Track Bed Total Route Evaluation for Track Renewals&Asset Management“A Network Rail Perspective”

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.

Advancements and Applications of Polyurethane Curing Technology in Railway Track Bed Construction in China

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.

Stress on Ballast-Bed and Deterioration of Geometry in a Railway Track

In Greece extended cracking of twin-block concrete sleepers （ties） and fouling of the ballast-bed were observed with implied problems of gauge widening and deterioration of track＇s geometry. This led to a ten-year investigation program, during which a new method was developed for the estimation of actions on track panel as well as of the pressures / stresses that develop under the seating surface of the sleeper on the ballast-bed. Results from the tests performed on the ballast used in the Greek network are also presented, conducted in laboratories in France, Austria, and Greece. The influence of the actions -static and mainly dynamic- on the track response and the stress and strain of the ballast-bed are also discussed as derived from the tests and theoretical analysis.

Impact of train speed on the mechanical behaviours of track-bed materials

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.

Influence of the Randomness of Longitudinal Resistance of Ballast Bed on Track-Bridge Interaction

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.

Incompatible thermal deformation of interlayers and corresponding damage mechanism of high-speed railway track structure

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.

Computational study of bubble coalescence/break-up behaviors and bubble size distribution in a 3-D pressurized bubbling gas-solid fluidized bed of Geldart A particles

A computational study was carried out on bubble dynamic behaviors and bubble size distributions in a pressurized lab-scale gas-solid fluidized bed of Geldart A particles.High-resolution 3-D numerical simulations were performed using the two-fluid model based on the kinetic theory of granular flow.A finegrid,which is in the range of 3–4 particle diameters,was utilized in order to capture bubble structures explicitly without breaking down the continuum assumption for the solid phase.A novel bubble tracking scheme was developed in combination with a 3-D detection and tracking algorithm(MS3 DATA)and applied to detect the bubble statistics,such as bubble size,location in each time frame and relative position between two adjacent time frames,from numerical simulations.The spatial coordinates and corresponding void fraction data were sampled at 100 Hz for data analyzing.The bubble coalescence/break-up frequencies and the daughter bubble size distribution were evaluated by using the new bubble tracking algorithm.The results showed that the bubble size distributed non-uniformly over cross-sections in the bed.The equilibrium bubble diameter due to bubble break-up and coalescence dynamics can be obtained,and the bubble rise velocity follows Davidson’s correlation closely.Good agreements were obtained between the computed results and that predicted by using the bubble break-up model proposed in our previous work.The computational bubble tracking method showed the potential of analyzing bubble motions and the coalescence and break-up characteristics based on time series data sets of void fraction maps obtained numerically and experimentally.

Stability Analysis and Evaluation of Jointless Track Based on Ballast Surface Parameters

In formulas that use the probabilistic method to calculate the stability of the CWR, the value of the cross-resistance of the track beds hasn’t fully taken into account the influence of the type of the parameter combination of the track bed, making the calculation results for a particular line undifferentiated. The analogy of the trajectory of the lateral displacement of the trackless bed is proposed. It is proposed that the lateral resistance of the track bed is also ambiguous within the allowable lateral displacement limit, and equivalent randomization is performed. Through the analysis of the characteristics of the appearance parameters of the track bed, a calculation formula containing multiple surface parameters for the lateral resistance of the track bed was established, and the values of various factors were reasonably analyzed. The purpose of this paper is to point out that in the stability evaluation formula, the value of the lateral parameters of the ballast bed lacks the consideration of the surface parameters. Based on the surface parameters, a model to evaluate the lateral resistance of the track bed is proposed. It can be seen as a refinement of the formula.

基于准动态评估的桥上有砟轨道最优级配研究

道砟级配是有砟轨道的重要参数,对桥上有砟道床准动态稳定性和容重有较大影响。通过离散元法建立桥上有砟道床模型,研究各国级配下道床准动态稳定性差异;采用极限思维法,揭示各粒径含量对桥上有砟道床准动态稳定性的影响程度,并对道床容重特性进行初探。结果表明:当桥上道床密度为1.7 g/cm~3时,道床横向阻力值为:俄罗斯B类>中国特级>中国一级>美国4A;大粒径道砟含量越高,道床横向阻力值越大;小粒径道砟含量增加,道床横向阻力值先减小后略有增大;为保证道床具有较高稳定性,建议小粒径道砟含量应大于0但不超过30%,中粒径道砟含量应不为0,大粒径道砟含量应不低于15.5%;采用最优级配区间所建立的桥上有砟道床具有工程上所青睐的道床容重特性。

