Ballastless Track Research Articles

Analysis of bending waves and parametric influence on band gaps in periodic track structure

Vibration of railway tracks generated due to rail-wheel interaction is a key research concern. A rail with equally spaced supports can be regarded as a periodic structure. Such a structure possesses unique property of band gap because of that they act as vibro-acoustic filters. Here, the propagation behavior of vertical and lateral bending waves is studied in a periodic ballastless track structure. Bloch-Floquet theorem is used to formulate the dispersion relations for the propagation of two types of waves which is validated by corresponding finite element model. The results show coexistence of both resonance and Bragg type band gaps they are owing to locally resonant units and spatial periodicity in the track. Furthermore, the study also explores the impact of track parameters, such as pad stiffness and sleeper spacing, on the properties of these band gaps.

Influence of Reflective Coating on Temperature Field and Temperature Effect of CRTS III Slab Ballastless Tracks on Bridges.

To minimize the adverse effects of high temperatures on the service performance of track structures, research on the application of reflective coatings on track structures is urgently needed. Based on meteorological data and the characteristics of the multi-layer structure of the ballastless track, refined finite element models (FEMs) for the temperature field and temperature effect analysis of the CRTS III slab ballastless track structure on bridges were established. The temperature deformation characteristics and temperature stress distribution of the CRTS III slab ballastless track under natural environmental conditions were investigated. Similarly, the influence of a reflective coating on the structural temperature field and temperature effect was studied. The results showed that the temperature and vertical temperature gradient of the track slab were significantly reduced after the application of the reflective coating. Meanwhile, the thermal deformation and thermal stresses of the track slab and the self-compacting concrete (SCC) layer were minimized. Under high-temperature conditions in summer, the maximum temperature of the track slab decreased from 47.0 °C to 39.6 °C after the application of the reflective coating, and the maximum vertical temperature gradient of the track slab decreased from 61.5 °C/m to 39.1 °C/m after the application of the reflective coating. Under the maximum positive temperature gradient, the peak displacement of the upper arch in the middle of the slab and the peak displacement of the sinking in the slab corner decreased from 0.814 mm and 1.240 mm to 0.441 mm and 0.511 mm, respectively, and the maximum transverse tensile stresses of the track slab reduced from 2.7 MPa to 1.5 MPa as well. In addition, the reflective coating could also inhibit the failure of the interlayer interface effectively. The results of this study can provide a theoretical basis and reference for the application of reflective coatings on ballastless tracks on bridges.

Research on two-dimensional digital characterization of crushed stone aggregates in the SCC filling layer of the CRTS III slab ballastless track

Through the actual situation of on-site construction and building, it could be found that the filling quality of the SCC filling layer had a large correlation with the apparent morphology of crushed stone aggregates. This paper investigated the two-dimensional digital characterization of crushed stone aggregates in the SCC filling layer of the CRTS III slab ballastless track through field experiments and compared them with pebble aggregates from three perspectives. Two-dimensional feature data of crushed stone and pebble aggregates in the top view, front view, and left view were obtained using the 3D scanning equipment. The sphericity (or flatness, or circularity) of both crushed stone and pebble aggregates did not directly reflect a uniform pattern of variation in the three views. Pebble aggregates exhibited higher concentration of the sphericity (or flatness, or circularity), while crushed stone aggregates showed more dispersed values. Furthermore, the fractal dimension of crushed stone aggregates was greater than that of pebble aggregates in the corresponding view, with the fractal dimension of crushed stone aggregates tending towards larger values. Regarding the characteristic indices of crushed stone and pebble aggregates, including the sphericity, flatness, and circularity, significant differences were observed between the different characteristic indices. This research provided effective suggestions for the preparation of the SCC with excellent flow characteristics at the construction site.

