Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involvi...Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involving hydro-thermo-chemo-mechanical coupling.However,to date,research has not adequately described the early-age cracking mechanisms in track beds,and few risk control measures have been proposed.To solve this problem,we incorporated the hydration degree of concrete into multi-field coupling equations for early-age concrete,and set boundary conditions that account for environmental influences and various stress factors that typically cause early creep of concrete.A four-field coupled risk prediction model was built based on hydro-thermo-chemo-mechanical properties,and was used to calculate and analyze various time-varying behavior(including the risk and form of cracking)in the hydro,thermo,chemo,and mechanical fields of early-age concrete.Finally,we focused on material-related factors(maximum heat of hydration and peak heat release time),environmental factors(temperature difference between day and night,average daily cooling rate,and intensity of solar radiation),and construction technique factors(molding temperature,pouring time,and thermal insulation coefficient).The influence of these factors on the early-age cracking risk of the track bed was analyzed,and risk control measures against early cracking were proposed accordingly.展开更多
Over the last 10 years there have been significant developments and improvements in the understanding of railway track bed in the UK and its relationship and impact on track quality,ballast life and maintenance follow...Over the last 10 years there have been significant developments and improvements in the understanding of railway track bed in the UK and its relationship and impact on track quality,ballast life and maintenance following track renewals.This paper aims to describe the process adopted by Network Rail for track bed investigation and design which offers Network Rail optimum design solutions and value for money from an investigation and construction perspective,balancing design with possession availability to maximise construction output.It also describes innovative investigation and construction techniques that have been developed over the last 5 years maximising the use of rail mounted asset condition data collection systems which run at line speed,allowing targeted investigations and in some case removing the requirements for physical site investigation.It also allows Network Rail to predict sections of track bed which may be affected by line speed increases which would cause the track bed to fail prematurely or,retain its ability to maintain good track geometry post line speed increase.These problems can manifest themselves as stiffness related problems such as critical velocity issues(surface wave velocity,Rayleigh Wave velocity)or,sub-grade erosion resulting in high rates of deterioration in the vertical track geometry.The paper also describes the development and installation process for Enhanced Axial Micropiles to address stiffness related track bed problems whilst leaving the track in-situ a technique which is new to the UK railways.展开更多
This paper examines the application of polyurethane curing technology in the construction of railway track beds,with a specific focus on its implementation in China’s rapidly developing railway infrastructure.The stu...This paper examines the application of polyurethane curing technology in the construction of railway track beds,with a specific focus on its implementation in China’s rapidly developing railway infrastructure.The study begins by identifying the limitations of traditional ballasted track beds,especially under the demands of high-speed and heavyload railways.It then methodically analyzes the advantages of polyurethane-cured track beds,highlighting their improved mechanical properties,including enhanced stability and durability.The paper further explores the benefits of transitioning to prefabricated polyurethane track beds,emphasizing significant cost reductions,better construction quality,and enhanced maintainability.Through a detailed review of experimental data and practical applications,the paper demonstrates the efficacy of polyurethane track beds in various railway settings.A critical part of the research involves optimizing the structural parameters of polyurethane track beds to achieve the best balance of mechanical and damping properties.The conclusion of the paper underscores the potential of polyurethane curing technology as a transformative approach to railway track bed construction,offering a solution to the challenges posed by traditional methods and aligning with the evolving needs of modern railways.展开更多
Based on the research on the construction method of laying track in urban rail transit tunnel, this paper summarizes a set of construction method of laying concrete precast slab track bed with trackless equipment, whi...Based on the research on the construction method of laying track in urban rail transit tunnel, this paper summarizes a set of construction method of laying concrete precast slab track bed with trackless equipment, which is used to reduce labor force, improve track laying efficiency, enhance fine control of construction quality, and provide convenience for the later maintenance and replacement of track bed. The construction method can be widely applied to the construction of assembled track beds for subway, high-speed railway, inter-city railway and other traffic formed by tunnels.展开更多
For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is ...For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.展开更多
