Ballast Track Research Articles

Comparative analysis of methods for predicting train-induced vibrations

Railway systems cause more severe vibration pollution than road systems, and the vibration pollution caused by railway systems has been increasing annually over the past two decades. Despite this, there is limited investigation into the accuracy of train-induced vibration prediction methods. Therefore, the present study investigated the accuracy of the detailed and general procedures proposed by the US Federal Transit Administration (FTA) for predicting train-induced vibrations. The accuracy of these methods was determined by evaluating their predictions against in-situ measurements of ground vibration levels induced by passing trains. The field experiments conducted in this study involved the measurement of train-induced vibration levels, the estimation of line-source transfer mobility (LSTM) by dropping a weight on rail sleepers, the evaluation of force density levels, and the determination of ground LSTM by dropping a weight on the ground. In addition, graphs were plotted to determine the relationships of train-induced vertical vibration levels with train speed, distance from the track centreline, and train length. The study compared measured and predicted vibration levels to assess the accuracy of the FTA’s detailed and general prediction methods. Results indicate that detailed assessments tend to overestimate vibration levels, while an optimized general vibration assessment curve offers a more precise estimate. Additionally, on the basis of the measurement data, the study explored the impact of train length on ground vibration and demonstrated that track ballast can absorb vibration energy along the wave propagation path. A frequency propagation contour plot was also created to analyse vibration energy across different frequencies. These findings enhance the reliability of train-induced vibration prediction methods and provide insights for improving vibration mitigation strategies in urban railway systems.

Experimental and numerical study on mechanical properties of sand-contaminated ballast aggregates in confined condition

This study investigates the impact of sand contamination on the mechanical properties of railway ballasted tracks in confined condition. A combination of experimental confined uniaxial compression tests and discrete element method (DEM) simulations was employed. The experiments assessed the bulk density and elastic modulus of ballast aggregates, while the DEM simulations focused on sand movement, coordination numbers, and contact forces to elucidate the mesoscopic behavior. Findings from both experiments and simulations consistently demonstrate that sand contamination linearly increases the bulk density and causes a non-linear increase in the elastic modulus of ballast aggregates. With increasing degrees of sand contamination under vertical loading, both coordination numbers and contact forces are reduced. Sand intrusion initially leads to an uneven distribution of sand grains, primarily in the lower layer of the ballast aggregate; however, this distribution becomes more uniform when contamination exceeds 62.5%. The presence of sand particles diminishes the contact forces between ballast particles, thereby escalating the challenges associated with maintenance and repair.

Seismic response prediction method of train-bridge coupled system based on convolutional neural network-bidirectional long short-term memory-attention modeling

Seismic response prediction is crucial for the safety analysis of train-bridge coupled systems. However, due to the complexity, suddenness, and high-risk nature of earthquakes, there are strong nonlinear relationships among different parts of bridges, making it challenging to express their spatial correlations using analytical models and traditional neural networks. To address this, this paper establishes a ballast track shaker scaling model and employs the grating monitoring measurement method to construct a spatial quasi-distributed monitoring system for the ballast track, thereby collecting seismic strain responses of the train-bridge coupled system under various seismic conditions. A hybrid neural network method is proposed for predicting the seismic responses of the train-bridge coupled system. This hybrid neural network integrates the features of a Convolutional Neural Network (CNN), Bidirectional Long Short-Term Memory Neural Network (BiLSTM), and the attention mechanism, thereby termed the CNN-BiLSTM-attention hybrid neural network. The model was validated using strain responses from 54 seismic scenarios. The results indicate that the model has a Mean Absolute Error (MAE) of 0.2349 and a coefficient of determination (R2) of 0.9446. Comparing the prediction results with those from RNN and LSTM models, it was found that the CNN effectively extracts features under various seismic parameters, while the BiLSTM better captures the temporal information of the strain responses, ensuring effective prediction regardless of the magnitude of strain responses. Therefore, the CNN-BiLSTM-attention hybrid neural network model is recommended for predicting seismic response.

