Slab Track Structure Research Articles

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

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

Full-Scale Experimental and Field Investigations into Expansion Mechanism of Foamed Polyurethane and its Lifting Behaviors for Repair and Maintenance of Railway Slab Track Systems.

Excessive settlement of the subgrade seriously reduces the service quality of slab tracks and threatens trains' running safety. While the utilization of foamed polyurethane is recognized as an effective solution, previous research on its expansion mechanism and its impact on track lifting requires further refinement. Accordingly, a series of full-scale tests, including expansion force tests on foamed polyurethane with diverse qualities and lifting tests of polyurethane grouting with varied qualities on the track structure, have been conducted. The expansion development process of foamed polyurethane is meticulously elucidated, and key expansion parameters are analyzed. Simultaneously, this research explores the lifting behavior of foamed polyurethane grouting under the slab tracks, yielding new insights into essential lifting parameters for track formation repair and maintenance. Based on the experimental data, this study proposes new empirical formulas to comprehensively describe both the expansion mechanism of foam polyurethane and its lifting behavior under the slab tracks. The outcomes of this research offer a new breakthrough for the design of lifting mechanism for maintaining slab track structures through the utilization of foam polyurethane slurry grouting, such as determining the optimal grouting quantity. In addition, these results are instrumental to the evaluation of lifting effects and service life, enhancing the circular economy of railway track systems.

A hybrid reliability assessment method for slab track with changing structural parameters

Changes in the dynamic properties of high-speed rail (HSR) slab track structures can have a great impact on train safety and ride quality. However, the dynamic response of wheel–rail systems, which is related to operational safety, has rarely been considered in existing service reliability assessments of track structures. To solve this problem, a hybrid method was developed, with the serviceability limit state (SLS) first defined with respect to the derailment coefficient (DC) and wheel unloading rate (WUR). In calculating the reliability index, the response surface method and the first-order reliability method were used to solve the implicit expression of wheel–rail force in the SLS equation. To reduce the computation cost, a surrogate model expressing the non-linear mapping of the wheel–rail interaction is proposed. The computation efficiency and accuracy of the hybrid method were compared with Monte Carlo simulation and a back-propagation neural network (BPNN). The computation time of the hybrid method was only 1/8.4 of the BPNN method, while the accuracy of the reliability index was 98% for the DC and 97% for the WUR. The hybrid method was used to assess the reliability of a typical slab track structure under changing stiffness and damping coefficients of the fasteners, cement asphalt mortar and foundation. The stiffness and damping of the fasteners had the most impact on wheel–rail dynamics and track reliability. This research provides new insights into reliability assessments for HSR slab track with respect to train operational safety.

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.

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.

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.

Thermal arching and interfacial damage evolution of CRTS-II slab track under solar radiation in alpine and plateau regions

Arch deformation and interface failure of CRTS-II slab track have become crucial issues for the operation safety of high-speed railways. However, few researchers investigated the mechanics and deformation behaviour on CRTS-II slab track exposed to high-altitude plateau climatic environments. This study proposes an analysis approach for thermal arching and interface damage evolution of the slab track structure under solar radiation in alpine and plateau environments. The time-dependent solar temperature distribution is loaded on the refined finite element model (FEM) of the slab track structure’s thermal deformation in high-altitude plateau climatic environments. The analysis approach is validated by comparing the calculated and experimental data. The track slab's maximum and minimum vertical temperature gradient (VTG) are 94.49 °C/m and −45.02 °C/m, respectively. The narrow joint damage is an incentive for the inverted V-shaped thermal arching and interface separation of the slab track structure under solar radiation. The interfacial gap of slab track structure in alpine and plateau regions reaches more than 14 mm during summer. The proposed analysis approach is a valuable reference to the construction temperature, maintenance, and damage monitoring of slab track structure in alpine and plateau regions.

