TRACK SYSTEMS FOR HIGH SPEED RAILWAYS: GETTING IT RIGHT

随着时间的推移，随着技术的进步，列车速度稳步提高，拟议中的英国第二条高速铁路线(HS2)的设计可能会为未来以400公里/小时的速度运行提供“被动准备”。这比世界上任何有碴轨道铁路都要快。目前尚不清楚，使用传统的道床、更高工程化的轨道形式(如板式轨道)还是两者的混合体来建造速度可能达到400公里/小时的铁路轨道会更好。尽管板式轨道可能具有更持久的优势，但有碴轨道的建造成本较低，如果能够克服或减少持续维护的需要，可能会提供终身成本和碳效益。从HS1的运营经验和HS2的轮廓设计中，与有碴轨道有关的某些知识空白已经变得明显。这些令人担忧的问题。轨道几何：HS1(伦敦至英吉利海峡隧道)的经验是，某些轨道路段，如过渡区(有碴轨道与隧道和桥梁上使用的更高工程化轨道形式之间)和某些曲线需要过度夯实。这导致道碴加速退化和地面振动增加；在材料使用和对周围环境的影响方面，这两者都对铁路的环境性能产生了不利影响。因此，目前的设计规则在速度、垂直和水平曲线半径的允许组合方面是否合适，以及这些规则如何影响持续维护以保持乘坐质量和乘客舒适性的必要性是不确定的。临界速度：在松软的地面上，列车速度可能接近或超过地面波动的速度，从而引起共振型效应和变形增加。通过采取一些缓解措施，例如使用压实填土和土工格栅重建路堤、安装桩筏和使用深层干土搅拌桩或控制模数桩进行地基处理，这种现象已得到克服。这种补救措施的成本可能非常高，特别是如果这些措施主要是在预防的基础上采取的话。然而，许多分析方法都是不完善的(例如，经常假设线弹性行为或忽略了地面、轨道支撑系统和列车动力学的非均质性)，而传统的经验方法可能会大大高估动力放大效应。因此，如果能够更好地理解基础科学，那么通过指定更具成本效益的解决方案来实现可观的经济效益是有余地的。3.压载飞行，即在超高速列车通过时，压载颗粒有可能上升到空气中。如果一小块道碴落在钢轨上，然后被压碎，这可能会对列车底部和钢轨本身造成广泛的损害。研究表明，有碴飞行取决于机械和空气动力的组合，因此与列车运行条件和轨道布局都有关，但产生这种飞行的确切条件尚不完全清楚。研究思路是，通过了解与高速铁路相关的基本科学，并通过适当的、合理的工程设计进步来实施它，我们可以极大地提高有碴铁路的效率，并减少对线路速度至少为400公里/小时的维护需求。

Train speeds have steadily increased over time through advances in technology and the proposed second UK high speed railway line (HS2) will likely be designed with "passive provision" for future running at 400 km/hour. This is faster than on any ballasted track railway in the world. It is currently simply not known whether railway track for speeds of potentially 400 km/hour would be better constructed using a traditional ballast bed, a more highly engineered trackform such as a slabtrack or a hybrid between the two. Although slabtrack may have the advantage of greater permanence, ballasted track costs less to construct and if the need for ongoing maintenance can be overcome or reduced, may offer whole-life cost and carbon benefits. Certain knowledge gaps relating to ballasted track have become apparent from operational experience with HS1 and in the outline design of HS2. These concern1. Track Geometry: experience on HS1 (London to the Channel Tunnel) is that certain sections of track, such as transition zones (between ballasted track and a more highly engineered trackform as used in tunnels and on bridges) and some curves require excessive tamping. This results in accelerated ballast degradation and increased ground vibration; both have an adverse effect on the environmental performance of the railway in terms of material use and impact on the surroundings. Thus the suitability of current design rules in terms of allowable combinations of speed, vertical and horizontal curve radius, and how these affect the need for ongoing maintenance to retain ride quality and passenger comfort is uncertain.2. Critical velocity: on soft ground, train speeds can approach or exceed the speed of waves in the ground giving rise to resonance type effects and increased deformations. Instances of this phenomenon have been overcome using a number of mitigation measures such as the rebuilding of the embankment using compacted fill and geogrids, installation of a piled raft and ground treatment using either deep dry soil mixing or controlled modulus columns. The cost of such remedial measures can be very high, especially if they are taken primarily on a precautionary basis. However, many methods of analysis are unrefined (for example, linear elastic behaviour is often assumed or the heterogeneity of the ground, track support system and train dynamics are neglected), and conventional empirical methods may significantly overestimate dynamic amplification effects. Thus there is scope for achieving considerable economic benefits through the specification of more cost effective solutions, if the fundamental science can be better understood. 3. Ballast flight, ie the potential for ballast particles to become airborne during the passage of a very high speed train. This can cause extensive damage to the undersides of trains, and to the rails themselves if a small particle of ballast comes to rest on the rail and is then crushed. Investigations have shown that ballast flight depends on a combination of both mechanical and aerodynamic forces, and is therefore related to both train operating conditions and track layouts, but the exact conditions that give rise to it are not fully understood.The research idea is that, by understanding the underlying science associated with high speed railways and implementing it through appropriate, reasoned advances in engineering design, we can vastly improve on the effectiveness and reduce maintenance needs of ballasted railway track for line speeds up to at least 400 km/h.