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• Temperature field of ballastless tracks is derived theoretically and validated by an on-site experiment. • A quasi-dynamic method (QDM) is proposed by extending an explicit integration algorithm from the dynamics field to statics. • Interfacial debonding of track layers induced by thermal loads is solved by applying the QDM for the first time. • Nonlinear distribution properties of temperature field, evolution process of interface damage and its failure modes are revealed. Interfacial debonding of multi-layered ballastless track systems has proved to be one of the most common diseases in the high-speed railway during long-term operations. This paper focuses on the theoretical modeling of track temperature field and consequent bond-slip behavior between track layers under thermal loading. By establishing heat conduction differential equations, whose boundary conditions are combined with complicated geographical and meteorological factors, the temperature field of a multi-layered track structure is obtained via the integral transform technique. The reliability of the heat conduction model is well-validated by an on-site experiment in a high-speed railway line. Then, we originally extend an explicit integration algorithm for dynamics analysis to solve nonlinear statics problems with small deformation by proposing a quasi-dynamic method (QDM). Equilibrium equations of a track slab subjected to quasi-dynamic equivalent thermal loads and mixed-mode interfacial cohesive forces are constructed based on the Mindlin plate in-plane and flexural vibration equations. The application of the QDM to solve interface responses is verified by comparing results obtained from finite element (FE) software. Finally, numerical discussions are conducted to reveal the nonlinear distribution characteristics of temperature field, evolution process of the interface damage and failure modes under time-varying thermal loads, which provide a better understanding of the interfacial debonding phenomenon encountered in ballastless track systems. [ABSTRACT FROM AUTHOR]

The fastener system is an important component of the ballastless track, and the fastener looseness threatens the safety of the railway track. This paper proposes a Bayesian model updating method integrated with a Python–Abaqus interface framework to identify the fastener partial looseness of the ballastless track via vibration data. By following the technical standards of Chinese Railway Industry, a laboratory scaled ballastless track model was constructed for the demonstration and verification of the proposed methodology. Not only the damage location can be accurately identified, but also the damage severity can be evaluated. In addition, the associated posterior uncertainties of the identified results can be quantified by calculating the posterior probability density functions of all uncertain model parameters, which can provide valuable information to engineers for ballastless track system damage detection. [ABSTRACT FROM AUTHOR]

The key issues in designing ballastless track for high-speed railway bridges are to reduce maintenance and improve track smoothness by understanding fatigue damage characteristics. This paper is based on the principle of bridge-rail interaction and train-track-bridge coupling dynamics, the refined simulation model of bridge-CRTS I Bi-block ballastless track system is established by using the finite element method. The longitudinal force distribution law of CWR (Continuously Welded Rail) and the dynamic response characteristics of coupling systems are studied, based on the Miner rule and S-N curve. The fatigue characteristics of ballastless track system laying on long-span bridge under the dynamic train load and the effect of ballastless track system design parameters changes on fatigue characteristics are discussed. The results show that the extreme values of longitudinal force of CWR all appear in the middle of the bridge span or near the bridge bearing, and attention should be paid to the strength checking of CRW laying on long-span bridge. Under the dynamic train load, the fatigue life curve of rail on the bridge is relatively smooth and the minimum life of rail which is laying on continuous bridge decreases from 27.1 years to 17 years that which is laying on cable-stayed bridge. The life curve of track plate laying on continuous bridge is relatively smooth, and the life curve of track plate laying on cable-stayed bridge is related to the stiffness of elastic cushion, which decreases in a stepped manner, and there will be no fatigue failure on the track plate during service. The life curve of the baseplate is related to the type of bridge, the minimum life value of the baseplate appears near the bridge bearing, and there will be no fatigue failure on the baseplate during service. Increasing the stiffness of elastic cushion can effectively improve the fatigue life of track plate, and increasing the vertical stiffness of fasteners can enhance the connection between rail and track plate and improve the fatigue life of rail. The increase in train speed will increase the dynamic stress amplitude of track structure and reduce the fatigue life of the rail. [ABSTRACT FROM AUTHOR]

