Sir - The articles which appeared in the feature on 'Track Research' in your December 2000 issue were most informative to track engineers. Detailed information on the performance of different trackforms is very difficult to obtain, particularly for ballasted track - the most common type.
Dr Hunt provided us with a concise and useful reference article ('Eurobalt optimises ballasted track', p813) on the long-awaited Eurobalt report which showed in graphic detail how the ballast stone deteriorates under traffic, resulting in differential settlement of the track. By providing a model for assessing the life-cycle costs of ballasted track, including those for maintenance and renewal, a more accurate comparison with non-ballasted trackforms will now be possible. However, there are still many important questions that remain to be answered, which may be dealt with in subsequent stages of the Eurobalt research:
- What is the comparative performance of monobloc, twin block, steel and ladder sleepers in ballasted track for maintaining track geometry?
- What is the optimum grading of ballast stone to reduce track settlement under traffic?
- What is the optimum period for tamping cycles? Presumably the vertical bars in Fig 1 refer to the tamping cycles on the test section, which are at approximately 9 to 12 month intervals.
The article 'Assessing the quality of ballastless track' (p819) describes the use of baseplated track as the 'reference track structure' for the Dutch HSL-Zuid, but does not refer to other trackforms which may be more suitable. The baseplated system is actually constructed 'bottom-up', which is very difficult to achieve in practice - as those who have been involved with the installation of such a system in Hong Kong MTRC and the Heathrow Express tunnel line will be able to confirm.
The references to 'broken baseplate fastenings', 'wear of collar bush' (on baseplate), 'grinding of the concrete surface of the support slab' and 'differences in deviation of inclination between adjacent fastenings' are all commensurate with 'bottom-up' track installation methods. It is therefore recommended that a 'top-down' system be considered as the reference track structure for this strategic main line in Holland, both for quality concerns and speed of construction.
In the article 'Britain's busiest crossover replaced' (p823) it is stated that 'the original plan to use roller baseplates was rejected as they placed too much stress on the safety critical point motor linkages'. Unfortunately, it does not state what alternative system was used. As the roller plate should actually provide the lowest stress on the point motor linkages, this additional information would be of interest.
Michael Baxter
Taipei, Taiwan
