High-speed Railway Ballastless Track Research Articles

Flexural fatigue performance of recycled sand concrete for high-speed railway track bed

To investigate the applicability of recycled sand concrete in high-speed railway ballastless track bed, in this study, the fatigue life, strain evolution curve and calculated stiffness of C40 concrete incorporating 0, 50 % and 100 % recycled sand were explored. Digital image correlation (DIC) and the nanoindentation test were used to explore the influence of recycled sand on the performance of concrete. The results show that the flexural fatigue life of recycled sand concrete conforms to a two-parameter Weibull distribution. The fatigue strain progression and calculated stiffness demonstrate a distinct three-stage trend. Compared to natural aggregate concrete, the first-stage strain contribution of recycled sand concrete decreases by approximately 10 %. With the increase of fatigue cycles, the calculated stiffness decreased significantly, the dissipated energy increases gradually. Compared with recycled sand-free concrete and full recycled sand concrete, the concrete containing 50 % recycled sand possesses the highest elastic modulus and lowest thickness of the interfacial transition zone (ITZ), thus the average fatigue life of recycled sand concrete increased by 4.9 and 10.2 times.

Fracture behavior investigation of ballastless track of high-speed railway based on DIC technique

To investigate the issues of transverse through cracks and interlayer damage of the CRTS III slab ballastless track under train loading, the digital image correlation (DIC) technique was employed to reveal the damage mechanisms of the reduced-scale concrete of track slab structural concrete (TSSC) and track slab-filled laminated structural concrete (TSLSC). The results indicate that under train loading, the transverse through cracks of TSLSC exhibit a multi-stage, layer-by-layer cracking characteristic, and there is a risk of cracking in ballastless track when the bottom longitudinal strain exceeds 0.0004. The sudden increase in interlayer longitudinal shear strain difference in the third stage under train loading demonstrates that shear stress is the primary cause of interlayer damage in ballastless track. Tensile damage models based on ultimate stress–strain relationship and yield-fracture strain were established, and a non-contact testing method for the constitutive relationship and energy absorption effect of ballastless track was proposed using DIC technology, aiming to provide reference for the analysis and prediction of ballastless track damage under train loading.

Assessment of the Simultaneous Use of Asphalt Concrete and Foam Concrete as a Full Cross-Section Layer in the Substructure of the China Railway Track System (CRTS) III Slab Ballastless Tracks

This paper proposes the simultaneous application of asphalt concrete (AC) and foam concrete (FC) as a full cross-section layer in the substructure of the high-speed railway ballastless track. AC is designed as a waterproof layer and is placed as part of the top surface layer of the subgrade bed where the mixture is made from three types of performance grade (PG) binders (normal, high, and modified grade binders) named PG64-22, PG70-22, and PG76-22, respectively. FC is designed as a subgrade material to replace the traditional material in the bottom layer of the subgrade bed. It has a target density of 500–700 kg/m3 and polypropylene (PP) fiber is added at a ratio of 0.25% and 0.40% by volume. The mechanical properties of both materials are reviewed from the authors’ previous research, in which they were assessed through laboratory testing in accordance with ASTM standards. In addition, the numerical model analyzed the dynamic response of the whole structure when AC and FC were applied as full cross-section layers under different thicknesses of FC and then compared with traditional track structures. Laboratory test results indicate that PG76-22, or modified asphalt binder and FC at a density of 600 kg/m3 with the addition of 0.25% PP fiber, is suitable for use in slab ballastless tracks. In addition, the prediction of the model shows that AC at a thickness of 0.12 m and FC at a thickness of 1.00 m can reduce the stress and vibration of the track structure better than the traditional structure, resulting in stabilization and long-term service life.

Evaluation index and improvement method for interlayer bonding property of ballastless track

Inadequate bonding can bring detrimental interlayer separation problems in high-speed slab ballastless tracks. Thus, it is imperative to elucidate the stress characteristics of the interlayer in high-speed railway ballastless track when subjected to the combined influence of train and environmental factors. The present study employs finite elements to elucidate the change pattern, with the CRTS III slab ballastless track serving as an illustrative case. The findings indicated that interlayer separation of ballastless track under coupling effect of temperature gradient and train load was primarily attributed to shear stress. An evaluation index of “shear bond strength ≥2.50 MPa” was proposed and used to assess interlayer bonding performance of ballastless track in high-speed railway. Additionally, based on polymer modification technology, a method of using phenylpropylene and styrene-butadiene emulsions has been developed to improve the interlayer bonding behaviour of high-speed railway ballastless track. This work is expected to provide theoretical and technical support for a prolonged service life of high-speed railway ballastless track.

