trackbed quality related information at traffic speeds (20–200 km/h). Information on ballast quality, formation settlement and the presence of saturated materials is used to plan maintenance and budget material replacement. Ballast fouling levels and moisture content are key properties of ballast quality that affect the stiffness of the trackbed. Due to the often highly heterogeneous composition of trackbed materials, extracting related information from GPR data alone is challenging. This paper considers in detail how electromagnetic properties of trackbed materials, relating to varying degrees of ballast fouling and moisture content, affect attributes derived from reflected and scattered GPR signals. It is shown that the inherent ambiguities in the response of GPR to fouling and moisture within the trackbed mean that neither can be uniquely determined by the method. We present the less ambiguous measure of the thickness of clean ballast, a useful proxy for the overall fouling condition of the trackbed. • GPR attributes are modelled for a range of ballast fouling and moisture conditions • Ballast fouling and moisture content each influence the GPR response of a trackbed • Proportions of moisture and ballast fouling cannot be independently measured by GPR • Clean ballast thickness measured by GPR avoids the ambiguity from water content [ABSTRACT FROM AUTHOR]

Slab track is replacing obsolete ballasted track. This work proposes crushing out-of-service ballast and sleepers for use as aggregates for constructing the slab track. Three kinds of recycled self-compacting concretes were designed; the first one with aggregates from crushed ballast, the second one with aggregates from crushed sleepers and the third one with both kinds of aggregates in the proportion they appear in the track. The mechanical and durability properties of these concretes were analysed. The durability test was focused on freeze-thaw and drying-wetting cycles. The results obtained lead to the conclusion that out-of-service track could be used to build the new one, closing the loop. • The use of out of service railway superstructure wastes is validated. • Durability and mechanical properties of self-compacting recycled concrete have been analysed. • The same crushing procedure can provide different tribological properties for different wastes. • Recycled concrete fulfils the requirements of slab track standards. [ABSTRACT FROM AUTHOR]

Abstract Railway ballast is now subjected to dynamic train loads with higher frequency components due to the continue increase of the train speed. However, the effect of load frequency on ballast permanent deformation was ignored in most laboratory tests. This study aims to clarify the importance of load frequency in applying cyclic loads to investigate the ballast permanent deformation under high-speed rail loading conditions. A three-dimensional discrete element model was established using clumps with realistic ballast particle shapes and validated with a laboratory test. Numerical simulations were then conducted with the validated DEM model to study the ballast deformation behavior. The simulated ballast deformation under high-speed train loads and that under cyclic loads with different load frequencies were compared to demonstrate the quantitative discrepancy between them. The results from this study confirm that under high-speed rail loading scenarios, the load frequency has significant influence on ballast permanent deformation and there is significant importance to take the effect of the load frequency into account when investigating the permanent deformation of high-speed railway ballast by applying cyclic loads. It is recommended to apply the cyclic loading with the same amplitude to the high-speed train load and with the frequency equivalent to the passing frequency of the train's wheelbase to the ballast in laboratory tests so as to obtain quantitative ballast deformation results by using one load cycle to simulate two axle loads of a train. Highlights • A three dimensional discrete element model with realistic ballast particle shapes is established. • Permanent deformation of ballast under repeated high-train loads are simulated using discrete element method. • Discrepancy between the ballast deformation results under train loads and those under cyclic loads are analyzed. • Cyclic loading for achieve quantitative ballast deformation in laboratory test is recommended. [ABSTRACT FROM AUTHOR]

Highlights • Lateral resistance of ladder sleepers is investigated by the lateral track panel test. • The contribution of ballast components to the lateral resistance is obtained. • The DEM simulation of a ladder sleeper on the ballast layer was performed. Abstract The sleeper-ballast interface of railway tracks directly is associated with lateral resistance which plays an important role in the mechanical behavior of ballasted tracks. In a real-case implementation of ballasted track for speeds as high as 400 km/h, sufficient lateral resistance is vital to prevent the lateral movement of the track. In view of the future development, a series of full-scale lateral track panel tests (LTPT) were conducted to evaluate the lateral resistance of ladder sleepers as a substitution of monoblock sleepers. The experimental results revealed that the application of the ladder sleepers caused an increase in lateral resistance of the ballasted track as well as a reduction in the use of ballast aggregates. In addition, the contribution of the ladder sleeper facets to the lateral resistance was investigated by the discrete element method (DEM). In conclusion, crib ballast has the main role in the lateral resistance of ladder sleeper tracks. [ABSTRACT FROM AUTHOR]

