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Virtual coupling of railway trains is an emerging technology that has the potential to significantly increase railway operational efficiency by reducing the train following distance from absolute braking distances to relative braking distances. Current research in this topic is mainly focused on passenger trains and uses distance-based headways. This paper studied virtual coupling for heavy haul freight trains and demonstrated that the distance headway scheme was challenging and sometimes impractical for heavy haul trains to achieve virtual coupling. A time-based headway scheme was then proposed to set the follower train to be a certain time behind the schedule of the leader train rather than a distance headway. The time-based headway required the follower train to reproduce the leader train's operational status at the same track location. This also allowed the follower train to copy any optimized train driving strategies from the leader train. Demonstrative simulations were carried out without the consideration of communication errors and train localization errors. The results show that a conventional distance headway simulation had maximum distance and speed errors of 716 m (36%, reference 2 km) and 24 km/h (66%, reference 36 km/h), respectively. A time-based headway simulation reduced the maximum distance and speed errors to 0.07 m (0%, reference 2 km) and 0.1 km/h (9%, reference 1.18 km/h), respectively. [ABSTRACT FROM AUTHOR]

The improvement in component service life and railway service reliability has been viewed from an environmental perspective. Delays and train accidents carry enormous costs and greenhouse gas (GHG) emissions potential due to the increased fuel burn and the need to replace heavy equipment prematurely. The use of higher-performance materials, more efficient vehicle design, and modern technology by Canadian railways to reduce service interruptions are presented. Their resulting cost savings not only can provide financial incentives for the continuous optimization of asset utilization but can also lead to significant contributions to the decarbonization of the railway industry. The authors have estimated a total reduction of 2.4 kt-CO2e per year in embodies carbon emissions due to life extensions of wheelsets compared to 2017 levels on a Class 1 railway. System-wide, the rail life extension has resulted in a saving of 8.1 kt-CO2e per year compared to 2017 for the same railway. Compared to 2004, the Canadian railway industry has achieved an annual reduction in embodied carbon emission of 6.7 Mt-CO2e from the reduction in mainline derailments. [ABSTRACT FROM AUTHOR]

Purpose – This research addresses the diverse characteristics of existing railway steel bridges in China, including variations in construction age, design standards, structural types, manufacturing processes, materials and service conditions. It also focuses on prominent defects and challenges related to heavy transportation conditions, particularly low live haul reserves and severe fatigue problems. Design/methodology/approach – The study encompasses three key aspects: (1) Adaptability assessment: It begins with assessing the suitability of existing railway steel bridges for heavy-haul operations through comprehensive analyses, experiments and engineering applications. (2) Strengthening: To combat frequent crack defects in the vertical stiffener end structure of girder webs, fatigue performance tests and reinforcement scheme experiments were conducted. These experiments included the development of a hot-spot stress S-N curve for this structure, validating the effectiveness of methods like crack stop holes, ultrasonic hammering and flange angle steel. (3) Service life extension: Research on the cruciform welded joint structure (non-fusion transfer type) focused on fatigue performance over the long life cycle. This led to the establishment of a fatigue S-N curve, enhancing Chinese design codes. Findings – The research achieved several significant outcomes: (1) Successful implementation of strengthening and retrofitting measures on a 64-m single-span double-track railway steel truss girder on an existing heavy-duty line. (2) Post-reinforcement, a substantial 26% to 32% reduction in live haul stress on bridge members was achieved. (3) The strengthening and retrofitting efforts met design expectations, enabling the bridge to accommodate vehicles with a 30-ton axle haul on the railway line. Originality/value – This research systematically tackles challenges and defects associated with Chinese existing railway steel bridges, providing valuable insights into adaptability assessment, strengthening techniques and service life extension methods. Furthermore, the development of fatigue S-N curves and the successful implementation of bridge enhancements have practical implications for improving the resilience and operational capacity of railway steel bridges in China.

