Track Bed Research Articles

Identification of Abnormal Vibration Signal of Subway Track Bed Based on Ultra-Weak FBG Sensing Array Combined with Unsupervised Learning Network

The performance of the passing train and the structural state of the track bed are the concerns regarding the safe operation of subways. Monitoring the vibration response of the track bed structure and identifying abnormal signals within it will help address both of these concerns. Given that it is difficult to collect abnormal samples that are symmetric to those of the normal state of the structure in actual engineering, this paper proposes an unsupervised learning-based methodology for identifying the abnormal signals of the track beds detected by the ultra-weak fiber optic Bragg grating sensing array. For an actual subway tunnel monitoring system, an unsupervised learning network was trained by using a sufficient amount of vibration signals of the track bed collected when trains passed under normal conditions, which was used to quantify the deviations caused by anomalies. An experiment to validate the proposed procedures was designed and implemented according to the obtained normal and abnormal samples. The abnormal vibration samples of the track beds in the experiment came from two parts and were defined as three levels. One part of it stemmed from the vibration responses under the worn wheels of a train detected during system operation. The remaining abnormal samples were simulated by superimposing perturbations in the normal samples. The experimental results demonstrated that the established unsupervised learning network and the selected metric for quantifying error sequences can serve the threshold selection well based on the receiver operating characteristic curve. Moreover, the discussion results of the comparative tests also illustrated that the average results of accuracy and F1-score of the proposed network were at least 11% and 13% higher than those of the comparison networks, respectively.

Load–Temperature Coupling Effect on the Base Plate End of the Whole Tram Road

Although trams have been widely recognized, systematic and comprehensive research on their design and construction is lacking. Based on the ABAQUS finite element software, we constructed a three-dimensional finite element analysis model of the overall track bed of the tram. Taking the most unfavorable working condition of load and temperature coupling as the research object, that is from 5:30 to 6:00 a.m., the load was applied to the plate end position. The simulation experiments were carried out by selecting different thicknesses of the track bed slab, support layer thickness, contact conditions between the track bed slab and the support layer, the modulus of the track bed slab, the modulus of the support layer and the soil foundation strength, and the stress and deflection of the subgrade were calculated. The most unfavorable load–temperature coupling condition was taken as the research object, that is, applying a load of 5.5–6 points on the plate end. Different track bed slab thicknesses, support layer thicknesses, contact conditions between track bed slab and support layer, track bed slab moduli, support layer moduli, and foundation strengths were utilized to conduct simulation tests for calculating the stress and deflection of the subgrade. Under the coupling effect of load on the end of the slab and the effect of temperature, changing the thickness of the track bed slab and the coefficient of friction between layers can improve the lateral force and deflection of the track bed slab. The effect of deflection is small. Changing the thickness of the support layer has an insignificant effect on the stress on the top surface of the soil foundation and the deflection of the top surface of the subgrade. The modulus of the track bed slab can affect the lateral force and deflection of the track bed slab, but it only slightly affects the longitudinal force and deflection of the track bed slab and the longitudinal and lateral force and deflection of the soil foundation. The modulus of the supporting layer only slightly affects the vertical and horizontal force and deflection of the track bed slab and soil foundation. The soil foundation modulus has the greatest influence on the vertical and horizontal forces and deflection of the track bed slab and soil foundation.

Comparative Research on Vibration Characteristics of Cast-In-Place Steel-Spring-Floating Slab Track under Different Subway Line Conditions

Purpose: Steel-spring-floating slab tracks are widely used in subway lines. It is necessary to analyze and study the vibration damping and transmission characteristics of the steel-spring-floating slab track in various frequency bands under the action of train loads. Method: A steel-spring-floating slab track and ordinary monolithic track tunnel sites with similar line conditions on straight and curved segments were selected. The vibration signals of rail, track bed, and tunnel walls were collected and the analysis results of vibration damping and vibration transmission between the steel-spring-floating slab track and the ordinary monolithic track were compared. Results: The dynamic responses of the rail in the four working conditions are relatively close, and the acceleration of the steel-spring-floating slab track bed is significantly larger than that of the ordinary monolithic track. The vibration response generated in the curved segment is significantly greater, and each frequency band will generate more peak points, and the high-frequency vibration will be more severe. Conclusions: The steel-spring-floating slab track can significantly reduce the acceleration response of the tunnel wall; the bottom constraint of the steel-spring-floating slab track is less, and the vibration response of the track bed is more severe.