The construction of the track is solved as a conventional (with track ballast) or as a ballastless track (without track ballast). When deciding on the choice of the most suitable track design for high-speed rail, it is necessary to emphasize that with increasing line speed, the requirements for the quality of the track geometry increase, including the size of the deviations of individual geometric parameters of the track from the projected values. When assessing the choice of track structure – especially for high-speed rails – it is therefore necessary and correct to assess the total costs (investment and operational) for a sufficiently long time. DB Netz AG’s present experience with a ballastless track since its first implementation in 1972 in Rheda station, for almost 50 years, shows that the required lifetime of 60 years has its real justification. In addition, current research and development in the field of ballastless track is moving towards extending the life of ballastless track well beyond this limit. The paper is focused on the comparison a ballasted and ballastless track construction. It deals in more detail with evaluation of the advantages and disadvantages of a ballastless track construction. The main objective is to assess the use of ballastless track structure for the construction of high-speed lines. [ABSTRACT FROM AUTHOR]

• The car body vibration characteristics of different arching states were analyzed. • Arching vibration index was proposed to quantify arching-induced characteristics. • An arching degree evaluation model was proposed based on multiple feature indexes. Due to structural deterioration and the external environment, the ballastless track is prone to slab arching during high-temperature periods. Arching will weaken the constraints between components, affect the smoothness of the line, and even endanger train safety in severe cases. Therefore, it is necessary to identify the arching in time and clarify the arching severity, which is of great significance for scientifically formulating maintenance plans and ensuring line stability. The existing research has established track geometry-based methods for arching identification, but they are difficult to recognize small arching and cannot quantitatively evaluate arching degree. To this end, this paper proposed a set of arching identification and evaluation methodology based on track dynamic inspection data. Combining the simulated and measured data, the time–frequency characteristics of car body vertical vibration caused by arching were finely extracted, and the arching-induced vibration index was established for identification. Then, a deep learning hybrid model for arching degree evaluation was proposed based on the analysis of the relationship between multiple feature indexes and arching gap height. The results showed that car body vibration could identify the arching defects with gap heights exceeding 1 mm, and the arching degree could be evaluated quantitatively based on multiple feature indexes. In practice, the proposed method can be used to detect arching of different degrees, assist maintenance decision-making, and help avoid the occurrence of serious failures. [ABSTRACT FROM AUTHOR]

This paper presents a full-scale physical modeling investigation on the mud pumping in ballastless trackbed. The physical model was equipped with a rainfall device to simulate the in situ precipitation and various testing sensors were installed to monitor the dynamic response of the track-subgrade system. Results showed that the whipping of the track structure induced by high-speed train passages caused a separation between the track structure and the underlying roadbed, which allowed rainwater to intrude into the roadbed. The intruded rainwater infiltrated vertically and then permeated laterally from the bottom of the roadbed, eventually saturating the entire roadbed. Train moving loads partially promoted this rainwater infiltration. The excess pore water pressure (EPWP) was formed in the saturated roadbed caused by train moving loads, and it increased with train speeds and loading carriages. A noticeable upward EPWP gradient and a slight longitudinal EPWP gradient towards the expansion gap were also created in the saturated roadbed. Accordingly, both the vertical hydraulic gradient (HG) and longitudinal HG increased with train speeds and loading carriages, most of which, especially the vertical HG, exceeded the critical HG for particle migration with a diameter smaller than 7.1 mm. It caused severe upward particle migration and slight longitudinal particle migration towards the expansion gap. This spatial fine particle migration process, known as mud pumping, was driven by the HG-induced seepage force and further promoted by the EPWP amplification induced by high-speed train passages. Mud pumping resulted in a significant decrease in stiffness of the trackbed and a noticeable increase in vibration velocity of the track slab. • Mud pumping in ballastless trackbed was reproduced in a full-scale physical modeling test. • Rainwater intrusion route and saturation process of roadbed were discovered. • Dynamic responses of the track-subgrade system before and after mud pumping conditions were monitored. • Effects of train speeds and loading carriages on excess pore water pressure and hydraulic gradient were analyzed. • Mechanism of mud pumping in ballastless trackbed was revealed. [ABSTRACT FROM AUTHOR]