Ballistic performance of aluminum alloy plates with polyurea coatings for high-speed train structures

Polyurea coatings have been widely promoted in explosion and ballistic impact protection applications due to their excellent hyper-elasticity performance. In rail transportation, high-speed trains face potential impact threats from track ballast, which can affect the strength performance of the base material. To address these challenges, we examined the ballistic performances of aluminum alloy plates with polyurea coatings under large-scale impact (>30 mm). Four different configurations of target plates were investigated: A, P-A, A-P, and P-A-P. We fabricated samples and performed dynamic impact tests using an air cannon system to demonstrate the feasibility. Results show that ballistic performance is significantly improved by applying polyurea coatings on aluminum alloy plates. In particular, the growth rate of limit velocity of configuration A-P, P-A, and P-A-P to that of configuration A are 5.5 %, 19.4 %, and 22.8 %, respectively. The enhancement mechanism was further uncovered through stress wave propagation analysis and lateral energy diffusion effect. Explicit formulas for predicting the limit velocity and residual velocity were derived and demonstrated with reasonable accuracy over a wide range of parameter spaces. The observed enhancement in ballistic performance through polyurea coatings on aluminum alloy plates offers promising ways to design and implement more resilient and impact-resistant high-speed train structures.

Selection of track form in railway tunnel from a life cycle analysis perspective

AbstractThe use of greenhouse gas (GHG) emissions as a criterion for decision-making within the rail industry is increasing. The demand for considering this criterion affects the type of decision models acceptable by railway infrastructure managers in the planning, construction, and maintenance of railway assets. The total amount of GHG emitted from a track solution in tunnels during its service life depends on the track form (i.e., ballasted track or ballastless track), the type of construction, maintenance machines used, current traffic profile, and tunnel length. However, the development in the design of ballastless track systems during recent decades to make them environmentally friendly motivates infrastructure managers to rethink and consider the use of the system. This study examines the effect of several design and maintenance factors not adequately addressed in previous research. These factors are (i) the modulus of elasticity of track support affecting the design of track forms, (ii) differences in maintenance and renewal required for track forms in the corresponding line condition, and (iii) recent developments in optimizing the environmental impact of ballastless tracks. The GHG emissions, represented by life cycle carbon dioxide equivalent (CO2e) emissions, are calculated using the climate impact software developed by the Swedish Transport Administration Trafikverket. The result is compared with the estimated emission from the conventional ballasted tracks. The method proposed in this paper is applied in a case study to study the effect of applying the optimized ballastless track system Rheda 2000® in a railway tunnel (the Hallsberg-Stenkumla tunnel) as part of a new line project in Sweden. The model applied in the study is an integral part of an integrated decision support system for effectively selecting track solutions from a lifecycle perspective. The study´s findings are: (i) the life cycle CO2 equivalent emissions by a ballastless track during its life cycle are 10% lower than that of the ballasted track, (ii) the primary total emission driver for both track form solutions is the emissions generated at the manufacturing of rails. (iii) the second important emission factor for the ballasted track solution is the emission from the renewal of the track form during its life cycle, and (iv) the second important emission factor for the ballastless track solution is concrete manufacturing.

Characterization of elastic wave propagation in high-speed railway tracks considering temperature effects

This study establishes a three-dimensional infinite-length periodic ballasted track model, considering the effect of coupling between bending and torsion and the impact of sleeper width. The GPWE method is employed to investigate the energy bandgap structure of the track. The results show three vertical bending wave bandgaps below 1500 Hz: 0–109 Hz, 110–167 Hz, and 1081–1126 Hz. The node responses from a hammer impact experiment are used in the WSM to calculate the frequency dispersion curves, which confirms the validity of this model. The model is then utilized to analyze the influence of rail temperature forces and temperature-dependent fastener stiffness on the vibration transmission characteristics of the track within a temperature range of −35°C to 25°C. As temperature increases, the starting and cutoff frequency values and the width of bandgaps both decrease nonlinearly and later stabilize, with the width of the Bragg bandgap showing a significant reduction of 83%. The vibration attenuation rate in the bandgap gradually increases and finally stabilizes, especially above 15°C, while the vibration transfer characteristics are not significantly affected by temperature.

