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Safety risk identification is the premise and foundation of safety risk management for railway construction. However, due to some characteristics of railway projects, which include large volumes of work, complex construction environments, and long construction cycles, etc., the risk factors of railway projects are often hidden in all stages of engineering construction. It results in the comprehensive identification of safety risks of railway projects being usually difficult, and this problem is more serious when the railway is constructed in complex and dangerous areas. Therefore, to identify the safety risks comprehensively, this paper constructs a safety risk identification method applicable to railway construction in complex and dangerous areas. This method studies the spatial and temporal distribution of risks and their relationship with subprojects by using a work breakdown structure (WBS), a risk breakdown structure (RBS), grid-based management, and forming a safety risk identification matrix, which can help researchers analyze the characteristics of risks. In order to verify the effectiveness of the method, the A Railway, which is located in the western of China, was selected as a case study, and risk identification for its civil engineering was carried out. The research results show that in the construction process of the A Railway, the main types of safety risks suffered by various branch projects were different. In addition, some risk factors only appeared at specific times in space, and there is a strong interaction between these risk factors. Based on this method, safety risk identification can intuitively discover the spatial and temporal distribution of risk factors and analyze the interaction between risk factors, which can provide help for the formulation of targeted risk control measures.

This paper aims to explore the seismic performance of a novel earthquake-resilient bridge column with replaceable elements, including external ultra-high-performance concrete (UHPC) cover plates an...

This paper presents random dynamic analysis on a high-speed train moving over a long-span cable-stayed bridge. In the study, the train, slab track, and bridge are regarded as an integrated system, ...

A novel connection adopting lap-spliced large-diameter bars and ultra-high performance concrete (UHPC) grout was developed to accelerate the assemble progress of precast bridge columns. The precast bridge column adopting the connections was testified to be on a par with the monolithic concrete counterpart in terms of seismic performance in previous research. This paper aims to develop a numerical model to further investigate the seismic behavior of the proposed bridge column considering the bar-slip effect. A finite element model was established for the bridge columns considering deformation components of flexure, shear, and bar-slip. The bond behavior between the deformed bar and UHPC was defined using a new practical model, which was developed based on a pullout test including five specimens in this research. The established finite element model was verified by the cyclic loading test in literature in terms of the overall hysteretic curve and local responses. The validated model was used to conduct parametric analysis to study the contributions of the different deformation components to lateral deformation as well as the effects of large-diameter bars on seismic performance. Results show that all the pullout specimens have the tensile fracture of bars, which indicates that the development length of 5 times bar diameter is sufficient for deformed bars in UHPC when the bar diameter is no more than 32 mm. The practical model is effective to consider the effects of the slip between the deformed bar and UHPC. The finite element model can predict the overall hysteretic curve and local responses at different drift ratios. The bar-slip has a considerable even dominative contribution to the lateral deformation of the proposed bridge column. Larger bar diameter can enhance deformation capacity as well as reduce energy dissipation and residual drift ratio.

The paper aims to provide a simplified method for modeling seismic performance of precast segmental UHPC bridge columns based on the identified flap-shaped hysteretic model (IFSHM), of which four key parameters, including the elastic stiffness, the yield lateral force, the post-yield stiffness ratio, and the energy dissipation coefficient, are calculated with design parameters in the simplified method. Theoretical and parametric analyses were conducted to build the relationships among the four key parameters and two characteristic states, including the yield and ultimate states. The simplified method was established by respectively deducting the calculation procedures to determine the yield and ultimate states. Applying the simplified method to determine the four parameters of the IFSHM was validated by the reported cyclic loading test including three 1/3-scale specimens in literature. A proposed finite element model in previous research was used to check the feasibility of using the simplified method to predict nonlinear dynamic responses. Results show that the ultimate state is a suitable calculation state to determine the energy dissipation coefficient. The simplified method has the capacity of calculating the four parameters of the IFSHM. The simplified method can predict nonlinear static responses, including lateral force-drift ratio skeleton curve and energy dissipation per cycle. The determined IFSHM with the simplified method can be used to estimate nonlinear dynamic responses, including the maximum drift ratio and cumulative energy dissipation, when precast segmental UHPC bridge columns are subject to strong earthquake motions.

