Railway Ballastless Research Articles

In-situ testing and finite element model updating of a long-span cable-stayed bridge with ballastless track

Ballastless track is widely used in high-speed railways due to its long service life, low maintenance costs, and excellent riding comfort. However, laying a ballastless track on a long-span bridge remains a challenge because of the large deflection and uneven stiffness of the long-span bridge. Limited research has been reported on the experimental behavior of the long-span railway bridge laid with the ballastless track. This study presents the in-situ testing and the finite element model updating (FEMU) of the Ganjiang Bridge, China’s first long-span ballastless railway cable-stayed bridge with a main span that reaches up to 300 m before its opening for operation. The study’s primary purposes include evaluating the mechanical properties of the ballastless railway bridge and establishing a baseline finite element model for subsequent structural health monitoring. The general test plan, sensor placement, and measured responses are described. The static deflection, the stress of the main girder, and the rotation angle at the beam end are used to evaluate the static performance of the bridge. The natural frequencies and mode shapes are used to assess the dynamic performance of the bridge. A FEMU framework that utilizes displacement assurance criterion (DAC) and frequency to construct a single-objective function is proposed to update the initial finite element (FE) model of the bridge. The results show that the deflection to span ratio is 1/1016 (less than1/1000), and the rotation angle at the beam end under live load is 0.032 ‰ rad (<1‰), indicating that the bridge has sufficient vertical stiffness and excellent riding comfort. The stress of the main girder is smaller than the material yield strength, indicating that the bridge has sufficient load-bearing capacity. All the requirements allowing the bridge to start service have been met. The updated FE model shows that the DAC performs better than the displacement and provides more accurate updating results. The updated FE model can well reflect the static and dynamic characteristics of the actual bridge and can be used as a baseline FE model for subsequent studies.

A survey of Ballastless track defects in China’s high-speed railway after ten years of service

Abstract A considerable amount of data have been obtained after more than 10 years of operations on China’s high-speed railway ballastless tracks; however, there is still a lack of survey in the operation and maintenance of ballastless tracks. Based on the results of an on-site survey of the service status of China’s high-speed railway ballastless tracks conducted in 2021, the common defects and related treatment measures for four main types of ballastless tracks, namely, CRTS I, CRTS II, CRTS III slab, and CRTS double-block, are systematically summarised in this study. The most critical defects in the diverse types of ballastless tracks are comparatively analysed. In addition, suggestions for ballastless track selection are presented by considering different factors, which will guide the development and construction of ballastless tracks in the future and be vital for improving the safety, comfort, and durability of high-speed railway operations.

The Influence of the Type of Fibers on the Reduction of the Threshold Effect in the Transition Zone of a Railway Track

The presented article concentrates on the influence of various concrete additives in the form of fibers on the mechanical parameters of concrete so as to obtain the effect of gradual changes in these parameters, which is very important in the transition zone of the railway track. Steel, polymer and glass fibers, as well as concrete without additives, were accepted for the study. The effect of additives on the consistency of the mixture, compressive strength, frost resistance and elastic modulus was studied. The research concerned concrete samples and models of elements of the ballastless railway surface, i.e., track slab and concrete block supports. The track slab model was made of concrete without additives, while the models of supports were made both without and with additives. The studies were carried out in laboratory conditions. As a result, the tested concrete samples with various additives were ranked so that they could be used as a material for elements of the railway surface in the transition zones of engineering facilities on railway roads, which is important from the point of view of reducing the threshold effect occurring in these zones. Detailed laboratory tests were presented, the results of these studies were discussed, and final conclusions were drawn regarding the technology of materials and the methodology of constructing the transition zones of the railway surface in order to avoid or at least reduce the threshold effect existing in such zones.

Estimating running safety factor of ballastless railway bridges using tail modelling

Excessive vertical acceleration of ballastless railway bridges subjected to vibrations induced by passing trains is one of the governing design criteria for bridges in high-speed lines. However, to the authors’ knowledge, the corresponding design limit is not based on a solid theoretical or experimental background. Moreover, the traditionally applied safety factor also suffers from these concerns. Therefore, in the present study, a crude probabilistic approach is adopted to evaluate the consistency and reliability of this safety factor. For this purpose, deterministically designed bridges (using conventional methods) with short to medium spans are considered. Then, their reliability is evaluated using simulation-based techniques and extreme value theory, i.e., tail approximation. Then, the existing safety factor is calculated to evaluate the consistency of the current approaches, and possible new values are proposed based on the desired target reliabilities.