Vulnerability Analysis of Catenary-Bridge-Track System

Continuous welded rails on bridges are extensively employed in high-speed railways, where trains are predominantly electrically powered, and the open-air catenary represents the weakest link in the system. Despite the widespread use of continuous welded rail on bridges for high-speed railways, there exists a relative dearth of research on their vulnerability, particularly regarding seismic vulnerability studies that consider the catenary, track type, and bridge collectively. The vulnerability of fasteners and catenary on bridges under the longitudinal resistance of the line was investigated by constructing a 7−32 m high-speed railway double-line simply-supported box girder bridge. It reveals, for the first time, the influence of the longitudinal resistance of the line on the vulnerability of fasteners and catenary under seismic action. The study indicates that both the fasteners’ and catenary’s vulnerability increases with the intensity of ground shaking, with the catenary being more susceptible. The longitudinal resistance of the line has a greater impact on the fasteners’ vulnerability than the catenary. When the degree of damage is minimal, the order of damage to the fasteners is the ballasted track, small resistance fastener, and ballastless track when the probability of exceedance is 5%. The ballastless track can significantly increase the probability of no damage to the fasteners, and it is recommended that the ballastless track be used when designing high-speed railway bridges in earthquake-prone regions.

Defect Recognition in Ballastless Track Structures Based on Distributed Acoustic Sensors

Defect recognition in ballastless track structures, based on distributed acoustic sensors (DASs), was researched in order to improve detection efficiency and ensure the safe operation of trains on high-speed railways. A line in southern China was selected, and equipment was installed and debugged to collect the signals of trains and events along it. Track vibration signals were extracted by identifying a train track, denoising, framing and labeling to build a defect dataset. Time–frequency-domain statistical features, wavelet packet energy spectra and the MFCCs of vibration signals were extracted to form a multi-dimensional vector. An XGBoost model was trained and its accuracy reached 89.34%. A time-domain residual network (ResNet) that would expand the receptive field and test the accuracies obtained from convolution kernels of different sizes was proposed, and its accuracy reached 94.82%. In conclusion, both methods showed a good performance with the built dataset. Additionally, the ResNet delivered more effective detection of DAS signals compared to conventional feature engineering methods.

Warping deformation of the track slab and their influence on the interlayer stiffness and vibration transmission characteristics of the unit ballastless track

The unit ballastless track partially segments the concrete track bed in the longitudinal direction, and relieves the concrete temperature stress by isolating the upper and lower layers. However, the layer isolation leads to the incompatible deformation of the upper and lower track structures under the effect of the temperature gradient. A large temperature gradient on the track slab will cause local contact between layers, the contact area between layers will then decrease, thus leading to “stiffness softening” between layers. When the vehicle passes, the contact area between layers will gradually increase, which, in turn, leads to “stiffness hardening”. The analysis results show that the greater the design stiffness between layers, the more significant the “stiffness softening” effect will be under the temperature gradient. When k0 = 400 × 106 (N·m−1)·m−2 and Tg = 90 °C·m−1, the interlayer stiffness decreases by 88%.The simulation analysis results of the wheel-drop impact test show that under a positive temperature gradient, the peak value of rail vibration acceleration increases, and the peak value of the track slab and base plate vibration acceleration decreases. The greater the stiffness designed between layers, the more obvious the influence will be. With the increase of the positive temperature gradient, the vibration acceleration of the rail and the track slab will be reduced in the 1–30 Hz and 40–100 Hz frequency domains. With the increase of the negative temperature gradient, the vibration acceleration of the rail in the 4–10 Hz, 20–50 Hz frequency domains, and the vibration acceleration of the track slab in the 70–200 Hz frequency domains will be increased. A large positive temperature gradient inhibits the transmission of high-frequency vibrations above 40 Hz to the substructure, while a negative temperature gradient inhibits the transmission of low-frequency vibrations within 30 Hz and 70–200 Hz to the substructure. A positive temperature gradient is beneficial to restrain the downward transmission of low-frequency vibration. When k0 = 200 × 106 (N·m−1)·m−2, the low-frequency vibration transmission loss of the track slab to the base plate is close to 0 dB without temperature gradient, but the positive temperature gradient increases the transmission loss by about 10 dB, the greater the temperature gradient, the higher the transmission loss of the track slab to the base plate under high stiffness.