• The cause of 1-2m shortwave irregularity in bi-block ballastless track construction has been discovered. • A vehicle-track coupled dynamic model considering 1–2 m shortwave irregularities was established and validated. • The dynamic effects of different amount of 1–2 m shortwave irregularities under different running speed were evaluated. • Control standards for 1–2 m short wavelength irregularities are proposed under different running speed conditions. Compared with slab ballastless track, bi-block ballastless track has the advantages of simpler constructed components and better economy, and has been used in high-speed railways for nearly 20,000 km in China. During the construction, the position deviation between sleepers and the disturbance of sleeper position caused by track bed concrete pouring can easily lead to shortwave irregularity with wavelength of 1 ∼ 2 m of bi-block ballastless track. Massive detection data on several high-speed railway lines showed that the standard deviation of vertical wheel-rail contact forces on bi-block ballastless track was about 58% higher than that on slab ballastless track. In this paper, a vehicle-track coupled dynamic analysis model was established, which can consider 1 ∼ 2 m shortwave irregularities of the track. Under the current construction and operation control standards, the dynamic responses of vehicles and tracks under different running speeds were studied. The results showed that vertical shortwave irregularity mainly affected the dynamic response of the wheel and rail, and rarely affected the dynamic response in other components. Compared with no shortwave irregularity, when the track had shortwave irregularity with σ v = 0.8 mm, the peak value of the vertical acceleration of wheelset increased by 4.1 times, the standard deviation of wheel-rail contact force increased by 3.9 times, the vertical acceleration of frame increased by 1.7 times, and the vertical acceleration of track bed increased by 1.8 times, while the vibration acceleration of car body had almost no effect. When the track had shortwave irregularity with σ h = 0.8 mm, the lateral acceleration of wheelset increased by 2.3 times. When the track had shortwave irregularity with σ v = 0.8 mm and the vehicle speed increased to 450 km·h−1, the wheel load reduction rate reached 0.85, which exceeded the safety limit. Consider the results of this study, following suggestions can be obtained:(1) the shortwave irregularity with wavelength of 1 ∼ 2 m can be measured indirectly by the standard deviation of wheel-rail vertical contact force or wheelset vibration acceleration. (2) To control the wheel load reduction rate within 0.6, the standard deviation of random vertical irregularity should be controlled within 0.6 mm when running speed is 350 km/h, and within 0.4 mm when running speed is 400 km/h or above. [ABSTRACT FROM AUTHOR]

• Fatigue tests on full-scale CFT sleeper ballastless track subjected to 5 million loading cycles were carried out. • The static response evolutions of CFT sleeper ballastless track with fatigue loading cycles were studied. • The dynamic responses of CFT sleeper vibration-damping track with fatigue loading cycles were studied. • The mechanical performances and fatigue properties of the new type CFT sleeper ballastless track performed well. The new-type concrete-filled steel tube (CFT) double-block sleeper ballastless track structure can better serve urban rail transit by overcoming the problems such as easy rusting and cracking of the traditional track structure. In this paper, a full-scale CFT sleeper ballastless track structure was manufactured by 11 new-type concrete-filled steel tube sleepers cast in place. A series of fatigue tests were carried out based on the CFT sleeper ballastless track, the distribution law and the variations of the strain and deformation on the ballastless track structure during the train fatigue loadings were obtained. The falling-shaft impact test was also conducted on the CFT sleeper ballastless track with Under Slab Mats (USM) before and after the fatigue tests, and the dynamic performance of the vibration-damping track structure were obtained. The following conclusions were obtained: The static response variations, namely the strain and deformation behaviors of the CFT sleeper ballastless track structure increase slightly under the fatigue loadings. There is no cracking phenomenon during the fatigue tests. The vertical self-vibration frequency of the CFT sleeper ballastless track with vibration-damping mat decreases by 9.26%. The vibration isolation effect of the vibration-damping track decreases from 15.37% to 13.76% during the fatigue tests, and the variations of VLzmax on the RC base, track bed and rail increase less than 7%. The findings of this research have a certain significance for promoting the engineering application of CFT sleeper ballastless track structure, and provide a reference for future research. [ABSTRACT FROM AUTHOR]

• High-cycle fatigue behavior of cement mortar for ballastless track was tested. • The S - N curve of cement mortar was obtained. • Fatigue strain evolution curves of cement mortar were investigated in depth. • Fatigue modulus degradation of cement mortar was studied in detail. • Fatigue damage model of cement mortar was established. Cement mortar (CM), an important component of concrete, is the phase where fractures and failures predominately appear. The present paper conducted static and fatigue tests regarding four maximum stress levels (0.65, 0.70, 0.75, and 0.80) on CM specimens, aiming at determining the flexural fatigue properties of CM for ballastless track concrete. The S-N curve were fitted, and the fatigue damage model were established. Results demonstrate that the fatigue strain evolution curves showed a three-stage inverted S-shaped law. The CM specimens' fatigue modulus degradation values ranged between 3.2 and 4.5 GPa. The fatigue damage evolution curves rose as stress levels increased, indicating that higher fatigue loads would lead to larger damage in earlier stages and smaller damage in later stages. [ABSTRACT FROM AUTHOR]