Semi-analytical solution for interfacial debonding of high-speed railway ballastless track under thermal loading using a quasi-dynamic method

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.

Experimental study on high-cycle flexural fatigue behavior of cement mortar for ballastless track of high-speed railway

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.

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

Investigation of the seismic performance of CRTS III slab ballastless track of high-speed railway under low-cycle reciprocating load

In the China Railway Track System (CRTS) III slab ballastless track (SBT) system, the self-compacting concrete filling layer (SCCFL) and the base slab are connected via a rubber pad, geotextile, convex platform, and groove. This is a complex interaction between the SCCFL and base slab. As a buffer member between SCCFL and base slab, the rubber pad significantly impacts the seismic performance of CRTS III SBT. To explore the failure mode and seismic performance of CRTS III SBT, four CRTS III SBT specimens with different rubber pad thicknesses were designed and subjected to low-cycle reciprocating load tests in this study. The characteristics of the load-displacement hysteresis curve and load-displacement skeleton curve of CRTS III SBT specimens were then analysed. The failure mode, energy-dissipation capacity, ductility, stiffness degradation of CRTS III SBT specimens, and the influence of rubber pad thickness on the seismic performance of CRTS III SBT specimens were studied. It was found that when the low-cycle reciprocating loading was applied on the CRTS III SBT specimens, the interlayer bonding between the SCCFL and the base slab was the first to fail, followed by compressive deformation of the rubber pad. The concrete at the convex platform-SCCFL interface cracked, and the concrete in the four corners of the groove cracked until failure. When the rubber pad thickness was increased, the ultimate bearing capacity of the CRTS III SBT specimens under low-cycle reciprocating loads remained constant. However, the corresponding energy-dissipating capacity, ductility, and seismic performance all improved.

Fracture parameters and influencing factors of cement asphalt mortar

Cement asphalt mortar (CAM), which is composed of cement, emulsified asphalt, sand and admixture, is an important component material of slab ballastless track of high-speed railway. The fracture resistance of CAM is very important for the ride comfort and stability of high-speed railway. This study was mainly aimed at using semi-circular bending (SCB) test to study the fracture parameters and influencing factors of CAM with high asphalt content. Through SCB test, the fracture parameters such as peak load and fracture energy of CAM were studied. The effects of temperature, loading rate, notch depth and material ratio on fracture parameters were analyzed. The microstructure and pore characteristics of CAM were studied by scanning electron microscope (SEM) and CT scanning. With the increase of temperature, the peak load and fracture energy of CAM decrease. For CAM samples with A/C ratio (mass ratio of emulsified asphalt to cement) of 1.6, when the temperature increases from −15℃ to 25℃, the maximum decrease of peak load and fracture energy is 76.5% and 67.2%, respectively. With the increase of loading rate, the peak load and fracture energy of CAM increase. For CAM samples with A/C ratio of 1.2 at 25℃, when the loading rate increases from 0.5 mm/min to 5.0 mm/min, the maximum increase of peak load and fracture energy is 44.0% and 48.2%, respectively. When the temperature is −15℃ and 25℃, there is an optimal A/C ratio for peak load and fracture energy. When A/C ratio varies between 1.2 and 1.6, both peak load and fracture energy have the maximum value. When the temperature is −15℃, the fracture occurred in CAM is semi-brittle fracture, and the fracture toughness and fracture energy are suitable to evaluate the fracture resistance of CAM. When the temperature is 5℃ and 25℃, the fracture occurred in CAM is ductile fracture, and the fracture energy is more suitable to evaluate the fracture resistance of CAM.

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.

Experimental investigation on dynamic performance evolution of double-block ballastless track under high-cycle train loads

This paper aims to investigate the dynamic performance evolution law of double-block ballastless track under long-term train load through a full-size laboratory experiment. The experiments are conducted based on a comprehensive test platform of a full-size double-block ballastless track-subgrade system, and the test contents are composed of the fatigue loading test and dynamic performance test. The full-size acceleration test method is adopted for the fatigue test to simulate the fatigue process of the ballastless track under different accumulative loading cycles. Moreover, the fatigue loading stage is divided into several periods according to the accumulative loading cycles, and the dynamic performance test is conducted after each fatigue loading period to study the dynamic performance evolution law of the ballastless track. The test results show that the static rail displacement relative to the subgrade displacement presents a development progress from initial decline to gradual stability along with the increase of loading cycles. However, the accelerations of the ballastless track structure components present a gradual increase trend with the accumulation of loading cycles. The deformation resistant capacity of the double-block ballastless track decreases gradually with the increase of loading cycles. This study may provide useful reference for scientific operation and maintenance of ballastless track in high-speed railway.

