Slab Track Research Articles

Acceleration-Guided Acoustic Signal Denoising Framework Based on Learnable Wavelet Transform Applied to Slab Track Condition Monitoring

Acoustic monitoring has recently shown great potential in the diagnosis of infrastructure condition. However, due to the severe noise interference in acoustic signals, meaningful features tend to be difficult to infer. It creates a considerable obstacle for an extensive application of acoustic monitoring. To tackle this problem, we propose an acceleration-guided acoustic signal denoising framework (AG-ASDF) based on learnable wavelet transform to automatically denoise the acoustic signal and extract the relevant features based on the acceleration signal. This denoising framework requires the acceleration signal only for the training stage. Therefore, only acoustic sensors (non-intrusive) need to be installed during the application phase, which is convenient and crucial for the condition monitoring of safety-critical infrastructure. A comparative study is conducted among the proposed AG-ASDF and other feature learning / extraction methods, by using a multi-class support vector machine to evaluate the detection effectiveness of slab track condition based on acoustic signals. Different healthy and unhealthy states of slab tracks are imitated with three types of slab track supporting conditions in a railway test line. The classification based on the proposed AG-ASDF features outperforms other feature extraction and learning methods with a significant accuracy improvement.

Study on Temperature Force Control Mechanism of CRTSⅡ Slab Track: Control Conditions of Temperature Cracking

Study on Temperature Force Control Mechanism of CRTSⅡ Slab Track: Control Conditions of Temperature Cracking

Study on the threshold for superposed deformation of simply supported bridge creep and track slab upwarp in high-speed railway

Based on long-term inspection data about track geometric irregularity of 32 m-span simply supported girder bridge in China Railway High-Speed for nearly 10 years, it is found that there is continuous periodic track longitudinal level (TLL) with different wavelengths, thereinto, simply supported girder bridges creep and ballastless track slab upwarp are the primary reasons. Moreover, there are two types of variation trends for bridge creep of 32 m simply-supported bridges with ballastless track, that is, stable type and increasing type, and the maximum [Formula: see text] (the peak-to-peak value of track longitudinal level) is 7.1 mm for track longitudinal level caused by bridge creep, and the maximum [Formula: see text] caused by upwarp deformation of ballastless track slab is 3.2 mm. Hence, this paper investigated the effects on running performance and structure service performance of random track irregularity and additional track irregularity caused by bridge creep, track slab upwarp deformation or superposition of both, a three-dimensional finite element model of vehicle-track-bridge for dynamic simulation calculation was established, the threshold values for bridge creep and track slab deformation under 350 km/h were proposed based on running performance and structure service performance. Finally, research results show that bridge creep influences on the ride comfort significantly, but running safety barely. Due to the short wavelength of TLL, the track slab upwarp deformation affects both the ride comfort and running safety heavily. The car bodies are more sensitive to bridge creep and produce mainly low-frequency vibration, but the rate of wheel load reduction is more sensitive to the track deformation and shows the high-frequency vibration. For 32 m simply supported bridges without track slab deformation, the [Formula: see text] caused by bridge creep should be limited to 7 mm, and 9 mm in difficult situations. When the [Formula: see text] caused by bridge creep is small (less than 5 mm), the [Formula: see text] caused by track slab upwarp deformation must be less than 4 mm. When both deformations exist simultaneously, the [Formula: see text] caused by superposition deformations of both should not exceed 10 mm, with track slab upwarp deformation not exceeding 4 mm. In the presence of both structural deficiencies, it is suggested that the track slab deformation must be eliminated when it is difficult to eliminate the bridge creep.