Abstract The underbody flow of high-speed trains is a matter of concern in the railway industry because of its relation to the ballast flight phenomenon, and several experimental campaigns are focused on evaluating its characteristics. Computational simulations are considered as a flexible and economical alternative. However, the aforementioned simulations include only simplified track models with a flat ground that do not include the sleepers or the profiles of stones. The present study uses a previously developed methodology to reproduce the passing of a high-speed train over a scanned real profile of stones and sleepers and determines the effect on the surrounding flow and compares the results relative to those of a flat ballast bed. The simulations are validated relative to experimental data published in the bibliography with satisfactory results. The results confirm expected differences between flat and rough configurations, thereby revealing a more chaotic velocity field near the rough ballast and the presence of a larger number and smaller size of turbulence structures. The rough configuration also allows for the measurement of the pressure on the surface of the stones and the application of a predictive model for ballast flight. The obtained results are similar to those in experimental tests. Highlights • An innovative CFD methodogy for the simulation of high-speed trains is proposed. • A reallistic ballast profile from in situ scan measurements was included in the CFD model. • This methodology allows to reproduce the passing of a high-speed train over a real profile. • Validation against previous experimental results from literatura was done. • Differences in velocity and turbulence flows were revealed when compared with flat bed results. [ABSTRACT FROM AUTHOR]

• Using 3D image processing and advanced data analytics to differentiate fresh and used ballast morphological parameters. • A machine learning algorithm was trained to distinguish between fresh and used ballast automatically. • Sphericity and convexity were crucial for differentiating fresh and used ballast, with identified threshold values. This study presents a method that utilizes 3D digital image processing and advanced data analytics to differentiate between fresh and used railway ballast materials. Railway ballast degrades over time, necessitating replacement with fresh material. However, fresh ballast may be scarce in some areas, and replacement costs have risen significantly. Recycling large aggregates from deteriorated ballast offers a solution to reduce track maintenance costs and greenhouse gas emissions, gaining popularity in track maintenance activities. Current ballast recycling practices, however, do not account for the morphological changes in the aggregates and their impact on the ballast's mechanical behavior. A machine learning algorithm is trained to differentiate fresh and used ballast automatically. The study examines the morphological parameters of fresh and used ballast materials using 3D scanning and image analysis techniques. A machine learning algorithm was trained to automatically distinguish between fresh and used ballast. The results reveal that sphericity and convexity were crucial parameters for differentiating fresh and used ballast, with identified threshold values of 0.89 for convexity and 0.8 for sphericity. The insights from this study may assist the decision for ballast recycling, reducing the demand for fresh ballast while maintaining track performance. [ABSTRACT FROM AUTHOR]

Highlights • Increase in breakdown fouling does not result in the loss of strength at constant water content. • With the increase in breakdown fouling, the friction angle increases non-linearly. • The effect of fouling on the relationship between ballast strength and volumetric strain rate during dilation is significant. • Ballast elastic modulus decreases linearly with an increase in water content. • An increase in confining pressure results in an increase in ballast breakage. Abstract This paper discusses the drained static triaxial testing on granite ballast material with different amount of breakdown fouling and water content. Large-scale, 10 in., triaxial equipment was used for this testing program at the University of Massachusetts, Amherst. These tests were performed to study the effect of fouling and its inseparable associate, water content, on the strength properties and degradation characteristics of railroad ballasted track. Ballast with three different fouling percentages (defined as the ratio of dry weight material passing 3/8″ (9.5 mm) sieve to dry weight of the total ballast sample) from clean to highly fouled ballast (<5%, 15% and 30%) and four water contents from dry to field capacity were tested under three different confining pressures (5, 10 and 15 psi). The results show that although increase in breakdown fouling at dry conditions increases the strength of the ballast, by an increase in water held by fouling material the ballast starts degrading. [ABSTRACT FROM AUTHOR]

Highlights • The performance of steel sleepers reinforced by rubber layers and web steel stiffeners are evaluated. • Lateral resistance of steel sleepers is investigated by the single tie push test. • The contribution of ballast components to the lateral resistance are obtained. Abstract In this study, the lateral resistance of different types of steel sleepers, placed on the ballast layer with a variety of shoulder height and shoulder width, has been investigated. A number of single tie push tests were conducted to examine the effect of bumped-rubber layers and web steel stiffeners on the ballast/sleeper interaction. In the next step, DEM simulations of STPTs were developed by PFC3D to estimate the contribution of shoulder ballast height to the lateral resistance of steel sleepers. According to the laboratory results, the use of 3 web steel stiffeners caused about 70% increase in the lateral resistance in comparison with the conventional steel sleeper. On the other hand, DEM simulation results indicate that ballast bed had a higher proportion to the lateral resistance of steel sleepers than that of all the other ballast components and using web steel stiffeners could increase by 9% the contribution of the bottom surface of steel sleepers to ballast/sleeper interaction. [ABSTRACT FROM AUTHOR]