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Mixed freight trains have more diversified vehicle characteristics and train combination modes than unified freight trains, so it is more difficult for mixed freight trains to predict the accident caused by longitudinal impulse. At present, train dynamics theories and numerical simulation methods have been increasingly used to reduce longitudinal train impulse and decrease freight wagon instability. According to these research experiences, this paper focuses on the marshalling modes of mixed freight trains and their effects on the longitudinal in-rain forces. For this purpose, an advanced simulation model for mixed freight trains was developed and several typical mixed marshalling modes were designed and simulated. The results indicate that, for the mixed train including empty and loaded wagons, empty wagons should be arranged at the tail of the train and should avoid being marshalled together. For the mixed train including marshalled wagons with various actual live loads or nominal axle loads, heavier wagons should be centrally arranged in the front part of the train, and meanwhile marshalled wagons should avoid being sorted by weight in the concave and ascending distribution mode. For the mixed train including marshalled wagons with various body types, container flat wagons and oil tank wagons should be arranged as much as possible in the front of the other wagons. [ABSTRACT FROM AUTHOR]

A train–tunnel–surrounding rock numerical model was established by using ABAQUS to analyze the dynamic response of a heavy-haul railway tunnel in hard rock, quantify the influence of the train axle load on the tunnel dynamic response and determine its potential vulnerable position. The results suggested that: Under the 30 t train load and surrounding rock pressure coupling, the maximum principal stress caused by rock pressure was 1.27 MPa, located at the bottom of the structure below the side drain; the maximum dynamic response of the tunnel structure and base rock was located directly below the rail. The lower part of the side drain and rail was the vulnerable position in the tunnel bottom structure, and the probability of base disease under the rail may be higher than that in soft-rock tunnels, for it has a greater dynamic response and thinner structure compared to a soft-rock tunnel. The maximum principal stress amplitude of the tunnel structure and base rock were 129.3 kPa and 43.0 kPa, respectively. When the axle load increased by 1 t, the dynamic amplitude of the structure's maximum principal stress increased by about 4.14 kPa, and the base rock's maximum principal stress increased by about 1.33 kPa. The rock pressure was not negligible in the dynamic analysis of the railway tunnel, and the dynamic response of the tunnel bottom structure and base rock will decrease, obviously, when the rock pressure is ignored. [ABSTRACT FROM AUTHOR]

A train–tunnel–surrounding rock numerical model was established by using ABAQUS to analyze the dynamic response of a heavy-haul railway tunnel in hard rock, quantify the influence of the train axle load on the tunnel dynamic response and determine its potential vulnerable position. The results suggested that: Under the 30 t train load and surrounding rock pressure coupling, the maximum principal stress caused by rock pressure was 1.27 MPa, located at the bottom of the structure below the side drain; the maximum dynamic response of the tunnel structure and base rock was located directly below the rail. The lower part of the side drain and rail was the vulnerable position in the tunnel bottom structure, and the probability of base disease under the rail may be higher than that in soft-rock tunnels, for it has a greater dynamic response and thinner structure compared to a soft-rock tunnel. The maximum principal stress amplitude of the tunnel structure and base rock were 129.3 kPa and 43.0 kPa, respectively. When the axle load increased by 1 t, the dynamic amplitude of the structure’s maximum principal stress increased by about 4.14 kPa, and the base rock’s maximum principal stress increased by about 1.33 kPa. The rock pressure was not negligible in the dynamic analysis of the railway tunnel, and the dynamic response of the tunnel bottom structure and base rock will decrease, obviously, when the rock pressure is ignored.