Simulation study on the influence of wheel irregularity on the vertical dynamics of wheel–rail interaction for high-speed railway track using bond graph

Dynamic interaction between train wheel and high-speed slab is an important issue when evaluating the contact force at the wheel–rail interface under the influence of an irregularity either on the train wheel or on the rail. In this paper, an influence of amplitude of irregularity along with the vehicle speed on the dynamics of wheel–rail interaction for high-speed railway tracks is being analyzed. For this purpose, single-wheel high-speed railway (HSR) track interaction models are developed using the bond graph modeling technique. The HSR track model consists of two layers of beam, i.e., rail and concrete slab. Both the rail and slab track is modeled using the Euler–Bernoulli beam theory. The Hertzian contact theory at the wheel–rail interface has been considered for this analysis. The vertical dynamic interaction between a train wheel and a high-speed slab track is compiled in the time domain using a bond graph approach coupled with a technique known as modal superposition. Irregularity present on the wheel is characterized as smooth, moderate, and severe depending upon the variation of irregularity amplitude. An expeditious increase of maximum contact force has been observed between the speed range of 200 and 250 km/h. Beyond the speed of 250 km/h, there is a gradual increment of contact force up to its peak value. When the train speed is beyond 288 km/h, there is a gradual decrease in maximum contact force. This kind of several other useful dynamic responses in terms of wheel acceleration and wheel–rail overlap are also evaluated.

Intelligent identification of mortar void in ballastless slab track using the wheelset acceleration combined with CNN-SVM

Intelligent identification of mortar void in ballastless slab track using the wheelset acceleration combined with CNN-SVM

Experimental study on vibration characteristics of the floating slab with under-slab polyurethane mats considering fatigue loading effect

Under-slab polyurethane mats (USPM) are commonly recommended as a reliable vibration-damping measure in metro traffic. Since the design speed and axle load of the urban rail transit lines are different from those of the ordinary speed lines, the vibration characteristics of polyurethane mat floating slab track (PMFST) during long-term service need to be studied furtherly. This study investigated the vibration characteristics and transmission law of PMFST during the fatigue process and compared it with ordinary track (OT), which is the same as PMFST but without the under-slab mat using full-scale indoor laboratory models. The results show that: 1). Under-sleeper subsystem (including track slab, USPM, and foundation) experienced hardening during the fatigue process. The static and dynamic stiffness change rates after 5 million cycles were 6.4% and 10.8%; The overall change rates of static and dynamic stiffness after 10 million cycles were 8.7% and 12.8%. 2). The time-domain analysis showed that PMFST could significantly reduce the vibration duration and ground acceleration; Fatigue loading accelerated the degradation of the USPM, reducing the capacity of dissipating energy. 3). The slab-ground subsystem was the main attenuation section for PMFST, which could significantly reduce the energy transfer ratio. Compared with OT, PMFST performed better in dissipating the vibration energy along the longitudinal direction; However, fatigue loading would aggravate the vibration level. Overall, the vibration levels of PMFST (0 million, 5 million, and 10 million) can be reduced by 14.4 dB, 13.5 dB, and 10.9 dB, respectively.

Padma Bridge Rail Link Project with Special Emphasis on Padma Multipurpose Bridge, its Technological Uniqueness

The South and Southwestern part of the country is devoid of direct communication with the central part of Bangladesh due to the presence of the most important tributaries of Lower Ganges i.e. Padma River. To establish direct communication with those areas Government of Bangladesh Constructed Padma Multipurpose Bridge with the provision of road and rail traffic at the upper and lower deck of the bridge respectively. The Padma Bridge Rail Link Project (PBRLP) is the main passage connecting the East and the West of Bangladesh and is also a part of the Bangladesh-China-India-Myanmar corridor. This line is a single-track passenger-freight railway with a total length of 168.6 km. For the first time in Bangladesh, State of the Art technology ballast less tracks in Padma Bridge, its approach to viaducts and other viaducts are being adopted for providing a smooth operation for both freight and passenger traffic. Precast and prestressed long sleeper embedded in cast in-situ track slab ensures a maintenance-free track system for the railway. PBRLP, once completed will restore the missing link with the Trans-Asian railway and will provide a platform for connecting with the Dedicated Freight Corridor (DFC) of India in future. It will also contribute to the Gross Domestic Product (GDP) of the country by 1.0%.