Influence of Uneven Subgrade Frost Heave on Deformation and Damage of CRTSIII Slab Track

The problem of uneven frost heave deformation of high-speed railway subgrade in seasonal freezing areas seriously affects the service state and service life of slab track structures and threatens the safe operation of high-speed vehicles. Based on the damage plasticity theory of concrete, in this study, an analytical model is established for CRTSIII slab track with damage plasticity and reinforcement. The influences of various frost heaving parameters on track structure deformation, interlayer seam, as well as the stress and damage behaviors were analyzed in detail. The results show that, as compared with a linear elastic model, the damage plastic model better reflects the softening behavior and stress attenuation of track structure concrete after reaching its tensile strength. The deformation and the interlayer seam reach their maximum values when the frost heaving wave peak acts at the position that is one-sixth of the base length from the edge of the concrete base. When the frost heaving wave peak acts on grooves at the base center, initially, the track structure is seriously damaged. The interlayer seam and damage decrease with an increase in frost heaving wavelength and increase with an increase in frost heaving wave amplitude. The interlayer seam of the track structure is more sensitive to frost heave deformation having a wavelength of less than 10 m. The extent of damage to the concrete base gradually increases with a decrease in the wave/amplitude ratio. It undergoes three stages of damage evolution: (i) no damage, (ii) upper surface bending damage, (iii) reverse bending damage. In order to improve efficiency, it is recommended, during track maintenance, to focus on the position of the central groove of the base and the position that is one-sixth of the base length from the edge of the concrete base.

Finite element analysis on properties evolution of slab track FLC under the coupling action of rainfall and fatigue load

The filling layer concrete (FLC) is the crucial component materials in the CRTS III slab track structure. In order to investigate the properties evolution of FLC under the coupling action of environment and fatigue load, a three-dimensional finite element model of the CRTS III slab track structure system was established, and extended finite element method (XFEM) was used to calculate the stress intensity factor (SIF) of the crack tip under different conditions through the domain interaction. Results show the fatigue load significantly decreases stiffness of FLC. Coupling actions of water-saturated and fatigue load, acid-rain and fatigue load accelerate the deterioration of FLC. The decrease of stiffness leads to stress redistribution in FLC. With the increase of fatigue load, the stress of FLC decreases, but the stress of steel in the FLC increases. Positions of fatigue load on FLC take on significant influence on the evolution of properties. The deterioration rate of FLC at the end of the slab is greater than that of the middle FLC. Under the coupling of fatigue load and environment, FLC at the end of the slab is more likely to crack and propagation, and the cracks are most likely to appear from the bottom of the FLC. Due to the influence of the stress field and displacement field at the crack tip, with the fatigue load increasing, the SIF at the external crack of FLC has an exponential decrease. The coupling action of environment and fatigue load accelerates the deterioration of FLC, and also leads to the rapid reduction of SIF. In this study, the coupling of acid-rain and fatigue reduces the properties of FLC most obviously.

A Review of Numerical Models for Slab-Asphalt Track Railways

Higher train speeds and heavier axle loads trigger elevated stresses and vibrations in the track, potentially increasing track deterioration rates and maintenance costs. Alternative track forms made of combinations of reinforced concrete and asphalt layers have been developed. A thorough understanding of the slab and asphalt tracks is needed to investigate track performance. Thus, analytical and numerical models have been developed and validated by many researchers. This paper reviews numerical models developed to investigate railway track performance. The synthesis of major finite element models is described in detail, highlighting the main components and their outputs. For slab track models, the use of a structural asphalt layer within the railway track remains an active research topic and firm conclusions on its efficacy are not yet available. It can be expected that slab track structures will also be affected by train-induced ground vibrations. There is thus a gap in the literature regarding the measurement of dynamic effects on high-speed railway lines, and further research is needed to investigate the dynamic behaviour of slab–asphalt track systems. In this review, novel solutions for mitigating the vibrations in high-speed rail are discussed and compared. The use of asphalt material in railways appears to have beneficial effects, such as increasing the bearing capacity and stiffness of the structure and improving its dynamic performance and responses, particularly under high-speed train loads.