Heavy haul transportation (load over 30 tons/axle), as well as the axle load, has been more and more used in Brazil and worldwide. The stress generated in the wheel-rail contact with loads up to 30 tons/axle is around 760 MPa, which causes premature wear and cracks of conventional wheels (AAR (Association of American Railroads) class C). Microalloyed wheels are fundamental on heavy haul transport, whose main function is to combine high hardness, ductility, and yield strength of the material in order to prevent shelling. The main purpose of this research is to develop a new microalloyed wheel steel with niobium addition that meets all the requirements of the AAR class D material with mixed microstructure composed of pearlite and bainite. The 0.71C/0.020Nb steel developed in this study (Nb material) for railroad achieved the standards required for AAR class D in all mechanical properties, with fracture toughness higher than the usual vanadium microalloyed steel used in comparison. The Continuous Cooling Transformation (CCT) diagram showed the presence of bainite even at very low cooling rate, in the range between 0.3 - 2 °C/s. These cooling rates to form bainite are much lower than those observed in other steels with similar composition.

This article focused on the microstructure characterization and residual stress measurements of the flange from classes D and C railway wheels (called 7D and 7C steel, respectively) to contribute with the residual stress level on new forged wheels flange area. A correlation with the hardness was conducted. The residual stress was measured in three points of the flange using the x-ray diffraction technique, and the microstructure characterization on SEM microscopy. We found the 7C steel has fine pearlite and ferrite microstructures, and 7D steel has degenerated pearlite and bainite microstructures. In the 7D steel, the compressive residual stress in the flange region was higher than in the 7C steel, which is related to the presence of bainite on the microstructure. There was a correlation between the hardness and residual stress value. The knowledge of the residual compression stress level is important for safety train wheels operation. The traction stress generated by the brake system on the wheel is attenuated by residual compression stress. [ABSTRACT FROM AUTHOR]

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects.

The Haoji railway in China is the longest heavy haul railway in the world, including 235 tunnels located along the 1837 km railway. With the increasing axle load of the new line and the basal deterioration of the existing heavy haul railway in China, studying the fatigue performance of the newly designed tunnel structure is essential. To study the coupling effect of the surrounding rock pressure and 30 t axle load train, in this study, we combined three-dimensional numerical simulation and three-point bending fatigue tests to investigate the fatigue performance of the basal structures. The results of numerical simulation indicate that the center of the inverted arch secondary lining is the position vulnerable to fatigue in the lower tunnel structures; the surrounding rock pressure performance exerts a stronger influence on the stress state of the vulnerable position than the dynamic train loads. The S–N formula obtained from the experiment showed that the fatigue life of tunnel bottom structures decreases with increasing surrounding rock pressure and dynamic load. In typical grade V surrounding rock and 30 t axle loads, fatigue failure will not occur in the newly designed tunnel bottom structures within 100 years if bedrock defects are lacking and pressure of surrounding rock is not excessive. [ABSTRACT FROM AUTHOR]

This paper presents a closed loop simulation model that represents the mining logistics chain of the Vitória Minas Railway (VMR), Brazil. The simulator includes the loading process, circulation of loaded trains, unloading of ores for external and internal markets and the distribution of empty trains for new loads. General cargo and passengers trains are also included in the model, which, along with the queues formed in the circulation and the preventive and corrective maintenance of rolling stock, tracks and equipment, interfere with the transportation of iron ore. The primary objective of the iron ore transport is to meet the daily loading and unloading schedules and minimize queues by maximizing the operations at the loading and unloading points. The VMR simulator developed uses macro-mesoscopic approach with Monte Carlo simulation. To validate the simulator, we used actual data of the railway and compared with reality. We obtained a very good adhesion to the value of 2.9% for the validation scenario (Scenario 1) and 3.4% for the scenario with reducing the number of lots of wagons (Scenario 2). We concluded with this simulation that it is possible to reduce the number of GDE wagons without reducing the current level of productivity of the rail system.