Enhancing sustainability in pavement Engineering: A-state-of-the-art review of cement asphalt emulsion mixtures

Cement asphalt emulsion mixture (CAEM) is an environmentally sustainable substitute for hot mix asphalt and can trigger a substantial economic benefit. This paper systematically reviews the interactions between the organic–inorganic composites and their influence on the performance of CAEM. First, the interactions between asphalt emulsion (AE) and cement are introduced. Next, the demulsification of AE and hydration of cement in the CAEM system are analyzed. Finally, the fresh properties of CA paste, the static and dynamic mechanical properties of CA mortar and its applications in ballastless slab tracks, and the road performance of CAEM and its applications in pavement construction are discussed. This review allows for a better understanding of the interaction of the organic–inorganic composite and thus has a better strategy to regulate the performance of CAEM and promote its practical application.

Experimental study on mechanical properties of new FRP trusses reinforced sleepers under the stacking condition

The main objective of this research was to overcome the problem of the closed-loop created in the steel truss of the ballastless track slab. Therefore, a new type of FRP truss was proposed and fabricated. However, the mechanical performance of the sleepers reinforced by this new FRP truss under the stacking condition was not clear. In this paper, five different types of truss reinforced sleepers were fabricated and tested in the stacking state by the compressive test. The test results show that: (1) the new FRP truss reinforced sleepers still have sufficient stiffness and bearing capacity compared to the traditional sleepers, and the hand-made FRP joints not only have high strength, but also provide early warning of joint failure; (2) the height of the FRP truss has a significant effect on the failure modes, including joint failure after the web rod yielding (the height less than 89 mm) and the FRP truss buckling after the web rod yielding (the height greater than 108 mm); (3) the finite element model of the friction coefficient is set up can accurately predict the load–displacement curves of specimens under the stacking condition.

Seismic response of high-speed railway system under actions of ground motions from deterministic physics-based simulation

In order to investigate the response of a high-speed railway bridge under seismic excitations in the near-fault area, a deterministic physics-based method is used to construct the ground motion field in the near-fault area of a scenario earthquake. A finite element model of an assumed high-speed railway system is established, which consists of a finite length CRTS III ballastless track laid on a 15-span simply-supported girder bridge. The simulated ground motions and a group of three-component as-recorded accelerograms are used to provide non-uniform and uniform excitations at bridge piers, respectively. The seismic response of the rail-track-bridge system is calculated, and the effects of using different types of seismic excitations for the seismic analysis of the high-speed railway bridge in the near-fault area are analyzed. The results show that two end piers of a multi-span simply supported girder bridge could encounter remarkably different excitations in terms of waveform and frequency content for different bridge alignments in the near-fault area. The vertical response of the railway bridge system is more sensitive to the pattern of the excitation than the longitudinal response. Considering the spatial difference of ground motions among piers could increase the difference of the rail vertical displacement between the beam joint and mid-point of span, forming a remarkable periodic vertical irregularity of the rail. Using non-uniform excitation could lead to a reduction in DPeak and APeak which is most significant for DPeak in the vertical direction.

Microstructure characteristics and evolution of the bonding interface between SCC and steam-cured concrete

The microstructure of the bonding interface in CRTS III ballastless track structures is critical to the mechanical properties and durability of high-speed railway structures. The microstructure evolution of the bonding interfacial zone between steam-cured concrete and SCC (self-compacting concrete) is widely studied. This paper investigates the pore structure and phase evolution of the bonding interface zone using backscattered electronic and energy dispersive spectroscopy (BSE + EDS). Based on the nanoindentation test, the microstructure characteristics of the bonding interfacial zone were studied. The results show that the microstructure reveals a gradient change at the bonding interface zone, and the gradient characteristics of the microstructure weaken as curing age increases (especially at 7 days and 56 days). The width of the bonding interface zone is about 15 μm, and the width is more about 20 μm at 1 day. The elastic modulus of C-S-H at the bonding interface zone is low and the C-S-H is mostly LD C-S-H. VMA is beneficial to improve the elastic modulus of C-S-H.