Elastic discrete element analysis of natural vibration characteristics and settlement behavior of railway ballasted track

An elastic multi-body model of a ballasted track, consisting of an aggregate of ballast gravel and a single prestressed mono-block concrete sleeper, is constructed. Field-measured traffic load waveforms from an operational existing railway track are then applied to the left and right rail positions on the upper surface of the model using elastic discrete element method. The numerical results are subjected to frequency analysis to examine the relation between track settlement and natural vibration phenomena in ballasted tracks. The relative error between the measured and analyzed frequency values for the natural vibration modes of the ballasted track under 500 Hz is 2.23%, indicating that the current ballasted track model accurately reproduces the natural vibration characteristics of existing ballasted track structures. The analysis results reveal that the phenomenon of plastic deformation within the ballast layer occurs primarily in the upper part of the ballast layer, just below the sleeper. Additionally, for the bounce mode of the ballast layer in the frequency range of generally 100 Hz and below, it has been identified as the primary factor promoting significant vertical motion of the sleeper, along with the associated reverse U-shaped deformation of the sleeper, which accelerates the track structure degradation. Furthermore, when loosening occurs, the vibrational energy of this bounce mode increases, contributing directly to ballast degradation.

Repose angle prediction of railway ballast based on Hopper Flow Test and PCA-Stacking ensemble learning method

The deterioration of track ballast is mainly reflected in the fragmentation of ballast particles and the evolution of grading. The repose angle of the ballast is the internal friction angle, reflecting the shear strength of the track ballast. The angle of repose of 158 ballast samples with varying gradation parameters was tested by conducting hopper flow tests on ballast particles. Then, based on this database, a stacking ensemble regressor-based principal component analysis (PCA) was proposed for the repose angle prediction. The data are first processed by PCA and then randomized into the train (80%) and test (20%) data. Besides stacking ensemble regressor, five different individual regressors, including support vector regressor, k-nearest neighbors, random forest, gradient boosting decision tree, and adaptive boosting, are compared and analyzed. The results indicate that the stacking ensemble regressor performs better than single regressors and demonstrates enhanced robustness and generalization capabilities. Additionally, the Effect of the number of principal component indicators on the prediction accuracy is determined, and the difference in stacking ensemble prediction performance with and without PCA is discussed. Finally, a computer prediction system for ballast repose angle was developed to make the proposed stacking ensemble regressor directly applicable to the railroad construction site. This model can be used in practical track maintenance decisions, whereby the ballast gradation can facilitate rapid assessment of the angle of repose.

Experimental study and numerical simulation of the impact of under-sleeper pads on the dynamic and static mechanical behavior of heavy-haul railway ballast track

AbstractLaying the under-sleeper pad (USP) is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload. To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system, numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method (DEM)—multi-flexible body dynamic (MFBD) coupling analysis method. The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models. The results show that using the USP results in a 43.01% reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers. It effectively reduces the load borne by the sleeper directly under the wheel load, with a 7.89% reduction in the pressure on the sleeper. Furthermore, the laying of the USP changes the lateral resistance sharing ratio of the ballast bed, significantly reducing the stress level of the ballast bed under train loads, with an average stress reduction of 42.19 kPa. It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50% to 70%, which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs. In summary, laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.

Enhanced Imaging Analysis of Aggregates for Road and Railway Applications

The South African pavement community has shown a keen interest in the use of imaging techniques to characterize the morphological characteristics of aggregates used in road and railway construction. This interest arises from the need to overcome the limitations of the traditional methods currently employed to quantify the shapes of these materials. Recent advancements and the use of enhanced aggregate imaging techniques for quantifying the shapes of crushed stone and ferro slag materials from 10 sources across the country are presented in this paper. A wide range of railway track ballast and road aggregates were selected from various quarries and sources across different provinces for this study. As part of this research, an improved protocol was developed to standardize imaging acquisition and ensure the repeatability of shape property measurements, thereby providing meaningful results and facilitating data analysis. The imaging analysis conducted in this study, which involved close to 2000 aggregate particles, revealed valuable insights into the angularity, surface texture, and flat and elongated ratio properties of coarse aggregates. Preliminary specification limits for these shape properties have been established. This contribution represents an initial step toward supporting the South African road and railway industry in adopting advanced techniques for the selection of aggregate materials.