In this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavyhaul locomotive. For wear calculations, a methodology based on Archard's wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000 km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out. [ABSTRACT FROM AUTHOR]

The main task for heavy haul railway operators is to reduce the cost of exported minerals and enhance the long-term viability of rail transport operations through increasing productivity by running longer and heavier trains. The common opinion is that this is achievable by means of implementation of high adhesion locomotives with advanced AC traction technologies. Modern AC high adhesion locomotives are very complex mechatronic systems and can be designed with two alternative traction topologies of either bogie or individual axle controls. This paper describes a modelling approach for these two types of AC traction systems with the application of an advanced co-simulation methodology, where an electrical system and a traction algorithm are modelled in Matlab/Simulink, and a mechanical system is modelled in a multibody software package. Although the paper concentrates on the analysis of the functioning for these two types of traction control systems, the choice of reference slip values also has an influence on the performance of both systems. All these design variations and issues have been simulated for various adhesion conditions at the wheel–rail interface and their influence on the high traction performance of a locomotive equipped with two three-axle bogies has been discussed. [ABSTRACT FROM PUBLISHER]

Energy saving achieved by application of top of rail (TOR) friction modifier (FM) in heavy haul are modeled, and the effects of curve radius and rail profile on the energy saving are discussed. A vehicle model for a C70 freight car running on the track of a heavy haul line was established. The coefficient of friction and Kalker coefficient were adjusted to simulate the creepage/force relationship when the TOR FM is applied to the wheel/rail interface. Friction work is used to represent the energy dissipation due to wheel/rail creepage. Energy saving achieved by applying TOR FM was calculated. The energy saving was studied under different operating conditions, and the effects of track curve radius and rail profile were studied. It is found that the curve radius of the track has significant influence on the energy saving. The energy saving was also found to behave differently on new and worn rails. The dramatic increase of lateral creepage on new rail when FM is applied and the decrease of the difference of wheel rolling radius when the rail profile changes from new to worn were found to be the main reasons that cause the difference. [ABSTRACT FROM AUTHOR]

This paper presents a closed loop simulation model that represents the mining logistics chain of the Vitória Minas Railway (VMR), Brazil. The simulator includes the loading process, circulation of loaded trains, unloading of ores for external and internal markets and the distribution of empty trains for new loads. General cargo and passengers trains are also included in the model, which, along with the queues formed in the circulation and the preventive and corrective maintenance of rolling stock, tracks and equipment, interfere with the transportation of iron ore. The primary objective of the iron ore transport is to meet the daily loading and unloading schedules and minimize queues by maximizing the operations at the loading and unloading points. The VMR simulator developed uses macro-mesoscopic approach with Monte Carlo simulation. To validate the simulator, we used actual data of the railway and compared with reality. We obtained a very good adhesion to the value of 2.9% for the validation scenario (Scenario 1) and 3.4% for the scenario with reducing the number of lots of wagons (Scenario 2). We concluded with this simulation that it is possible to reduce the number of GDE wagons without reducing the current level of productivity of the rail system. [ABSTRACT FROM AUTHOR]

Locomotives for the iron ore line in northern Sweden and Norway have a short wheel life. The average running distance between two consecutive wheel turnings is around 40,000 km which makes the total life of a wheel around 400,000 km. The main reason of the short wheel life is the severe rolling contact fatigue (RCF). The train operator (LKAB) has decided to change the wheel profiles to get a better match with the rail shapes in order to decrease the creep forces leading to RCF. Two wheel profiles optimised via a genetic algorithm were proposed. They have, however, not been analysed for long term wear development. There is a risk that the optimised profiles might wear in an unfavourable way and after a while cause even higher RCF or wear than the original one. This study predicts wheel profile evolution using the uniform wear prediction tool based on Archard’s wear law. RCF evolution on the surface of the wheel profiles is also investigated. The impact of wear on polishing the wheel surface and avoiding the RCF cracks to propagate is considered via introducing a correction factor to the calculated RCF index. Traction and braking are also considered in the dynamic simulation model, where a PID control system keeps the speed of the vehicle constant by applying a torque on the loco wheels. The locomotives are also equipped with a flange lubrication system, therefore the calculations are performed both for lubricated and non-lubricated wheels. The simulation results for the wheel profiles currently in use, which are performed to validate the model and the simulation procedure, show a good agreement with the measurements. It is also concluded that the lubrication system partly does not perform as expected. Comparison between the proposed optimised profiles for their long term behaviour suggests that one of them produces less RCF and wear compared to the other one. [ABSTRACT FROM AUTHOR]