Understanding melt pool characteristics in laser powder bed fusion:An overview of single-and multi-track melt pools for process optimization

Laser powder bed fusion(LPBF)has made significant progress in producing solid and porous metal parts with complex shapes and geometries.However,LPBF produced parts often have defects(e.g.,porosity,residual stress,and incomplete melting)that hinder its large-scale industrial commercialization.The LPBF process involves complex heat transfer andfluidflow,and the melt pool is a critical component of the process.The melt pool stability is a critical factor in determining the microstructure,mechanical properties,and corrosion resistance of LPBF produced metal parts.Furthermore,optimizing process parameters for new materials and designed structures is challenging due to the complexity of the LPBF process.This requires numerous trial-and-error cycles to minimize defects and enhance properties.This review examines the behavior of the melt pool during the LPBF process,including its effects and formation mechanisms.This article summarizes the experimental results and simulations of melt pool and identifies various factors that influence its behavior,which facilitates a better understanding of the melt pool's behavior during LPBF.This review aims to highlight key aspects of the investigation of melt pool tracks and microstructural characterization,with the goal of enhancing a better understanding of the relationship between alloy powder-process-microstructure-properties in LPBF from both single-and multi-melt pool track perspectives.By identifying the challenges and opportunities in investigating single-and multi-melt pool tracks,this review could contribute to the advancement of LPBF processes,optimal process window,and quality optimization,which ultimately improves accuracy in process parameters and efficiency in qualifying alloy powders.

A study on characteristic indexesof railway ballast bed underhigh-frequency radar

Purpose–In this paper,a high-frequency radar test system was used to collect the data of clean ballast bed and fouled ballast bed of ballasted tracks,respectively,for a quantitative evaluation of the condition of railway ballast bed.Design/methodology/approach–Based on original radar signals,the time–frequency characteristics of radar signals were analyzed,five ballast bed condition characteristic indexes were proposed,including the frequency domain integral area,scanning area,number of intersections with the time axis,number of timedomain inflection points and amplitude envelope obtained by Hilbert transform,and the effectiveness and sensitivity of the indexes were analyzed.Findings–The thickness of ballast bed tested at the sleep bottom by high-frequency radar is up to 55 cm,which meets the requirements of ballast bed detection.Compared with clean ballast bed,the values of the five indexes of fouled ballast bed are larger,and the five indexes could effectively show the condition of the ballast bed.The computational efficiency of amplitude envelope obtained by Hilbert transform is 140 s$km
1,and the computational efficiency of other indexes is 5 s$km
1.The amplitude envelopes obtained by Hilbert transform in the subgrade sections and tunnel sections are the most sensitive,followed by scanning area.The number of intersections with the time axis in the bridge sections was the most sensitive,followed by the scanning area.The scanning area can adapt to different substructures such as subgrade,bridges and tunnels,with high comprehensive sensitivity.Originality/value–The research can provide appropriate characteristic indexes from the high-frequency radar original signal to quantitatively evaluate ballast bed condition under different substructures.

不锈钢激光选区熔化单道成形表面介观模拟与实验验证

目的为了获得不锈钢激光选区熔化单道成形质量好的加工参数,提高成形质量。方法对于316L不锈钢材料的激光选区熔化(SLM)成形,采用离散元方法(DEM)构建颗粒随机分布的三维介观模型,采用流体体积法(VOF)动态追踪SLM成形过程熔池传热、流动和凝固等行为,该模拟考虑相变潜热、热物性参数随温度非线性变化、Marangoni效应,研究了温度梯度引起的表面张力和蒸汽反冲力等现象对熔池液态金属流动和凝固的影响,并对不同激光参数和扫描速度对熔池温度场和内部流动的影响规律进行了分析。结果当激光功率为150 W、扫描速度为400 mm/s时,激光能使不锈钢粉末充分熔化,凝固后的轨迹形貌连续光滑。通过提高激光扫描速度和降低激光功率使得热输入减小,熔道表面成形出现球化等缺陷。结论通过单道成形实验观察和分析熔池与熔道的三维尺寸与形貌,有效验证了数值模拟的正确性,较好地预测出SLM过程中的缺陷种类,为深入理解SLM过程中的复杂物理现象和优化工艺参数提供了参考。