Railway ballast (RB) layer has to limit tie movement by resisting vertical, lateral and longitudinal forces from the train and the track, to reduce the stresses from train loads applied to the subgrade, thus limiting permanent settlement. It also has to provide immediate water drainage from the track structure, to aid in alleviating frost problems, to facilitate maintenance surfacing and lining operations, to provide support for ties with the necessary resilience to absorb shock from dynamic loads. Secondary functions include retarding vegetation and resisting effects of fouling from surface deposited materials, absorbing airborne noise, providing adequate electrical resistance between rails, facilitating the redesign or reconstruction of the track. These properties are obtained through the use of proper gradation crushed granite, by determining its proper laying and compacting technological parameters, by ensuring sufficient thickness and profile of the layer. This paper presents statistical investigations of the four samples of crushed granite taken from transporter belt (TB), plant stockpile (PS), wagon (W) and railway construction (RC) uncompacted layer used to RB course. The gradation (particle size distribution), density of crushed granite particles ( DEN P ), water absorption ( WA 24 ), Deval index ( M DE ), Los Angeles coefficient ( LA RB coefficient) and resistance to crushing ( SZ RB ) of four samples were measured. Statistical parameters of crushed granite qualitative indicators, histograms, theoretical curves of normal distribution are presented. Their compliance with normal distribution was verified by employing the criteria of skewness, kurtosis, Pearson, Shapiro-Wilk and Kolmogorov-Smirnov. Dependance of standard deviations of percent passing through sieves on the means of percent passing through these sieves was obtained from regression analysis. The use of Kruskal-Wallis test by ranks showed that means obtained in different sample-taking locations did not differ statistically. The maximum value of standard deviation of this dependance, equal to mean of 50% percent passing, was used to evaluate the homogeneity of crushed granite used to construct the ballast layer according to the variation of its gradation. Absolute allowable error of minimum sample size n, equal to 5%, 10%, 15% and 20%, was calculated. Investigation results indicated that due to segregation the homogeneity of the gradation of crushed granite used to construct the ballast layer from its production site to its exploitation site decreased by 78%. During the technological processes of loading, transporting and spreading the gradation has hardly changed. [ABSTRACT FROM AUTHOR]

Abstract This paper outlines a three-dimensional modeling study conducted on straight and curved geocell-reinforced embankments. The study uses the discrete element method to represent varying angularities of ballast infill and models their mechanical response under monotonic and cyclic loading conditions. The simulation results show good agreement with test results and the case studies indicate that the geocell enhances embankment stiffness under monotonic loading and improves its resilience when subjected to cyclic loading. The geocell more evenly distributes stresses within the ballast embankments. The reinforced ballast embankments also exhibit less vertical displacement and lateral spreading than the unreinforced ballast embankments do. [ABSTRACT FROM AUTHOR]

A series of large-scale direct shear tests were conducted to investigate the behavior of unreinforced and geogrid-reinforced ballast at different rates of shearing. Fresh granite ballast with an average particle size ( D 50 ) of 42 mm and five geogrids having different aperture shapes and sizes was used in this study. Tests were performed at different normal stresses ( σ n ) ranging from 35 kPa to 140 kPa and at different rates of shearing ( S r ) ranging from 2.5 to 10.0 mm/min. The laboratory test results revealed that the shear strength of ballast was significantly influenced by the rate of shearing. The internal friction angle of ballast ( φ ) was found to decrease from 66.5° to 58° when the shearing rate ( S r ) was increased from 2.5 to 10.0 mm/min. It is further observed that the interface shear strength has improved significantly when the ballast was reinforced with geogrids. The interface efficiency factor ( α ), defined as the ratio of the shear strength of the interface to the internal shear strength of ballast, varies from 0.83 to 1.06. The sieve analysis of samples after the testing reveals that a significant amount of particle breakage occurs during shearing. The value of breakage, evaluated in terms of Marsal's breakage index ( B g ), increases from 5.12 to 13.24% with an increase in shearing rates from 2.5 to 10.0 mm/min. Moreover, the influence of aperture shape and size of geogrid on the behavior of ballast-geogrid interfaces was also examined in this study. [ABSTRACT FROM AUTHOR]

Ballast track is the most widely used track for the railway transport, and ballast bed plays a significant role to provide resistances during train operation. Generally, the ballast bed consists of crushed stones. To achieve the mitigation of ballast degradation, the first priority is to describe the degradation development and to study its effect factors. The influence of ballast morphology (particle size and shape) on ballast degradation is examined here using the Los Angeles Abrasion (LAA) test in combination with 3-D image analysis. LAA tests are used to obtain the deteriorated ballast. Then, based on the 3-D images, the changes of ballast particles after the tests were analysed. To quantify the ballast degradation (abrasion and breakage), the Abrasion Depth based on the analysis of 3-D images were proposed, while ballast breakage was estimated using the broken particles ratio. The results have shown that ballast degradation is directly related to the ballast morphology. The proposed image-based procedure can effectively be applied to assess ballast degradation. The results can be used for ballast material standardization, modelling of ballast degradation process and maintenance cycle prediction. [ABSTRACT FROM AUTHOR]

