Slab Track Research Articles

钢弹簧浮置板轨道减振效果现场与实验室测评研究

钢弹簧浮置板轨道减振效果现场与实验室测评研究

Hybrid Pixel‐Level Crack Segmentation for Ballastless Track Slab Using Digital Twin Model and Weakly Supervised Style Transfer

Crack detection at the pixel level across complex scenarios (structural interference and adverse working conditions) is a critical consideration in the maintenance of ballastless track slab (BTS). Although existing deep learning models achieve acceptable accuracy on cracks with a monotonous background, the ground truth with high labor cost is inevitable and their performance in complex scenarios may fall far below their theoretical bounds or even cause “all‐black images.” A hybrid algorithm based on synthetic data from digital twin model and weakly supervised style transfer is proposed in this paper for addressing the above challenges. The algorithm uses a region‐attention strategy to enable the uncontrolled generative adversarial network (GAN) focusing its attention on weak labels containing crack regions, directly obtaining segmentation results with the same style as the ground truth of the crack forest dataset. In addition, a digital twin model that can simulate the real inspection working conditions is established to generate a synthetic crack dataset, enabling the hybrid algorithm to extract the most discriminative features. The results show that the performance of the hybrid algorithm on inspection images across complex scenarios is nearly 25% higher than that of the DeepLabv3+ network, while the time cost consumed is only 0.5% of the latter. The deployment of the region attention strategy also enables the hybrid algorithm to achieve a mean intersection of union (MIoU) of 79.38%, which is nearly twice as much as that of GAN. It not only eliminates the oversegmentation caused by structures such as rails and fastener systems but also overcomes “all‐black images.” In addition, synthetic data can greatly enlarge the range, type, and number of discriminative crack features compared with data augmentation based on limited real data, thus enhancing the performance of the hybrid algorithm for uncertain inspection data. Particularly, the fully trained hybrid algorithm based on the synthetic dataset shows good adaptability and generalization to adverse working conditions such as uneven lighting, noise, and blur.

Mapping the relationship between the temperature gradient of CRTS Ⅲ slab track on bridge and rail deformation in high-speed railways

Temperature gradient is an important factor affecting the periodic rail deformation of CRTS Ⅲ and the running stability of high-speed trains. The Comprehensive Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method is employed for the analysis of test data in site from CRTS III slab tracks on high-speed railway bridges. The correctness of the coupling model has been validated through data on-site. To analyze the mapping relationship between the temperature gradient of the CRTS Ⅲ slab track on the bridge and rail deformation in high-speed railways, a rail-slab track-bridge thermal coupling model was established, and the rail deformation distribution characteristics of the slab track on the bridge under the complex temperature gradient load were calculated. Furthermore, a prediction model of rail deformation under the action of the complex temperature gradient was proposed. The study results showed that the intrinsic mode function (IMF) decomposed by the CEEMDAN method reflects the sensitive wavelength of track irregularity and quantitatively describes the corresponding relationship between amplitude and seasonal temperature. In the measured data, the maximum amplitude of rail deformation caused by temperature differences in different seasons was 1.99 mm, reflecting the significant impact of temperature gradient on the additional track irregularities on the bridge. Under the action of the temperature gradient, the rail deformation of CRTS Ⅲ slab track on the bridge is the superposition of periodic sinusoidal fluctuation of the track and parabolic fluctuation of the simply supported beam. This study could provide a new method for predicting rail deformation and controlling track smoothness, so as to improve the stability and operation efficiency of trains.

