Life-cycle assessment and repair of the railway transition zones of an existing bridge using geocomposite materials

The railway infrastructure is a very important component of the world’s total transportation network. Investment in its construction and maintenance is therefore significant on a global scale. Up to now, some results of the life-cycle assessment (LCA) of open railway line, as well as railway bridges and tunnels, have been published, but detailed analyses of transition zones have not so far been performed. In railway networks, transitional zones are a critical area where the transition from open rail to solid bridge construction can cause significant settlements. The goal of these analyses was to compare two different types of track renewal methods for railway transition zones. In the first method, traditional cement stabilisation is used, whereas the second solution makes use of a geocomposite anchored by steel anchors. The paper presents some results from an environmental study for railway transition zones based on the demonstration case. The results of the performed LCA showed that, in the case of track renewal for transition zones by means of a geocomposite and anchors, the environmental impact is lower than in the case when cement stabilisation works are performed. Less extensive excavation works and thus lower quantities of used material are additional benefits.     

Mitigation of track buckling in transition zones of steel bridges by geotextile reinforcement of the ballast layer

Track thermal buckling is one of the primary safety issues of continuously welded rail tracks. It has been shown that transition zones of open deck steel bridges are more prone to track buckling, as the thermal loads from the bridge and lower track lateral resistance in this region can destabilize the track in the lateral plane. The aim of this paper is to assess the possibility of reinforcing the ballast layer with geotextiles to mitigate the track buckling problem in the transition zones. To do so, a number of laboratory experiments are performed using one and two layers of geogrids and various depths of ballast layer. Single tie push tests are performed on the track and force-displacement curves are derived for the sleepers. It is shown that adding the geotextile layer to the ballast layer can increase its lateral resistance by up to 41%. The results are then introduced in the numerical model of a track developed in Abaqus finite element software for track buckling analysis. It is shown that adding the geogrid layer can increase the track buckling temperature by up to 11.33 °C, an increase of almost 21%, compared to that of an unreinforced track.     

梯形轨枕轨道结构的加速度分析

根据梯形轨枕自身的特点,针对国内外研究现状,从加速度方面分析了梯形轨枕轨道结构的动力特征,表明了梯形轨枕轨道中频率与加速度的关系,得出与普通轨枕相比梯形轨枕轨道有较好的减振性能的结论。     

浅述铁路轨枕结构设计方法与分析

针对轨枕在铁路轨道结构中的重要性,通过力学理论,分析研究了在行车荷载条件下,轨枕的应力和变形情况,并根据轨道结构特点而确定其承载能力和稳定性,在重载铁路和非标准铁路发展建设中将起到很大的作用。     

不同轨道结构形式对高架箱梁结构噪声的影响

为探讨不同轨道结构形式对高架混凝土箱梁结构噪声的影响规律,在考虑多轮对相互作用影响的基础上,建立车辆-轨道耦合系统频域内分析模型及桥梁噪声统计能量仿真模型。以某城市轨道交通30m混凝土简支箱梁现场噪声试验为依据,对仿真分析模型进行验证。在此基础上,分别对埋入式轨枕、梯形轨枕及钢弹簧浮置板三种轨道结构形式下作用于箱梁的力、输入功率及箱梁结构噪声的频变规律进行了探讨。结果表明：仿真值与实测值吻合良好,能较好对箱梁结构噪声进行预测;输入到箱梁的总功率及子系统的功率取决于作用于箱梁的力;场点噪声的频变规律主要受箱梁输入功率的影响;轨道结构形式对箱梁噪声的影响较大,辐射总声级大小关系为：埋入式轨枕情况下最大,梯形轨枕情况下次之,钢弹簧浮置板情况下最小。     

A new approach for evaluating lateral resistance of railway ballast associated with extended sleeper spacing

Recently, attempts have been made to replace wooden sleepers with concrete sleepers with expanded sleeper spacing, especially on conventional railway lines. By extending sleeper spacing in the replacement process, the number of sleepers required is lower. A reduction in the number of sleepers can reduce replacement costs. Behind this attempt to change materials and spacing is the generally held notion the lateral resistance of a ballast is unchanged after the change in the sleeper spacing, whether it is a wooden or a concrete sleeper. However, the changes in the interference degrees of adjacent sleepers and in the rail weight supported by each sleeper are expected to affect the lateral resistance of the ballast. They can change the lateral stability of ballasted tracks in a more complicated fashion than the simple effect of a reduced number of sleepers. However, the current standard design does not consider the combined effects of these changes on the lateral resistance of a ballast. Accordingly, the design of ballasted tracks with extended sleeper spacing cannot be optimized.Therefore, the aim of this study was to investigate the lateral resistance characteristics of a ballast as associated with changes in the sleeper spacing of conventional railway lines. First, single-sleeper pullout tests were conducted on models based on various sleeper spacing conditions to evaluate the lateral resistance of the ballast. The effect of the rail weight on the lateral resistance of the ballast was determined from the test results. An increased frictional resistance at the sleeper bottom was considered to contribute to an increase in the lateral resistance; thus, the friction angle between the ballast and sleeper bottom was used to evaluate the degree of increase. Subsequently, track panel pullout tests were conducted by simulating an expansion of the sleeper spacing. Based on the test results, the effect of the interference between adjacent sleepers on the lateral resistance per sleeper was investigated. The obtained results were quantitatively modeled as a function by using the sleeper width as a parameter (as normalized by the sleeper spacing). Finally, a new approach was proposed for estimating the lateral resistance of a ballast which considered the change in the sleeper spacing for conventional railway lines. The method considered the combined effects of change in the interference of adjacent sleepers and in the rail weight supported by each sleeper on the lateral resistance. Based on the results calculated by the proposed method, practical applications were examined by determining the extent to which the sleeper spacing could be increased without reducing the lateral resistance of the ballast when replacing wooden sleepers with concrete sleepers. It was demonstrated that the proposed method could improve the estimation accuracy of the lateral resistance of a ballast track with extended sleeper spacing.     