Insights of the vehicle-track-girder system dynamic response changes caused by the thermal deformation of CRTS III ballastless track in the natural environment

The regularity of the high-speed railway track plays an important factor in ensuring the stability and safety of vehicle operation. The study of the influences of the slab warping deformation on the dynamic response of the vehicle-track-bridge is of great engineering significance. Currently, in relevant research work, only the impacts of track irregularity caused by the track or bridge warping deformation on the dynamic responses are considered, but the influence of structural modal changes induced by the thermal deformation is commonly ignored. This article focuses on the temperature deformation of the CRTS III track on the elevated bridge and the deformation-induced vehicle-track-girder dynamic response changes. Firstly, based on the CRTS III slab temperature deformation monitoring experiment and theoretical analysis, the warping deformations of the CRTS III track and girder in natural environments were studied. Secondly, the deformation-induced modal changes of the track-girder were fully considered, and the dynamic response changes of the vehicle-track-girder were analyzed when the warping deformation of the slab reached the maximum. Through a comparative analysis of three scenarios: no structural temperature deformation, only track irregularity caused by the deformation, and the combined effects of deformation-induced irregularity and modal changes, it was found that the time–frequency domain variation characteristics of wheel-rail force and rail acceleration can be acceptably simulated in the case of only deformation-induced track irregularity, but the dynamic response changes of the slab and girder will be underestimated. Therefore, in the study of the dynamic responses of the vehicle-track-girder with temperature effects, full consideration should be given to the deformation-induced track irregularities and structural modal changes.

Service performance of CRTS II ballastless track in high temperature tunnel

Considering the dynamic balance of heat conduction between tunnel floor and track structure, heat convection and heat radiation between track surface and air, a finite element model for the temperature field of CRTS Ⅱ ballastless track in the high temperature tunnel is proposed and the dynamic responses of the vehicle-track coupling system are studied. Firstly, the influences of the temperature of the tunnel floor on the temperature distribution and warpage of the track are investigated. Secondly, the dynamic responses of the VTCS excited by the additional irregularity of the track induced by the temperature of the tunnel floor are investigated, and the effects of track deformation on dynamic characteristics at different speeds are compared. The findings demonstrate a linear relationship between the maximum and minimum temperatures of the upper and lower surfaces of the track slab and the temperature of the tunnel floor. In comparison to rail, the maximum displacement of the slab is larger, and the warpage deformation with symmetrical distribution of the track slab is characterized by concave in the middle and arching on both sides. The fastener stiffness has no effect on the deformation of the slab, but the vertical displacement of rail increasess as the fastener stiffness enlarge. Temperature load enlarges the excitation of the wheel-rail system so that intensifies the dynamic response. The faster of the speed of vehicle is, the effect of additional track irregularity on the dynamic response is the more pronounced. The research reveals the mechanism of high temperature tunnel on the service state of track, which supplies a theoretical basis for the design and maintenance of track.

Track Unevenness Prediction Based on Static Track Inspection Data Matching

A track static misalignment prediction model based on track median deviation is created using an IGA-BP neural network in order to precisely predict the trend of ballastless track static misalignment. The historical static track median deviation detection data are matched using actual compensation edit distance (ERP) to finish the correspondence processing of the original data. The precisely matched data are used to train the model, forecast irregularities in the track median, and compare results with other traditional prediction techniques. The outcomes demonstrate that the IGA-BP neural network can more accurately predict the nonlinear time series data development trend. In comparison to other prediction models, the IGA-BP neural network model’s average relative error and root mean square error are 0.091 and 0.110, respectively. The prediction accuracy is raised by between 43% and 60%, demonstrating the IGA-BP neural network model’s efficacy in predicting static upsets on ballastless tracks and presenting a workable strategy for track predictive maintenance.

