Search Results (31)

Transition zones are located at points on a track where there has been a change in the main composition of the railway infrastructure; as such, there are many sections that undergo a sudden change in the stiffness of the structures built. When trains are running, a longitudinal shockwave is created by the wheels, hitting these building objects with a greater stiffness and deforming the surroundings of these zones. The greatest amount of attention should be paid to the transition points from the fixed track to the classic track with a track bed, including objects of the railway substructure, such as bridges and portals of tunnels. As part of the research on the main corridor lines, long-term inspection and monitoring studies were carried out using a trolley with a continuous measurement system; height changes in the deflections of rails are evidence of their behaviour. The measurements took place on a fixed track and a track with ballast. The changes in the height jumps between the fixed railway track and the track with a gravel bed are significant. These height deflections allow designers to develop new, more durable construction designs. Full article

During railway operations, changes in the support conditions of sleepers, owing to various internal and external factors, can damage rails and concrete sleepers and alter the structural characteristics of gravel-ballasted tracks. However, current methods for evaluating gravel ballast conditions primarily rely on visual inspection. This study proposes a quantitative approach using modal testing to assess ballast conditions. This is achieved by analyzing and experimentally verifying the relationship between track ballast loosening (caused by subgrade deformation) and track support performance. Finite element analysis results and field experimental values were compared using spring stiffness as a parameter. The results showed that natural frequencies and mode shapes changed in response to variations in the vertical spring stiffness of the gravel-ballasted track. Therefore, the sleeper support condition of a gravel-ballasted track can be readily identified by analyzing the natural frequency corresponding to different sleeper support conditions. Full article

This study investigates the influence of ballast and sub-ballast thicknesses on the structural behavior of a heavy-haul railway platform by using finite element modeling with SysTrain software (v. 1.84) A parametric analysis was conducted to assess how variations in layer thickness affect key performance parameters, including total deflection, bending moments in the rails, and vertical stresses within the railway track. The results indicate that reducing ballast thickness increases deflection and vertical stresses, while excessive thickness elevates system stiffness, reducing its ability to dissipate stresses. This condition can intensify the transmission of dynamic loads to track components, accelerating rail and sleeper wear and requiring more frequent corrective interventions, thereby increasing maintenance costs. Deflections remained within the 6.35 mm limit established by AREMA, except for one case (6.85 mm), where an excessive ballast thickness (160 cm) combined with low material stiffness resulted in non-compliance. Vertical stresses in the substructure ranged from 106.9 kPa to 155.9 kPa, staying within admissible limits. Additionally, the study highlights the significant role of material properties, particularly the resilient modulus, in the overall track performance. The findings enhance the understanding of how ballast and sub-ballast geometry affect railway structural behavior, demonstrating how numerical modeling with SysTrain can support decision-making in track design and maintenance strategies. Full article

This study investigates the impact of sand-induced ballast fouling on railway track performance, focusing on track stiffness (modulus), settlement, and overall degradation. The research utilized an 18-cubic-foot ballast box designed to replicate real-world track conditions under controlled laboratory settings. A key focus was quantifying voids within clean ballast to establish baseline characteristics, which provided a foundation for evaluating the effects of sand fouling. Two distinct test series were conducted to comprehensively analyze track behavior. The first series investigated pre-existing fouling by thoroughly mixing sand into the ballast to achieve uniform fouling levels. The second series simulated natural fouling processes by progressively adding sand from the top of the ballast layer, mimicking real-world conditions such as those in sandy environments. These methodologies allowed for detailed analysis of changes in track stiffness, deflection, and settlement under varying fouling levels. The findings demonstrate a direct correlation between increasing sand fouling levels and heightened track stiffness and settlement. Dynamic load testing revealed that as void spaces were filled with sand, the track’s flexibility and drainage capacity was significantly compromised, leading to accelerated degradation of track geometry. Settlement patterns and deflection data provided critical insights into how fouling adversely affects track performance. These results contribute significantly to understanding the broader implications of sand-induced fouling on track degradation, offering valuable insights for railway maintenance and design improvements. By integrating void analysis, test series data, and load-deflection relationships, this study provides actionable recommendations for enhancing railway infrastructure resilience and optimizing maintenance strategies in sandy terrains. Full article