模态分析在梯形轨枕轨道结构上的应用

在建立梯形轨枕轨道系统的分析模型基础上,对梯形轨枕轨道系统进行了模态分析,得到该系统的振动动力特性,可为轨道结构的合理设计提供一定的依据,从而推动轨道交通的发展。     

铁路钢桥环氧沥青柔性保护层受力控制指标值研究

研究轨道高低动态不平顺引起的列车随机动荷载作用下铁路钢桥柔性保护层的力学行为。采用有限单元法,建立高速列车-轨道-柔性保护层-桥梁耦合体系有限元模型,其中轨道体系采用一次梁(单层)轨道模型和离散支撑体系。将轨道高低不平顺作为列车随机动荷载的激励源输入,通过典型铁路钢桥面系算例分析可见,轨枕两侧、纵肋上方及轨枕下方对应的保护层区域较易出现开裂破坏;钢板和保护层之间较容易发生横向剪切滑移;考虑轨道高低动态不平顺的柔性保护层力学响应明显大于静载计算结果。研究成果表明铁路钢桥柔性保护层设计时应重点考虑轨道随机不平顺的影响。     

Study of ground vibrations induced by railway traffic in a 3D FEM model formulated in the time domain: experimental validation

In this paper, a three-dimensional numerical model is applied for studying railway vibrations. The numerical model is based on finite element method formulated in the time domain with an implicit scheme of integration. In the first part of the paper the numerical approach is briefly described. An uncoupled scheme is applied: (i) firstly the train loads are calculated taking into account dynamic excitation with a 2D vehicle-track model; (ii) the computed loads on each sleeper are introduced into a 3D numerical model, developed in the commercial code Plaxis, which is used to simulate the wave propagation in the ground. In the second part of the paper a real case study, located in Portugal, is presented, being used for the experimental validation of the proposed model. The numerical results of ground vibrations show an acceptable agreement with real measurements. Therefore, the proposed approach can be used as a reliable prediction tool based on PLAXIS software, which allows simulating railway vibrations in some specific cases such as soft soils, inhomogeneous geometries in the longitudinal direction of the track and transition zones.     

某城市轨道交通短轨枕整体道床施工技术

以某城市短轨枕整体道床铺设施工为例,编制了短轨枕轨道的施工方案,详细叙述了施工方法及控制要点,并对施工提出质量保护措施,从而保证轨枕整体道床铺设质量,确保行车安全。     

时速350km旭普林无碴轨道施工精度控制

结合某客运专线无碴轨道施工实例,介绍了轨枕安装工艺流程及技术要求,从支脚安装、轨枕框架拼装、拆除、检验等方面阐述了轨道施工精度控制要求,以使轨枕安装精度满足使用要求。     

上海地铁隧道内整体道床混凝土长轨枕断裂原因分析及预防措施的研究

本文通过对上海地铁二号线整体道床混凝土长轨枕断裂的内在原因的分析研究,确定整体道床下空洞致轨枕支撑情况的改变是造成轨枕断裂的主因。轨枕离缝、钢轨接头震动荷载及地下水侵蚀是间接引起和加速断裂的辅因,并提出了预防轨枕断裂的建议。     

自制小型铺轨机具铺设隧道宽枕轨道

结合宝成复线新大滩隧道铺设J-82型预应力混凝土宽轨枕板采用的施工技术，就其机具的组成功用及施工方法作了介绍，指出了KPZ-50型铺轨机具的优点。     

地铁不均匀沉降地段的轨道类型比选分析

简要总结了地铁不均匀沉降易发生的地段、原因及不利影响,对有砟轨道、普通无砟轨道、钢弹簧浮置板、隔振垫浮置板及梯形轨枕轨道等常用轨道类型对不均匀沉降的适应性和相关技术特点进行了全面分析,梯形轨枕在自身抗弯能力、空吊的检测和整治方便性、排水、施工速度、铺设精度等方面均具有优势,对不均匀沉降的适应性最好。     

飞鸾隧道无砟轨道施工方案

结合双块式无砟轨道的结构特点，对其施工方案及其原理、施工工艺流程以及具体施工要点作了介绍，并对精确和固定轨道的几何尺寸及空间位置进行了详细的论述，从而为双块式轨枕预制积累了经验。     

