Heavy Axle Load Research Articles

Rutting and fatigue behavior of neat and nanomodified asphalt mixture with SiO2 and TiO2

Modern asphalt technology has adopted nanomaterials as an alternative option to assert that asphalt pavement can survive harsh climates and repeated heavy axle loading during service life and prolong pavement life. This work aims to elucidate the behavior of the modified asphalt mixture fracture model and assess the fatigue and Rutting performance of Hot Mix Asphalt (HMA) mixes using the outcomes of indirect Tensile Strength (IDT), Semicircular bend (SCB) and rutting resistance; for this, a single PG (64−16) nanomodified asphalt binder with 5 % SiO2 and TiO2 have been investigated through a series of laboratory tests, including: Resilient modulus, Creep compliance, and tensile strength, SCB, and Flow Number (FN) to study their potential role of these nanomaterials to improve the rutting characteristics and fatigue life of wearing asphalt mixture at different temperatures. The outcome of this study revealed the positive role of these materials in enhancing mixture IDT characteristics, fracture energy, and viscoelastic deformation component of crack propagation; on the other hand, at higher temperatures, the modified mixture exhibited a superior performance in reducing the permanent deformation of asphalt mixture with SiO2 followed by TiO2 as compared to neat asphalt mixture.

Istraživanje upotrebe betona i uvaljanog betona umjesto vruće bitumenske mješavine pri izgradnji kolnika autoceste u regijama s visokim temperaturama

This study examines the impact of temperature on the Cizre-Silopi highway’s bituminous hot mix asphalt (HMA) pavement, focusing on rutting issues exacerbated by high temperatures, which can reach up to 50 °C in the region. Despite rapid deterioration, especially under heavy truck traffic, the HMA pavement exhibited significant stability and flow resistance loss (approximately 52 %) between 20 and 50 °C. Concrete (C25) and roller-compacted concrete (RCC) pavements displayed minimal strength reductions under the same temperature conditions. These findings suggest that given the prevalent high temperatures and heavy axle loads in the region, concrete (C25) or RCC should be prioritised over HMA for pavement construction to enhance resistance against wheel rutting and temperature-induced damage. The observed rutting issues, even in the initial summer post-construction, underscore the urgency of adopting more temperature-resistant materials for road infrastructure under specified climatic conditions.

A Review on Developing HiPER Bituminous Mix Using Existing Binder and Modifier

Heavy commercial vehicles combined with high pavement temperatures induce higher stresses in base and surface courses layers resulting in premature pavement distresses such as rutting and cracking. Therefore, it's essential to create a binder that performs better in heat and is more elastic and rigid so that it may be utilized to bear heavy axle loads. For several years, efforts have been made in India and worldwide to develop new pavement materials and improve the specifications of paving mixes and their constituents. One of the emerging solutions is use of a French asphalt mix known as “Enrobé à Module Élevé (EME)” or “High-Modulus Asphalt (HiMA) Mix”. This mix offers unique performance characteristics such as high stiffness and durability, good resistance to permanent deformation and fatigue. Therefore, HiMA mixes also referred as High Performance (HiPER) Bituminous Mixes. EME mixes uses a hard grade binder (HB), have higher binder content and lower air voids. The unique challenges in preparation of HiPER bituminous mix is selection of bitumen, which shall be hard grade bitumen (stiffer than VG40). In India, binder stiffer than VG40 are not commonly available commercially. Also, selection of modifiers used to produce hard grade binders and to enhance the performance of the binders that provides higher resistance to permanent deformation as well as to cracking. The main focus of this study is to find potential of modifier(s) to develop hard grade binder (HB) and use of HB for the preparation of mixes at various binder content and evaluated with the target of producing HiPER bituminous mix. Marshall stability and indirect tensile strength (ITS) tests are conducted to assess the mixes for HiPER bituminous mix