• An efficient and accurate vehicle-track-subgrade spatial coupled dynamics model is constructed. • Combined with the fixed interface modal synthesis method and wheel/rail contact theory, the joint simulation of ABAQUS and UM is realized. • Take the average value of 10 groups of irregularities for track irregularity. • System dynamic characteristics of the 400 km/h and 350 km/h vehicle speeds under subgrade differential settlement conditions are compared. • The increase of train speed has a great impact on the vertical acceleration of rail. Whether the existing ballastless track subgrade settlement control standard of 350 km/h is applicable to the high-speed train of 400 km/h remains to be further research. This paper established a complete rigid flexible coupling dynamic model of vehicle-track-subgrade space based on the finite element method and multi-body dynamics theory. Combined with the fixed interface modal synthesis method and wheel/rail contact theory, the joint simulation of ABAQUS and UM is realized. The dynamic response of 400 km/h high-speed train under the condition of subgrade differential settlement is analyzed and compared with the current 350 km/h high-speed train. The results show that under the same subgrade differential settlement condition, when the train speed increases from 350 km/h to 400 km/h, the wheel rail interaction increases significantly, but does not exceed the specification limit. The amplitude of derailment coefficient is far lower than the maximum specification limit, while the amplitude of wheel load reduction rate exceeds the quasi-static limit in the specification. The impact of the increase of train speed on the lateral stability of the vehicle is greater than that on the vertical stability of the vehicle. At 400 km/h, each stability index of the train does not exceed the maximum specification limit, and sufficient safety margin is reserved. The increase of train speed has a great impact on the vertical acceleration of rail, and has little impact on the vertical acceleration of track plate and baseplate. In summary, the current subgrade settlement control standard of 350 km/h high-speed railway is also applicable to 400 km/h high-speed trains, and there is room for further speed increase. [ABSTRACT FROM AUTHOR]

Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails. • Combination of static and dynamic vehicle–track interaction models. • Design optimisation to minimise environmental footprint. • Design improvement potential, compared to an existing standard, is identified. • The influence of cracks in the concrete panel on dynamic wheel loads is small. • The restraint degree affects the steel stress and crack width significantly. [ABSTRACT FROM AUTHOR]

• A model of the elastic–viscoelastic double-layer composite beam is established. • The reliability of the double-layer composite beam model is verified by test data. • The mechanical response of ACWSS under temperature load is analyzed. • The leading cause of passive tensile damage of ACWSS is a strain mutation. • ACWSS at the expansion joint mainly bears axial tensile/compression deformation. The theoretical development of the temperature effect of the full-section asphalt concrete waterproof sealing structure (ACWSS) of the ballastless track subgrade lags the engineering practice. In order to reveal the passive tensile damage behavior of ACWSS from the perspective of theoretical analysis, in this paper, the base plate of the ballastless track and the ACWSS is simplified into an elastic–viscoelastic double layer composite beam model. The analytical calculation method for passive tensile damage of ACWSS under temperature load is derived theoretically. The change of surface stress and strain of ACWSS with time is calculated and analyzed. The theoretical analysis and calculation results show that the variation of the surface strain, the maximum strain, and the time corresponding to the strain peak of ACWSS are consistent with the measured results. The model of the double-layer composite beam has high reliability, and the analytical calculation method of passive tensile damage is reasonable and practical. The temperature stress of ACWSS at the expansion joint of the base plate is synchronized with the temperature change, indicating that the asphalt concrete at this location is mainly subjected to axial tension (or compression). It is suggested that the structural design should be judged by comparing the number of periodic temperature loads and the allowable fatigue number of asphalt concrete, which further improves the design method and technical system of the ACWSS in China's high-speed railway. It has important theoretical and practical significance. [ABSTRACT FROM AUTHOR]