Push plate test is a powerful tool to evaluate the interfacial bond performance of China railway track structure type-II slab ballastless track structure (CRTS II SBTS). However, there is still a lack of theoretical explanation of the push plate test. In this paper, a linear proportional distribution method is proposed in terms of a series of analytical formulas to describe the interfacial force-displacement variation of CRTS II SBTS in different damage stages of the horizontal push plate test. The force-displacement relationship established by the linear proportional distribution method agrees well with that observed in full-scale test. The horizontal push plate test is then simulated, in which a bilinear cohesive zone model (CZM) was adopted to simulate the interface within track structure. The parameters of the CZM are calculated based on the force-displacement curves obtained from scale push plate test. Particularly, the normal cohesive parameters are determined based on the scale vertical push plate test instead of the traditional splitting tensile test. The simulation proves that both the maximum affected length in the undamage stage and the maximum damaged length in the damage stage depend rather on the interfacial stiffness and the material parameters of SBTS than the horizontal load. These two lengths given by the simulation are close to those defined by the proposed linear proportional distribution method. This indicates the reliability of the proposed method and the capability of scale push plate test in determining cohesive parameters.

Rail corrugation is a common railway defect that involves diverse and complex factors. Rail grinding is also the most commonly used method to address corrugations. Through numerous irregularity tests and one-third octave frequency spectrum analyses, this study determined the characteristics and development process for rail corrugation on high-speed rail tracks. The vibration transmission properties of the grinding train were tested using the force hammer impacting method. Thereafter, using a simulation, the influence of the vertical vibration behavior of the grinding stone and the stiffness of the hydraulics were determined. Through a series of field tests and numerical simulations, this study revealed a clear correlation between rail corrugation and rail grinding and confirmed that the technical operation of rail grinding is closely associated with regular grinding marks at a wavelength of approximately 60 mm on rail surfaces. The combination of the natural vibration of the grinding stone (frequency of 60 Hz) and an inappropriate operational process can aggravate the grinding marks on the rail surfaces, thereby forming an initial excitation of rail corrugation. Although a large number of irregularity tests are performed after rail grinding, these wavelength-fixing grinding marks can cause the formation and development of rail corrugation. Suggestions for improving the high-speed rail-grinding technology are also provided.

During the running of a high-speed train, the wheel may bounce on the rail due to the track irregularity. The wheel bounce could generate a vertical impact, leading to the initiation and expansion of delamination between layers of the track structure. In this paper, the evolution of the interfacial damage and delamination subjected to the vertical impact is simulated using finite element analysis (FEA). In the FEA, a bilinear cohesive zone model (CZM) is adopted to simulate the interface between the track slab and the CA mortar layer. For different levels of impact energy, the contact force, vertical deformation, absorbed energy, area of interfacial damage, and area of delamination are calculated and compared. The effects of the tangential and normal stiffness of the interface on the distribution of interfacial damage and delamination are investigated. The results show that the contact force, vertical deformation, absorbed energy, area of interfacial damage, and area of delamination increase with the increase of the impact energy. The area of interfacial damage in the compression stage is closely related to the tangential stiffness, whereas the area of delamination depends on the normal stiffness. The normal stiffness that gives the largest area of delamination is recommended to be taken as the lower bound of the normal stiffness for both controlling the delamination and preventing an exceedance of the track irregularity limit.

The forecasting of the railway short-term volume plays an essential role in the railway company, which is the basement of the ticket assignment, the line planning, and the passenger station management, and so on. However, the short-term flow forecasting tends to yield poor performance in holidays in China and leads to a low service-of-level for the passengers. In order to improve the accuracy of the short-term passenger flow volume forecasting of high-speed railway, and overcome the challenges in holidays, transfer learning with a time series decomposition is managed. The proposed decomposition-based forecasting method with transfer learning is based on a boosting method which is an instance-based transfer. Firstly, the time series is decomposed into linear time series and nonlinear time series. Using the SARIMA model to predict linear time series, the nonlinear time series is acquired and transformed as feature-label samples with a feature selection to the transfer learning. To limit the negative transfer, two sample filtering methods are proposed by the computing of similarity of time series. Finally, the samples in the source domain are learned by a TrAdaboost model which is embedded with Random Forest adjusting the weights of training samples to reduce the negative transfer. The 24 stations of the Jinghu High-speed railway are tested in our experiments. Our transfer learning model outperforms the baselines. The results also show the effectiveness of feature selection and sample filtering methods. It is proved that this method can be applied to the short-term passenger flow prediction of high-speed railway efficiently, and it is beneficial to improve the efficiency of resource allocation and the service level of high-speed railway transportation.