力稳定车稳定装置-有砟轨道耦合系统动力学特性研究

提出了一种针对动力稳定车作业过程动力学响应分析的稳定装置-轨排-道床耦合动力学模型。参照铁路行业标准设定了5种道床状态,基于ADAMS建立了虚拟样机仿真模型。系统地讨论了道床状态和作业参数对耦合系统横向振动响应的影响效果,以及各研究对象间的相互作用关系。研究结果表明:在5种道床范围内,系统共振频率随道床状态参数提升而增大;垂向下压力与系统振动响应幅值呈线性负相关,且其对振幅的影响效果显著低于激振频率;稳定装置与轨枕的横向加速度、速度和位移振幅相近,显著大于道床振幅,激振器振动能量主要为道床吸收;2级道床状态下,稳定作业过程中,自第3号响应输出点起,轨枕和道床块的各响应参数振幅急剧减小。

重载铁路钢轨焊接不平顺对道床动力特性的影响

在车轮反复碾压作用下,钢轨接头区域易出现马鞍形不平顺、低塌等缺陷。为分析重载铁路钢轨焊接不平顺对有砟道床动力特性的影响,首先建立车辆-轨道耦合动力学模型,计算钢轨焊接不平顺影响下的轨枕上动压力;然后采用离散元分析方法,建立有砟轨道结构二维模型,将焊接不平顺影响下的轨枕上动压力作为荷载输入,模拟分析钢轨焊接不平顺对有砟轨道结构道床动力特性的影响。结果表明:钢轨焊接不平顺显著增加了接头两侧轨枕上动压力,且不平顺短波波长越长,影响范围越大,当波长为0.2 m、波深为0.7 mm时,接头两侧轨枕上动压力增加显著,最大值相较于随机不平顺时增加了50.52%;随着焊接不平顺短波波长的减小及波深的增加,道床垂向加速度、摩擦耗能以及累积变形均随之增加;道砟颗粒间最大接触力受焊接不平顺影响较为显著,尤其当短波波深大于0.5 mm时,最大接触力随波深增加而显著增大;当短波波长为0.1 m、波深为0.7 mm时,相较于随机不平顺,道床应力增加55.89%,距道床顶面0.15 m深度处的道砟颗粒加速度增加了449.42%。

运营地铁盾构隧道基底沉降的影响因素分析

隧道基底沉降不仅影响地铁列车的正常运行和乘客的舒适性,严重时会造成隧道结构病害,目前的研究主要集中在长期沉降预测和单因素影响分析,非常有必要开展隧道基底沉降的多影响因素分析。以郑州地铁1号线某盾构隧道区间为工程实例,构建三维有限元数值模型,采用人工激振力模拟地铁列车竖向荷载,提取数值模拟结果的动应力和静偏应力数据,引入循环荷载作用下累积塑性应变计算公式,采用分层总和法计算得到隧道基底沉降,研究了隧道周围土层性质、道床脱空深度和地铁列车运行速度等因素对隧道基底沉降的影响,研究结果表明:数值模拟的隧道基底沉降和发展规律与现场实测结果具有较高的吻合度,验证了有限元模拟的准确性;隧道基底沉降随着周围土层砂粒含量的提高而减小;道床脱空尺寸会加剧隧道和道床板中应力集中和振动放大现象,增大隧道下卧土层的动偏应力和基底沉降;提高车速会增大基底沉降的横向影响范围;采用正交试验法、极差分析法和方差分析法得到了隧道沉降对各因素的敏感性,从大到小依次为:土层性质、车速和道床脱空,其中,土层性质为高度显著水平、车速为显著水平。研究成果对运营地铁盾构隧道的变形监测、安全评估和加固处理具有一定的参考价值。

地铁连续刚构桥上无砟轨道无缝线路纵向力分析

【目的】为研究地铁连续刚构桥上无砟轨道无缝线路纵向受力与变形规律,对地铁连续刚构桥上无砟轨道无缝线路设计改进、运营养护维修提供理论指导。【方法】根据梁-板-轨相互作用原理,建立地铁连续刚构桥上整体道床式无砟轨道无缝线路空间耦合模型,计算伸缩、挠曲、制动、断轨工况下轨道结构和桥梁纵向力及位移,并对轨道结构静力特性进行对比分析,为地铁连续刚构桥上无缝线路轨道结构设计提供参考。【结果】结果表明:双线列车荷载中点与中部梁端处重合时为列车垂向荷载最不利工况,此时钢轨纵向力与钢轨、桥梁纵向位移均为最大,均出现在中部梁端附近,数值分别为70.3 kN与0.6,0.8 mm;双线制动荷载列车尾部位于两侧梁端时为列车制动荷载最不利工况,此时钢轨纵向力与钢轨、桥梁纵向位移均为最大,数值分别为107.8 kN与1.6,1.7 mm。【结论】伸缩力作用下各个端部桥缝处为薄弱部位,在平时养护中应特别注意梁端部桥缝处轨道结构,防止因伸缩力过大而产生断轨;钢轨发生断轨时,在断缝处纵向力、纵向位移均发生突变,严重影响线路行车安全。