Effects of joint stiffness degradation on vertical stability of CRTSII slab ballastless track

Joint damage of the China Railway Track System (CRTS)II slab track leads to typically non-uniformity of the longitudinal stiffness of the track slab, which tends to produce different degrees of arching at the joint. The objective of the present study was to investigate the arching mechanism of the non-uniform track slab. The buckling eigenvalues and arch curves of the non-uniform track slab were obtained using the Newton iterative eigenvalue algorithm. An analytical expression for the equilibrium path of the slab with an initial arch was obtained using the energy method. Then, the arching law and stability of the non-uniform track slab were analysed. The following results were obtained. 1) The reduction of the joint bending stiffness significantly affects the arching deformation and buckling mode of track slab, thus, it is necessary to consider the non-uniform characteristics of the track slab when analysing its stability. 2) The most unfavorable wavelength of track slabs is between 6 m, and 7.5 m considering the different joint bending stiffnesses and elastic moduli, and the reduction of the bending stiffness of the joint is the main factor for reducing the most unfavorable wavelength. 3) The reduction of the joint bending stiffness is the most important factor for causing the instability of the track slab, the maximum allowable temperature rise decreased from 83.97 to 49.12 ℃ when the bending stiffness of the joint was reduced by a factor of 100. 4) For improving the stability of the track slab, releasing part of the temperature force in the track slab by reducing the elastic modulus of the joints is a feasible method, the maximum temperature rise of track slabs can be rapidly increased when the elastic modulus of the joints is < 5000 MPa.

Noise contribution and coherence analysis of high-speed train head shape under moving slab track

Aerodynamic noise generated by 1:8 scale three carriages high-speed train was investigated by numerical simulation and wind tunnel test. The difference of far-field noise below 1600 Hz between simulation based on dense mesh and test is less than 3 dB(A), which indicates that the current simulation method has reasonable accuracy. It is found that dipole source can be used as the only sound source to calculate the far-field noise because its intensity is more significant than that of the quadrupole source. The subdomain method is applied to investigate the noise contribution and coherence analysis of full-scale head shape. It is found that the far-field noise contributions of the frame, bogie cavity and wheel set are significant, and the peak frequency occurs at the frequency of 630 Hz. Coherence analysis indicates that the far-field noise with the train body as the sound source has a relatively high correlation with the pressure pulsation caused by the vortex structure generated at the wiper housing and the bogie. Also, the side vortex near the front wheel has a higher correlation with the far-field noise at a higher frequency, while a stronger correlation between that near the rear wheel and the far-field noise occurs at a lower frequency.

Feasibility study on the solution of replacing track slab with lateral pushing rail in one maintenance window time

The slab ballastless track is the primary type of high-speed railway. When the track slab in the ballastless track is severely damaged, the typical way to replace it requires cutting the jointless rail above the damaged track slabs. This paper discusses a solution of pushing the rail in the lateral direction (i.e., without cutting the rail) to replace the track slab. To study the feasibility and reliability of this solution, a finite element model for simulating the construction process of rail pushing is established. The necessary spacing of the support slides and the capability of the pushing device are analyzed. The influence of parameters such as the rail release length and the construction temperature on the mechanical state of the rail after being pushed is discussed. In practice, the repair time is limited to one maintenance window (i.e., 4 h). The control of the stress is critical in repairing progress. The corresponding relationship between the deformation curvature of the rail and the stress is studied, and the number of unlocking fasteners is reduced by optimizing the spacing of the rail support slides, which can effectively reduce the fine-adjustment range of the rail after changing the slab. By calculation and design, a “16 + 8 + 16 m” optimization plan is proposed, which can meet the needs of replacing the track slab in the four-hour maintenance window time of high-speed railway. Finally, the feasibility of the finite element model is verified through the comparative analysis of the monitoring data of the lateral pushing of the rail and the simulation analysis results.