The nonlinear mechanical properties of ballasted tracks along railways result in complex dynamics of the vehicle–track systems. Employing localized characterization of ballast and a simplified model might underestimate the vehicle–track system’s dynamical responses and safety. This paper presents a new dynamical stiffness model of railway ballast by incorporating the ballast’s time-varying, nonlinear viscoelastic, and elastoplastic properties. The new nonlinear stiffness model is a versatile tool that comprehensively characterizes the ballast characteristics of displacement-dependent stiffness, frequency-dependent stiffness, hysteresis, and time/space-varying features. These features, widely reported in previous experimental research, can now be effectively understood. Conventionally, to characterize time/space-varying characteristics of ballast along the track, ground-penetrating radar (GPR) has been used as the most efficient approach to survey railway networks quickly and to infer track dynamical properties. Aiming to improve the present technique for characterizing time/space-varying properties of ballast stiffness by using a GPR signal, the adaptive optimal kernel time–frequency representation (AOKTFR) method is used to process a typical GPR signal from a railway ballast scanning. It is found that the results of AOKTFR exhibit a clear time-varying pattern and precise frequency modulation. In contrast, the conventional time–frequency methods failed to give a clear time-varying pattern. The results illustrate that AOKTFR is a practical approach for processing the time-varying nonlinear signal of GPR and correlating it with the time-varying nonlinear stiffness of ballast. Full article

Track decay rate (TDR), meaning the rate of attenuation of bending waves through the rail, is the most important indicator of a track’s dynamic characteristic impacting the rail noise emission. TDR depends on various parameters related to the construction of the track, and it can be increased using rail dampers. These are mechanical devices working on the principle of dynamic absorbers and are attached to the rail. This paper addresses the track with light rails needing improvements to reduce the rail noise emission using a particular rail damper with a mixed damping system (rubber–oil). The bending waves that propagate through the rail, the frequency response function of the rail, and TDR are investigated considering different scenarios regarding the parameters of the track: soft/stiff rail pad, tampered/settled ballast, and sleeper bay. To this end, an analytic model of the track featuring rail dampers consisting of an infinite Timoshenko beam with discrete attached oscillators is used. Numerical results show the possibility to increase TDR of railway track with light rails for both soft/stiff rail pads from 4 to 500 Hz up to 1250–1600 Hz using rail dampers with a mixed damping system. Full article

One of the primary challenges in the railway industry revolves around achieving a comprehensive and insightful understanding of track conditions. The geometric parameters and stiffness of railway tracks play a crucial role in condition monitoring as well as maintenance work. Hence, this study investigated the relationship between vertical ballast stiffness and the track longitudinal level. Initially, the ballast stiffness and track longitudinal level data were acquired through a series of experimental measurements conducted on a reference test track along the Tehran–Mashhad railway line, utilizing recording cars for geometric track and stiffness recordings. Subsequently, the correlation between the track longitudinal level and ballast stiffness was surveyed using both frequency-based techniques and machine learning (ML) algorithms. The power spectrum density (PSD) as a frequency-based technique was employed, alongside ML algorithms, including linear regression, decision trees, and random forests, for correlation mining analyses. The results showed a robust and statistically significant relationship between the vertical ballast stiffness and longitudinal levels of railway tracks. Specifically, the PSD data exhibited a considerable correlation, especially within the 1–4 rad/m wave number range. Furthermore, the data analyses conducted using ML methods indicated that the values of the root mean square error (RMSE) were about 0.05, 0.07, and 0.06 for the linear regression, decision tree, and random forest algorithms, respectively, demonstrating the adequate accuracy of ML-based approaches. Full article