Purpose – This paper aims to present the theoretical and experimental investigation of the temperature of high speed and heavy haul tilting pad journal bearing. Design/methodology/approach – The bearing is 152.15 mm in diameter with three slenderness ratios (L/D) and three clearance ratios. The equations that govern the flow and energy transport are solved by the finite difference method, and the experimental tests are conducted in a test rig of high speed and heavy haul tilting pad journal bearing. The shaft speed ranges from 3,000 to 16,500 r/min (the highest linear-velocity equals 131.4 m/s), and the three static loads are 10, 20 and 30 KN. Findings – The comparisons between numerical results and experimental results show better correlations. It is shown in the theoretical and experimental results that the temperature increases with static load and shaft speed and decreases with clearance ratio and L/D. Originality/value – The theoretical models presented in this paper can be used to predict the temperature of tilting pad journal bearing when the shaft’s linear velocity is up to 130 m/s. [ABSTRACT FROM AUTHOR]

In order to alleviate the wear of heavy-haul wheel/rail materials, the wear experiments of wheel/rail rollers undergoing laser quenching were carried out using rolling-sliding testing apparatus. The results indicate that laser quenching produces a hard martensite layer with a certain depth. The improvement of wear resistance of materials resulting from laser quenching markedly decreases the wear volume of wheel/rail rollers. The maximal decrease rate of wear volume of wheel and rail materials is about 92.9% and 89.5%, respectively. Furthermore, the worn surfaces of wheel/rail rollers present different surface morphology and damage mechanisms due to difference of hardness matching. When the surface hardness of wheel/rail rollers undergoing laser quenching is high, the spalling damage and adhesion wear are dominating. When a single wheel or rail roller undergoes laser quenching, the damage mechanism of wheel and rail rollers are significantly different. According to the severe wear region of the heavy-haul wheel/rail, it is proposed that the rail side and wheel flange may undergo laser quenching treatment for alleviating wear of heavy-haul wheel/rail materials. However, further work should be carried out for clarifying the fatigue characteristic of wheel/rail with laser quenching. [ABSTRACT FROM PUBLISHER]

This paper presents an analysis of the influence of materials that can be present in the so-called “third-body layer” at the wheel/rail interface on curving forces generated in heavy haul operating conditions. The third-body layer is the interfacial layer whose shear properties determine the bulk frictional characteristics that emerge in wheel/rail contact. It is often postulated that precipitation (rain) provides an effective form of lubrication at the wheel tread/rail head interface, reducing curving forces and corresponding wear. The postulate is explored through the analysis of lateral and vertical force data collected under a wide range of environmental conditions in full-scale revenue service. The effects of precipitation are rigorously explored and compared with the effects of top of rail friction modifiers, which are intentionally introduced into the third-body layer.This paper originated from the 2011 IHHA Conference. [ABSTRACT FROM AUTHOR]

Shuohuang Railway (SHR) is one of the major coal carriers in China, with a total network length of 590 km running from Shenchi to Huanghua. Significant increases in annual operating tonnage have generated accelerated rail wear and rolling contact fatigue (RCF) growth problems for many sharper/lower radius curves. In order to address these rail problems, SHR is interested in the state-of-the-art total friction management (TFM) technology currently deployed by some North American heavy haul freight railroads and is evaluating the impact of TFM via a field trial at SHR’s Yuanping subdivision. This paper presents an evaluation of the effect of TFM, which includes both wayside gauge face lubrication and wayside application of a thin film top of rail friction modifier on control of lateral forces, rail wear and RCF. [ABSTRACT FROM AUTHOR]