Static and dynamic effects of train-track-bridge system subject to environment-induced deformation of long-span railway bridge

Laying ballastless tracks on a long-span railway bridge with a main span greater than 300 m is a challenge in engineering practice and has aroused significant concerns. Influenced by complicated environmental factors, long-span railway bridges in service deform with large amplitudes and complex shapes, which may result in damage to the track structure and threaten the running safety and ride comfort of trains. In this study, we investigate some typical statics and dynamics problems under the actual conditions of a long-span cable-stayed high-speed railway bridge with a main span of 400 m and laying ballastless track. The track-bridge finite element model and dynamic interaction model of the train-track-bridge system are first established. Furthermore, the influences of the complicated environment-induced bridge deformations are comprehensively investigated using the curvature method that reveals the deformation compatibility of the bridge-track system and indicates the dynamic interaction behavior of the train-track-bridge system subject to train running speeds and bridge deformations. Results indicate that excellent dynamic performance of the train-track-bridge system can be achieved by setting an elastic cushion of 0.1 N/mm3 under the track bed. Interface damage between track layers will not occur directly because of the complex deformations of the bridge decks. The bridge deformations induced by the environmental temperature and the concrete creep are qualified. The dynamic responses of the train-track-bridge system are also excellent under the excitations of bridge deformations. Dynamic simulations of the train-track-bridge system are proposed to evaluate long-span bridge deformations subject to complicated service situations in comparison with an oversimplified statics evaluation.

Research on the working performance of fouled ballast bed under the multi-scale effect

In order to explore the influence of different particle size gradations of dirty materials on the service performance of the ballast bed, the clean track bed, the completely fouled ballast bed polluted by coarse coal and fine coal, respectively, were studied based on the discrete element method. In order to explore the influence of the multi-scale particle size gradation of the dirty material on the service performance of the ballast bed, the clean ballast bed, the completely dirty ballast bed polluted by coarse-particle coal, and the completely dirty ballast bed polluted by coarse-particle coal were simulated, respectively, based on the discrete element method, which are used to analyze the dynamic response of track bed under different working conditions under cyclic load. The model is verified by the lateral resistance and vertical stiffness of the ballast bed to prove the accuracy of the discrete element model. On this basis, the dynamic cyclic load is considered to analyze and study the mechanical response and change law of the ballast bed with different degrees of contamination. Studies have shown that after the ballast bed is contaminated, its lateral resistance and vertical support stiffness are reduced, the amount of settlement increases, the coordination number between ballasts is declined, and the fine-grained dirty material has a worse effect on the ballast bed; The displacement value of the ballast particles decreases with the increase of the depth of the ballast bed; The displacement value of the ballast particles under the rail is the largest, and the ballast particles on the ballast shoulder appear dilatancy; The displacement of the ballast particles at the laterally symmetrical position of the track structure is close to but not completely same; Dirty materials aggravate the frequency of ballast particles, and the impact of fine-particle coal powder is particularly significant.

Research on Construction of Intelligent Laying Concrete Precast Slab Track Bed with Trackless Equipment

Research on Construction of Intelligent Laying Concrete Precast Slab Track Bed with Trackless Equipment

Evaluation of the fractures of asphalt concrete added with rubber particles based on the fine aggregate mixtures

In railway construction, the solidified track bed has gained significant attention from researchers in recent years. Asphalt concrete added with rubber particles is a substitute for the polyurethane cured track bed. In this study, two fine aggregate mixtures (FAM) for different asphalt concrete mixed with rubber particles as the material for the solidified trackbed have been evaluated. Semicircle bending (SCB) test and CT scanning were used to evaluate the mechanical properties of four FAM. Acoustic emission (AE) was used to collect the AE signals during the SCB test. The energy analysis results of AE reveal that the temperature sensitivity of epoxy-FAM is better than that of rubber-FAM. Further, the AE signals can be classified according to the cracking type by clustering analysis. The results demonstrate that the epoxy-FAM with 11% rubber content has the best fracture resistance. AE technology provides an effective evaluation of the microscopic cracking process of FAM.