A Multi-Depth Deflectometer/Global Navigation Satellite System Method for Measuring Concrete Slab Track Deformation

This study introduces a Multi-Depth Deflectometer (MDD) combined with a Global Navigation Satellite System (GNSS) which was developed for measuring the deformation of railway slab track layers. We newly designed the MDD with the addition of laser sensor modules for increasing precision in which the MDD head is fixed at the top of the track slab. The MDD/GNSS system can measure the relative deflection between each track layer as well as the total deflection at the top of the track slab, which makes it possible to evade the fixed condition problem of classical MDD. The new MDD/GNSS system was installed at the transition zone between a tunnel entrance and its embankment, which experienced high settlement levels prior to repair. The system was used to monitor whether the repaired concrete track foundation with pressurized cement grouting was stabilized effectively and what track layer position was most unstable so that it had the most influence. The GNSS system was designed and built for computing net settlement at each track layer even when the MDD could not be fixed firmly at the end point, which is a major drawback of classical MDD. The results obtained from MDD and GNSS measurements indicated significant potential in aiding railway track settlement measurements.

Dynamic analysis of vibration response of track structure considering rail pads in low-temperature condition

To analyze the impact of the temperature-dependent properties of the rail pads on the vibration response of the track structure over a wide temperature range, taking into account the frequency-dependent properties of the rail pads, firstly, through its dynamic mechanical properties test and based on the high-order fractional derivative FVMP(fraction Voigt and Maxwell mode in parallel) model combined with the principle of Time-Temperature superposition, then the frequency-dependent properties of rail pads was characterized. Then the model was applied to the vertical vehicle-track coupled system. Finally, the impact of rail pads on track vibration response under extreme low temperatures was analyzed. According to the present study for vibration response of track structure, the rail acceleration shows that the case considering frequency-dependent property of rail pads is much greater than that without considering, while the slab track and base plate shows the opposite trend, the influence of temperature- and frequency- dependent properties of rail pads on the vibration response of track structure is mainly concentrated in the medium and high frequency band. Therefore, in order to improve the accuracy of track structure prediction, it is necessary to consider the temperature- and frequency-dependent properties of rail pads.

The influence of uneven frost heave and thermal conditions on the deformation and damage of slab track in seasonally frozen regions

To ensure the secure operation of high-speed trains in seasonally frozen regions, this paper investigates the deformation and failure patterns of slab tracks subjected to uneven frost heave and environmental issues. Utilizing our team’s previous research findings, finite element analysis software was employed to construct a mechanical transfer calculation model for the subgrade and slab track. This model was used to explore the relationship between uneven frost heave and slab track deformation at different time periods, along with the track structure’s damage behavior. In addition, comprehensive temperature field tests were conducted on the China railway track system (CRTS) III slab track, probing temperature variations, warping deformations, and stress distributions within the track structure. Finally, the interaction of uneven frost heave and thermal loads unveiled the interlayer debonding and stress characteristics of slab track structures across different months in seasonally frozen regions. The results revealed that the greater amplitude of frost heave and the smaller wavelength led to a higher change rate of rail irregularity. The uneven lateral deformation of the subgrade surface due to the sunny-shady slopes effect resulted in significant rail level irregularity of slab tracks. The combined impact of short-wavelength frost heave and temperature gradient loads emerged as the primary cause of macroscopic damage and stiffness degradation of concrete materials within slab track structures. These findings will help to understand the mechanical behavior of slab tracks in cold regions, thereby improving the quality of high-speed railway operations.

Spatial temperature characteristics of CRTS III slab track of railways on plateaus

With the construction of railways on plateaus, the slab tracks of railways are facing rigorous temperature challenges and adverse thermal effects. This paper analyzed the temperature field and thermal effects of the CRTS III slab track on plateaus. Firstly, the pivotal thermal parameters of the geotextile and rubber pad of the slab track were obtained by tests. Subsequently, a coupled thermal-fluid-solid model for the CRTS III slab track on plateaus was established, followed by experimental validation. Based on the model, the temperature field and thermal effects of the slab track on Tibetan Plateau were revealed. The main conclusions are as follows: the thermal conductivity, specific heat capacity, and heat flux of the rubber pad and geotextile were very small, resulting in poor heat conductivity. The temperature of the track on plateaus showed obvious non-uniformity along both lateral and vertical directions, and changed with time significantly. Compared with that on the plain, the CRTS III slab track on the plateau had low temperature and large temperature variations. Compared with the conventional simplified temperature load, the spatial temperature field can fully reflect the non-uniform thermal effects of the slab track on plateaus. The method and conclusions presented in this paper can provide scientific guidance for the construction, operation, and maintenance of railways on plateaus.