A new device for restraining rail vibration of ballastless track and its effect study

A new device for restraining rail vibration of ballastless track and its effect study

Numerical investigation into hydrodynamic behavior of graded aggregates of high-speed ballastless track considering the degree of saturation

The ballastless track inevitably suffers from some functional defects, such as expansion joint cracking, due to the long term combined effect of dynamic train loads and environmental factors. As a result, water can be somehow retained in the graded aggregates of the roadbed surface layer under ballastless track, which is a key structural component subject to high-speed train loads. Accordingly, it is of significance to study the hydrodynamic behavior of roadbed surface layer that can be prone to depend on variation of the degree of saturation (Sr) in graded aggregates. A coupled hydrodynamic model of roadbed surface layer under ballastless track subject to high speed train loads was established based on homogenization theory and elastic wave theory involving Sr of graded aggregates. The proposed model is validated by degrading to Biot's dynamic model in saturated porous medium and analytical method of unsaturated soil. The effect of different Sr on the pore fluid pressure, spatial seepage velocity of graded aggregates is investigated based on this model with the practical seepage boundaries in ballastless track considered. On this basis, the influence of different spatial locations on the dynamic seepage index is discussed, and the differences in the stress paths in the roadbed surface layer under different Sr at different depths are analysed. The numerical results show that the increase of Sr has a spatial and critical effect on the increase of pore water pressure and seepage velocity in the roadbed surface layer. When the expansion joint of ballastless track cracks, the hydrodynamic erosion in the surface layer of ballastless track roadbed has been accumulating continuously. The erosion is more serious within the depth of 15 cm under the surface of roadbed. For Sr above 0.7, extra attention should be given to prevent internal erosion diseases in the roadbed surface layer during maintenance of ballastless track.

Fuzhou–Xiamen high-speed railway: a new paradigm for China’s cross-sea railways

The new 277 km Fuzhou–Xiamen high-speed railway in China is the country’s first cross-sea railway designed for operational speeds of 350 km/h. Completed in 2023, it involved various advanced construction technologies, including the world’s first 1000 t bridge-building machine to be used offshore, advanced corrosion-resistant steel, pioneering rotation of a main bridge pylon, and aerodynamic steel–concrete composite bridge decks with ballastless tracks. The innovative project represents a milestone for China’s high-speed railway, heralding a new era of cross-sea transportation.

Vortex-induced vibration performance and mechanism of long-span railway bridge streamlined box girder

To investigate the vortex-induced vibration (VIV) characteristics of a narrow-streamlined railway box girder and optimize its VIV performance, a long-span railway cable-stayed bridge was analyzed. Based on sectional model wind tunnel tests, the influence of the wind attack angle and the damping ratio on the VIV performance of the girder was investigated. The main inducing factors of the VIV of the narrow railway box girder were explored and a series of corresponding optimization schemes was put forward. The results show that there is no VIV when the wind attack angles are −5°, −3° and 0°, and the damping ratio is 0.2%. The non-dimensional maximum amplitudes 1000 y/ D of the girder at wind attack angles of +3° and +5° are 14.4 and 19.4, respectively. The maximum amplitudes decrease with the increase of the damping ratios. The railing base is the influence factor that induces the vertical VIV, because the separation vortices between the railing base and ballast wall, as well as behind the railings, cause the VIV of the railway steel box girder. Compared with that of the girder section with the ballastless track board, the non-dimensional maximum vertical VIV amplitude of the girder without the ballastless track board greatly increases from 19.4 to 63.5, which could effectively suppress the VIV of the main girder. Lastly, in the construction state, vertical VIV occurs for girder sections I and II, which have respective aspect ratios of 4.3 and 4.6, at wind attack angles of +3° and +5°. Girder section III, which has a 6.7 aspect ratio and is more streamlined, does not have a VIV. The greater the aspect ratio of the bridge girder, the better the VIV performance. The relevant results could serve as a guide for wind resistance design of railway streamlined box girders.