Railway Accident Prevention using Ultrasonic Sensor with Microcontrollers

Railway Transport is indispensable in modern day life, both for business and private users. Nowadays, rail networks across the world are getting busier with trains travelling at higher speeds and carrying more passengers and heavier axle loads than ever before. The combination of these factors has put considerable pressure on the existing infrastructure, leading to increased demands in inspection and maintenance of rail assets. But nowadays, it is not that much safer as lot of accidents occur due to improper communication among the network like wrong signalling , worst weather condition, immediate route change, etc., The train driver doesn‟t get proper information on time and before time so that the hazardous condition can occur. While maritime and air transport are already benefiting from collision avoidance application based on infrastructure less communications. We propose this system to avoid train collision by using Ultrasonic Sensors to provide communication between trains and to avoid same track collisions

Performance of Geogrid-Reinforced Rubber-Coated Ballast and Natural Ballast Mix under Direct Shear Conditions

Rubber-coated ballast (RCB) is a new innovative ballast aggregate obtained by coating natural aggregates with recycled crumb rubber by using polyurethane binder. The objective of RCB is to reduce the ballast degradation, thereby reducing the deterioration of rail track geometry and also maintenance costs. Natural ballast; crumb rubber of sizes 0.4, 0.8, and 2 mm; Elastan polyurethane; and geogrid (triangular, 69 mm aperture size) were used in this study. The results of abrasion, impact value, and soundness tests show that RCB has a higher resistance to abrasion, impact, and weathering compared to natural ballast. Subsequently, the shear behavior and particle breakage of natural ballast, RCB, unreinforced, and geogrid-reinforced RCB–natural ballast mix was explored using the large-scale direct shear apparatus at different normal stresses and shearing rates (Sr). The test results indicate that due to rubber coating the peak friction angle (φ) of RCB samples reduces as compared to natural ballast. The reduction in φ of RCB samples is attributed to a change in surface texture. Moreover, 0.4-RCB (RCB made with rubber crumbs of size 0.4 mm) shows the least reduction in φ compared to 0.8-RCB and 2-RCB (RCB made with rubber crumbs of size 0.8 and 2 mm). It was further observed that with the increase in proportion of 0.4-RCB in geogrid-reinforced natural ballast both the peak friction angle and particle breakage (Bg) of ballast decreased significantly. The current study established the optimum content of 0.4-RCB to be mixed with geogrid-reinforced natural ballast to be in the range of 44%–53%.Practical ApplicationsThe problem of excessive degradation of ballast particles and the associated changes in the track geometry owing to the repeated application of heavy axle loads is addressed by coating the natural ballast with crumb rubber generated from waste tires. The rubber-coated ballast (RCB) is found to offer better abrasion, impact, and weathering resistance when compared to natural ballast. Moreover, it undergoes negligible particle breakage under direct shear conditions. The decrease in the extent of particle breakage helps in reducing the frequency of ballast replacement operations and hence tracks maintenance costs. Furthermore, RCB, when reinforced with geogrid, offers better shear strength than that of natural ballast alone. These observations imply that the tracks with geogrid-reinforced RCB can effectively reduce the risk of track instability.

Permanent Deformation Monitoring and Remaining Life Prediction of Asphalt Pavement Combining Full-Scale Accelerated Pavement Testing and FEM

Permanent deformation (rutting) is one of the typical failure modes of asphalt pavement with a semirigid base in high-temperature areas. To address issues of pavement structure deformation and remaining life prediction, a method of combining accelerated pavement testing and finite element (FE) simulation was proposed. A modified Burgers model considering creep parameter damage was obtained using strain monitoring data and laboratory test values, which was performed in the FE model to analyze rutting development. The results showed that high temperature and heavy axle loads greatly influenced rutting development: the tested road was loaded 360,000 times at high temperature, contributing 50% to accumulated rutting; rutting increased by 90.7% under the condition of 50% overload under high-temperature seasons from the simulated results. Then, the ratio of the bulge area to the depression area (KR) was proposed to define the rutting deformation mechanism. The KR analysis results illustrated that rutting development was a transition process from compaction rutting to flow rutting. Finally, the relationship between the action times of axle load in the tested and in-service roads was established based on the rutting equivalence principle. When the action times of axle load reach approximately 25 million times (insufficient remaining life) for the investigated Hu-Ning highway, necessary maintenance measures should be taken to treat rutting deformation.

Recycling COVID-19 health care wastes in bitumen modification: a case of disposable medical gloves.