Ballast plays an important role in the stability of railway track systems. The effectiveness of the ballast in maintaining the track stability is very much dependent on its mechanical conditions. The available ballast maintenance approaches are mainly based on only track geometry conditions (such as track profile) which do not sufficiently reflect the ballast mechanical behaviors. That is, the ballast potential of degradation (i.e., ballast long term behaviors) has been omitted. This makes the effectiveness of the current ballast maintenance approach questionable, indicating a need for a more comprehensive and effective ballast conditions assessment technique. In response to this need, two ballast condition indices based on ballast geometry degradation (BGI) and the level of ballast fouling (BFI) as the main indicators of ballast mechanical behavior were developed. The BGI is a function of the standard deviations of track alignment, unevenness and twist. The BFI was developed based on the data obtained from the ground penetration radar (GPR). Making use of the new indices, a more reliable maintenance algorithm was developed. Through illustrations of the applicability of the new maintenance algorithm in a railway line, it was shown that the new algorithm causes a considerable improvement in the maintenance effectiveness and an increase in the life cycle of railway tracks by making more effective allocation of resources and more accurate maintenance planning. [ABSTRACT FROM AUTHOR]

In order to guarantee safety and driving comfort and to maintain an efficient railway infrastructure, the first step is to carefully monitor the track geometry and wear level of the materials constituting the superstructure. To that end diagnostic trains are widely used on main lines, in that they can detect several geometric track parameters and rail wear, but under no circumstances they can yet detect ballast gradation. Due to the practical implications for the planning of maintenance operations on the railway network, this article presents a “DIP” digital image processing technique for measuring the transverse profile and corrugations of the rails as well as ballast gradation. The research was carried out in the laboratory on samples of worn-out rails taken from operational railway lines and in situ in the case of ballast analyses. For the latter, the reliability of the results obtained was assessed by comparison with available results yielded by traditional testing methods. It is shown that the proposed technique can be used not only for laboratory analyses, but most conveniently for high-efficiency in situ surveys, along with the methods traditionally adopted by the railway managing authorities thus contributing to lowering the maintenance cost associated with rail inspection. [ABSTRACT FROM AUTHOR]

The violent vibration and excessive settlement of trackbeds under high-speed train moving loads are the main problems of ballasted tracks encountered in practice, which limits the rise of operation speed for ballasted railways. To date, the possibility of extending the widely used geogrid in conventional ballasted railways to high-speed railways has not been adequately validated. The stabilization mechanism of geogrids under high-speed train moving loads remains unclear. Herein, a ballasted track DEM model containing five sleepers that reproduced high-speed train moving loads was developed through EDEM software and validated by full-scale model tests. Both cases of ballasted tracks with and without the geogrid were examined. The results showed that the geogrid significantly decreased the total and differential settlement of the ballasted track. After geogrid installation, the coordination number of ballast particles was increased, and the contact forces among ballast particles were reduced, which potentially lowered the ballast breakage. The geogrid effectively constrained the displacement and rotation of ballast particles. The reduced migration of ballast particles led to a smaller and more uniform volumetric strain field of the ballasted trackbed. By investigating the working mechanism of the geogrid, it was shown that the penetration of the ballast particles into the geogrid aperture induced the expansion of the geogrid aperture, and therefore, the lateral force from the geogrid ribs limited the movement of the ballast particles. [ABSTRACT FROM AUTHOR]

This paper presents the results of full scale measurements of the underbody flow characteristics and track behaviour beneath a high speed train on a line in the south of England. Simultaneous measurements were made of the flow velocities and pressures beneath the train, sleeper displacements and ballast accelerations. The results showed that, while the mechanical measurements of displacement and acceleration were essentially deterministic and varied little from one train passage to another, the aerodynamic measurements were highly variable with substantial run-to-run variation. Vertical ballast accelerations with peaks greater than the acceleration due to gravity were measured for short durations. Velocity and turbulence intensity profiles were derived, from which aerodynamic shear forces at the ballast surface were estimated. Assessment of the magnitudes of the different forces acting on the ballast showed that the mechanical forces associated with track displacement and the aerodynamic forces were of similar order of magnitude on well performing track. For poorly maintained track with higher accelerations, the effects of track vibration on the initiation of ballast motion are likley to be much more significant. [ABSTRACT FROM AUTHOR]

The two main functions of ballast are train-load distribution and track-water drainage. Repeated train passage subjects ballast aggregates to abrasion and, eventually, breakage. Mixing of bonding materials such as polyurethane into aggregates can effectively mitigate ballast degradation. In the present study, large-scale triaxial tests were carried out to investigate the characteristics of polyurethane-mixed ballast materials. The stiffness and strength of the materials could be predicted in terms of the polyurethane contents, and the linear relationships could be established. According to those relationships, the performance of polyurethane-mixed aggregates as enhanced railway ballast materials can be simply but reasonably estimated. [ABSTRACT FROM AUTHOR]