To get the influence of the randomness of longitudinal resistance of ballast bed (LRBB) on track-bridge interaction, the statistical law of LRBB was studied with existing test data and the Shapiro-Wilk test. Based on ...To get the influence of the randomness of longitudinal resistance of ballast bed (LRBB) on track-bridge interaction, the statistical law of LRBB was studied with existing test data and the Shapiro-Wilk test. Based on the principle of track-bridge interaction, a rail-sleeper-bridge-pier integrated simulation model that could consider the randomness of LRBB was established. Taking a continuous beam bridge for the heavy-haul railway as an example, the effect of the randomness of LRBB on the mechanical behavior of continuous welded rail (CWR) on bridges under typical conditions was carefully examined with a random sampling method and the simulation model. The results show that the LRBB corresponding sleeper displacement of 2 mm obeys a normal distribution. When the randomness of LRBB is considered, the amplitudes of rail expansion force, rail bending force, rail braking force and rail broken gap all follow normal distribution. As the standard deviations of the four indexes are small, which indicates the randomness of LRBB has little effect on track-bridge interaction. The distributions of the four indexes make it possible to design CWR on bridges with the limit state method.展开更多
In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field w...In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers,leading to a considerable difference in the force bearing of different structure layers.Unit Ballastless Track Bed(UBTB)is most significantly affected by temperature gradient.The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient,resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail.When the train travels on the periodically irregular rail,the structure layers are locally contacted,and the contact zone moves with the variation of the wheel position.This wheel-followed local contact greatly magnifies the interlayer stress,causes interlayer damage,and leads to a considerable increase in the bending moment of the track slab.Continuous Ballastless Track Bed(CBTB)is most significantly affected by the overall temperature variation,which may cause damage to the joint in CBTB.Under the combined action of the overall temperature rise and the temperature gradient,the interlayer damage continuously expands,resulting in bonding failure between structural layers.The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab,and the loss of constraint boundary of the horizontal stability.For the design of a ballastless track structure,the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.展开更多
基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影...基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影响规律。结果表明随着输入线能量密度的升高,熔道稳定性先升高后降低。当输入线能量密度在0.55~1.0 J/mm时,熔道表面光滑,粉末黏附颗粒少,熔道高度数值离散程度小,成形质量稳定。当线能量密度相同时,适当增加激光功率可以提升熔道成形质量的稳定性。展开更多
基金supported by the National Key R&D Program of China(No.2021YFF0502100)the National Natural Science Foundation of China(Nos.52278461 and 52308467).
文摘Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involving hydro-thermo-chemo-mechanical coupling.However,to date,research has not adequately described the early-age cracking mechanisms in track beds,and few risk control measures have been proposed.To solve this problem,we incorporated the hydration degree of concrete into multi-field coupling equations for early-age concrete,and set boundary conditions that account for environmental influences and various stress factors that typically cause early creep of concrete.A four-field coupled risk prediction model was built based on hydro-thermo-chemo-mechanical properties,and was used to calculate and analyze various time-varying behavior(including the risk and form of cracking)in the hydro,thermo,chemo,and mechanical fields of early-age concrete.Finally,we focused on material-related factors(maximum heat of hydration and peak heat release time),environmental factors(temperature difference between day and night,average daily cooling rate,and intensity of solar radiation),and construction technique factors(molding temperature,pouring time,and thermal insulation coefficient).The influence of these factors on the early-age cracking risk of the track bed was analyzed,and risk control measures against early cracking were proposed accordingly.
文摘Over the last 10 years there have been significant developments and improvements in the understanding of railway track bed in the UK and its relationship and impact on track quality,ballast life and maintenance following track renewals.This paper aims to describe the process adopted by Network Rail for track bed investigation and design which offers Network Rail optimum design solutions and value for money from an investigation and construction perspective,balancing design with possession availability to maximise construction output.It also describes innovative investigation and construction techniques that have been developed over the last 5 years maximising the use of rail mounted asset condition data collection systems which run at line speed,allowing targeted investigations and in some case removing the requirements for physical site investigation.It also allows Network Rail to predict sections of track bed which may be affected by line speed increases which would cause the track bed to fail prematurely or,retain its ability to maintain good track geometry post line speed increase.These problems can manifest themselves as stiffness related problems such as critical velocity issues(surface wave velocity,Rayleigh Wave velocity)or,sub-grade erosion resulting in high rates of deterioration in the vertical track geometry.The paper also describes the development and installation process for Enhanced Axial Micropiles to address stiffness related track bed problems whilst leaving the track in-situ a technique which is new to the UK railways.