Structural damage identification has been a focus of civil engineering research in recent years. Therefore, this paper focuses on the advantages and disadvantages of various damage identification methods, including model updates, genetic algorithms, neural networks, support vector machines, dynamic fingerprints, wavelet transformations, and the Hilbert-Huang transform. This paper also discusses the latest research on damage identification combined with building information modeling (BIM) and deep learning. Finally, it is demonstrated that comparing the accuracy of different machine learning algorithms for damage identification and obtaining the optimal algorithm will become an important research direction in the future.

In this paper, the potential of using foam concrete as a lightweight filling material for high-speed railway roadbeds was studied. The influence of coarse fly ash on the workability, mechanical, shrinkage performances and durability of foam concrete were analyzed. X-ray Computed Tomography (XCT) was used to characterize the microstructure and quantitatively in situ monitor the water transfer behavior of foam concrete. The results show that coarse fly ash enhances many properties of foam concrete, including workability and mechanical and freeze-thaw resistance properties, while the reverse phenomenon is observed for water absorption and drying shrinkage properties. A good linear relationship was provided between the fine content and the absorption coefficients. Finally, continuous field testing of settlement, lateral displacement and soil pressure in the Hangzhou east railway station project shows good loading and differential settlement reduction properties when foam concrete was used as a filling material.

The type and fineness of soil are commonly recognized as the two major factors affecting the frost heave behavior of foundation. This paper aims to study the effect of soil type and fineness on frost heave behavior by experimental and numerical methods. Optical and scanning electron microscopes were employed to study the microstructure of kaolin and montmorillonite soils. A finite volume method, considering the changes of thermal and water fields simultaneously, was used to model the frost heave behavior of finely grained soil. By coupling the rigid ice model with the modified Kozeny–Carman equation and estimating the hydraulic conductivity, the relationship between the frost heave ratio and specific surface area of fines was established. Based on the modeling results, a region of proportion range of three typical soil (silty, clay and sandy soil) was proposed based on the ternary plot of frost heave values. Microscopic test results show that the multilayer microstructure of kaolin results in high content of bonded water compared with that of montmorillonite, leading to higher frost heave value. This model is proved to be reliable by a good agreement between the predicted and measured frost heave values.

In this study, an ultra-stable foam used for foamed concrete was fabricated by modifying the gas–liquid interface by coupling the effects of an organic surfactant and nanoparticles. A serial of techniques was employed to study the products and microstructure development of foam and foamed concrete, respectively. The results show that nano-silica and hydroxypropyl methylcellulose can slow the coalescence and disproportionation of the bubbles by adsorbing at the air bubble surface and increasing the viscosity of cell wall paste, thus preventing gas transfer and hindering physical drainage between the gaseous and liquid phases. Also, a more homogeneous and finer pore structure is generated with the inclusion of the organic surfactant and nanoparticles. The pozzolanic reaction between the nano-silica and Ca(OH)2 results in an increased C-S-H content and the densification of the cell wall structure. In addition, the stability of foamed concrete with modification and relevant stabilization mechanisms were also investigated.

This paper proposes a numerical method to study the effect of pore shapes on the effective thermal conductivity (ETC) of cellular concrete by a two-dimensional model. Cellular concrete can be seen as a composite of two phases with pore and cement paste. The model is established by two steps. Firstly, a generation of two-dimensional representative volume element of cellular concrete microstructure is necessary. Secondly, a finite element method is adopted to simulate heat transfer through the pixelated microstructure. Simulations are validated against analytical approximations, as well as experimental data from the literature. The model can also be used to evaluate the pore size distribution and orientation effects that are hard to measure only in laboratory experiments. It is concluded that ETC decreases when triangle pores substitute for circular pores on account that the tortuosity increases continuously. The other shapes of non-circular pores (square, pentagon and hexagon) have negligible effects on ETC. For ellipse cases, ETC decreases with increase in aspect ratio and volume fraction of pore. In the case of aligned pores, the ETC is larger along the principal axis. However, the size distribution of pores seems to have an insignificant influence. The numerical results suggest that the finite element method (FEM) considering quantitative data of thermal transfer behavior of cellular concrete can be obtained by the pore shapes, and it may be of great help to the optimization of materials.