Design theories and maintenance technologies of slab tracks for high-speed railways in China: a review

Abstract The durability and reliability of slab track structures are essential for the long-term safety and stable operation of high-speed railways. In order to provide a solid theoretical basis and technical reference for the advancement of high-speed railway quality, this paper comprehensively discusses design theories of slab track structures, service performance evolution and maintenance technologies, and reviews the innovation happening in the industry. On top of that, the damage evolution, fatigue features and durability of slab tracks, which are highly relevant to serviceability, are summarized, and the future research trend of slab track service behaviours is pointed out. In addition, this paper summarizes the rules of establishing standards for damage maintenance, typical solutions for repairing damage and methods of evaluating the maintenance outcomes that combine field tests and numerical simulations. It also envisions a future direction where advanced testing technologies would assist the evaluation of maintenance effects.

Fatigue damage analysis of ballastless slab track in heavy-haul railway tunnels

A ballastless slab track, which is commonly used in the track structures of heavy-haul railway tunnels, was analysed based on field measurement data of the Fuyingzi Tunnel on the Zhangtang Railway. In accordance with the measured data, the dynamic load thresholds and distributions on the surface and bottom of the ballastless slab track were investigated. A fatigue damage analysis of the ballastless slab track was performed based on the dynamic load time–history curve. The results show that the ballastless slab track can accomplish train load attenuation and reduce the dynamic load from heavy-haul trains by 47.22% from the surface to the bottom. In addition, the distribution at the bottom of the ballastless slab track exhibited a triangular shape, and the dynamic load threshold at the line centre accounted for 78.67% of that at the track position. Meanwhile, the distribution at the surface was saddle-shaped; the dynamic load threshold at the track position accounted for 79.55% of that at the line centre position. The fatigue damage of the ballastless slab track was analysed effectively by combining the measured data and the linear fatigue damage theory. Moreover, the accuracy of the calculation results was verified based on the measured dynamic stress of the ballastless slab track structure. The dynamic action of the train load led to more-concentrated damage to the track bed, and the damage occurred earlier than that in the ordinary line. The axle load was the primary influencing factor of the track bed fatigue damage, and the damage mainly occurred in the track position. These results provide a theoretical basis for performing stress analysis and designing parameters for ballastless slab tracks in heavy-haul railway tunnels.

A feasibility study on void detection of cement-emulsified asphalt mortar for slab track system utilizing measured vibration data

This paper reports the feasibility study on the use of measured vibration of a railway slab track system in detecting void on the cement-emulsified asphalt (CA) mortar layer utilizing the Bayesian approach. By following the specification of the China Railway Track System (CRTS)-I ballastless slab track structure, two scaled models (with and without void in the CA mortar layer) were built and tested in the laboratory to demonstrate and verify the proposed CA void detection methodology. A three-dimensional finite element model was built using ABAQUS to calculate the time-domain data of the ballastless track system for Bayesian model class selection and model updating. A new two-phase model class selection algorithm was developed for identifying the CA void region. The proposed methodology identified the distribution of CA mortar stiffness using impact hammer test data from the scaled CRTS-I ballastless slab panel under laboratory conditions. The model updating results are consistent with the simulated CA mortar stiffness distribution. In addition, the posterior uncertainties of the identified CA mortar stiffness under different sensor configurations were quantitatively investigated. The results from the experimental case studies show that the proposed Bayesian methodology is feasible to detect CA void even with only a single accelerometer with the associated posterior uncertainties being kept at an acceptable level.