Calibration of a Finite Element Model to Predict the Dynamic Response of a Railway Track Bed Subjected to Low- and High-Speed Moving Train Loads

Calibration of a Finite Element Model to Predict the Dynamic Response of a Railway Track Bed Subjected to Low- and High-Speed Moving Train Loads

Analysis of Antideformation and Antivibration Effect of Different Track Beds under Subway Train Vibration

Running metro trains would inevitably influence the vibration deformation in the lower part of the roadbed structure. In order to study the effects of vibration, Qingdao metro line 3 tunnel was taken as the research background. The track coupling model was established using Abaqus-Simpack to analyze the train velocity, train axle load, and trackbed vibration forms for the vertical deformation of roadbed calendar effect to provide the reference in practical engineering design and deformation control. According to the analysis, influenced by the formation of Qingdao Metro Line 3, the time-history curve of the displacement excitation of the trackbed presents the distribution law of “large in the middle and small at both ends.” According to the sensitivity analysis, the deformation of the trackbed is most obviously affected by the form of trackbed; the second was the influence of the axle load of the train. The speed change of the subway train presented relatively little influence on the displacement of the trackbed. Although the deformation control ability of the integral trackbed was better, its vibration reduction performance was poor. The vibration reduction performance of the rubber cushion floating trackbed was the best, followed by the steel spring floating trackbed.

Research on the Variable-Temperature Cracking Mechanism of CRTS I Type Double-Block Ballastless Track on a Bridge.

The CRTS I type double-block ballastless track (CRTS I TDBBT) has the advantages of convenient construction and low cost, but it has low crack resistance and the temperature field distribution of the railway on the bridge is uneven and frequently changes, so it is necessary to study the mechanical properties of the CRTS I TDBBT under the load of a temperature field. The temperature field model of the CRTS I TDBBT on the bridge is established by finite element software, the real-time temperature field of the track bed slab is brought into the coupled model as a load, and the variation laws of the temperature stress of the CRTS I TDBBT under different schemes are compared. The temperature gradient in the CRTS I TDBBT track bed slab has the largest fluctuation range, and the positive and negative temperature gradient range can reach 93.34 °C. For the temperature longitudinal stress around the sleeper block of the track bed slab, the edge is the largest; the temperature longitudinal stress is reduced by at most 5.27% after the anti-cracking diagonal bars are added. When the expansion joint is added, the temperature stress can be reduced by up to 80.29%. The fluctuation range of the temperature gradient of the track bed is basically consistent with the fluctuation range of the local air temperature. The huge temperature difference leads to the occurrence of cracks in the track structure, and cracks are more likely to occur at the corners of the sleeper block. The addition of both anti-crack diagonal bars and expansion joints has an anti-crack effect, but the effect of adding expansion joints is better.

An efficient model for the dynamic vehicle-track-bridge-soil interaction system

A semi-analytical approach based on a lumped parameter model is presented for the analysis of the dynamic interaction system of train, track, bridge, and subsoil. Herein, the bridge and the track are modeled as Euler–Bernoulli beams, which are connected through the viscoelastic track bed. The viscoelastic supports of the bridge model capture the flexibility and damping of the subsoil below the foundations. Complex modal expansion of the deformation approximates the response of the non-classically damped bridge-soil subsystem, while a Rayleigh–Ritz approximation is used to efficiently describe the track deflection. To achieve the coupling of the mechanical equations of these subsystems, a variant of component mode synthesis (CMS) is applied. The mass–spring–damper (MSD) system representing the moving train is coupled to the resulting system of equations for the track-bridge-soil subsystem by a discrete substructuring technique (DST). Geometric track irregularities describing the deviation of the track from perfectly straight and smooth are accounted for by random irregularity profile functions. The results of the proposed model are compared with a finite element model to validate the modeling approach. In an application example, the effects of track irregularities and the influence of the track on the dynamic response of a bridge are discussed. The comparison of results with and without soil–structure interaction of the bridge outlines the great influence of the subsoil properties on the dynamic response in case of resonance.