Optimisation model to schedule railway track renewal operations: a life-cycle cost approach

Besides high initial construction costs, ballasted railway tracks also have high investment requirements, related to maintenance and renewal (M&R) works. Decision support tools for railway track components that optimise these works are increasingly gaining in importance. This paper presents an optimisation model that integrates ballast, rail and sleeper degradation models in a mixed integer linear programming model. This model links the decisions to renew these components with their condition and takes advantage of the integrated planning of renewal works to minimise the railway track life-cycle cost (LCC). The practical utility of the model is illustrated with a case study involving the Portuguese Lisbon–Porto line. The results indicate a reduction in track renewal cost if the grouping of components, track segments and time interval for renewal operations are optimised. Furthermore, this paper demonstrates that possible annual budget restrictions for railway track M&R operations can have an important influence on the railway track LCC.     

Ⅲ型重载混凝土轨枕的设计与试验研究

由于重载列车速度的提高和运量的增加,轨道结构伤损破坏加速、线路设备病害发生和发展速度加快。目前,我国尚无27 t及以上重载铁路专用轨枕,为有效解决线路用枕需求,采用预应力混凝土轨枕设计方法,对设计荷载分析、结构型式尺寸及结构强度计算进行了设计,并完善了27 t轴重重载轨枕的制造工艺,通过试验和检测,满足重载轨枕的质量要求。     

Impact of track irregularities and damping on the fatigue damage of a railway bridge deck slab

The structural response of reinforced concrete slabs in railway bridges is strongly influenced by local dynamic effects and, therefore, detailed calculations of internal forces have to be performed for a realistic fatigue assessment. In this context, this paper discusses the influence of track irregularities and modal damping coefficients in the dynamic response and fatigue behaviour of a railway bridge deck slab. For that purpose, track irregularities were measured (at different instants of time) and damping coefficients were determined based on acceleration records for passing trains in a real bridge. The bridge behaviour was calculated using a train–bridge interaction methodology, considering calibrated numerical models of the viaduct and the train. The fatigue damage was quantified through the linear damage accumulation method. This methodology allowed to understand the way track irregularities and damping coefficients affect the magnitude of applied bending moments and fatigue damage in the slab.     

循环荷载下土工格栅加筋铁路道床累积#br# 沉降模型试验研究

散粒体道床层的循环累积变形是有砟轨道沉降的主要来源，文章采用有砟轨道路基模型试验来研究道砟层与底砟层间布置土工格栅加固道床控制有砟轨道沉降，开展了高速和重载等不同列车荷载下与不同类型土工格栅加固条件下的多组循环加载试验，加载过程中全程监测道砟层累积沉降、轨枕振动、道砟层底部土压力与土工格栅应变数据并进行分析，以研究土工格栅控制有砟轨道道床沉降的作用机理。研究结果表明：土工格栅对于控制道砟层累积沉降具有较显著的效果，但当土工格栅的刚度达到一定程度后刚度对土工格栅控制沉降效果的影响不大；土工格栅能够显著减小轨枕下方道砟层土压力峰值，从而降低道砟磨耗破碎程度及由此引起的道床沉降；道砟层累积沉降的发展意味着道砟颗粒的错动，而道砟颗粒的错动与位移将引起嵌锁于道砟层中的土工格栅发生张拉，从而土工格栅将反过来对道砟颗粒的进一步位移错动形成侧向约束，体现于宏观即表现为道砟层累积沉降得到控制。     

Impact fatigue responses of pre-stressed concrete sleepers in railway track systems

Pre-stressed concrete sleepers are the main components of railway track systems. To carry and transfer the dynamic wheel loads from the rails to the ground, their current design and construction are limited by allowable flexural stress constraints under service conditions. In current design practice for such a component, the dynamic load effects due to wheel/rail interactions are treated as a quasi-static load using a dynamic impact factor. Then, the allowable stresses eliminate a crack initiation. In reality, the impact events are frequently recorded because of the uncertainties of wheel or rail irregularities such as flat wheels and dipped rails. These effects cause cracking in the concrete sleepers, resulting in excessive maintenance. Limit states design philosophy for the pre-stressed concrete sleepers, containing ultimate and fatigue limit states, has been recently proposed based on structural reliability concept to rationalise the design method and minimise the maintenance. On the basis of probabilistic approach, the high-magnitude low-cycle fatigue limit states, which are more significant in terms of damage evolution, have been addressed in this article. Series of repeated impact tests for the in-situ pre-stressed concrete sleepers were carried out using the Australian largest high-capacity drop weight impact testing machine at the University of Wollongong. The impact forces have been simulated in relation to the probabilistic track force distribution obtained from a heavy haul rail network. This article focuses on the impact responses of the cumulatively damaged sleepers. The effects on such responses of the track environments including soft and hard track supports are also highlighted in this article. It is found that a concrete sleeper damaged by the impact fatigue cycles could possess significant reserve capacity for resisting the axle load in a similar manner as the undamaged sleeper.