Rail corrugation is very common in metro systems, and serious noise problems produced by rail corrugation, especially short-wavelength corrugations (25–50 mm), are a common cause of passenger complaints. For metro trains, the wheel-rail interface is the main source of noise, and the wheel-rail roughness, especially in the presence of rail corrugation, is the main excitation source. Rail grinding is a fast, economical, and effective control measure for reducing vibration and noise. However, the existing grinding cycle is not sufficient to meet the requirements of interior noise. There is no rail grinding standard based on interior noise limits for metro trains running on slab tracks in tunnels, which covers the vast majority of situations in China. Therefore, there is an urgent need to understand the effects of rail corrugation on interior noise for metro trains running on slab tracks in tunnels. At the same time, a rail grinding standard based on interior noise limits for such metro trains is very important. In this paper, the characteristics of the serious noise problems caused by rail corrugation are identified and suitable rail grinding controls based on noise limits are presented.

Rail decarburized layer has significant impact on the wear and rolling contact fatigue in the wheel-rail interaction. Due to the lack of constitutive relation of rail decarburized layer, it is impossible to analyse accurately the influence of rail decarburized layer on wheel-rail contact. To obtain the constitutive relation of this layer of decarburized non-uniform material, nano-indentation experiments were carried out at different vertical positions in the decarburization layer on a rail specimen with decarburization thickness of 0.55 mm. Young’s modulus and hardness were determined using Oliver and Pharr method. Axisymmetric two-dimensional finite element models were established in ABAQUS to simulate the nano-indentation loading process and the power law elastic–plastic stress–strain relationships were obtained for material at different vertical positions in the rail decarburized layer. A set of dimensionless functions were proposed for Young’s modulus, hardness, yield stress and strain hardening exponent at arbitrary depth in a rail decarburized layer or in a decarburized layer treated by rail pre-grinding. The results show that the Young’s modulus and hardness decrease from the rail bulk to the surface of the decarburized layer. The Young’s modulus and hardness near the surface are 11% and 35% lower than those in the rail bulk, respectively. However, the yield stress exhibits an increasing trend from rail bulk to the decarburized surface, where yield stress is 20% higher than the rail bulk. Analysis shows that the main reason that causes the reduction of hardness at the decarburized layer surface is the reduction of Young’s modulus but not the yield stress.

A rotating flexible wheelset model is developed and integrated into a vehicle/track dynamic model. Flexible wheelset modes with natural frequencies less than 1000 Hz are considered in the wheelset modelling. An innovation of the paper is that wheel/rail rolling contact calculation considers the effect of the wheelset flexibility and the rotating effect. By introducing two half dummy rigid wheelsets the rolling contact between the flexible wheelset and the two rails can be transformed to that between a rigid wheelset and the rails. As an extension application, the wheel OOR (Out-Of-Round) wears with the 11th, 15th, and 17th orders are used to the vehicle system dynamic model with rigid, flexible and rotating-flexible wheelset model. The results of the three models are compared to study the influence of wheelset flexibility and rotation. The ‘online searching contact method’ developed in this paper is compared with the traditional contact method with considering the rotating flexible wheelset. And then a me...

A novel UHPC grout-filled pipe sleeve with bolts was put forward for connecting large-diameter deformed bars and its feasibility was experimentally verified in a previous study. But it is not easy to rapidly broaden its application partly due to the lack of relevant calculation and design knowledge. This study aims to establish an analytical model on the tensile resistance that is dependent on the deformed bar-UHPC grout and UHPC grout-steel pipe interfaces, and develop a design method for the proposed pipe sleeve. In the model, the former interface resistance was analytically calculated considering the friction resistance, bearing of ribs against UHPC grout, and steel pipe's confinement. A dimensionless index ηb-g was defined to measure the relationship of the bond stress and pressure at the interface, and calibrated based on the experimental results. The latter interface resistance was analytically calculated considering the interface bond strength and resistance of bolts. Experimental results were adopted to verify the analytical model. A design method was developed for the pipe sleeve based on the verified analytical model, and a design case was given to illustrate how to use it. Results show that the analytical model can accurately predict the two interface resistances. ηb-g is respectively recommended for three categories of pipe sleeves, that are distinguished by the existence of bolts and grout type. The design method is convenient to provide a feasible design scheme of the pipe sleeve for a specified large-diameter deformed bar, of which the embedded length can be reduced to be 6 ~ 7 times bar diameter.