三枕捣固作业过程中道砟细观运动及能量演变分析

使用大型捣固车对有砟轨道进行作业,是改善道床质量状态最有效方法和通用手段,是保障列车安全运营的必然选择。但我国大型养路机械源于引进国外技术,对捣固车捣固作业机理认识不足,无法进行科学养护维修。为加深对目前铁路养修作业中常用DWL-48捣固稳定车的三枕捣固装置作业过程的认识,该文借助离散元与多体动力学协同仿真分析方法,建立了三枕捣固装置-轨排-有砟道床三维空间精细化耦合仿真模型,并结合现场实测结果验证了模型的正确性,分析了捣固作业动态过程中道砟颗粒平动、转动特性及能量演变规律。研究结果表明:捣镐对道砟颗粒平动、转动和能量的影响主要位于枕下0 mm~175 mm区域;道砟颗粒速度与角速度变化规律具有很好的同步性,有助于快速填充枕下空隙。捣固作业过程中捣镐采用“道砟平动为主,转动为辅”的方式填充枕下空隙,并且在该过程中伴随着道砟颗粒平动动能、旋转动能逐渐向道砟颗粒势能的不断演变。

活动断裂带下聚氨酯固化道床受力与变形传递规律及其影响

为研究活动断裂带下聚氨酯固化道床结构的受力和变形传递规律及其影响,针对活动断裂带地质特征和聚氨酯固化道床结构特点,基于有限元法和仿真分析软件建立相应的有限元模型。研究结果表明:断裂所致的基础错动将直接映射到轨面,形成明显轨道不平顺,轨面不平顺线形与断裂面线形相近,但不完全重合;断裂位移导致轨面高低、方向变化率增量大于断裂角影响,断裂位移由5 mm增至20 mm,轨面高低、方向变化率增量分别为2.18,0.77 mm/m,断裂角由30°增至90°,轨面高低、方向变化率增量分别为0.11,0.03 mm/m,断裂位移是影响轨道不平顺的主要因素;正断层和走滑断层形成的钢轨变形波长分别为6.1~7.0 m和17.0~19.6 m,后者约为前者的3倍;正断层作用下,固化道床底部离缝宽度随断裂竖向位移v的增加而增大,断裂位置离缝明显,断裂位移为20 mm时,最大离缝宽度达10 mm以上;固化道床纵向应力分布连续,变形曲率最大处应力最大,但应力水平整体较低。

既有线有砟道床注浆加固技术研究进展

随着列车速度和轴重的不断提高,既有线路道床劣化现象严重,其成为影响铁路运输安全的重要因素。针对道床劣化机理及危害,对比不同加固方法,着重围绕有砟道床注浆加固技术,深入了解国内外道床注浆技术的研究进展,详细介绍了日本、韩国和伊朗等国家在注浆道床性能测试方面的主要工作。并从有砟道床的成分和组成、注浆作用机理、注浆力学特性等方面,探究了有砟道床加固技术的发展方向。

三维球床几何稀疏条数长特征线加速方法

特征线法具有非常强的几何适应性,可用于三维球床高温气冷堆全堆芯求解,但存在迭代次数多、计算速度慢的缺点。本文将长特征线加速方法应用于三维球床高温气冷堆以解决非规则几何数值加速的问题,基于三维模型特征线布置较二维模型稠密的分析,提出了稀疏条数长特征线加速方法,极大地减少了加速方程的计算量,在不降低角度离散精度的前提下,获得了非常好的加速效果。通过基准题对加速参数的选取方式进行了研究,条数稀疏度取3~5、长特征线长度取2.0 cm左右、加速迭代步取20~60步可获得良好的加速效果。小型轻水堆三维基准题和球床堆芯简化模型的计算结果表明,采用稀疏条数长特征线加速可获得7倍左右的时间加速比,此时对应的迭代步加速比为20倍左右。