Influence of metro track parameters on vibration characteristics of vibration damping track

In view of the abnormal wear of the vibration damping track with small radius curve on the subway, the vibration and noise problems associated with it have been widely concerned by society. The dynamic model of vehicle-track system including elastic damping track is established by using simulation software. The influence of structural parameters of steel spring floating slab track (SSFST) with small radius curve on the mode and vibration frequency, as well as the resonance characteristics of elastic track structure are analyzed. The results show the following: (1) Increasing the length of floating slab can effectively reduce natural frequency, while the range of frequency variation caused by the thickness of floating slab is relatively small. The length and thickness of floating slab can be properly adjusted to avoid the track resonance. (2) It is more integrated for the rail and floating slab through increasing the vertical stiffness of fastener, which increases the vibration frequency of the track structure. There is little effect on the vibration characteristics of SSFST for changing the installation spacing of steel springs. (3) It is more obvious for resonance to occur between the inner rail and floating slab at 116 Hz, 130 Hz and 161 Hz, and the track vibration mode shows multi-step reverse vibration on both sides and overall vertical bending vibration. (4) Due to the unbalance load caused by curve superelevation, the inner wheel weight plays the restraining role, which makes the inner rail and floating slab have various forms of bending deformation in a certain frequency range, increasing the complexity of the bending deformation of the track structure.

Parametric analysis of railway infrastructure for improved performance and lower life-cycle costs using machine learning techniques

Rigorous and efficient management of the railway infrastructure is crucial to avoid accidents and reduce operation and maintenance costs. This requires in-depth knowledge of the assets, the interaction among them and the effect that each track parameter has on the overall infrastructure performance. In this study, a large set of studies are carried out, on a previously calibrated finite element slab track model, where the relevant track parameters are varied within their usual ranges. The results are then used to train and validate a series of predictive models based on Machine Learning algorithms. This methodology provides greater understanding and enhanced prediction of the behaviour of tracks, which are composed of multiple variables such as the soil/subgrade, supporting layers, sleepers, pads and rails. The study also considers train axle loads and service speeds, which are other key elements that influence the track performance. The results show that the parameters that have greatest influence on the railway infrastructure are the properties of the soil, characteristics of the rail pads and the axle loads. This work can support the implementation of predictive maintenance procedures for railway tracks and the development of innovative technological solutions, providing responses to the industrial needs of reducing costs and contributing to improve the competitiveness of railway transport.

Research on the Bearing Performance of Prefabricated New Type Subway Track Slab with Basalt Fiber

Currently, most ballastless tracks in Chinese subways are traditional cast-in-situ concrete structures, which require long construction progress. In contrast, prefabricated ballastless tracks can greatly reduce the construction period. However, there are few theoretical and experimental analyses on the prefabricated new type of subway slab track. Hence, to study the mechanical properties of the new type of subway track slab, static bending crack tests of one standard slab track and nine prefabricated full-scale track slabs with basalt fiber were carried out in this paper. The influence of the reinforcement arrangement method and the basalt fiber content on the performance of the track slabs was studied. Results showed that with the increase in the basalt fiber content in the range of 0.1–0.3%, the load–strain curve growth rate increased, the stiffness decreased, and the flexural resistance reduced. All the specimens exhibited a linear portion (elastic) and then a nonlinear portion (plastic) followed by flexural failure. During the elastic stage, the basalt fiber helped to improve the rigidity of the track slab. During the plastic stage, the influence of the basalt fiber content on the failure load varied with different reinforcement arrangements. With the reinforcement arrangement F2 and 0.1% basalt fiber content, the specimen had the smallest load–strain curve growth rate and the best overall flexural performance and crack resistance, and its strain was 23.35 με at an elastic limit of 95 kN. The results can provide a reference for the design of the prefabricated slab ballastless track.

