P. J. C. C. M. Jorge, Luxembourg
The proposal for a smaller-size crib ballast specification brought to mind the problem of ‘flying ballast’ or ‘ballast flurry’ that arose in recent years in the Belgian high-speed network, at the time of test running of German high-speed ICE (inter-city express) trains for speeds higher than 320 km/h. This problem had not previously arisen in Germany: much of the high-speed network there has slab track and, presumably, ballast specifications were/are different from those in Belgium and France.
Because of this problem the speed of ICE trains running in the Belgian network was restricted; I presume this is still the case for the ICE Brussels–Frankfurt services, unless there have been new developments that I am not aware of. Also, the ICE train recently undergoing homologation in France for the future Paris–Frankfurt services had changes made to improve its underside aerodynamics, for this very reason.
Given this situation, I believe it would be interesting to have the authors' views on a few issues.
Are the authors aware of any problem of this nature for smaller-size ballast at speeds below the high-speed spectrum, notably in the research and testing that they have been involved with?
Particularly for those strategic sections of the British conventional network that might in future see the passage of high-speed trains from continental Europe, would it not be prudent to carry out additional research and testing before implementing such a specification?
Author's reply
We agree that live track trials on the proposed two-layered ballast system should be carried out to supplement results available from full-scale laboratory tests, before implementing the proposed specification on high-speed lines. We believe the way forward is to implement the proposed specification initially on the slower-speed lines before extending it to the complete British railway network.
Very limited research material on the phenomenon of ballast movement under high-speed trains was available to the authors when carrying out the literature review, and the cause or factors affecting this phenomenon are not clear. We did not find any reports indicating problems with smaller ballast that is left on the surface after stone-blowing operations. A simple but effective way of reducing ballast movement under high-speed trains would be to cover the proposed smaller ballast with a layer of larger stone on top. As mentioned in the paper, this method has been used in France, where sand ballast was covered with a layer of broken bricks or stone to prevent the sand from being displaced under the movement of the trains. This method is still used in India with sand ballast, as reported in the paper. Ballast gluing would also be effective in preventing movement of ballast under high-speed trains. We suggest that the indicated benefits in ride quality and reduced maintenance would outweigh the cost of these measures.