Current railroads require significant upgrading to meet the challenges of heavier loads at higher speeds. Due to excessive track degradation, the Australian rail industry spends large amounts on frequent track repair and maintenance, as well as ground improvement prior to track construction where soft and saturated subgrade soils pose considerable difficulties in design and construction. Moreover, the degradation of ballast particles under impact loading seriously hampers the safety and efficiency of rail tracks, which leads to speed restrictions and more frequent track upgrading. Hence, there is a need for innovative design solutions that can extend the service life of tracks to cater for faster and heavier train traffic. The use of planar geosynthetics and recycled rubber mats placed at the interface of ballast and subballast layer has proven an effective approach to mitigate ballast degradation and improve track longevity. This paper presents the current state-of-the-art knowledge of rail track geomechanics conducted at the University of Wollongong (UOW) including topics relating to laboratory testing and computational modeling approaches. The load-deformation responses of rubber mat/geogrid-stabilised ballast are studied in the laboratory using a large-scale drop weight impact testing facility, and Track Process Simulation Apparatus (TPSA). Numerical modelling using discrete element methods (DEM) are used to model geogrid-reinforced ballasted tracks, capturing both the discrete nature of ballast subject to various types of loading and boundary conditions. These results provide promising approaches to incorporate into the existing track design routines catering for future high speed and heavy haul trains. [ABSTRACT FROM AUTHOR]

The paper describes cohesion and friction angle research results of new granite railway ballast. It was found out that crushed stone abrasion degree increase leads to ballast cohesion decrease and has not effect on ballast friction angle. Authors determined that strength properties of new and reclaimed ballast mixtures depend on initial abrasion degree significantly. When using a mixture of 70% reclaimed and 30% new ballast it becomes possible to provide mixture ballast strength properties closely approximated to requirements for new ballast. [ABSTRACT FROM AUTHOR]

In the paper the problem of pollution of the railway ballast by heavy metals is considered. Heavy metals migrate into the soil under the action of precipitation and acid rain. Environmental pollution caused by heavy metal ions is particularly hazardous. Unlike other pollutants in soils the heavy metal ions reserve for a long time even after removal of the pollution source. The ability of heavy metal ions to migrate to soil, into the underground, ground and surface water, to accumulate in food leads to the need of consideration of their impact on human health. Heavy metals are carcinogenic. To solve this ecological problem we offer to reinforce contaminated ballast by means of binder systems having geoecoprotective properties against heavy metal ions. [ABSTRACT FROM AUTHOR]

Nowadays requirements for strength and stability of railway subgrade are increased. It is due to raising of train speed and axle load. Some sections of subgrade that were previously considered stable do not satisfy safety requirements. In this regard, superstructure reinforcing solutions need to be developed. This paper highlights ballast and subgrade reinforcement applications of geogrids in railway infrastructure. In recent years, geosynthetics are widely used for this purpose. Geosynthetics influence on the stress-strain state of subgrade is an important and extremely urgent problem. The paper describes recent research efforts in field studies, which helped to identify geosynthetics reinforcement influence on ballast layer. [ABSTRACT FROM AUTHOR]

Structural Health Monitoring (SHM) of aging railway tracks is important for safety, to prevent catastrophic failure, and to reduce maintenance costs. The tracks and foundations are complex systems that may contain defects or damage including internal rail cracks, pitting or surface erosion, degradation of ballast support, or railway crosstie-ballast failures. In recent years, interest has grown in performing SHM by measuring structural deformation, full-field strain, and geometry profiles using three-dimensional (3D) Digital Image Correlation (DIC) systems. In this study, a novel approach to use DIC and pattern projection to assess the deformation of railway tracks is proposed. The proposed sensing approach should allow a railcar mounted sensing system to perform interrogation while moving at typical operating speeds (e.g. 60 mph). The feasibility of the proposed 3D DIC system is evaluated through extensive laboratory testing. The approach’s ability to measure the crosstie’s full-field displacement and shape (i.e. at levels similar to what is found in the field) as different loading conditions are applied is demonstrated. The influence of motion similar to what might be found in a railroad service environment on the accuracy of the measurements is also quantified. [ABSTRACT FROM AUTHOR]

Transparent Exopolymer Particles (TEP) have received considerable attention since they were first described in the ocean more than 20 years ago. This is because of their carbon-rich composition, their high concentrations in ocean’s surface waters, and especially because of their ability to promote aggregation due to their high stickiness (i.e. biological glue). As large aggregates contribute significantly to vertical carbon flux, TEP are commonly seen as a key factor that drives the downward flux of particulate organic carbon (POC). However, the density of TEP is lower than that of seawater, which causes them to remain in surface waters and even move upwards if not ballasted by other particles, which often leads to their accumulation in the sea surface microlayer. Hence we question here the generally accepted view that TEP always increase the downward flux of POC via gravitational settling. In the present reassessment of the role of TEP, we examine how the presence of a pool of non-sinking carbon-rich particulate organic matter in surface waters influences the cycling of organic carbon in the upper ocean at daily to decadal time scales. In particular, we focus on the role of TEP in the retention of organic carbon in surface waters versus downward export, and discuss the potential consequences of climate change on this process and on the efficiency of the biological carbon pump. We show that TEP sink only when ballasted with enough high-density particles to compensate their low density, and hence that their role in vertical POC export is not solely linked to their ability to promote aggregation, but also to their contribution to the buoyancy of POC. It follows that the TEP fraction of POC determines the degree of retention and remineralization of POC in surface waters versus its downward export. A high TEP concentration may temporally decouple primary production and downward export. We identify two main parameters that affect the contribution of TEP to POC cycling; TEP stickiness, and the balance between TEP production and degradation rates. Because stickiness, production and degradation of TEP vary with environmental conditions, the role of TEP in controlling the balance between retention versus export, and hence the drawdown of atmospheric CO 2 by the biological carbon pump, can be highly variable, and is likely to be affected by climate change. [ABSTRACT FROM AUTHOR]