Excessive fastener spacing of high speed railway ballastless track at beam end by the construction errors and environment temperature

Excessive fastener spacing of high speed railway ballastless track at beam end by the construction errors and environment temperature

Stiffness of Ballastless Railway Embankments Determined by Repetitive Static Plate Load Tests

In the repetitive static plate load test, a plate is loaded in two cycles where the second loading cycle provides a modulus denoted Ev2. When calculating the stiffness of a railway embankment, Young’s modulus is often assumed to be equal to Ev2 throughout the embankment. This approach, however, provides inaccurate results, mainly due to soil nonlinearity and the influence of confinement stress. Currently, there exists no method to account for these aspects to derive reliable deformation properties of embankments. Occasionally, correction factors are applied to Ev2, resulting in crude estimations. In this study, plate load tests were simulated in PLAXIS 2D using the Hardening Soil Model and calibrated against four field tests, conducted on crushed rock-fill sub-ballast. The calibrated soil properties were applied in finite element simulations of railway embankments with ballastless slab-track systems. Based on the results of finite element analyses, a semi-empirical approach is proposed, which considers confinement stress through a hyperbolic stress–strain relationship. Soil properties for compacted rock-fill with particle grading 0–150 mm were assumed through the results of the calibrated finite element analyses and the method was verified against 43 plate load tests. This semi-empirical method is more accurate than assuming a constant Young’s modulus, while maintaining simplicity and ease of use.

A novel cohesive zone model for predicting the interface bonding behaviours of the ballastless track of high-speed railway

The interface damage is one of the main concerns for high-speed railway ballastless track structures during its whole service life, as it would affect the reliability of track structures or even cause the high-speed train accident. In this paper, various existing cohesive zone models (CZMs) were identified and compared regarding the performance in modeling the interface behaviors of ballastless track structures. The results show that the existing CZMs cannot accurately represent the nonlinear relationship of the ascending and descending sections in the interface traction-separation curve concurrently. Therefore, a new CZM was proposed in this study, and the feasibility of the proposed model was examined by the experimental results. It indicates that the proposed model can reasonably describe the nonlinear behaviors of the ascending and descending sections in the traction-separation curve by introducing exponential coefficients. The proposed CZM also exhibits higher accuracy in predicting the normal and tangential cracking behaviors of the interlayer interface of the ballastless track structures in comparison with the existing models, with the coefficients of determination (R2) in the fitting results all above 0.85. As a result, this model can be used for the analysis of the interface behaviours of ballastless track structures.

Feasibility analysis of magnesium phosphate cement as a repair material for base slab of China railway track system II ballastless track

This study proposed using magnesium phosphate cement (MPC) to repair the base slab of the Chinese ballastless railway track. Laminated members were subjected to static and fatigue bending tests. Results showed that the damage to the laminated members was caused first by bending and then by horizontal shear at the interface between the old and new materials. Fatigue test results showed that the stress level on the base slab was below the endurance limit and thus should not cause failure. Microscopic tests also revealed that the bond between Portland cement and MPC played a crucial role in the repair process.

Ballastless railway track transition zones: An embankment to tunnel analysis

Railway track transition zones are characterised by an abrupt change in track support stiffness, which increases dynamic wheel loads and leads to the acceleration of differential settlement and track degradation. The performance of transition zones is a concern for railway Infrastructure Managers due to the increased maintenance operations and costs typically associated with these short track sections. To date, the majority of transition zone studies are focused on the analysis of ballasted tracks, however, the popularity of ballastless track has been increasing, especially on high-speed lines. Therefore, this work aims to study concrete slab track transition zones, with a focus on embankment/plain line-to-tunnel sections. The analysis uses a hybrid methodology, combining 3D finite element modelling with empirical settlement equations, in an iterative manner. The finite element model is capable of simulating train-track interaction and uses contact elements to simulate the potential detachment (voiding) between the slab’s hydraulically bound layer and frost protection layer. At each iteration, firstly the track-ground stress fields are calculated using a 3D model, before passing them to a calibrated empirical equation capable of computing settlement across the transition. Then, before starting the next iteration, these settlements are used to modify the 3D model geometry, thus account for the effects of the previous settlement, before computing the updated stress fields. The model is used to analyse settlement and stresses for a transition zone case-study, before study the ability of a resilient mat to improve the performance of the track.