A reliability assessment approach for slab track structure based on vehicle-track dynamics and surrogate model

The reliability assessment of rail infrastructure is directly related to the safety and effectiveness of railway transportation and critical for railway management department. This paper presents an approach for service reliability analysis of slab track from the point of view of the vehicle-track system operational safety. The vehicle-track dynamics is simulated by the established finite element model (FEM) and the limit state function (LSF) is defined on the danger of derailment. To reflect the real state of track geometric condition, the track irregularity spectrums (TISs) are extracted from the measured track irregularity data and fitted by the seven-parameter formula. Then, a set of time series can be obtained from the TISs using a binary wavelet-based inversion method and then input to the FEM to obtain the value of LSF. Finally, Monte Carlo simulation (MCS) is used in the calculation of track reliability. To overcome the slow convergence of the vehicle-track models, this study develops a surrogate model based on support vector machine (SVM). It is validated that the established SVM can well approximate the relationship between the track irregularities to the derailment coefficients in terms of small error and high correlation. More importantly, the efficiency is more than 1000 times higher than traditional FEM. This is a pioneering study to incorporate vehicle-track dynamics into the reliability assessment of slab track in service. For a 1024-m section of slab track, results show that its reliability index can satisfy the requirement in specifications.

Study on the Mechanical Characteristics of the Sleeper Slab Track on a Long-Span Steel Truss Bridge

This paper uses the long-span steel truss slab track as its research subject to analyze the new type of sleeper slab track structure with an experimental method. Firstly, a full-scale model was established in the laboratory to form a “rail–sleeper slab–self-compacting concrete cushion–steel beam” composite structure, and a fatigue test was performed on the track structure. The cyclic load was set up as a sine form with a range between 75 and 375 kN at a 5 Hz interval and 3 × 106 cycles. Based on the test, the performance of the track structure under cyclic train load was studied. Secondly, after every 106 loading cycles, the vertical static loading test and horizontal resistance test of the track structure were carried out to obtain the strain and displacement under different loading cycles. Finally, after 3 × 106 cycles of sine cyclic loading, the horizontal ultimate resistance test of the track structure was carried out to study its horizontal failure mode. The aims of this paper were to verify the applicability of the sleeper slab track, identify the mechanical properties, and determine the unfavorable position. The findings can provide an important reference for the practical use of the sleeper slab track structure.

Dynamic Analysis of Ballastless Rail Superstructure on a Track Switch

Proposed article presents design procedure and dynamic analysis of a ballastless rail superstructure used to decrease the vibration from the moving trains in underground tunnels located adjacent to residential and commercial buildings. The rail superstructure features a floating slab consisting of a reinforced concrete (RC) slab with direct fixation of railway fastenings and elastomeric bearings, that transfer the loads from the floating slab to the tunnel casing. A track switch is mounted on a FST. The aim of the design procedure is to select required static and dynamic properties of elastomeric bearings made of cellurar polyurethane as well as the amount of reinforcement taking into account deteriorating properties of both materials. FE-model created in MSC Patran/Nastran software package is used to get an insight on stress-strain state of this floating slab track structure. Proposed FE-model consists of switch track with direct fixation railway fastenings, RC track slab, elastomeric supports. Static analysis is performed to get the upper-track structure elements’ deflections as well as stress-strain state of RC slab under moving trains. Dynamic interaction of the ballastless rail superstructure is investigated using derived from FE-analysis transfer-function between the superstructure and tunnel invert. Vibration isolation efficiency under excitation frequencies of moving trains over different speed is obtained from the transfer function.

Effects of Differential Subgrade Settlement on Slab Track Deformation Based on a DEM-FDM Coupled Approach

Slab track structures become deformed under the effects of differential subgrade settlement. According to the properties of the China Railway Track System (CRTS) II slab track on a subgrade, a three-dimensional (3D) coupled model based on both the discrete element method (DEM) and finite difference method (FDM) was developed. The slab track and subgrade were simulated using the FDM and DEM, respectively. The coupled model was verified. The deformation of the slab track and contact forces of gravel grains in the surface layer of the subgrade were studied under differential subgrade settlement. The effects of settlement wavelength, settlement amplitude, and other types of settlements were also discussed. The results demonstrate that the settlement amplitude and settlement wavelength of the subgrade have significant effects on track deformation. The deformation amplitude of the slab track increases nonlinearly with an increasing settlement amplitude of the subgrade. Increases in the settlement wavelength and amplitude of the subgrade significantly increase the maximum value of the contact force of the gravel grains in the subgrade. The maximum contact force of gravel grains near the boundaries of the settlement section can reach two to three times that of the unsettled condition, which makes it easy to accelerate the plastic settlement of the subgrade.