Experimental Study on Vibration Absorption Performance of Floating Slabs of Vibration Isolation Pads in Metro Shield Tunnels

The monolithic track bed with isolated damping pad and floating slab is a common design of urban subways in recent years.The type of track bed, urban subway lines usually pass through densely populated areas of the city, and subway trains.In the course of driving, it is inevitable that large track vibration noise will be produced. In order to reduce the impact of track vibration noise on the daily life of surrounding residents, noise reduction measures must be considered during track design. Isolated shock absorber floating board The monolithic track bed is one of them. Compared with the steel spring floating slab monolithic track bed, it has the technical characteristics of “low engineering cost, more convenient construction, and good noise reduction effect”. In order to study its damping effect, we selected two working conditions of straight line and curve for comparison. It can be seen from the comparison results with the ordinary track bed: (1) The acceleration level of the shock-absorbing cushion tunnel wall in the straight section is greater than the ordinary track bed section within 1∼10Hz, and is close to the ordinary track bed section within 12.5∼20Hz, at 25 It is smaller than the section of ordinary track bed within ∼1000Hz. (2) The maximum Z-vibration level measured from the tunnel wall is most suitable for evaluating the seismic source intensity of the subway, and the seismic source intensity of the subway line is 65.69 dB.

Study on Precast Epoxy Asphalt Track Bed for Transition Zone in High-Speed Railway: A Numerical Approach

Study on Precast Epoxy Asphalt Track Bed for Transition Zone in High-Speed Railway: A Numerical Approach

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.

Development of a simplified design approach for shallow ballasted track forms with geocells reinforced sub-ballast

ABSTRACT With increasing demands for higher axle loads and line speeds, designers are left with no choice but to significantly increase track bed design thickness to accommodate the new operating conditions. In recent years, the use of geosynthetic materials has become more common in railway construction to reduce construction depth. Geosynthetic materials such as geocells have shown promising potentials to achieve this. However, there is no universally agreed method to design track bed with geocells. Therefore, the aim of this paper is to quantify the reinforcing effect of geocells on the track bed via means of laboratory testing and then incorporate the findings with existing track bed design methods to propose a simplified approach to design track bed with geocells. The research is further supported by case studies from the UK railways and found that the use of geocells can significantly reduce track bed thickness, resulting in significant cost savings.

A hybrid methodology for predicting train-induced vibration on sensitive equipment in far-field buildings

The prediction of train-induced vibration on far-field buildings is a challenging issue in the transportation environment communities. In this work, a hybrid prediction method is put forward utilizing the idea of substructure analysis, which can high-effectively calculate the train-induced vibration under different operation conditions. Based on vehicle-track coupled dynamics theory, wavenumber finite element theory (2.5D FEM) and Green’s function method, this method could comprehensively analyze vibration characteristics of the source, propagation path and sensitive target/vibration receiver by appropriately considering the boundary conditions between each part. The proposed model possesses the advantages of 2.5D FEM in calculation efficiency and could consider the dynamic interaction between vehicle and track system more elaborately. In addition, the vibration response under different operation conditions can be high-efficiently obtained by updating the track supporting forces without repeatedly solving the Green’s functions of the system. On this basis, this work predicts the vibration impact of subway train operation on the sensitive equipment in a far-field large-scale building, and uses the generic vibration criteria for sensitive equipment to evaluate the vibration responses. Further, to mitigate the impact of train-induced vibration, floating slab track is adopted to achieve the vibration attenuation in the concerned frequency. Results show that the train-induced vibration on the monolithic bed track exceeds the limit specified in the standard in some frequency bands. The use of floating slab track can effectively reduce the vibration response of the building and ensure the routine use of sensitive equipment.