Most constitutive models can only simulate cumulative deformation after a limited number of cycles. However, railroad ballast usually experiences a large number of train passages that cause history-dependent long-term deformation. Fractional calculus is an efficient tool for modelling this phenomenon and therefore is incorporated into a constitutive model for predicting the cumulative deformation. The proposed model is further validated by comparing the model predictions with a series of corresponding experimental results. It is observed that the proposed model can realistically simulate the cumulative deformation of ballast from the onset of loading up to a large number of load cycles. [ABSTRACT FROM AUTHOR]

To investigate the stress concentration at the interface between crushed ballast and soil subgrade, this study developed a coupling program of discrete element method (DEM) and finite element method (FEM) using OOFEM and YADE software. Based on the penalty function method, an interface element was introduced for the DEM-FEM coupling simulation. Moreover, an adaptive volume coupling algorithm was proposed to address the unrestricted behavior of the particles across the interface elements. Therefore, the change in the interface contact stress distribution was analyzed in the process of ballast particles penetrating the subgrade soil. Based on the statistical analysis of the ballast shape scanning results, a morphology reconstruction method was adopted to restore the real irregular shapes of the ballasts. Consequently, a DEM-FEM coupling model of a ballasted railway was established and validated through laboratory test results. The meso-scale mechanism revealed the discontinuous characteristics of the contact stress caused by the ballast aggregates. In addition, the adaptive volume coupling algorithm in the case of ballast penetrating subgrade soil was preliminarily proven to be reasonable. This study provides a more accurate approach for calculating the interface stress between ballast and subgrade, which can support a further refined analysis of ballast railway subgrade deterioration. [ABSTRACT FROM AUTHOR]

• Cyclic responses of sand fouled ballast reinforced with geogrid were investigated. • Effect of sand content and geogrid properties on ballast settlement was derived. • A novel model for prediction of ballast settlement was developed. • Method of geogrid reinforcement for the best ballast performance was derived. A ballasted railway track is contaminated when passes through sandy areas. Due to sand penetration into the ballast voids, mechanical behavior of tracks deteriorates. Despite the dynamic nature of the load in the railway system, mechanical behavior of ballast reinforced with geogrid and contaminated with sand under cyclic loading have not been investigated. To study the influence of geogrid on improvement of cyclic mechanical properties of contaminated ballast, extensive laboratory tests were performed in this research. To this end, a ballast box machine was used in order to model in-situ cyclic loads. The tests were carried out on ballast samples contaminated with various sand dosages and reinforced with different geogrids. The results indicate that sand materials make ballast aggregates move and slide easier, causing more ballast settlement. It was shown that by geogrid reinforcement, settlement decreases (up to 75%), degradation (breakage) of ballast reduces (up to 23%), and its stiffness increases (up to 50%). An innovative model was developed which takes into account sand content and geogrid reinforcement that provides the settlement of ballast. An effective method of geogrid reinforcement for obtaining the best performance of ballast under cyclic loading was derived. [ABSTRACT FROM AUTHOR]

• Understanding the behaviour of ballast under dynamic loading. • Describing ballast stiffness using methods from soil dynamics. • Approach for vertical and horizontal ballast stiffness in a linear calculation. • No significant change in the first natural frequency of bridges due to ballast. Railway bridges are subjected to intensive dynamic loading. In structural calculations, the resulting response is estimated by dynamic calculations. As the basis of these calculations, the system's natural frequencies are to be numerically determined. Various studies have shown that a discrepancy between these measured natural frequencies and the numerical determination often occurs for short-frame bridges. In common practice, the ballast is assumed to be non-contributing to the global structural stiffness. In some cases, rheological models are developed to consider possible ballast stiffnesses based on small-scale model tests. The resulting spring-damper models are based on empirical values and are not directly related to the material behaviour of ballast. This paper discusses the ballast stiffness at the material level using relationships known from soil dynamics. The research shows that the material properties of the ballast can be determined in terms of stress and shear strain dependence. An equivalent ballast stiffness can be determined and considered in dynamic calculations for a known stress state and corresponding superstructure accelerations. The paper presents an approach for determining vertical and horizontal ballast stiffness according to shear strains and superstructure accelerations. This developed approach is validated by experimental tests using a small-scale bending beam and accompanying numerical calculations. Furthermore, a parameter study shows that the stiffness of the ballast does not contribute significantly to the global bending stiffness. Thus, the first bending natural frequency is hardly influenced by the ballast track. [ABSTRACT FROM AUTHOR]