Assessment and Control of Metro-induced Vibration and Secondary Noise of TOD Buildings

Metro-induced vibration and structural secondary noise are becoming increasingly outstanding, which greatly restrict the further development of TOD (Transit-oriented development) project. To solve this problem, an evaluation methodology and dynamic model of vibration and secondary noise induced by metro train is developed firstly. Then the characteristic and distribution of vibration and secondary noise of the TOD subject to running train are studied. Finally, the control effect of steel-spring floating slab track (FST) on vibration and secondary noise of TOD project is evaluated. Results show that: when evaluating environmental problem caused by metro train, the standard of secondary noise is more strict than that of vibration. Main frequency of metro-induced vibration is concentrated in 40–63 Hz, and the second main frequency is concentrated in 6.3–16 Hz. The business building has the largest vibration due to its closest distance to the metro line. Secondary noises of most of the TOD buildings exceed the limit value, and the maximum exceeding value is 11.7 dB(A). FST is effective in controlling train-induced vibration and secondary noise of TOD buildings. FST cannot reduce vibrations in full frequency band, and vibration in some frequency bands are even amplified according to the stiffness of steel spring.

A Study on the Influence of Steel Structures in Concrete Subgrades on the Detection of Subgrade Distresses by Ground-Penetrating Radar

The detection of subgrade distresses in ballastless track railways poses a formidable challenge due to the presence of steel interference caused by the unique characteristics of high-speed rail track slabs and the dense arrangement of the steel reinforcement mesh within them. Here, we aim to examine the influence of varying distribution patterns of steel reinforcement in ballastless tracks on the detection of subgrade distresses using ground-penetrating radar. Through a combination of on-site testing and forward modeling, this paper analyzes the interference of steel reinforcement on the detection of voids beneath the steel using electromagnetic waves. The research findings reveal that incident electromagnetic waves from the ground-penetrating radar experience attenuation near steel reinforcements, with only a fraction able to penetrate the surface layer and propagate into the subsurface through interstitial gaps between the reinforcing bars. Furthermore, this influence diminishes as the spacing between the reinforcing bars increases and the bar diameter decreases. When steel bars are distributed on the upper and lower layers, the detection results of the lower void are most significantly influenced by the interlocking of the steel bars in the two layers. These research results can offer theoretical and technical support for the detection of ailments in high-speed railway subgrades.

Method for Controlling Full-Frequency Band Environment Vibration by Coordinating Metro Vibration Sources and Propagation Paths

Floating slab tracks (FSTs) are used to reduce the impact of vibration on precision instruments and historical relics along metro lines; however, ground vibration is universally amplified at the natural frequency of the tracks. In this study, a full-frequency control method that considers frequency matching for environmental vibrations, in combination with metro vibration sources and propagation paths, was developed based on the bandgap theory of the periodic structure. The effectiveness of this method was analysed by establishing a three-dimensional metro train–FST coupled model and a finite element analysis model of track bed–tunnel–soil–row piles. The results show that ground vibration can be reduced by approximately 3–5 dB at the natural frequency of the FST by adjusting the bandgap range of the periodic piles to 7–9 Hz, eliminating the adverse effect of vibration amplification at the natural frequency of the FSTs. The proposed control method shows good vibration control effects and can effectively minimise ground vibration in the full-frequency range.

Experimental study of friction performance degradation in sliding layer of CRTS II slab track considering dust incursion

The track-bridge interaction force in the China Railway Track System II slab track can be significantly reduced due to the effect of the sliding layer, thus its friction performance is crucial for the operational safety of the track. However, because of the micro delamination between the base plate and bridge deck under certain conditions, the dust inevitably infiltrates the sliding layer. This study performed abrasion experiments to investigate the influence of dust incursion on the friction performance of the sliding layer. The experimental apparatus was designed to simulate repeated sliding and normal pressure between the base plate and the bridge under actual working conditions. Different sizes of dust particles were employed, and the friction performance, characterized by the friction coefficient and surface topography of the geomembrane, was obtained and analyzed. The experimental results show that the growth rate of the friction coefficient was 1.46–2.88 times greater than that without dust incursion. The results of this study can serve as a reference for the actual friction performance degradation of the sliding layer and shed light on maintenance decision-making.