In order to study the influence of an unsupported sleeper on the vertical bearing characteristics of heavy-haul railway ballast, a three-dimensional discrete element model (DEM) was established for a ballasted track, by removing ballast particles that come into contact with the bottom of the sleeper from the model to simulate the unsupported sleeper. Vertical bearing characteristics for ballast on different types of unsupported sleepers were studied. The results showed that an unsupported sleeper could reduce the bearing area of the ballast below the sleeper and reduce the number of ballast particles that were in contact. It could also lead to an increase in the maximum contact force between the particles, accelerating the deterioration of the particles (thus affecting the overall performance of the ballast) and reducing the vertical stiffness of the ballast. As the unsupported length and width increased, vertical stiffness gradually decreased. The vertical ballast stiffness for an unsupported sleeper was then used in a dynamic coupled vehicle/track model, and the effect of the unsupported sleeper on wheel/rail interaction was analyzed. Results showed that increasing the unsupported length and width leads to a decrease in the supporting force on the unsupported sleeper and to an increase in the supporting force on the adjacent sleepers. Full article

In this paper, a novel railway track monitoring approach is proposed that employs acceleration responses measured on an in-service train to detect the loss of stiffness in the track sub-layers. An Artificial Neural Network (ANN) algorithm is developed that works with the energies of the train acceleration responses. A numerical model of a half-car train coupled with a track profile is employed to simulate the train vertical acceleration. The energy of acceleration signals measured from 100 traversing trains is used to train the ANN for healthy track conditions. The energy is calculated every 15 m along the track, each of which is called a slice. In the monitoring phase, the trained ANN is used to predict the energies of a set of train crossings. The predicted energies are compared with the simulated ones and represented as the prediction error. The damage is modeled by reducing the soil stiffness at the sub-ballast layer that represents hanging sleepers. A damage indicator (DI) based on the prediction error is proposed to visualize the differences in the predicted energies for different damage cases. In addition, a sensitivity analysis is performed where the impact of signal noise, slice sizes, and the presence of multiple damaged locations on the performance of the DI is assessed. Full article

This study assesses and compares lifecycle (LC) greenhouse gas (GHG) emissions from the two main railway track construction types: ballasted track and slab track. In this study, preexisting soil conditions are considered, as they significantly influence necessary measures during the construction phase for each type. This study is executed for Austrian boundary conditions with speeds up to 250 km/h. The results show that ballasted track is associated with 11–20% lower LC GHG emissions, whereby the variation in relative emission reduction is associated with additional soil reinforcement treatments due to varying preexisting soil conditions. Poor preexisting soil conditions increase LC GHG emissions by 26%, underlying the necessity to integrate this parameter into the lifecycle assessment of railway track. In contrast to the higher service life of slab track construction, this type amounts to higher masses of concrete and demands more extensive measures for soil enhancement due to the higher stiffness of the track panel. Only in tunnel areas does slab track cause lower GHG emissions since soil reinforcements are not necessary due to an existing concrete base layer after tunnel construction. For both construction types, over 80% of the GHG emissions stem from material production. Hence, circular economy as well as innovations within steel and concrete production processes hold significant potential for reducing GHG emissions. Full article

The guardrail is an indispensable part of ballasted track structures on bridges. In order to reveal its influence on the track–bridge interaction of continuous welded rail (CWR), the longitudinal resistance model of the guardrail fastener and its influential factors are established through tests. By taking a continuous girder bridge (CGB) for railways as an example, a stock rail-guardrail-sleeper-bridge-pier integrated simulation model is developed. The effects of the guardrails, installation torque of the guardrail fastener, and joint resistance of the guardrail under typical conditions are carefully examined. The research results indicate that the nominal longitudinal resistance of the guardrail fastener and the elastic longitudinal displacement of the rail prior to sliding approximately grow linearly with the growth of the installation torque. The presence of a guardrail can alleviate the track–bridge interaction in the range of the CGB, but exacerbate the interaction near the abutment with moveable bearings. This fact enables the abutment position to be considered as a new control point for the design of CWR on bridges. Considering the changing rules of the rail longitudinal force and rail gap, it is recommended that the installation torques of the guardrail fastener and guardrail joint are 40–60 N·m and 700–800 N·m, respectively. The recommended maximum longitudinal stiffness of piers for CGBs is evaluated. When the longitudinal stiffness of the pier for a CGB is lower than the recommended value, the influence of the guardrail can be neglected in the design of the CWR. Full article