Disposable medical gloves (DMGs) have long been used to mitigate the risk of direct exposure to diverse microorganisms and body fluids; hence, they are a critical weapon to protect patients and healthcare staff from infectious diseases. Measures to control the spread of COVID-19 have sparked the production of an excessive number of DMGs, most of which are eventually being disposed of in landfills. Untreated DMGs in landfills do not only pose a direct risk of transmitting coronavirus and other pathological germs but also pollute air, water, and soil dramatically. As a healthier alternative, recycling discarded polymer-rich DMGs into bitumen modification is considered to be a prospective waste management strategy applicable to the asphalt pavement industry. In this study, this conjecture is tested by examining two common DMGs - latex gloves and vinyl gloves - at four different percentages (1%, 2%, 3%, and 4% by weight). The morphological characteristics of DMG-modified specimens were inspected by using a high-definition scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDX). A wide range of laboratory tests including penetration, softening point temperature, ductility, and elastic recovery were undertaken to evaluate the impact of waste gloves on the conventional engineering properties of bitumen. Moreover, viscoelastic behavior and modification processing were studied by conducting the dynamic shear rheometer (DSR) test and the Fourier transform infrared spectroscopy (FTIR) analysis. Test results have revealed the outstanding potential of recycled DMG waste for modifying neat asphalt binder. More specifically, bitumens modified with 4% latex glove and 3% vinyl glove were seen as capable of superiorly withstanding permanent deformations caused by heavy axle loads at high service temperatures. Furthermore, it has been shown that 1.2 tons of modified binder would embed approximately 4000 pairs of recycled DMGs. This study shows that DMG waste can be used as a viable modifier, which would help open a new avenue for mitigating the environmental pollution arising from the COVID-19 pandemic.

Comprehensive performance evaluation of high embankments in heavy-haul railways using an improved extension model with attribute reduction algorithm

Effectively evaluating high-embankment deformation and stability is important for heavy-haul railway safety. An improved extension model with an attribute reduction algorithm was proposed for the comprehensive evaluation method. First, a hierarchical evaluation system for high embankments in heavy-haul railways was established using the attribute reduction algorithm, which includes the principal component analysis, maximum information coefficient, coefficient of variation, and improved Dempster-Shafer evidence theory. Furthermore, the improved extension model was used to evaluate high-embankment performance in heavy-haul railways. In this improved extension model, the combination weighting method, an asymmetric proximity function, and the maximum membership principle effectiveness verification were used. Finally, three high embankments in a Chinese heavy-haul railway were studied. The results illustrate that the main influencing factors for high-embankment performance in a heavy-haul railway are annual rainfall, annual temperature, and 21 other indicators. The performance of the three embankments is level III (ordinary), level II (fine), and level III (ordinary), respectively, indicating that these embankments have generally unfavourable performance. The three embankments’ performance matches field measurements, and the proposed method outperforms the Fuzzy-AHP method, cloud model, and gray relational analysis. This study demonstrates the feasibility of the proposed method in assessing the high-embankment performance under heavy axle loads.

Pavement Performance Investigation of Asphalt Mixtures with Plastic and Basalt Fiber Composite (PB) Modifier and Their Applications in Urban Bus Lanes Using Statics Analysis.

A new type of plastic and basalt fiber composite (PB) modifier, which is composed of waste plastic and basalt fiber using a specific process, was used for bus lanes to address severe high-temperature deformation diseases due to the heavy loads of buses. The dense gradations of asphalt mixture with a nominal maximum aggregate size of 13.2 mm (AC-13) and 19 mm (AC-20) were selected to fabricate asphalt mixtures. The impact of the modifier PB on the high-temperature rutting resistance, low-temperature crack resistance, and water damage resistance was investigated experimentally. The experimental results showed that adding the modifier PB could enhance the rutting resistance and water damage resistance of asphalt mixtures significantly while maintaining the low-temperature crack resistance. Then, PB-modified asphalt mixtures of AC-13 and AC-20 were employed into a typical pavement structure of a bus lane in Yangzhou city, China, and three types of designed pavement structures were proposed. On this basis, statics analyses of all of the designed structures were performed using the finite element method. The statics analyses revealed that, compared with the standard axle load, the actual over-loaded axle made the pavement structure of the bus lane suffer a 30% higher stress and vertical deformation, leading to accelerated rutting damage on the bus lanes. The addition of the modifier PB could make the pavement structure stronger and compensate for the negative effect caused by the heavy axle load. These findings can be used as a reference for the pavement design of urban bus lanes.