Experimental Monitoring of Transition Zones in Railway Tunnels

Abstract The expert research activity of transition zones of tunnels is one part of the overall set of these places on the railway line. Typical places where the stiffness of the railway changes are the portals of tunnels, where undesirable deformations occur during the operation of trainsets due to the changes in materials. In the places of the portals, there can be a ballastless track or slab track (with concrete bearing layer) or classic structure with a railway ballast. The paper presents long-term research on monitoring height changes in these sections. The results of the expert activity will be the basis for the subsequent proposal of new measures, i.e. changes to built-in objects or modification of the materials of structural layers in a given place of the transition zone.

An adaptive hybrid deep learning-based reliability assessment framework for damping track system considering multi-random variables

Reliability assessment is essential in the design and management of rail transit system (RTS), with a heightened focus on damping tracks that feature low-stiffness structures and various uncertainties. However, existing research on RTS has notable gaps: one is the unexplored nonlinear track irregularities in surrogate model, while the other is the significant computational burden of current reliability analysis. Therefore, Firstly, based on a database acquired from simulations of rigid-flexible coupling dynamic models, a hybrid deep learning (DL) surrogate model is developed and trained. Notably, it accommodates both time-series and feature parameters data as inputs, and integrates a novel algorithm featuring slide window with variational decomposition mode-sample entropy, optimization algorithm and adaptive learning strategy (AS). Subsequently, an advanced reliability assessment framework is proposed, utilizing AS hybrid DL-based Probability Density Evolution Method (PDEM), which thoughtfully designed to analyze the two aforementioned categories of random variables and then applied to a train-steel spring floating slab track. Experimental studies show the proposed surrogate model effectively and robustly predicts four safety metrics, with each component's excellence confirmed. Furthermore, this framework shows higher accuracy than the Monte Carlo Method and enhances computational efficiency by 10 ∼ 30 times compared to traditional mechanism-based PDEM. Consequently, reliability assessments indicate values of 0.9312 and 0.9214 for wheel-load reduction rate and rail displacement, respectively, with other metrics showing zero safety hazards. Findings of this study have practical applicability in the field of RTS design and maintenance.

Towards real-time condition monitoring of a transition zone in a railway structure using fibre Bragg grating sensors

Differential settlement of ballast and subgrade is a common issue in ballasted railway tracks. In transition zones between two different track forms, such as between a ballasted track and a slab track, a dip in longitudinal level often develops on the ballasted side. To ensure the safety of railway operation and reduce maintenance and life cycle costs, it is necessary to monitor the condition of the transition zone in an economical manner and to detect any operational change at an early stage. In recent years with the advancement of fibre-optic technology, fibre Bragg grating (FBG) sensors have been more commonly applied in condition monitoring of railways due to their high precision and high acquisition rates. In this study, an FBG-based setup for in-situ long-term condition monitoring of track bed degradation in a transition zone has been developed and implemented to provide data for verification and calibration of a simulation model. The system is designed for measurements in an operational railway track in harsh conditions in the north of Sweden. The instrumentation along the transition includes four clusters, each with an optical strain gauge array on the rail web in one sleeper bay, and an accelerometer and a displacement transducer on the sleeper. It is shown that the implemented displacement and strain sensors are able to effectively capture the overall dynamic range of the system, indicating that the collected data can accurately represent the dynamic response of the transition zone in the short term and long term and be applied for the calibration of a simulation model.