Environmental safeguards promote innovative construction technologies for sustainable pavements. On these premises, this study investigated four hot mix asphalt (HMA) mixtures—i.e., A, B, C, and D—for the railway sub-ballast layer with 0%, 10%, 20%, and 30% reclaimed asphalt pavement (RAP) by total aggregate mass and a rejuvenator additive, varying the bitumen content between 3.5% and 5.0%. Both Marshall and gyratory compactor design methods have been performed, matching the stability, indirect tensile strength, and volumetric properties of each mixture. Dynamic stiffness and fatigue resistance tests provided mechanical performances. Laboratory results highlighted that the RAP and the rejuvenator additive increase the mechanical properties of the mixtures. In addition, the comparative analysis of production costs revealed up to 20% savings as the RAP content increased, and the life cycle impact analysis (LCIA) proved a reduction of the environmental impacts (up to 2% for resource use-fossils, up to 7% for climate change, and up to 13% for water use). The experimental results confirm that HMA containing RAP has mechanical performances higher than the reference mixture with only virgin raw materials. These findings could contribute to waste management and reduce the environmental and economic costs, since the use of RAP in the sub-ballast is not, so far, provided in the Italian specifications for railway construction. Full article

In this paper, a drive-by damage detection methodology for high-speed railway (HSR) bridges is addressed, to appraise the application of Mel-frequency cepstral coefficients (MFCC) to extract the Damage Index (DI). A finite element (FEM) 2D VTBI model that incorporates the train, ballasted track and bridge behavior is presented. The formulation includes track irregularities and a damaged condition induced in a specified structure region. The feasibility of applying cepstrum analysis components to the indirect damage detection in HSR by on-board sensors is evaluated by numerical simulations, in which dynamic analyses are performed through a code implemented in MATLAB. Different damage scenarios are simulated, as well as external excitations such as measurement noises and different levels of track irregularities. The results show that MFCC-based DI are highly sensitive regarding damage detection, and robust to the noise. Bridge stiffness can be recognized satisfactorily at high speeds and under different levels of track irregularities. Moreover, the magnitude of DI extracted from MFCC is related to the relative severity of the damage. The results presented in this study should be seen as a first attempt to link cepstrum-based features in an HSR drive-by damage detection approach. Full article

Under ballast mats (UBM) have demonstrated their capacity to reduce section stiffness and ballast degradation. However, UBM can cause ballast destabilisation under some circumstances due to excessive vertical track deflections, requiring the installation of geogrids over the mat which increases costs and time. As alternative to this solution, this paper shows the design of GridMat: a sustainable technology for ballasted railways that combines the concepts of geogrids and under ballast mats (UBM) manufactured from recycled crumb rubber. This aims to provide damping capacity while limiting the oscillations and settlement of ballast layer. To obtain the optimal GridMat design, five different configurations varying the aperture size and void areas were assessed through laboratory box tests reproducing the track section including the GridMat. Results showed that the optimal Gridmat was of 55 mm aperture seize and 25% void area. To evaluate the sustainability of this design, the expected number of conservation and renewal operations were calculated from full-scale laboratory tests and a life-cycle assessment and life-cycle cost analysis were undertaken. GridMat showed long-term reduction in ballast degradation and track settlement, reducing need for maintenance and renewal operations in comparison with standard mats. Full article

In the UK, High Speed Rail 2, (London to the ‘North’) is surrounded by a number of questions regarding construction technologies which can minimise the impact of the route. The rail industry in the UK has vast experience based with ballasted track, but this is not necessarily the most appropriate choice for new high speed rail construction when crossing problematic soils. This paper aims to investigate the use of different track types (ballasted and ballastless) and the influence they will have on the underlying soil in areas predominated by non-engineered mudrock backfills, relics of the UK’s mining heritage. Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. Structural performance of the railway track strongly depends on the level of stress that is transmitted to the ground and this must be reduced to an acceptable level to minimise deterioration in the mudrock if they are to be utilised effectively. The main objective for this paper is to investigate the impact of the initial stress conditions and dynamic stress on the permanent deformation of mudrock under different physical conditions. Triaxial testing is used to estimate the stiffness characteristics of the mudrock. The results show that the resilient modulus increases with a decrease in the stress amplitude. In addition, ballasted track shows a higher suitability for use in design in terms of the stiffness generated within the mudrock. Full article