Investigation of usability of mineral fiber in stone mastic asphalt

Stone mastic asphalt (SMA) pavements were developed to prevent rutting, abrasion, and various pavement deteriorations and to increase the life of the superstructure. They certainly stand out with their high grain contact, stone-stone interlocking ability, and high bitumen ratio on heavy-traffic roads with heavy axle loads. This study aimed to investigate the effects of basalt fiber in different sizes, partly cellulose, and partly basalt fiber addition, on the drain down of the performance of bitumen and the changes in rutting performance as additives to stone mastic asphalt pavements. To determine the absorption performance of bitumen fiber additives, 19 mixtures were pre-pared and the Schellenberger drain down test was carried out. The results, including the witness mixture, showed that the Schellenberger test result was below the value specified in the motorway technical specification by a maximum of 0.3%. For the Hamburg wheel tracking test (HWTT) additive and witness mixtures were prepared at optimum bitumen ratios using a gyratory compactor. HWTT was applied to the mixtures numbered 1, 4, 10 and 14, which have the best the Schellenberger drain down performance, and the witness sample. As a result of the experiments, the highest rutting deformation was measured at the samples using 12mm basalt fiber at the rate of 0.2%. The lowest rut deformation was measured in samples containing 12mm basalt fiber at the rate of 0,3% and cellulose fiber at the rate of 0.2%. It was determined that the combined use of cellulose and basalt fiber mixture improved the resistance against rutting by 37%. As a result of the HWTT, it was determined that stone mastic asphalt mixtures with basalt and cellulose fiber additives were more resistant to rutting than the witness and basalt-only mixtures.

Influence of Type of Sleeper–Ballast Interface on the Shear Behaviour of Railway Ballast: An Experimental and Numerical Study

The shear resistance at the sleeper–ballast interface of a ballasted track is an important contributor in maintaining track stability under faster and heavier axle loads where the ballast undergoes significant lateral sliding. Different types of sleeper–ballast interfaces based on the type of sleeper arrangements, such as concrete sleepers, timber sleepers, and under sleeper pads (USPs) attached to the concrete sleepers influence the lateral stability of railway tracks. Therefore, in this study the shear and degradation behaviour of ballast at concrete–ballast, timber–ballast, and USP–ballast interfaces were examined in the laboratory using large-scale direct shear tests under 60 kPa normal stress. The use of waste materials in the construction of civil infrastructure is gaining a lot of interest in the engineering community. Therefore, in addition to commercial USPs manufactured using raw materials, recycled USPs manufactured from granulates of end-of-life rubber tyres were also tested in this study. The discrete element modelling (DEM) approach was used to predict the shear behaviour of ballast at 30, 90, 120, 150, and 180 kPa normal stresses. The bonded particle model (BPM) was adopted in the DEM to simulate the effects of particle breakage during shearing. The results exhibited that both commercial and recycled USPs significantly improve the shear resistance at the sleeper–ballast interface while reducing particle degradation compared to concrete and timber sleeper interfaces.

Prediction Method of Heavy Load Wheel/Rail Wear Mechanical Properties Based on GA-BP Hybrid Algorithm