Laboratory investigation on the fracture toughness (Mode I) and durability properties of eco-friendly cement emulsified asphalt mortar (CRTS II) exposed to acid attack

Cement Emulsified Asphalt Mortar (CEAM) has gained prominence as a vital material for its energy and noise damping properties between the concrete roadbed and track slab in a high-speed railway system. Therefore, it is evident that CEAM properties need to be better understood and optimized. Since cracking caused by traffic loading and atmospheric conditions is one of the primary causes of failure in CEAM, addressing this issue is of great importance. Furthermore, there is a growing need for more environmentally friendly and durable CEAM due to the environmental impact of cement production in the form of greenhouse effect. The objective of this study is to assess the impact of partially replacing cement content in CEAM Type II (CRTS II) specimens with pozzolanic materials such as silica fume, metakaolin, and granite sludge to investigate how these pozzolans affect the fracture toughness (Mode I) performance under both normal (water curing) and sulfuric acid exposure conditions with the main focus on evaluating the pozzolans ability to resist acid attack from a fracture toughness perspective as the research novelty. For this purpose, specimens containing pozzolans at 5 %, 10 %, and 15 % substitution level (by weight of cement) were subjected to Semi-Circular Bending (SCB) test both under normal and exposure to 5 % sulfuric acid solution conditions. Moreover, water absorption test was conducted on specimens in normal condition as a durability index. The test results of this study revealed that substitution of these pozzolanic materials enhanced the fracture toughness in normal condition. Specifically, at a 10 % substitution as the optimal level, silica fume and metakaolin resulted in 18 % and 15 % increase in fracture toughness performance compared to the control specimen in normal condition. However, granite sludge exhibited almost the same performance as the control specimen at 5% substitution as its optimal level. In acid exposure condition, the detrimental effect of acid on the fracture toughness performance of specimens was reduced by 61 %, 55 % and 13 % for samples containing silica fume, metakaolin and granite sludge at 15% substitution level, respectively. Furthermore, water absorption test results showed that inclusion of silica fume and metakaolin at a substitution level of 15 % results in 56 % and 47 % reduction in water absorption compared to the control specimen, respectively, while for granite sludge, it was almost the same as control specimen. These results were also confirmed by SEM studies. Since the use of these pozzolans as cement substitution not only improves the fracture toughness in normal condition but also provides protection against acid-induced degradation, this study contributes to the development of a more durable and environmentally friendly CEAM.

Mechanical behavior of longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load

Adhesive anchors have been widely used as a post-reinforcement measure to strengthen longitudinally continuous slab tracks. However, the mechanical behavior of the longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load has not been thoroughly investigated. Therefore, this paper was motivated to conduct experimental and numerical investigation on the temperature-induced deformation and damage of the reinforced track. Firstly, experimental tests were carried out to investigate the influence of the borehole conditions on the bond properties of post-installed adhesive anchors. Next, the bond-slip relationships between anchors and concrete were established for anchors in various borehole conditions. Then, a novel finite element model of the reinforced track incorporating a nonlinear cohesive zone model of structural interfaces was developed and validated by filed monitoring data. Finally, the effects of borehole conditions and number of invalid anchors on the deformation and damage behavior of the reinforced track under nonlinear temperature load were systematically studied. Results show: (1) The cubic compressive strength grade of concrete has a significant effect on the bond-slip curves between concrete and anchors of the longitudinally continuous slab track. (2) Wet boreholes and uncleaned boreholes would reduce elastic stiffness and ultimate bond strength between anchors and concrete by 11–37% respectively, compared with dry and cleaned boreholes. (3) The maximum vertical displacement of slabs could increase by 7% and 4% if the boreholes are wet and uncleaned respectively. (4) The interface at the center of slab end near damaged joint will not fail for the track with 1 or 2 invalid anchors when the temperature reaches its highest. However, interface debonding will occur with a temperature rise of 34.6 ℃ if there are 3 invalid anchors.