This paper develops a numerical model for wheel-rail noise analysis in the time-domain. This model for wheel-rail noise is based on vehicle-track coupling dynamics considering the effect of flexible wheelsets and track, and a transient wheel-rail noise prediction method. This model can approximatively characterize the components of vibration and noise in the frequency range up to 3.5 kHz. The wheel-rail forces are calculated and shown in both time and frequency domains by using the vehicletrack coupling dynamic model. Then the vibration and sound of the flexible wheelset are calculated by the transient finite elementboundary element (FE-BE) prediction model at 300 km/h, in which the effects of random irregularity and discrete supporting excitation are considered. The numerical results calculated by using the present model are discussed. The present model is also used to calculate the effect of corrugation with wavelengths of 40 mm to 300 mm on wheel-rail noise. The numerical results can be useful for academic research and engineering application to railway noise and vibration.

Grouted sleeve splice is a competitive alternative to reinforcement connections of accelerated bridge construction (ABC). When it is used to connect large-diameter deformed bars, overlong development length is required, although the decreased amount of connected bars and increased construction tolerance can accelerate construction speed. This paper aims to develop a novel ultra-high performance concrete (UHPC) grout-filled pipe sleeve with bolts for large-diameter deformed bars. It is expected to shorten the embedded length and delay grout crushing and splitting caused by bolts using UHPC's high material properties. A direct tensile test was conducted on 21 specimens to validate the feasibility, investigate the design parameters' effects, and explore the working mechanism of the pipe sleeve. Results show that the proposed pipe sleeve is feasible to connect large-diameter deformed bars with an embedded length of 5db. There are four failure modes including grout bond failure without/with bolts as well as bar bond failure without/with bolts in this test. UHPC without steel fiber is a preferred grout for the pipe sleeve because steel fiber can weaken grout fluidity and reduce bar-grout bond strength as well as grout-pipe bond strength. The existence of bolts can significantly enhance bar-grout bond strength as well as grout-pipe bond strength. The grout-pipe bond performance is sensitive to the depth of bolts in grout, amount of bolts, and distance of bolts to the end. When the pipe sleeve is used for deformed bars with higher strength, bearing capacity is slightly increased and deformation capacity is markedly weakened for bar-grout bond behavior. A greater cross dimension of the steel pipe is a good choice to avoid grout bond failure.

In this study, both two- and three-dimensional (2D and 3D) finite-volume-based models were developed to analyze the heat transfer mechanisms through the porous structures of cellular concretes under steady-state heat transfer conditions and to investigate the differences between the 2D and 3D modeling results. The 2D and 3D reconstructed pore networks were generated from the microstructural information measured by 3D images captured by X-ray computerized tomography (X-CT). The computed effective thermal conductivities based on the 2D and 3D calculations performed on the reconstructed porous structures were found to be nearly identical to those evaluated from the 2D cross-sectional images and the 3D X-CT images, respectively. In addition, the 3D computed effective thermal conductivity was found to agree better with the measured values, in comparison with the 2D reconstruction and real cross-sectional images. Finally, the thermal conductivities computed for different reconstructed porous 3D structures of cellular concretes were compared with those obtained from 2D computations performed on 2D reconstructed structures. This comparison revealed the differences between 2D and 3D image-based modeling. A correlation was thus derived between the results of the 3D and 2D models.

The Harbin–Dalian high-speed railway in northeastern China has a significant portion of track foundation built on seasonally frozen ground. Wide-spread frost heave was observed during the first winter of its operation and the heave occurred mainly in coarse fills that were considered not susceptible to frost heave. This paper first presents the field data of frost heave and frost depth observed along the railway. It then analyses alternative mechanisms that have been considered to have caused the observed frost heave. The three most likely mechanisms are poor quality control of fine content in the coarse fill, the top-down water supply mechanism, and the bottom-up water supply mechanism. The likelihoods of these mechanisms are analysed against observed field data, using a one-dimensional frost heave model. The results indicate that the most likely explanation for the unexpected frost heave is a combined action of different mechanisms.