文摘This paper examines the application of polyurethane curing technology in the construction of railway track beds,with a specific focus on its implementation in China’s rapidly developing railway infrastructure.The study begins by identifying the limitations of traditional ballasted track beds,especially under the demands of high-speed and heavyload railways.It then methodically analyzes the advantages of polyurethane-cured track beds,highlighting their improved mechanical properties,including enhanced stability and durability.The paper further explores the benefits of transitioning to prefabricated polyurethane track beds,emphasizing significant cost reductions,better construction quality,and enhanced maintainability.Through a detailed review of experimental data and practical applications,the paper demonstrates the efficacy of polyurethane track beds in various railway settings.A critical part of the research involves optimizing the structural parameters of polyurethane track beds to achieve the best balance of mechanical and damping properties.The conclusion of the paper underscores the potential of polyurethane curing technology as a transformative approach to railway track bed construction,offering a solution to the challenges posed by traditional methods and aligning with the evolving needs of modern railways.
文摘Based on the research on the construction method of laying track in urban rail transit tunnel, this paper summarizes a set of construction method of laying concrete precast slab track bed with trackless equipment, which is used to reduce labor force, improve track laying efficiency, enhance fine control of construction quality, and provide convenience for the later maintenance and replacement of track bed. The construction method can be widely applied to the construction of assembled track beds for subway, high-speed railway, inter-city railway and other traffic formed by tunnels.
基金part of the results obtained within the ‘INVICSA’ research project funded by SNCF-INFRASTRUCTURE and the ANRT with a CIFRE funding number 2012/1150
文摘For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.
文摘To get the influence of the randomness of longitudinal resistance of ballast bed (LRBB) on track-bridge interaction, the statistical law of LRBB was studied with existing test data and the Shapiro-Wilk test. Based on the principle of track-bridge interaction, a rail-sleeper-bridge-pier integrated simulation model that could consider the randomness of LRBB was established. Taking a continuous beam bridge for the heavy-haul railway as an example, the effect of the randomness of LRBB on the mechanical behavior of continuous welded rail (CWR) on bridges under typical conditions was carefully examined with a random sampling method and the simulation model. The results show that the LRBB corresponding sleeper displacement of 2 mm obeys a normal distribution. When the randomness of LRBB is considered, the amplitudes of rail expansion force, rail bending force, rail braking force and rail broken gap all follow normal distribution. As the standard deviations of the four indexes are small, which indicates the randomness of LRBB has little effect on track-bridge interaction. The distributions of the four indexes make it possible to design CWR on bridges with the limit state method.
基金supported by the National Natural Science Foundation of China(grant numbers 52278466).
文摘In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers,leading to a considerable difference in the force bearing of different structure layers.Unit Ballastless Track Bed(UBTB)is most significantly affected by temperature gradient.The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient,resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail.When the train travels on the periodically irregular rail,the structure layers are locally contacted,and the contact zone moves with the variation of the wheel position.This wheel-followed local contact greatly magnifies the interlayer stress,causes interlayer damage,and leads to a considerable increase in the bending moment of the track slab.Continuous Ballastless Track Bed(CBTB)is most significantly affected by the overall temperature variation,which may cause damage to the joint in CBTB.Under the combined action of the overall temperature rise and the temperature gradient,the interlayer damage continuously expands,resulting in bonding failure between structural layers.The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab,and the loss of constraint boundary of the horizontal stability.For the design of a ballastless track structure,the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.
文摘基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影响规律。结果表明随着输入线能量密度的升高,熔道稳定性先升高后降低。当输入线能量密度在0.55~1.0 J/mm时,熔道表面光滑,粉末黏附颗粒少,熔道高度数值离散程度小,成形质量稳定。当线能量密度相同时,适当增加激光功率可以提升熔道成形质量的稳定性。