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.

Failure analysis of fatigue damage for fastening clips in the ballastless track of high-speed railway considering random track irregularities

In order to study the influence of wheel-rail random dynamic interaction on the fatigue damage for fastening clips, a three-dimensional (3-D) high-speed railway vehicle-track coupling random dynamics model is established based on the random theory of the probability density evolution method (PDEM). The number theoretic method (NTM) and stochastic harmonic functions (SHF) are employed to generate the representative random track irregularities. Furthermore, a refined finite element model of WJ-8 fastening system is established, and the stress time history results of the clips are obtained based on the co-simulation analysis. Eventually, the rain-flow counting is introduced to study the influence of random track irregularities on fatigue damage of fastening clips combined with cumulative damage theory and the S-N curve of the clips. The results show that, the dynamic characteristics and stochastic probability evolution mechanism of the vehicle-track random system considering random track irregularities, as well as the evolution characteristics of the fatigue failure probability of clips with service time are accurately reproduced based on PDEM. Significantly, the fatigue damage of fastening clips caused by one vehicle passing by follows the lognormal distribution with a mathematical expectation of 2.35 × 10-8 and a variance of 1.48 × 10-12. The 95% confidence interval of mathematical expectation is [7.05 × 10-9, 5.89 × 10-7] and the 95% confidence interval of variance is [1.37 × 10-13, 1.59 × 10-11]. Additionally, the longer the service time of the fastening system, the more serious the fatigue damage of the clips and the greater the fatigue failure probability.

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...

Long-term prediction of fatigue crack growth in ballastless track of high-speed railway due to cyclic train load

This paper proposes a vehicle-ballastless track coupled model with consideration of concrete cracks in high-speed railways through finite element method. Cracked Euler beam elements are used to model the concrete slab and the supporting layer with through-transverse cracks. In addition, an iterative method is proposed to estimate the fatigue crack growth of concrete under long-term train dynamic load on the basis of the Forman model. The vehicle-ballastless track coupled model with concrete cracks is employed to obtain the crack-tip stress intensity factor (CTSIF) of concrete under the condition of initial crack depth. The CTSIF induced by a high-speed vehicle is adopted in the Forman model to calculate the crack growth rate. The crack depth is updated by the number of passing vehicles in each iteration step, which is determined by a crack growth increment threshold. The dynamic characteristics of the vehicle-ballastless track coupled system are re-calculated based on the updated crack depth. Then, the effects of the crack depth, the stiffness of CA mortar and subgrade on the CTSIF of the concrete slab and the supporting layer are investigated in detail. The fatigue crack propagation process and residual service life under different initial crack depths of the supporting layer are discussed. Some practical conclusions are drawn, which can provide some theoretical guidances for the routine maintenance of slab tracks.

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.

Laboratory full-scale model test of subgrade mud pumping for ballastless track of high-speed railway

ABSTRACT This paper aims to clarify the mechanisms and driving factors of subgrade mud pumping for ballastless track in high-speed railway. A full-scale model test system in which the train dynamic loading and rainfall condition could be simulated was developed, allowing the recurrence of subgrade mud pumping. The relationship between the degree of mud pumping and the hydrodynamic pressure characteristics of subgrade was investigated, and the mechanisms and driving factors of mud pumping were also clarified. It was shown that the subgrade surface layer under the cracked concrete base was always saturated under the condition of rainwater infiltration, and it was prone to mud pumping given a long-term action of the dynamic loading of trains. A significant increase in excess pore water pressure to a certain extent mobilized the mud pumping. Accordingly, the prevention and treatment of mud pumping can be the prevention of rainwater infiltration or more efficient drainage.

Study on control measures of the influence of shallow buried tunnel excavation on the subgrade settlement of high speed railway in operation

A finite element model is established to study the settlement control technology of the ballastless track of high-speed railway under the shield of shallow buried tunnel. In particular, the reinforcement mechanism and construction control technology of the Metro Jet System (MJS) method for horizontal reinforcement under complex geological conditions (medium coarse sand and strong permeable layer) are discussed. The results showed that when the ground is not reinforced, the shield tunnel directly passes through the high-speed railway, and the settlement caused by the construction of the railway gene tunnel directly above the tunnel has greatly exceeded the limit of the settlement control standard. Due to the limitations of site, planning and construction conditions, the horizontal jet grouting pile of MJS construction method is selected as an auxiliary measure through comprehensive comparison. After the completion of the MJS construction, the maximum settlement of the subgrade is 30 mm, and the settlement of the high-speed railway subgrade is about 25 mm.

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.