Dynamic evaluation of vehicle-slab track system under differential subgrade settlement in China's high-speed railway

Differential settlement is inevitable in soil subgrade which has a direct impact on the service performance of ballastless track systems and the running quality of high-speed trains. In order to estimate the effect of differential subgrade settlement on the dynamic performance of the vehicle–slab track system, a detailed theoretical model considering nonlinear subgrade support and track weight is established. The filtering effect of the layered composite track structure on the subgrade settlement is taken into account. Related dynamic performance indexes are evaluated in terms of running safety and ride comfort of high-speed trains as well as the dynamic performance of the infrastructure, to obtain a control threshold of the differential subgrade settlement for the slab track system of China's high-speed railway. The results show that the uncoordinated deformation between the slab track and the subgrade has significant influence on the dynamic characteristics of the system. Compared with the running safety, the ride comfort of the vehicle and the dynamic performance of the track structure are more susceptible to the differential subgrade settlement. The relative short-wave differential settlement below 20 m has significant impact on the track and subgrade vibration, especially the dynamic rail displacement. The differential settlement with a wavelength above 20 m is more detrimental to the car body acceleration, namely the ride comfort. In particular, a sensitive wavelength of the differential subgrade settlement at 10–20 m poses a high jumping derailment risk to the running safety. Accordingly, the dynamics-based control thresholds of differential subgrade settlement are put forward for different settlement wavelengths.

Evolution mechanism of interlayer fatigue properties of CRTS III slab track

This study proposed an improved fatigue cohesive zone model considering time-vary factors. Based on this model, an interlayer fatigue properties evolution finite element model of CRTS III slab track under the coupling effect of long-term temperature and train load was established. The evolution of interlayer fatigue properties between track slab and SCC under different bonding strengths was analyzed, and the evolution mechanism of interlayer fatigue properties was revealed. Results show that the CRTS III slab track mainly has minor interlayer damage near the corner of the slab under a well-bonded interlayer. The degradation of interfacial normal bonding strength mainly causes fatigue damage near the limit groove. The loss of interfacial tangential bonding strength leads to damage around the slab. With high tangential bonding strength, interlayer fatigue damage develops inward from the end of the slab. Otherwise, it simultaneously extends inward from the end and edge of the slab. The interlayer fatigue properties could be enhanced by increasing tangential bonding strength.

Emission of fugitive dust from railway maintenance vehicles operating on gravel track

The railway is using gravel to mitigate impact and noise. Since these gravel tracks are deformed due to wear and weathering, they must be replaced at regular intervals. A large amount of fugitive dust(FD) is generated during the gravel replacement work, but research on the amount of generation has not been conducted. The characteristics of FD generated from railway maintenance vehicles (RMVs) operating on gravel tracks were investigated. FD concentrations were measured during the operation of three types of RMV machines: the multiple tie tamper (MTT), ballast regulator (RE), and ballast cleaner (BC). The concentrations of FD generated from MTT, RE, and BC use were 10.69, 16.58, and 17.55 mg/m 3 , respectively. Annual FD fluxes were calculated based on FD concentrations and emission speeds as well as annual RMV operating times. The EPA AP-42 provides a formula for calculating the FD generated by cars, but this formula is not applicable to railroad vehicles. In previous FD studies, FD flux was calculated using nearby wind speeds, but in this study, we took the speed of the force each RMVs applied during maintenance work as the emission speed. The results of this study can be used as baseline data in future studies of the environmental aspects of gravel track and precast concrete slab track use.

Dynamic Responses of Ballastless High-Speed Railway Due to Train Passage With Excitation of Uneven Trackbed Settlement

The ballastless slab track has been widely used in newly-developed high-speed railways in China as well as in other countries for its high stability and low maintenance. However, loss of track vertical alignment due to uneven trackbed settlement will bring adverse impact on train’s running safety and track serviceability. In this study, a train-track-trackbed coupling model has been proposed to investigate the dynamic responses of track structure with the excitation of trackbed settlement with varied patterns. To validate the proposed analysis model, comparisons with both the analytical solution and in- situ measures have been performed. The influences of train speeds, settlement trough amplitude and length are discussed based on this analysis model. It’s indicated that the dynamic responses of train vehicle and track structure increase with increasing in train speed and settlement amplitude within certain settlement length. By introducing the standards for train operation safety and riding comfort, a new trackbed settlement control criteria is proposed. The computation results indicate that the standard for train operation safety is found to be the dominating factor for uneven settlements with the length less than 10 m, while the standard for riding comfort dominates the settlement control criteria in other cases. To further facilitate the settlement control criteria in engineering practices, the ratio of settlement amplitude and settlement length (which is defined as deflection ratio) is adopted to depict the envelop curves for various settlement patterns.