Impact of particle arrangement and model dimensions on DEM modeling of high-speed railway ballasted tracks in 2D and 3D

Modelling railway projects has a main challenge in the discrete element method (DEM). The granular material of the embankment consists of millions of fine angular particles which are difficult to model due to the long computational time. The long computational time also prevents the modeling of the higher number of loading cycles. As a result, researchers prefer to simulate the project in 2D to accelerate the simulation. While 2D simulations present a seemingly simple option for modeling railways, they tend to oversimplify the intricacies of particle interactions and the distribution of stress. Nonetheless, the extent to which these simplifications affect the authenticity of the simulations has remained ambiguous. In this study, the periodic cell replication method is used to build extensive long railway tracks significantly faster than conventional methods. Then, this DEM model is calibrated against the measurement results of a physical full-scale ballasted track. The model is then used to simulate several railway projects with different initial particle arrangements and model dimensions in both 2D and 3D. The results show that the 2D models are more dependant on the initial particle arrangement which shows different behavior for the same model. In addition, 2D simulations are incapable of reproducing the principal stress rotation in granular layers due to the moving load of the train wheel. As a result, 3D DEM simulations using the periodic cell replication method is suggested for studying the railway tracks.

Lite RGB-based measurement method for ballast fouling index prediction through subsampling

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.

Mechanical behavior and performance evolution of railway ballast track under dynamic stabiliser based on the hybrid MBD-DEM simulation

The uncertainty in local structure and time-variable compaction of ballast aggregates poses challenges in selecting suitable stabilization methods and parameters for ballast tracks in practical engineering, often resulting in suboptimal operational outcomes. To address this issue comprehensively, the spatial hybrid model of the double dynamic stabilisers-ballast track (MBD-DEM) is proposed in this paper. Subsequent numerical simulations of stabilisation operations are conducted to elucidate ballast vibration, migration behavior and the evolution of ballast track resistance under varying initial conditions of the ballast bed. Initially, leveraging multibody dynamics theory (MBD) and discrete element method (DEM), a MBD model of double stabilisers and a DEM ballast track model containing 6 sleepers were established respectively. Using the coupling interface, the real-time hybrid calculation of these two models is achieved through 6 sleepers in the middle of the ballast bed. Subsequently, the model's accuracy was validated by comparing test data from stabilisation vehicle operations on a Kunming Railway Bureau test line with simulation data from the dynamic double stabilisers-ballast track spatial hybrid model. Finally, utilizing the proposed hybrid model, the dynamic behavior, contact states, and movement rules of ballast particles during stabilisation operations on both loose and initially stable ballast beds (LBB and ISBB) were investigated at the mesoscopic scale. Concurrently, an in-depth analysis of lateral resistance changes in the ballast bed before and after the stabilisation operation is presented. The relevant findings effectively unveil the evolution of dynamic behavior in the ballast bed during stabilisation operations, concluding with practical suggestions for on-site operations. Simulation results illustrate that the rotation of ballast particles in the XY plane beneath each sleeper is predominantly characterized by harmonic rotation. With an increase in the depth of the ballast bed, the range of the rotation axis for combined angular velocity diminishes, leading to the phenomenon of rotation axis deflection. To ensure operational safety and efficiency, a minimum of two-times stabilization operations is recommended for loose ballast beds (LBB), with three-times operations considered optimal. For initially stable ballast beds (ISBB), one-time stabilization operation is basically sufficient.

Sustainable Performance of Recycled Rubber and Mining Waste Utilized for Efficient Rail Infrastructure

AbstractUtilizing waste byproducts from mining industries and recycled rubber as alternate materials in railway tracks promotes sustainability of transportation infrastructure, while also increasing track longevity by reducing ballast degradation. This paper provides an overview of two such applications including (i) rubber-intermixed ballast stratum (RIBS) by replacing 10% ballast aggregates with granulated rubber particles with the particle sizes carefully selected according to Australian Standards, (ii) synthetic energy absorbing layer using a mixture of steel furnace slag, coal wash and rubber crumbs to replace traditional capping layer. These materials when tested using large-scale triaxial apparatus and field trials proved that tracks with waste materials performed better than the conventional ballasted tracks by reducing ballast breakage and exploiting the higher damping potential of these materials. Though the vertical deformations of the track slightly increased by using these materials albeit within the specified standards, the overall stability improved by reduced dilation and track vibrations. Increasing the life of ballast layer can lead to long-term cost benefits by saving millions of dollars in track maintenance and provide environment benefits through minimizing quarrying of natural rock aggregates and reducing the carbon footprint of mining industries.