A finite element model for the process of a wheel passing a crossing is presented. In the dynamic model, one wheel, the wing rails and the crossing nose (frog) are modelled. The bogie, the complete wheel set and the support of the crossing are represented as a system consisting of masses, springs, dampers and friction-generating elements. The rolling/sliding behaviour between the wheel and crossing is studied using the proposed model. Due to the conical shape of the wheel tread and multiple contacts between the wheel and the crossing parts, sliding occurs during the transition of the wheel from the wing rail to the crossing nose or vice versa. At the same time, an impact occurs that produces high contact forces. The parameters of the model are the train speed and passing direction, the wheel and the crossing geometry, the axle load and the support of the crossing. In this paper, the crossover process is studied for high axle loads and compared with results of simulations using a normal axle load. Further parameters are three train velocities, both directions of passing and different crossing materials. The loading of the crossing nose is calculated for all cases (axle load, train speed and direction) and materials. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue on any railway system has a significant impact on the safety and efficiency of the operation. This is especially true for heavy haul railways where higher axle loads and demands for higher throughput have, over the years, challenged the limits within the wheel/rail interface. The objective of this paper is to present a methodology to manage this stress state using a detailed wheel/rail contact stress analysis. Based on the results of recent wheel profile and rail profile surveys, a kinematic wheel/rail contact analysis is performed to identify and eliminate profiles that cause high stresses. The results show that the current hollow wear criterion is effective, but that an alternative or additional criterion based on the gauge side false flange gradient or the calculated peak contact stress values can further reduce the stress state. Within the wheel and rail profile combinations investigated, the contact stresses were largely independent of the transverse profile of the high rail. [ABSTRACT FROM AUTHOR]

Abstract: The rolling tests of railway rail were performed using a JD-1 wheel/rail simulation facility on basis of Hertz Contact Theory. The wear and fatigue mechanism of rail rollers at different speed and axle load was investigated in detail by examining wear volume and wear scar using optical microscopy (OM) and scanning electronic microscopy (SEM). The results indicate that with speed increasing, the wear volume of rail is reduced, as well as many oblique cracks initiate and contact fatigue becomes severer; with axle load increasing, the plastic deformation becomes severer, increasing of wear volume and fatigue failure become slight due to removing of micro-cracks partly. For the rail material with a higher hardness, the wear volume is less and plastic deformation layer is thinner after the rolling test. However, its crack propagation is more significant and the fatigue damage is severer with better wear resistance. Meanwhile, for the rail material with a lower hardness, the wear volume is larger and the plastic deformation layer is thicker. In addition, high wear rate reduces the rolling contact fatigue damage by constantly removing surface cracks. The analysis shows that U75V quenched rail with better wear resistance is suitable for heavy haul railway and U71Mn hot rolled rail with better fatigue resistance is more suitable for the high-speed railway. [Copyright &y& Elsevier]

Life cycle cost (LCC) considerations are of increasing importance for all organizations making long-term investments. Developments for heavy haul applications were carried out in close cooperation with users identifying the key technical requirements and the overall cost situation.The design and material specifications of the components within a turnout have to be of the highest level with regards to axle load, dynamic forces, and accelerations to meet the demands for heavy haul.Aside from the price of a product, the supply-chain, installation, and maintenance costs coupled with the total life expectancy all have a significant impact on the LCC.Key influencing factors are: (a) initial track quality, (b) delivery logistics - track closing during installation, (c) inspection intervals, (d) time to maintain in track, (e) time for replacement of rails and components, (f) life expectancy of single components.LCC optimized turnout systems are influenced by the following features: (a) minimizing forces on rails, switches, and crossings by optimizing turnout curvature and contact/transition geometries, (b) providing ideal conditions for maintenance work (e.g. through automatic tamping throughout the whole turnout without dismantling of components), (c) using low-maintenance components in order to minimize costs for inspection and maintenance and to increase availability especially in the field of switching, detecting, and locking of the turnouts. The implementation of LCC philosophy in a state-of-the-art heavy haul turnout technology will be highlighted and demonstrated with examples. [ABSTRACT FROM AUTHOR]

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects. [ABSTRACT FROM AUTHOR]