Dynamic Damage Quantification of Slab Tracks—Finite Element Models on Winkler Soil and Finite-Element Boundary-Element Models on Continuous Soil

Train passages over intact or damaged slab tracks on different soils were calculated by two methods. The finite element method (FEM) uses a Winkler soil under the track model by adding a thin “soil layer”. The combined finite-element boundary-element method has a continuous soil model that is included by the boundary element method. The basic results are the distributions of the track (rail, track plate, and base layer) displacements along the track for a single axle load. These solutions were superposed to a complete train load and transformed to time histories. The influence of track and soil parameters was analysed. The main interest was the influence of the track damage. A gap between the track plate and base layer of different lengths was studied for changes in amplitudes and widths of deflection. A best fit to measured track displacements was found so that the track damage could be identified and quantified. The FEM model with the Winkler soil cannot be fitted to the amplitude and width with the same soil parameters. Therefore, the FEBEM model is preferable for these railway track problems.

Stress distribution in roadbeds of slab tracks with longitudinal discontinuities

Stress concentration occurs in the foundations of railway tracks where discontinuous components are located. The exacerbated stress under the expansion joints in slab tracks may trigger foundation failures such as mud pumping. Although the higher stress due to the discontinuities of track structures has been discussed in past studies, few focused on the stress response of roadbeds in slab tracks and quantitatively characterized the stress pattern. In this paper, we performed a dynamic finite element analysis of a track-formation system, incorporating expansion joints as primary longitudinal discontinuities. The configurations of CRTS III slab tracks and the contact conditions between concrete layers were considered. Numerical results show that longitudinal influencing length of induced stress on roadbed under wheel load relates to the contact conditions between concrete layers, increasing nonlinearly at a larger coefficient of friction. Given a measured coefficient of friction of 0.7, the calculated longitudinal influencing length (9.0 m) matches with field data. The longitudinal influencing length is not affected with the increasing velocity. As stress concentration arises with expansion joints, the worst-case scenario emerges when double-axle loads are exerted immediately above the expansion joints between concrete bases. A stress concentration factor Cv on the roadbed is proposed; it increases with the increasing velocity, changing from 1.33 to 1.52 at velocities between 5 and 400 km/h. The stress distribution on roadbeds transforms from a trapezoid pattern at continuous sections to a triangle pattern at points with longitudinal discontinuities. An explicit expression is finally proposed for the stress pattern on roadbed under expansion joints. Although structural discontinuities induce stress raiser, the extent of concentration is mitigated with increasing depth at different velocity levels.

Interlayer shearing and bending performances of ballastless track plates based on high-order shear deformation theory (HSDT) for laminated structures

Based on higher-order shear deformation theory (HSDT), the bending of China Railway Track System type II (CRTS-II) track laminated plates on elastic foundations and interlayer shearing performances are analyzed by meshfree radial point interpolation method (RPIM), which has the properties of the Kronecker function and discretizes the governing equations derived from HSDT. To verify the applicability of the model, the geometric configuration and key parameters of the CRTS-II slab ballastless track structure are analyzed, and the interlaminar slip model of the track structure is derived as a benchmark solution when calculating the track structure using HSDT-RPIM. The accuracy of the derivation is verified by comparing the HSDT-RPIM model with a double-layer slab model considering bidirectional interlayer slip. Then, the effect of resistant slip coefficient on the bending deformation of the track structure was analyzed using the bidirectional interlaminar slip model. The effect of elastic foundation coefficient on the bending of the track structure and the interlayer slip of the track structure (track slab – base slab) was analyzed. Finally, the effects of boundary conditions and elastic foundation coefficients on the interlaminar stresses of the track structure are investigated using HSDT-RPIM, and some interlaminar damages of the track structure are explained.