TRACK SYSTEMS FOR HIGH SPEED RAILWAYS: GETTING IT RIGHT

随着技术的进步，列车速度随着时间的推移而稳步提高，拟议中的第二条英国高速铁路线（HS 2）可能会被设计为“被动式”，未来将以400公里/小时的速度运行。这比世界上任何有碴轨道铁路都要快。目前根本不知道使用传统的道碴道床、更高工程化的轨道形式（例如板轨道）或两者之间的混合物是否会更好地建造用于潜在400 km/h速度的铁路轨道。虽然板式轨道可能具有更持久的优势，但有碴轨道的建造成本更低，如果可以克服或减少持续维护的需要，则可以提供整个寿命成本和碳效益。从HS 1的运行经验和HS 2的概要设计中，与有碴轨道相关的某些知识差距变得明显。这些问题1。轨道几何形状：在HS 1（伦敦至英吉利海峡隧道）上的经验是，轨道的某些部分，例如过渡区（在有碴轨道与隧道和桥梁中使用的更高工程设计的轨道形状之间）和某些曲线需要过度的弯曲。这导致加速道碴降解和增加地面振动;两者在材料使用和对周围环境的影响方面对铁路的环境性能产生不利影响。因此，当前设计规则在速度、垂直和水平曲线半径的允许组合方面的适用性，以及这些如何影响持续维护以保持行驶质量和乘客舒适度的需求，尚不确定。2.临界速度：在松软的地面上，列车速度可能接近或超过地面中的波速，从而引起共振型效应和增大的变形。通过采取一系列缓解措施，如使用压实填料和土工格栅重建路堤、安装桩筏和使用深层干土混合或控制模量柱进行地基处理，已克服了这一现象。这种补救措施的费用可能很高，特别是如果主要是在预防的基础上采取这些措施。然而，许多分析方法是不完善的（例如，线弹性行为往往是假设或地面，轨道支撑系统和列车动力学的异质性被忽略），传统的经验方法可能会显着高估动态放大效应。因此，如果能够更好地理解基础科学，就有可能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。3.道碴飞散（高速列车通过时道碴颗粒飞散的可能性）。这可能会对列车的底部造成广泛的损害，如果一小块碎石落在铁轨上，然后被压碎，也会对铁轨本身造成严重的损害。研究表明，道碴飞行取决于机械力和空气动力的组合，因此与列车运行条件和轨道布局有关，但引起它的确切条件尚未完全了解。研究思路是，通过了解与高速铁路相关的基础科学，并通过适当的工程设计中合理的进步来实现它，我们可以大大提高有碴铁轨的效率，并减少维修需要，使铁路线的速度至少达到每小时400公里。

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.