Cement asphalt mortar (CAM) softening is a common phenomenon that results from aging and rain soaking when a high-speed railway is in service. CAM softening seriously affects vehicle operation safety and track dynamics. In this paper, a 3D coupling dynamic model of a vehicle and a China railway track system I (CRTS-I) slab track is developed. By using the proposed model, the wheel-rail contact forces, derailment coefficient, wheelset loading reduction ratio, and the track displacements are calculated to study the influences of CAM softening on the dynamic characteristics of a vehicle-track system. A track-subgrade finite difference model is developed to study the effect of CAM softening on track damage. The results show that track interface shear failure develops when the CAM softening coefficients reach 10–100. The CAM softening coefficient should not be less than 1000, otherwise a high-speed running vehicle may risk derailment.

This paper aims to provide a novel quantitative design criterion for the self-centering (SC) capacity of precast segmental ultra-high performance concrete (UHPC) bridge columns based on the concept of the SC factor, which is deemed capable of depicting the formation mechanism of residual drift. A refined numerical model was developed to simulate the seismic performance and was verified by the results of the cyclic loading test. Parametric analysis was conducted to research the influence of seven common design parameters on the SC factor based on the proposed numerical model. According to the results of the parametric analysis, a simplified formula was established to assess the residual drift when the SC factor and the maximum drift were known. Nonlinear dynamic analysis was conducted to validate the simplified formula for precast segmental UHPC bridge columns subjected to far-field, no-pulse near-field, and pulse near-field earthquake motions. A design criterion for the SC capacity was proposed based on the SC factor limits determined by the simplified formula. Research results show that the SC factor corresponding to the ultimate drift is generally conservative for assessing the SC capacity of precast segmental UHPC bridge columns. The residual drift is dependent on the SC factor and the maximum drift. The residual drift decreases with the increasing SC factor or decreasing maximum drift. The proposed formula is verified by the results of nonlinear dynamic analysis to be conservative to calculate the residual drift. According to the proposed design criterion, the SC factor limits are increased with the drift demand up at the same earthquake design level. The adverse effects of pulse near-field earthquake motions on the earthquake resilience of precast segmental UHPC bridge columns should be taken seriously.

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem, especially when high-speed trains operate in rainy regions. This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics. By using this model, the basic dynamic characteristics, including water–soil interaction and without water induced by the high-speed train loading, are studied. The main factors-the permeability coefficient and the porosity-influencing the subgrade deformation are investigated. The developed model can characterize the soil dynamic behaviour more realistically, especially when considering the influence of water-rich soil.

A railway wheel installed with the web-mounted noise shielding and vibration damping assemblies is introduced in this paper. The shielding and damping assemble is alternant constrained to the both ends connecting to the tyre and hub. This design can produce shear strain in periodical variation, and then vibration energy of the shielding plate and the wheel is dissipated effectively. Assembles can also reduce the noise radiation from the wheel web. In order to investigate the vibration and sound radiation reduction of this new type of wheel relevant tests are carried out in a semi-anechoic room. In the test, damping ratio, acceleration, sound energy, sound field and directivity of the damping wheel are given and analyzed. The same tests are conducted for a standard wheel as a comparison. The test results show that the damping ratio of the damping wheel increases significantly compared to the standard one, especially for the damping ratios at the prominent resonance frequencies. The increase of the damping ratio is as much as 44 times. The sound energy levels (SEL) of the damping wheel in the overall range and at a dominant resonance frequency are, respectively, 15 and 40 dB, much less than those of the standard one. By comparing the sound fields and directivities of the two wheels, the sound radiation of the damping wheel is lower in all directions.