Due to its large axle load and high-density operation mode, heavy haul transportation has greatly improved the cargo transportation capacity, and is receiving unprecedented attention from all countries in the world. Since the development of heavy haul freight transport in China, wheel rail wear has been paid much attention, especially the use of heavy axle load locomotives on upgraded heavy haul lines, which makes reducing wheel rail wear and damage become a technical problem to be solved urgently. Considering that there are too many mechanical parameters involved in the prediction of heavy load wheel rail wear mechanical properties, the prediction accuracy is reduced. Therefore, this paper proposes a method based on GA-BP hybrid algorithm to predict the mechanical properties of heavy load wheel/rail wear. Hertz contact theory is used to simplify the wheel rail contact relationship, and the wheel rail contact model is established. According to the wheel/rail contact model, the expressions of heavy load wheel/rail in the case of vertical, horizontal, direction and gauge irregularity are analyzed, and based on this, a mechanical model of heavy load wheel/rail wear is established. In order to solve the problems of slow convergence speed and easy to fall into local optimum of BP neural network in the prediction of heavy load wheel/rail wear mechanical properties, the global convergence of genetic algorithm is used to optimize the BP network. According to the obtained mechanical parameters of heavy load wheel/rail wear, the mechanical parameters are input into the optimized model, and the relevant prediction results are output. So far, the research on the prediction method of heavy load wheel/rail wear mechanical properties based on GA-BP hybrid algorithm has been realized. The experiment is designed from three aspects of wear degree, hardness and tensile strength, and compared with the measured value, reference [4] method, reference [5] method and reference [6] method to verify the effectiveness of the proposed method. The experimental results show that the predicted results of wear degree, hardness and tensile strength by this method are closer to the measured results. It is proved that the proposed method has higher prediction accuracy and better practical application effect.

Development of FWD based hybrid back-analysis technique for railway track condition assessment

Track substructure is a key component of the railway transportation system. Similar to the built environment of other surface transportation systems, track substructures are subjected to aging and deterioration. This, frequently leads to the failure and collapse of the transportation systems, resulting in the imposition of costly repairs and maintenance. At the same time, the emergence of high-speed trains and heavier axle loads, together with a need for sustainable designs, has put additional pressure on asset owners. It has been shown that frequent condition assessments of railway substructures can considerably reduce the overall annual maintenance costs. Furthermore, limited knowledge of the substructure condition leads to the employment of inefficient, time-consuming, and expensive maintenance actions. Therefore, development of time- and cost-efficient techniques to frequently monitor existing railway track substructures is vital. The falling weight deflectometer (FWD) is recognised as an effective non-destructive test used to survey ballasted railway substructures through a back-analysis process. This paper presents a novel hybrid back-analysis technique that includes an artificial neural network (ANN) and genetic algorithm (GA) to estimate the substructure layer moduli of railway tracks using FWD testing data. To this aim, firstly a dynamic finite element (FE) model was developed and validated against experimental data from the literature. This FE model then were employed to generate a reliable dataset to train the ANN. In the next step, GA was employed as an optimisation tool within the back-analysis technique/framework to optimise the layer moduli (the ANN’s input). A comparison study was performed to evaluate the performance of the developed technique. The results of this comparison revealed excellent performance and robustness of the developed technique.

Getting freight trains back on track–How railway undertakings, infrastructure owners and regulators can navigate the main dilemmas in freight business to drive sustainable growth

Rail freight reportedly makes for an environmentally friendly means of transport. It also has significant potential for making a lucrative business, a stark contrast to rail passenger transport. Yet in Europe rail freight has long been displaced over its road equivalent and grown at rates inferior to overall land goods freight. Sustainable, profitable rail freight operations depend not only on goods volume, travel distance and pricing, but further on other key aspects permeating goods transportation by rail. Our research demonstrates that the choice for railway undertakings, infrastructure owners, and regulators alike, is in practice a complex one as depending on many, often competing factors. In fact, the key questions usually raised v.a.v. rail freight operations may be summed up to the following: (a) Mixed passenger and freight train operation or dedicated train corridors? (b) Conventional or heavy axle loads for freight trains? (c) Unitized wagonload or integrated trainload services? (d) Dangerous goods land shipping by rail or road? (e) Autonomous or manned freight train operation? Despite many individual contributions in the field, there is currently no single framework addressing the problem holistically. This paper breaks down what is seemingly a hard-to-balance decision-making process for rail freight players. It records and analyzes the forces and dynamics behind the dilemmas above and allows to: provide those partaking in the decision-making process with a robust framework identifying the key drivers behind sustainable rail freight growth; help them individually and collectively make more sound decisions regarding rail operations as a whole–including, in particular, strategic decisions regarding policy and/or investment; and, eventually, to enable them to craft and pursue viable, sustainable transport and business strategies. The research is underpinned by literature data review.