Bandgap mechanism and vibration reduction property of wave-resistance sleeper with negative effective mass density

Based on the capability of controlling low-frequency elastic waves in solids with subwavelength size, locally resonant phononic crystals have potential applications in track vibration reduction. By periodically embedding 3D locally resonant unit cells (LRUCs) in a concrete matrix, a wave-resistance sleeper with a negative effective mass density is proposed, and the generation mechanism of the bandgap and parameter sensitivity are studied. Furthermore, the vibration mitigation performance of the wave-resistance sleeper applied to the ballastless track is analyzed. The results show that the local resonance of the LRUC results in negative responses in the wave-resistance sleeper to the vibration excitation, and a bandgap is generated in this frequency range. By changing the elastic modulus of the coating or the core density, the boundary frequencies of the bandgap of the wave-resistance sleeper can be effectively adjusted, and the bandwidth can be expanded by increasing the ratio of core radius to coating thickness, or by increasing the filling fraction, and adopting a thinner steel spherical shell. The bandgap of the wave-resistance sleeper was verified by test results. Based on the local resonance mechanism, the wave-resistance sleeper can effectively prohibit vibrations at multiple design frequencies from transmitting to the track bed.

Geogrid Reinforcement for Stiffness Improvement of Railway Track Formation Over Clay Subgrade

Weak subgrade condition generally develops large settlements in ballasted tracks, leading to adverse performance. To ameliorate such problems, a commonly adopted technique is to provide a thick cushion of granular subballast/blanket over the subgrade. Owing to scarcity of natural resources, this is often a costly proposition. In the present study, application of geogrid reinforcement for possible reduction of the subballast thickness has been explored through large model plate load tests. The investigations include both single and multiple layers of reinforcement in the subballast. With geogrid reinforcement, stiffness and resiliency of track beds were found to have increased markedly. Optimum depth of single-layer geogrid in the subballast giving maximum performance improvement was about 0.33 times the loading diameter. The corresponding improvement in stiffness of the track bed was about 77%. With multiple layers of geogrid in the subballast, the improvement in stiffness was as high as 99%. It is observed that with just one layer of geogrid in the subballast, its thickness can be reduced by 33% (i.e., from 600 to 400 mm).

Characterisation of Geogrid and Waste Tyres as Reinforcement Materials in Railway Track Beds.

The engineering behaviour of ballast is an important factor to determine the stability and safety of railway tracks. This paper examines the stress–strain, shear strength, peak deflection stress and reinforcement strength ratio of different reinforcement materials and reinforcement locations in ballast track bed layers based on large scale static triaxial shear tests. The results show that geogrid and waste tyre reinforcement have a significant effect on the peak deviator stress of railway track bed layers and the stress–strain relationship is strain-hardened. The peak deviator stress and shear strength of geogrid reinforcement are greater under the same conditions compared with waste tyres. The reinforcement of geogrid and waste tires increases the shear strength of the track bed significantly. The more layers of geogrid reinforcement, the more energy is required for the deformation of the track bed. The energy required for deformation is greater in the centre of the waste tyre than in the other reinforced forms, and the energy required for deformation is minimal in the fully reinforced form. Excessive tyre reinforcement changes the stiffness of the track bed layer, leading to an increase in the settlement rate. The reinforcement strength ratio between geogrid and waste tyre increases significantly with the increasing of the confining pressure and reinforcement layers. Moreover, the reinforcement strength ratio of the geogrid is significantly higher than that of the waste tyre.

Preparation and Mechanical Properties of Polyurethane Material for Railway Ballast

ABSTRACTThe elastic solidification of track bed is a new track structure improvement technology between the traditional gravel track bed and the ballast less track monolithic track bed. It can effectively solve the main technical problems of heavy haul railway transportation, such as large impact force of wheel rail, serious deformation of track bed and frequent maintenance etc. In this paper, combined with the characteristics of polyurethane properties affected by its chemical composition, a solidified ballast polyurethane material suitable for heavy haul railway was developed by adding diluents and other materials. Physical property test and mechanical triaxial test were carried out to assess the influence of diluent content on the hardening effect of ballast; the physical process and mechanical properties of different proportion materials were analyzed. The experimental results show that adding appropriate amount of diluent into polyurethane material can effectively improve the integrity of ballast bed, increase the strength, reduce the deformation, and prolong the service life of ballast track bed.