Due to the chemical component and physical property, fines of coarse-grained soil (CGS) are prone to adsorb with each other forming cluster morphology during mixing and compacting process for high-speed railway roadbed construction. The clustering phenomenon of fines in CGS was quantitatively characterized by X-ray computed tomography (X-CT) and its effect on the frost heave behavior was investigated for the first time in this study. For this purpose, greyscale level based digital microstructures were generated by X-CT with a resolution of 20 um/voxel length. The frost heave ratios of samples with fine contents of 0%, 3%, 5%, 8%, 10% and 15% were tested under fully saturated condition in a close freezing system. To overcome the overlapping gray values between fines and aggregates, an image processing method based on a derivative function was introduced to segment the morphological features of the clustering fines from sectional X-CT images. Furthermore, a gray-based method was proposed to describe the fines distribution and to calculate the degree of clustering of fines. It is founded that the distribution of fines is an important factor affecting the frost heave behavior of CGS. When fines content is low, a ‘skeleton gap structure’ is formed, the unexpected frost heave comes from the regional frost expansion in fines cluster, which squeezed adjacent aggregate skeleton, overcoming the interlock force of CGS; When fines content is high and a ‘suspend dense structure’ is formed, fines clusters connect with each other and dominate the frost heave behavior of CGS, resulting in continuous frost heave. Compared with the fines content, clustering ratio shows more clear linear relationship with frost heave ratio because the regional ununiform distribution of fines was considered. The proposed method is regarded more promising as it captures the detailed microstructure of coarse-grained soil, which has the potential to unveil the inner relationship between micro characteristics and macro performance.

A wheel wear model that considers the effects of temperature during tread braking was established on the basis of Archard's wear model. In the model, the temperature field of wheel tread was calculated using a numerical algorithm based on finite element method. The influences of temperature on the size of contact patch, division of adhesion/slip zone, wear coefficient and wear depth are studied by taking the effects of temperature rising on wheel material properties, such as elastic modulus, tensile strength and hardness, in consideration. The results show that the area of contact patch, wear depth and worn area increase with temperature caused by tread braking.

One of the problems with high-speed tracks in service is the damage of their cement asphalt mortar layer. The development of cement asphalt mortar damage can lead to gradually failure of the slab supporting. In fact, the cement asphalt mortar damage is uniform. The effect of cement asphalt mortar damage location seriously affects the dynamic behavior of the track and even operational safety. It is important to clearly understand the effect of cement asphalt mortar damage location on dynamics, which is helpful to direct track maintenance. In this study, a three-dimensional coupling dynamic model of a vehicle and a slab track is developed. Using the proposed model, the wheel–rail contact forces and the displacements and accelerations of the track are calculated to study the influences of the size and location of the damaged cement asphalt mortar zone on the dynamic characteristics of the track system.

Due to the complex geometry of a railway wheel, the shape of its modes may have to be properly considered to understand and predict the sound radiation directivity around it. A straight-web metro wheel is studied in this paper with a radial excitation. First, the near-field sound radiation at the natural frequencies is measured in experiments performed in a semi-anechoic room. The natural frequencies here were determined by modal test. The corresponding mode shape is calculated from a finite element (FE) model. A good agreement is found between measurements and simulations in terms of natural frequencies. Further, the relationship between mode shape and sound field near the wheel is determined. Second, a rotating semi-circular frame of radius 2 m centered at the center of the wheel is employed to measure the directivity pattern. The directivities of A-weighted total level, one-third octave bands and modes are recorded at a total of 667 measuring points. A radial mode (r, 2) and an axial mode (1, 2) are taken as examples to derive empirical equations of directivity pattern. A model developed by the boundary element (BE) method is found to simulate the directivity pattern more precisely than the derived equations.

To determine the mechanical properties of cement asphalt mortar (CAM) in the field, this contribution first presents a model to elaborate the relationship of strength to ultrasonic pulse velocity (UPV). Next, a mechanical test (compressive, flexural strength, and static modulus) and a UPV test are conducted on CAM at different ages to calibrate the proposed model. Finally, three fitted formulas are established based on the proposed model and verified with additional test results. Results suggest that a UPV test is a helpful method for estimating the mechanical properties of CAM in the field and can reach a high precision.

In order to study the settlement characteristic of ram-compacted piles with bearing base (RPBB), pile-raft composite foundation in high-speed railway, RPBB, and Cement Fly-ash Gravel (CFG) piles were tested and compared under the Beijing-Shanghai high speed railway. Using hydrostatic levels, the settlements of test sections were monitored over the long term. Results show, because of the formation conditions and the construction technology of RPBB, the reinforced depth of RPBB is limited. Consequently, the settlement of RPBB is bigger than CFG. It also takes longer to reach stable settlement for RPBB. In addition, based on measured and modified soil compression modulus, the thicknesses of compressed layers and the settlements were calculated using control strain method and control stress method. The calculated results using control strain method and modified soil compression modulus are reasonably close to the testing data. This proves that the modified soil compression modulus can improve the precision and reliability of the settlement estimation. This can overcome the limitations of existing Chinese code.