Optimization of Rigid Pavement

Abstract: The construction of national highways nowadays is preferred by using rigid pavements as they are durable, have the high flexural strength, can withstand different heavy axle loads, higher design span and moreover they can sustain adverse environmental conditions more efficiently with better ease. Considering their remarkable qualities, the national highways should be constructed by providing the tied shoulders and dowel bars in the transverse joints because they can better resist the fatigue accumulations on the slab with minimum safe thickness which ultimately leads to reduction in the cost of making the road efficiently. In this chapter, for the two different CBR conditions (CBR-9 & CBR-10) and three concrete mix design grades namely (M40, M45, M50) along with different shoulders and dowel bars conditions, the trial methods were carried on the IRC58 Software for bottom-up cracking fatigue analysis for single and tandem axle for day-time (6 hour) traffic and positive temperature differential and top-down cracking fatigue analysis for single, tandem and tridem axle for day-time (6 hour) traffic and negative temperature differential for evaluating the flexural stresses and cumulative fatigue damage values for the slab having dimensions of (3.5m x 4.5m). For determining the safe design, different trails on the thickness parameter of the slab were being adopted so as to get the cumulative fatigue values of BUC and TDC for single, tandem and tridem axles less than one. The results obtained showed that for which grade and CBR condition, the values of flexural stresses and cumulative fatigue damage determined is maximum. It was concluded that the rigid pavements should be constructed by using higher grades like M45 and M50 as the fatigue stresses and cumulative fatigue damage values due to variable single, tandem and tridem axle load repetitions obtained are less as compared to M40 grade. Keywords: California Bearing Ratio (CBR); Bottom Up Cracking (BUC); Top Down Cracking (TDC); Mix Design Grade Value (M), Indian Road Congress (IRC); Flexural Stresses; Cumulative Fatigue Damage(CFD)

Evaluating the Service Performance of Heavy Axle Load Ballasted Railway by Using Numerical Simulation Method

To evaluate the service performance of the track substructure of heavy axle load (HAL) railway transportation, an inverse analysis was performed to estimate the resilient modulus values of the track substructure, based on the deflection data obtained from light falling weight deflectometer testing. Subsequently, a three-dimensional finite element model was developed to simulate the effect of the train speeds (v) and axle loads (F) on the typical dynamic responses in the railway track system. The results convincingly indicated that increasing v or F can amplify the track vibration. Finally, a critical stress ratio method was adopted to evaluate the service performance based on the numerical results. A recommended range of v and F was determined to maintain the long-term stability of the HAL railway line. The findings can provide guidance for designing the track and maintenance plans to avoid track support failures and ensure track infrastructure resiliency.

The Possibility of Minimizing Rutting Distress in Asphalt Concrete Wearing Course

The excessive permanent deformation (rutting) in asphalt-concrete pavements resulting from frequent repetitions of heavy axle loads is studied in this paper. Rutting gradually develops with additional load applications and appears as longitudinal depressions in the wheel path. There are many causes of the rutting of asphalt roads, such as poor asphalt mixing and poor continuous aggregate gradation. All factors affecting the mixture resistance to permanent deformation must be discussed, and all must be properly considered to reduce the rutting propensity of asphalt-aggregate mixtures. In this study, several mixtures were produced with the most common techniques in rutting resistance (using the most effective additives for each mixture), and their performance was compared with the (conventional) mixture currently used in Iraq. The tests focused on the asphalt-concrete mixture for wearing courses. Different mixtures types were tried, namely, dense hot asphalt mixture (HMA) with two different asphalt contents (4.7% and 5.3%), Open-Grade Friction Course (OGFC) mixture, Stone Mastic Asphalt (SMA) mixture, and Beton Bitumineux a Module Eleve (BBME). The modifiers included natural Sisal Fibers (SFs), Carbon Fibers (CFs), and mineral filler (hydrated lime, HL). Marshall test was carried out to find stability and flow values. Rutting was evaluated by the repeated load test for cylindrical specimens under two temperatures (40°C and 60°C) to obtain the permanent deformation parameters. The parameters were used as input to the VESYS 5W software to evaluate the rut depth during different times of design life under 7×10^6 Equivalent Single Axle Loads (ESALs). The results of the selected mixtures were compared with the mixture designed in the laboratory dense gradation mix Job-Mix Formula (JMF)) within the limits of the Iraqi specification (SCRB,2003). Manipulation of the aggregate gradation that is customary in the implementation of the local mixture showed that the best performance regarding rutting resistance was exhibited by JMF, which decreased the rut depth at 40°C and 60°C by 21.63mm and 44.304mm respectively, in comparison with the conventional mixture. Changing the aggregate gradation of the local mixture gives better performance in rutting resistance without additives or changing the percentage of asphalt, at the same cost.