Influence of vibration on sub-ballast layer induced by loading application on a fouled track ballast

The railway track’s sub-ballast layer is important, but it is often neglected, leading to the contamination and blockage of voids, as well as track deformation and degradation. These issues occur when fouling materials infiltrate the subballast due to load-induced vibration. The purposes of this paper are to investigate the influence of vibration on the sub-ballast layer when loads are applied to a fouled ballast and to determine whether sub-ballast saturation should be ignored. A ballast box was fabricated to represent actual railway conditions and filled with 100 kg of ballast aggregates containing fouling materials (crushed ballast, sand, clay, and coal) proportional to the ballast weight. In addition, a vibratory compactor plate machine was used to simulate load on the fouled ballast, inducing vibrations that caused fouling materials to migrate into the sub-ballast. The results indicate that 18% of crushed ballast, 20% of sand, 20.7% of clay, and 15% of coal infiltrated the sub-ballast due to loading-induced vibration, and fouling infiltration percentages rose as vibration from loading increased. These percentages exceeded the standard 10% weight of fouling infiltration into the sub-ballast, indicating an unfavourable subballast condition and showing that sub-ballast saturation should not be ignored. These findings have significant implications for maintenance engineers, as they underscore the need for continuous monitoring and upkeep to ensure optimal sub- ballast performance.

Modelling and numerical simulation of high-speed railway slab track structure

In terms of maintenance and structural behavior, slab track proves to be an advantage over conventional ballasted track due to increasing train speed, axle load, and traffic density. Since the vibration, noise, and risk of derailment, all accelerate as train speed increases, an in-depth investigation of track dynamics becomes essential for identifying the fundamental cause of the problem. In this paper modelling and numerical simulation of high-speed railway slab track structure has been studied using finite element method. Using the multi-body simulation approach and the finite element method a model of the 3D slab track system is developed. The slab track model has rail, rail pad, and concrete slab, HBL, and subgrade layers. In order to determine the fundamental frequency and the mode shapes associated with it, a modal analysis is carried out. Dynamic response, or acceleration against frequency curves derived via harmonic response analysis, is the result of the numerical simulation. The dynamic reaction of the structure of a high-speed slab track is studied, and the effect of elastic materials on reducing vibration is investigated. The results suggest that a layer of elastic material, like a slab of mat, inserted between a layer of concrete slab and a layer of HBL is capable of lowering the amount of vibration response of the track.

Social life cycle assessment of railway track substructure alternatives

The sustainable design of infrastructure involves assessing economic, environmental, and social impacts. While significant progress has been made in evaluating economic and environmental life cycle impacts since the Paris Agreement, there's a notable gap in techniques for assessing social aspects in infrastructure design. This study introduces social indicators tailored for evaluating the lifecycle of railway infrastructures. The indicators are applied to assess the social impacts of three common railway track substructure solutions: conventional ballasted track, embedded slab track (BBEST solution), and sleeper-based, ballastless (RHEDA2000) substructure solutions. Using the Analytic Network Process (ANP), the social performance of each alternative is synthesized into a single indicator for comparison. Results indicate that the conventional ballasted track outperforms, scoring 12% higher than BBEST and 61% better than RHEDA in social terms. This is attributed to its reliable capacity for generating high-quality employment and fostering economic activities in the defined product system regions.

Finite Element Modelling of Geogrids Reinforced Ballasted Tracks

This paper presents results obtained from three-dimension finite element modelling (FEM) to study the effects of geogrids on the deformation responses of ballasted tracks. In this study, a series of numerical simulations are carried out on track sections with and without the inclusion of geogrids. Sensitivity analysis was carried on parameters affecting the performance of geogrid, including the axial stiffness, interface property and the location of geogrid placement in the track substructure. The tracks are subjected to moving train loading under 150 kN wheel load travelling at a given speed of 72 km/h. Based on simulation results, it is found that geogrid provides a reinforcing function to rail track primarily in the form of confinement which resulted in reduced lateral displacement in a reinforced track compared to a traditional track. A significant reduction in vertical and lateral displacement is found from the inclusion of a geogrid layer at the ballast and capping interface while the effect of geogrid reinforcement is more pronounced with increased loading cycles. The effects of geogrid stiffness, interface conditions and geogrid placement are studied and it is found that the axial stiffness of geogrid is found to impact overall track deformation while the optimum placement of geogrid is found to directly at the ballast and capping interface.