Factors influencing the demulsification time of asphalt emulsion in fresh cement emulsified asphalt composite binder

Emulsified asphalt as an indispensable raw material for high-speed railway ballastless slab track and pavement structure is subjected to different combinations of material and construction parameters leading to uncontrollable demulsification time. By examining the demulsification time of cationic emulsified asphalt mixed with cement or cement and sand, the factors influencing the demulsification time of emulsified asphalt were studied. The increase of pH value is detrimental to the hydration of cement, and it is beneficial to prolonging the demulsification time. The incorporation of the stabilisers (Polyvinyl acetate, sodium carboxymethylcellulose, CaCl2 and NH4Cl), either increasing the viscosity of the fresh cement emulsified asphalt composite binder or changing the electric double layer on the surface of asphalt particles, this is detrimental to prolonging the demulsification time of emulsified asphalt mixed with cement. The increase of the stirring speed can shorten the demulsification time of emulsified asphalt. Meanwhile, increasing of additional water can dilute cement and asphalt particles, and prolong the demulsification time. Conversely, an increase amount of cement will lead to an increase in the amount of water used for wrapping and hydration, and shortening of demulsification time Meanwhile, with the treatment time prolonging, the demulsification speed of the asphalt emulsion increases. In addition, the demulsification process of emulsified asphalt in cement emulsified asphalt mortar actually is a process of asphalt re-aggregation observed by the optical microscope.

Laboratory Investigation of the Temperature-Dependent Mechanical Properties of a CRTS-Ⅱ Ballastless Track-Bridge Structural System in Summer

To study the mechanical properties of the China Railway Track System type II (CRTS-II) ballastless slab track structure, a 1/4-scale specimen of a CRTS-II slab ballastless track-32-m standard prefabricated simply supported box girder bridge with three spans and two high-speed railway lines was developed. The mechanical properties of the structure under the action of daily natural temperatures were studied under the natural environmental conditions. The structural strain and relative interlayer displacements were analyzed. The results show that the temperature of the CRTS-II ballastless track-bridge structural system changes periodically every 24 h. The strain of the structural layers of the track system first increases and then decreases sinusoidally, and the internal strain of the track system lags along the vertical depth direction. The relative displacement between the layers of the ballastless track bridge structure system increases with the increase in temperature. The extreme value of the vertical relative displacement appears between the track bed and the bridge at section 1/4 in the span, so it should be paid attention to by the maintenance personnel. Due to the constraint of the shear slots, the structural strain and relative displacement at the fixed end near the shear slots are smaller than those at the sliding end. The mid-span deflection is the largest, and the overall deflection during the cooling phase is more significant than that during the heating phase.

Critical Velocity of Short Floating Slab Track Using Alterable Element Method Considering Wheel-Rail Contact Loss

In actual line operation, the critical velocity is one of the key physical quantities of rail design owing to its great influence on the riding comfort and safety of vehicles due to the wheel-rail contact loss caused by the abrupt change of rail foundation rigidity, rail wear, or abruptness irregularities on rail. In this study, the short floating slab track (SFST) structure is regarded as a double-layer system. The Euler beam and the rigid body model are adopted for the rail and the floating slab, respectively, and the dispersion equation and the theoretical critical velocity of the rail structure under ideal conditions are deduced. Besides, this study considers the implementation of the SFST in the vehicle-structure coupling system. The alterable element method is introduced for accurately simulating the change of the wheel-rail contact state and coding a vehicle-structure dynamic analysis program (VSDAP) to calculate the critical velocity of rail structures from the dynamic response of vehicles and rail structures. The principle of its design at the beginning of the design is given on the basis of the theoretical value of the critical velocity and the simulation of the dynamic response, which can provide reference for practical engineering design.