Foreign object detection for railway ballastless trackbeds: A semisupervised learning method

This paper proposes a semisupervised algorithm for detecting foreign objects in ballastless beds based on the improved deep SVDD (Support Vector Data Description) algorithm. First, we use the improved Mask R-CNN algorithm to extract the rail and fastener areas in images, assuming that no foreign object exists in the rail and fastener areas. Second, we deepen the backbone network of the deep SVDD to enhance its ability to extract deep semantics from complex images. We perform pure color coverage processing with different colors and mean blur processing with different blur kernels on the rails and fastener regions extracted by the improved Mask R-CNN. The results show that the AUC (Area Under the Curve) of our improved deep SVDD algorithm is 89.23% and improves the AUC compared to that of the original model by 11.09%.

Frost heave force analysis of pre-embedded dowel in the high-speed railway ballastless track

The connection between the anchor bolt and the pre-embedded dowel largely determines the reliability of the railway fastener system. However, the failure of the pre-embedded dowel and the uplift of the anchor bolt are found in the process of railway operation. Therefore, a finite element model is established based on the frost heave force test of the pre-embedded dowel. Not only the relationship between the geometric size (height and diameter) of the space filled with water and the frost heave force is obtained when the water in the pre-embedded dowel is frozen, but also the theoretical formula of radial frost heave force is modified based on the empirical equation. The results show that the maximum vertical frost heave force of the pre-embedded dowel in WJ-7 fastener system is about 28.73kN when the anchor bolt is completely screwed. In order to protect the reliability of the fastener system, the waterproof measures should be strengthened to prevent water from infiltrating into the pre-embedded dowel in the cold region.

In-situ investigation on mud pumping in ballastless high-speed railway and development of remediation method

Mud pumping induced by intensive precipitation and traffic loading is a typical distress in high-speed railway either for ballasted or ballastless tracks. In this study, in-situ investigations, numerical simulation and laboratory tests were conducted to reveal the formation of mud pumping and to explore an appropriate method to remediate mud pumping in ballastless railway. Field investigations and numerical simulation indicated that there was a whipping effect in the dynamic responses of the slab track due to train passages, which induced detachments at the end of concrete base from the roadbed surface. This detachment provided infiltration routes for rainwater into the roadbed layer and initiated the mud pumping. An evaluation method was proposed to analyze particles stability of roadbed materials taken from the investigating site, and the results indicated that instable finer particles promoted an increasing instability of coarse particles. Based on the characteristics of particle stability of roadbed materials and the formation process of mud pumping, an optimized polyurethane chemical injection (PCI) method was proposed to remediate mud pumping and tentatively applied to a mud pumping reproduced ballastless slab track in the full-scale physical model test. Both static and dynamic performances of the remediated ballastless track were restored to their initial values before the occurrence of mud pumping. The accumulative track settlement was less than 2.2 mm even under more than one million train loads, indicating that the PCI method is effective in mud pumping remediation of ballastless slab track.

Упругие характеристики подрельсового основания безбалластного железнодорожного пути

Objective: Experimental determination track modulus and the coeffi cient of relative stiffness of underrail base and the rail, which are the main elastic characteristics that determine the stresses in the structural elements of track superstructure under the impact force from the train. The values of these parameters for a track with a ballast layer are well studied, in contrast to a ballastless track. Comparison of the elastic characteristics of a ballastless railway track with analogs of a track on ballast, as well as an assessment of their effect on the stress-strain state of the superstructure elements of a ballastless track. Methods: When carrying out full-scale tests, strain-gauge methods for measuring stresses in the elements of the track superstructure were used. The obtained values were processed by the methods of mathematical statistics. One statistical series included the values of stresses corresponding to one type of rolling stock, fi xed axle load and train speed, changing by no more than 10 km/h. The probability level in processing the results was taken in all cases equal to 0,994. Results: The values of track modulus and the coeffi cient of the relative stiffness of the underrail base and the rail were obtained for a ballastless structure of the RHEDA 2000 type. Practical importance: The results allow us to consider the rail as a beam lying on a solid elastic foundation in relation to the ballastless track and use the existing calculation methods for the design of ballastless track structures depending on the operating conditions.

Assessment of the Selection of Asphalt Binder for Full Cross-Section Asphalt Waterproof Layer in High-Speed Railway Ballastless Track

AbstractIn China, the application of asphalt layers in high-speed railway ballastless tracks has two functions. Asphalt layers can be used as a support layer or a waterproof layer; one of these fun...