Testing the fragmentation of railway ballast material by laboratory methods using Proctor compactor

The physical classification of crushed stone and gravel used in railway construction is based on their strength and endurance and is performed by a laboratory test method using a rotating drum or a mortar method. The values of fracture resistance calculated using the Los Angeles method and abrasion calculated using the Micro-Deval method show a corresponding correlation and require further investigation. Purpose. The development of a new method for measuring rock material fracture that is consistent with widely used standards while also being more comparable to real-world railway operating conditions. Certainly, both standard tests are essential for ensuring product homogeneity during production, so the new recommended method is only a supplement. Methodology. The Proctor device was used to induce so-called shock loads from above, similar to railway loading conditions. Unlike the standard method, the andesite material was placed in a standard cylinder in these tests. The samples were pre-screened and sorted; the specified weight was approximately 1,300 g, and the specified sizes of the individual particles were 6.3, 8.0 and 11.2 mm. Only prewashed and dried materials of NZ (fine crushed stone) or KZ (special crushed stone) from four different quarries (Tállya, Szob, Nógrádkövesd, Recsk) with different rock physics characteristics were considered. The Proctor compactor machine was used because of its calculable labor (19.86 J/impact) and the crushing effect of the calculable impacts (64, 128, 256 and 1,028 blows). Even after loading different numbers of impacts, homogeneous samples from different quarries were sieved to measure the masses of fragments per fraction. Findings. The set of measurements made it possible to establish a series of fragmentation and degradation curves for each of the three repeated measurements based on the composition of the material and the number of blows, which showed the degradation of samples with different physical and mechanical properties of the rock material and particle sizes. With an increasing number of impacts, the amount of crushed material in the sample increased, but the distribution of crushed material did not decrease evenly and proportionally as the number of impacts increased. Parameters and indices were also computed to identify various correlations (i. e., FV, d < 22.4, d < 0.5, d < 0.063 mm, CU, M ratio,  ratio). Some of them (e. g., FV) needed to be changed, but they were predefined due to the nature of the tests. Originality. While many standard and alternative railway track ballast fragmentation test methods and measurement tools are available, this paper proposes a new laboratory method and demonstrates the specific measurement and application effectiveness. Practical value. In addition to standard tests that are already widely used, the new method for measuring the fractional composition of railway ballast can help simulate real-world operating conditions of a railroad track in the laboratory. This method will improve the safety of railway operations.

Large-Scale Triaxial Testing of Geogrid-Stabilized Field-Sourced Fouled Ballast Under Simulated Progressive Rainfall Wetting and Cyclic Loading Conditions

Railroad track ballast composed of uniformly graded crushed aggregate is susceptible to fouling from substances like ballast fines degraded during track service, coal dust, clay, and sand. Fouling reduces the drainage capacity of ballast, often leading to water accumulation and subsequent performance degradation. Fouled ballast with high moisture content experiences excessive settlement and could benefit from stabilization for safe operations. While previous studies have highlighted the efficacy of geogrids in stabilizing fouled ballast and minimizing the overall track settlement, the effect of geogrid on the performance of fouled ballast under progressive rainfall wetting and continuous cyclic loading conditions remains unexplored. This study examines the performance of geogrid-stabilized field-sourced fouled ballast through large-scale triaxial tests. The findings reveal that the inclusion of a single-layer geogrid can effectively reduce settlement and deformation rates under equivalent water content conditions. A layer of geogrid could prevent sample failure under saturated conditions, retaining approximately 1,000 kPa post-cyclic shear strength. Furthermore, the results indicate that geogrid stabilization enhances the resilience of fouled ballast and maintains the track geometry under progressive rainfall conditions. These findings offer crucial insights for geogrid applications in railroad maintenance.