In the process of heat exchange with the external environment, the internal temperature of ballastless track structure presents a nonlinear distribution. The vertical temperature gradient will cause repeated warping and deformation of track slab, resulting in mortar layer separation, which will affect driving comfort and track durability. The traditional temperature field analysis method of concrete structure based on thermodynamics has the disadvantages of too many assumptions, difficult parameter selection and too much calculation of energy consumption. In this paper, based on the finite element software ANSYS, the heat exchange was transformed into the boundary condition of heat flux, which was applied to the thermodynamic analysis model to study the nonlinear temperature distribution law of ballastless track. The accuracy of the analysis method was verified by the measured data. On this basis, the regional distribution law of temperature gradient of ballastless track under different geographical coordinates and climatic conditions was studied. By adding a regional adjustment coefficient, the vertical temperature load model of ballastless track suitable for typical areas in China was proposed. The proposed temperature load model makes up for the lack of refinement of climate division and temperature load model in relevant specifications, and has strong engineering application and popularization value. [ABSTRACT FROM AUTHOR]

• An efficient and accurate vehicle-track-subgrade vertically coupled dynamics model is constructed. • Time-spatial distributions of Green's functions of track-subgrade system are analyzed. • Dynamic characteristics of the three types of ballastless tracks under different conditions are compared. • Attenuation properties of track-subgrade system against track depth are investigated. • Discrepancy among different tracks exerts noteworthy effect on the track-subgrade system. This paper contributes to evaluate the dynamic performance of different types of ballastless tracks, including the CRTS II, CRTS III as well as CRTS DB, subjected to a moving high-speed railway vehicle. To this end, a vertically vehicle-track-subgrade coupled dynamics model appropriating for both the longitudinally connected-type track structure and the element slab-type track structure is constructed by introducing the Green's function method, so as to achieve a full characterization of the vehicle-track-subgrade system with accurate and efficient solutions. The time-spatial distributions of the displacement and velocity Green's functions of the track-subgrade system are analyzed to ascertain the values of the truncation parameters employed in the model. Numerical examples are presented to illustrate and compare the dynamic characteristics of the three types of track structures under various track irregularities, vehicle speeds, fastener stiffnesses and subgrade elastic moduli. It is shown that the discrepancy among different track structures exerts an ignorable influence on the vertical wheel-rail force, but its effect on the vertical displacement, acceleration and stress of the track-subgrade system is noteworthy. Besides, the attenuation characteristics of the track-subgrade system with respect to track depth are further investigated. It is concluded that the system displacement against the track depth presents an approximately linear attenuation, whereas the system stress reveals an approximately exponential attenuation. [ABSTRACT FROM AUTHOR]

• The secondary development of fatigue damage constitutive for CA mortar was conducted. • A damage-finite element full-couple calculation method of CA mortar was established. • Stress redistribution of CA mortar for ballastless track was caused by severe damage. • 0.5 was a critical stress level to determine whether the redistribution should be taken into account. Ballastless track withstand tens of millions or even hundreds of millions of times of train loads, its functional parts are prone to fatigue failure. In this paper, the high-cycle fatigue damage constitutive relationship of CA mortar was developed as a material subroutine, to embed into the refined FE model of CRTS-I ballastless track, establishing a damage -finite element full-couple method to analyze the influence of key factors such as void, initial deterioration and wheel load on the accumulation of fatigue damage of CA mortar. Main conclusions are as follows: void plays a more important role in the accumulation of fatigue damage of the CA mortar than initial deterioration and wheel load change. When the void length is 2.0 m, the damage value of the structure under 15 million times of wheel loads has exceeded 0.36, which is 5 orders of magnitude higher than that under the non-void condition. Laterally, the load stress below the loading point on the rail is significantly larger than at other positions, and the load stress distribution gradually gets uniformed. Along the longitudinal direction of the CA mortar, the stress at core bearing elements gradually decreases with the increase of damage, while the decreased stress is compensated by the increased stress in a certain distance from the void end along the longitudinal direction. With an initial deterioration of 50%, when the wheel load is 150 kN, the position below the rail reaches the maximum damage first, followed by the void edge, and then the damage spreads further into the middle part of the CA mortar along the lateral direction until the whole elements from the top surface at the void edge is damaged. In our study that spanned 15 million times of fatigue loading cycle, the stress level 0.5 was a critical value to determine whether the load stress redistribution caused by damage should be taken into account when using the damage - finite element full coupled method. [ABSTRACT FROM AUTHOR]