Torsional Behavior of Ballastless Railway Plate Girder Bridge

Torsional Behavior of Ballastless Railway Plate Girder Bridge

Static Strain Analysis of CRTS I Bi-Block Ballastless Track

In this paper, relying on the National Engineering Laboratory of High-Speed Railway Construction Technology, a full-scale model of the double-block ballastless track structure is established, and the strain analysis of the layered track structure under different static loads is carried out, which has a certain practical significance for the design and maintenance of the high-speed railway ballastless track in our country. Research conclusion: (1) Under the action of static load, the sleeper directly under the rail is under compression; the four corners of the sleeper are tensile strain; (2) The strain at each measuring point on the surface of the track slab around the sleeper is compressive strain; the edge of the top surface of the track slab is compressive strain; The longitudinal strain at the bottom of the side of the track slab is tensile strain; (3) Under static load, the longitudinal strain measurement point on the top surface of the base plate is tensile strain at a distance of two sleepers from the static load position; the longitudinal strain at the bottom of the side of the base plate is tensile strain.

Expansibility classification of mudstone for high-speed railway ballastless track foundation

Expansibility classification of mudstone for high-speed railway ballastless track foundation

Study on the Calculation Method of the Diffusion Range of Grouting Slurry for a High-speed Railway Ballastless Track Subgrade

Grouting engineering is the most convenient and quick way to deal with postconstruction settlement. Based on the investigation of the Beijing Shenyang high-speed railway in the early stage, the microdestructive force of grout on the soil mass in the process of grouting with the method of fluid solid coupling theory was analyzed. The numerical simulation results show that, in the grouting process, the greater the grouting pressure, the wider the diffusion range of the slurry and the greater the damage to the microscopic contact force of the slurry to the soil; in addition, when the grouting pressure is below 0.15 MPa, the diffusion form of the slurry in the soil is osmotic grouting; when the pressure is about 0.3 MPa, the diffusion form of the slurry in the soil is compacted grouting; on the basis of the simulation results, a deeper research is carried out, and the calculation formula of the slurry diffusion curve is obtained. It fills in the blank of the theoretical study of the slurry diffusion curve. In this paper, the diffusion formula of grouting slurry can be used in the theoretical study of clay grouting, and it can be used as a reference for practical engineering.

A Defect Detection Method for Rail Surface and Fasteners Based on Deep Convolutional Neural Network.

As a result of long-term pressure from train operations and direct exposure to the natural environment, rails, fasteners, and other components of railway track lines inevitably produce defects, which have a direct impact on the safety of train operations. In this study, a multiobject detection method based on deep convolutional neural network that can achieve nondestructive detection of rail surface and fastener defects is proposed. First, rails and fasteners on the railway track image are localized by the improved YOLOv5 framework. Then, the defect detection model based on Mask R-CNN is utilized to detect the surface defects of the rail and segment the defect area. Finally, the model based on ResNet framework is used to classify the state of the fasteners. To verify the robustness and effectiveness of our proposed method, we conduct experimental tests using the ballast and ballastless railway track images collected from Shijiazhuang-Taiyuan high-speed railway line. Through a variety of evaluation indexes to compare with other methods using deep learning algorithms, experimental results show that our method outperforms others in all stages and enables effective detection of rail surface and fasteners.

Influence of malposition on the performance of elastic rail clip: Toe load, stress, and friction

In ballastless railway track, the elastic rail clip (i.e., an e-clip) is applied to maintain the rail in proper positions by mean of a compressive toe load. If the e-clip moves from its initial installation; the toe load may deviate from its specification. In this study, the influences of e-clip’s malposition on the toe load, stress, and friction were numerically evaluated. The toe loads of inner and outer e-clips increased with the increase in malposition. However, the toe loads of inner e-clip were slightly higher than those of outer e-clip because of the geometries of base plate and cast shoulder. The maximum von Mises stresses and the maximum normal stresses were found at the inner curvature of e-clip’s rear arch. The friction forces on the contacts between heel of e-clip vs. cast shoulder and toe of e-clip vs. insulator were slightly influenced by the malposition. However, the influence of malposition on the friction force on the contact between leg of e-clip vs. slot of cast shoulder was more prominent. The findings can be used as a guideline for the installation and maintenance to ensure the structural safety of a ballastless railway track.