Ground vibration from freight railway: environmental impact and potential mitigation measure at propagation path.

The freight train-induced vibrations and noise generate increasing environmental problems owing to its heavier axle loads and longer pass-by duration. To develop useful mitigation measures, the vibration characteristic induced by this type of rail transportation needs to be better learned. In the present work, firstly, the in situ measurements were carried out on two railway lines which were used for mixed freight and passenger trains. Both the track vibrations and ground vibrations resulted from different train types were measured and compared. Then, based on the dominant frequencies of ground vibrations from experimental results, the mitigation measure of periodic piles was proposed as a mitigation measure by impeding propagation. The periodic theory of solid-state physics was introduced and three-dimensional (3D) finite element (FE) simulation was employed to analyse the vibration reduction performance of periodic piles, while the attenuation zone (AZ) of the piles was also calculated. The measurement results indicate that the freight train can generate a larger level of vibrations on both the track structure and ground at the near field, especially below 10Hz. Even though the speed of freight trains is as low as 40-55km/h, the vibration exposure level (VEL) is higher than normal passenger trains (80-90km/h) and EMU trains (120km/h). The simulation results show that the proposed solution of installing periodic piles at the propagation path raises the positive influence on vibration reduction.

Mechanistic approach to predict service life of flexible pavements subjected to heavy traffic loads

Operation of specialty trucks with heavy axle and wheel loads can result in significant loss of service life of pavements. This study aimed to propose a mechanistic framework for the characterisation of the remaining service life (RSL) of pavements with heavy truck traffic operations. A field testing plan was devised to collect relevant information on traffic and pavement structural properties in ten heavily trafficked roadways in Texas. Portable Weight-in-Motion devices and Non-Destructive Testing were deployed to collect site-specific axle load spectra and pavement layer configurations, respectively. Furthermore, a novel methodology was developed for the mechanistic quantification of the loss of pavement life due to the recent changes in traffic characteristics, considering demanding loading conditions and environmental effects. The results underscored the importance of roadway type and its role in damage assessment procedures. Further comparison of the analysed results, using the developed framework, with field measurement records also showed sound agreements.

Dynamic Performance Analysis of a High-Speed Railway Bridge Under Train Actions Using Operational Modal Parameters

For high-speed railway bridges in operation, it is necessary to reveal the coupling dynamic performance of train–bridge systems in order to avoid extreme vibrations, which are not conducive to bridge safety. With the opening of long-span heavy-haul and complex-type bridges to traffic, the train–bridge interaction can hardly be explained by a mature and unified theory. Notably, field testing and monitoring analysis have become popular in tracking the dynamic performance of train–bridge systems. The vibration of railway bridges depends on the train-track configuration and the inherent characteristics of bridges. The inherent characteristics of bridges, which are reflected by the modal parameters, are extracted via operational modal analysis in this paper. In addition, the modal characteristics of bridges while the train is passing through are also investigated to explain the coupling dynamic effect with the help of the train configuration. Considering that the measured vibration responses are seriously polluted by non-white noise or excitation, the variational mode decomposition (VMD) technique is developed to extract the state-driven vibrations for modal analysis. Since VMD is a univariate technique that hardly ensures that the weak component can be obtained from each measuring channel, the multi-channel variational mode decomposition (MVDM) technique is extended in this paper. The field monitoring data of a high-speed railway bridge are taken for modal identification and vibration analysis. The results show that the weak structural modes can be tracked, even though the forced vibrations due to the passage of regularly spaced axles are dominant. In addition, the dynamic effects in train-induced vertical vibrations of bridges are closely related to the train speed, heavy axle loads and the span length.