Analysis on crack propagation of CRTS III slab ballastless track under temperature loads and freeze–thaw deterioration

In seasonal frozen region, the Chinese Rail Track System (CRTS) III slab track is subject to temperature loads and freeze–thaw deterioration, which may lead to further expansion of microcracks in track slabs. Mechanical parameters of track structure materials after freeze–thaw cycles are obtained through the experimental tests in this study. A finite element model of CRTS III slab track on subgrade section is then established by ABAQUS. Based on fracture mechanics theory, the types of cracks generated in track slabs under temperature loads and freeze–thaw deterioration, and crack expansion law are analyzed by using extended finite element method. The results show that under temperature loads, the expanded cracks in track slab are mainly Mode Ⅰ - Opening mode. There is the possibility of expansion for transverse cracks with larger size on the upper surface of track slab under negative temperature gradient load. Vertical capillary cracks at the location where track slab is bonded to self-compacting concrete are more likely to expand. Freeze-thaw deterioration will reduce the difference between the SIFs of cracks and fracture toughness of track slab material, which has a certain promotion effect on crack expansion.

Innovative requirements and evaluation methods for slab track design

With increasing train speeds and reduced time windows for maintenance work, the interest in the application of slab track technology to increase the capacity of high-speed railways has grown. Slab track may still be considered a relatively young technology, but with several different designs available on the market. Current research on slab tracks commonly focuses on improved methods. In contrast, the formulation of requirements, and evaluation towards these, are seldom investigated. In this paper, state-of-the-art simulation models are employed to illustrate and address the needs for innovative requirements in terms of structural integrity and robustness, life cycle cost (LCC) and environmental footprint of new and existing slab track designs. Based on demonstration examples, it is argued that current standards may lead to overly conservative designs inducing higher LCC and environmental footprint than necessary. Extensions of the standards in terms of LCC and environmental footprint are suggested. The conflict of interest between structural integrity and robustness, LCC and environmental footprint is discussed, and suggestions for how to optimise slab track structures are proposed.

Experimental study on the characteristics of vibration energy propagation in the subway turnout area

Due to the scarcity of urban land resources, the development model of building over rail transit has rapidly emerged. The turnouts near the train depots and stations have become significant sources of environmental vibrations. This paper employs on-site experimental methods to measure the vibration acceleration of rail, track slab, and tunnel wall at multiple sections in the turnout area when a subway train passes through. The vibration intensities at different sections of the turnout area are analyzed, and the vibration reduction effects of vibration isolation fasteners and steel-spring floating slabs in the turnout area under similar conditions are compared. Finally, an energy evaluation method is used to analyze the vibration propagation characteristics on the non-isolated turnout frog section. Obtained the propagation and attenuation characteristics of vibrations in different frequency bands in the turnout area based on on-site test data.

Numerical investigation on the failure mode of the upper shear hinge in steel spring floating slab track

Fracture on hinge bars and fixed bolts of upper shear hinges is a common problem in prefabricated steel spring floating slab tracks (SSFST), adversely affecting train operation safety and comfort. To investigate the potential failure modes, this paper established a four-slab SSFST model to analyze the force condition of upper shear hinges. Force transmission between floating slabs as well as the stress level of the hinge bars and fixed bolts under the most unfavorable vehicle cases were respectively simulated by the structural mechanics method (SMM) and the FEA software ABAQUS. Stress influence lines of hinge bars and fixed bolts under the moving vehicle load resulting from ABAQUS were extracted to evaluate the fatigue behavior based on the fatigue S-N curve by the post-processing software FE-SAFE. Furthermore, the influence of different pre-tightening force on fixed bolts’ fatigue behavior was discussed. The results of the two simulation methods match well, suggesting that force between floating slabs is mainly transmitted by rails, while shear hinges only account for about 1/3 of the bending moment and 1/5 of the shearing force. Hinge bars and fixed bolts are both sufficient in strength, yet fatigue problem is likely to happen to the latter. The fatigue failure mode and location of fixed bolts are related to the value of pre-tightening force. Large stress range or high stress mean always exists as the pre-tightening force varies, meaning that bolt fatigue is an intrinsic failure mode of the upper shear hinge in SSFST.