Influence of train speed and its mitigation measures in the short- and long-term performance of a ballastless transition zone

AbstractThe ballastless track is nowadays the most popular railway system due to the required low number of maintenance operations and costs, despite the high investment. The gradual change from ballasted to ballastless tracks has been occurring in Asia, but also in Europe, increasing the number of transition zones. The transition zones are a special area of the railway networks where there is an accelerated process of track degradation, which is a major concern of the railway infrastructure managers. Thus, the accurate prediction of the short- and long-term performance of ballastless tracks in transition zones is an important topic in the current paradigm of building/rehabilitating high-speed lines. This work purposes the development of an advanced 3D model to study the global performance of a ballastless track in an embankment–tunnel transition zone considering the influence of the train speed (220, 360, 500, and 600 km/h). Moreover, a mitigation measure is also adopted to reduce the stress and displacements levels of the track in the transition. A resilient mat placed in the tunnel and embankment aims to soften the transition. The behaviour of the track with the resilient mat is evaluated considering the influence of the train speed, with special attention regarding the critical speed. The used methodology is a novel and hybrid approach that allows including short-term and long-term performance, through the development of a powerful 3D model combined with the implementation of a calibrated empirical permanent deformation model.

Experimental study on the static and fatigue splitting failure behaviors of bonding interface between bi-concrete materials

The bi-concrete materials structure, steam-cured concrete (SC) and self-compacting concrete (SCC), has been widely utilized in the China Railway Track System (CRTS) III slab ballastless track structure. In this work, the static and fatigue splitting failure behaviors of the bonding interface between SC and SCC have been investigated. The specimen with a bonding interface between SC and SCC was prepared for the static and cyclic splitting tests, and cyclic splitting tests were conducted on four stress levels, including 0.6 Pt (static ultimate load), 0.65 Pt, 0.75 Pt, and 0.85 Pt. The results show that the debonding process of the interface under static loading contains three stages, linear stage, acceleration stage, and brittle failure stage. The evolution of fatigue strain of bonding interface also has three stages, initial increase stage, steady increase stage, and rapid increase to failure stage. The fatigue splitting life of the bonding interface obeyed the two-parameters Weibull distribution, the S-N-Pf model established in this study could predict splitting fatigue life of the bonding interface between SC and SCC well. The value of the fatigue strength was 0.418 of the static splitting ultimate load. In addition, a calculation of fatigue damage reliability based on Miner model is conducted to describe the fatigue damage process of bonding interface quantitatively.

Analysis of early-age mechanics and crack of the base plate on the bridge in summer based on eXtended FEM

Based on the eXtended Finite Element Method (XFEM), taking the base plate of the double-block ballastless track on the new high-speed railway bridge in the southeastern coastal area as the research object, the finite element model of the base plate was established to investigate the early-age mechanical properties and cracks under the high-temperature environment in summer. The on-site tests of temperature monitoring and crack observation were carried out on the base plate at an early age to validate the correctness of the model. The influence of the groove radius, anti-cracking rebar mesh, and curing methods on the mechanical properties of the base plate was further analyzed. As the age increases, the principal tensile stress in the groove exceeds the standard value of the concrete tensile strength, and the crack appears at the groove first. Increasing the radius of the chamfer can effectively reduce the maximum principal tensile stress in the groove, where the reduction rate is 15.80% and 31.11% respectively when the radii are 200 mm and 300 mm compared with the radius of 100 mm. The horizontal and vertical anti-cracking rebars in the groove have a significant reduction effect on the maximum principal tensile stress in the groove, of which horizontal laying is the most effective. A reasonable selection of curing methods is conducive to reducing the early-age cracking risk in the grooves, with plastic film covering curing being one of the more favorable methods. This paper provides a certain reference value for studying the early-age mechanical behavior of the base plate on the bridge and the influencing factors of the cracks at the groove.