This article presents the results of numerical simulations of loading tests conducted on coarse particles that simulate railroad ballast. The objective of this study was to evaluate the deformation of ballast under vertical loading and to study the influence of the two different particle size distributions. One of them was according to particle size distribution recommended by Indraratna and co-workers in the past as an improvement to Australian Standard and the other was prepared in accordance with Brazilian standard. The discrete element method offers a new means of studying the response characteristics of railway ballast. The basic idea of discrete element method (DEM) is that arbitrary discontinuities are divided into a set of rigid elements, making each rigid element satisfy the equations of motion, use time step iteration method for solving the equations of motion of rigid elements, and then obtain the overall movement patterns of arbitrary discontinuities. In this study, the discrete element method of analysis has been used to simulate the geotechnical behaviour of railway ballast observed during the triaxial testing. Three-dimensional numerical simulations were performed using discrete element modeling approach. [ABSTRACT FROM AUTHOR]

As several studies showed, mechanical performance of ballast depends greatly on its size, mineralogy and shape. Unlike the formers, particle shape remains a poorly specified property. The main objective of the study is then to first characterize the shape of ballast, then to understand its impact on the mechanical performance, by means of numerical simulations using the Discrete Elements Method (DEM), performed on LMGC90 software, with ballast grains represented as irregular polyhedrons. Starting from a description obtained experimentally by 3D digitization of the particle surfaces as point clouds, we will present a method to characterize and generate a set of virtual grains that are morphologically representative of real ballast grains. The model relies on a statistical modelling of the ballast grain morphology based on a dimensionality reduction approach leading to an optimal and nearly exhaustive shape characterization. In this paper, we will focus on the efficiency of both characterizing and generating methods and describe their advantages, as well as an outlook for numerical simulations. [ABSTRACT FROM AUTHOR]

The long-term settlement of railway tracks is a consequence of permanent deformations taking place in the track granular layers and subgrade. In the ballast layer, which experiences the highest stress amplitudes during train passages, these permanent deformations strongly depend on the loading conditions, which in turn depend on several factors as the train speed and axle loads, sleeper-ballast initial pressure, or track geometry quality. Moreover, under the action of moving loads from trains, further to a very significant increase of the vertical stress, the ballast layer experiences the rotation of the principal stresses, which is another aspect that significantly influences the long-term structural behaviour. This paper numerically analyses the stress changes in the ballast due to train passages, aiming at showing how these stresses may vary depending on the loading conditions. A numerical program of dynamic simulation is used that considers the nonlinear resilient nature of the ballast and the three-dimensional representation of the track-ballast-soil system using the FEM. The paper shows that dynamic effects due to trains travelling at very high speeds can significantly influence the stress path followed during loading and the principal stresses rotation inside the upper layers of the track. The paper also shows the importance of the consideration of the ballast nonlinear behaviour in the rotation of the principal stresses. [ABSTRACT FROM AUTHOR]

In this study, a series of monotonically drained triaxial tests were conducted using the large-scale cylindrical triaxial apparatus. The effect of particle breakage and confining pressure on the mechanical behaviour of ballast were investigated. Based on the experimental findings, mathematical expressions for critical state stress ratio and specific volume are proposed to incorporate the evolution of particle breakage during monotonic shearing. An elasto-plastic constitutive model is formulated within the critical state soil mechanics framework in order to capture the stress-strain behaviour and degradation of ballast. The non-linear variation of shear strength envelope at a given range of confining pressures is taken into account. Mathematical expressions for shear hardening and stress-dilatancy relations are proposed. The constitutive model is calibrated against the results of large-scale laboratory tests and further validated using experimental results available from past independent studies. It is proved that the proposed method can promisingly predict the deformation of the ballast layer in a typical railway environment. [ABSTRACT FROM AUTHOR]

The ballasted railroads form an integral part of the modern transportation infrastructure in Australia. However, they are subjected to large stresses especially on mixed traffic lines, where heavy freight trains are operated. Under such adverse operational conditions, ballast progressively degrades contributing to overall track deformations and frequent maintenance. Maintaining geometry of ballast embankments is necessary to improve safety and efficiency of railway operations. The use of artificial inclusions (geosynthetics and shock mats) as well as recycled (discarded) ballast in track can be economically viable options. In order to gain more insight, the CGRE has conducted extensive field trials on two rail lines in Bulli and Singleton in New South Wales supported by Sydney Trains and Australian Rail Track Corporation, respectively. In these studies, different types of geosynthetics (geogrid, geotextile and geocomposite) and shock mats were installed beneath the ballast layer constructed on varying subgrade conditions. Relative advantages of different geogrids were studied. Traffic induced stresses, ballast breakage, transient and permanent deformations were routinely monitored using precise instrumentation schemes. This paper discusses the details of track construction, instrumentation, monitoring processes and results of these field studies. [ABSTRACT FROM AUTHOR]

Rail track substructure (ballast, subballast and subgrade) is the most essential component of the railway system in view of track stability. The ballast is the largest component of the track substructure and it is the key load-bearing stratum packed with rock aggregates underneath and around the sleepers, thereby providing structural support against dynamic stresses caused by moving trains. However under large dynamic stresses exerted by heavy haul and high speed trains, the degradation of track substructure including ballast becomes significant. This in turn affects the track stability and creates frequent maintenance, thus increasing the life cycle cost of the rail network. Therefore, mitigating degradation of the ballast layer is vital in view of track longevity. In recent years, the use of resilient soft pads (shock mats) above the ballast (i.e. Under Sleeper Pad, USP) and below the ballast (i.e. Under Ballast Mat, UBM) has become a common practice. Many countries, including Australia have adopted the use of resilient pads in the rail track foundation. Currently, the studies on resilient mats are mostly limited to the reduction of vibration and noise. There is a lack of proper assessment of the geotechnical behavior of ballast when used along with shock mats. This paper provides an assessment of the triaxial behavior of the track substructure with and without shock mats under dynamic loading condition. A numerical model was developed based on the modified stress-dilatancy approach to capture the stress-strain and volume change behavior of ballast during impact loading. Model predictions are compared with laboratory results. It was found that the shock mats provide significant advantages in terms of reduced particle breakage and enhanced track stability. [ABSTRACT FROM AUTHOR]

• Common failure modes of concrete sleepers were deeply analysed. • Different design philosophies of concrete sleepers were discussed. • The influences of different material additives and geometry parameters were investigated. • The relationships between sleepers and elastic track components were explored. • The knowledge gaps have been critically defined. Prestressed monoblock concrete sleepers (PMCS) in railway ballasted tracks are the most recommended type of sleepers. They experience damage at an increasing rate with the increased demands for higher loads, train speeds, and traffic volume, concluding that an optimal design of this component will have a direct impact on the capital and maintenance funds, track system safety, and reliability. To this end, this study provides a comprehensive review pertinent to the structural performance of PMCS from perspectives including design philosophies, material and geometry properties, and relationships between PMCS and elastic track elements. In this study, the potential directions for improving the structural behaviour of PMCS were identified and analysed, and the gaps in knowledge were determined for further study. The outcomes of this research would contribute to improvements in the current design practices of concrete sleepers and ballasted railway tracks from perspectives including safety, financial value, reliability, and environmental impact. [ABSTRACT FROM AUTHOR]

• Big data analysis of railway track geometry using machine learning algorithms. • High-speed railway track quality assessment using artificial neural networks. • High-speed track maintenance (tamping) efficiency evaluation. • Techniques for railway track maintenance optimization. • Data taken from high-speed recording cars – not track based sensors. This study will address the opportunity of using a big data driven approach to providing a more specific description of track quality, mainly selecting segments of the track exhibiting higher settlement with the use of data analytics and machine learning. The focus will be on a high-speed line in the UK with data covering over 15 years of track geometry. Data sets describing track geometry quality have an enormous volume, which means that it is impractical to apply conventional methods to process it fully. The overall aim of this work was to apply an AI technique to analyse the big data. An Artificial Neural Network (ANN) was developed on features from the available data set and used to identify segments of the track where the condition has either improved or deteriorated in the period between two inspection runs. The model achieved an accuracy of ∼ 98 % during training and was able to reliably identify segments of the track which underwent significant changes in measurements. The ANN was used to perform an initial analysis of the geometry data, which revealed that maintenance works (mainly large-scale tamping) may include healthy portions of the track and potentially reduce its life span. Approximately 50 % of the tamped track was not found to improve significantly, based on several different geometric features. On the other hand, local works with a sprinter tamper were much more efficient at eliminating defects. [ABSTRACT FROM AUTHOR]

The overall aim of this project was to relate ground penetrating radar (GPR) to a ballast fouling index (FI). Laboratory research aimed at characterising the electromagnetic properties has enabled researchers worldwide to determine ballast thickness using impulse ground penetrating radar (GPR) – based upon derived values of the relative electrical permittivity or dielectric constant. In this paper, a series of GPR experiments, following on from these laboratory experiments, were undertaken on a full scale track bed using a range of bowtie antennas from 500 MHz to 2.6 GHz. The key innovation reported is the use of scatter analyses of the GPR waveforms, featuring area, axis crossing and inflexion point analyses. These scatter analyses were then used to predict the Ionescu ballast fouling index. A correlation coefficient greater than 0.9 was obtained by using a 500 MHz bowtie antenna in the parallel orientation in conjunction with a scan area analysis. [ABSTRACT FROM AUTHOR]

The life of ballast is dependent upon a number of factors mainly traffic loading, drainage, contamination and is clearly related to intervention levels and installation quality standards. The use of mechanised ballast replacement techniques has developed over the last 30 years ranging from intrusive and non-intrusive processes. UK national policies have now recognised refurbishment of ballasted systems as an economic alternative to complete renewal especially in locations of switches and crossing (S&C) layouts. There are ever increasing technical challenges associated with the formation and ballast layer interface which relate to localised track quality and the route based longitudinal integrity of these refurbished discrete locations. This paper identifies current best practice in terms of machinery and the recent specialist applications. Also discussed are the complexities of vehicle and product acceptance and introduction including the development of complementary decision support tools. [ABSTRACT FROM AUTHOR]