Railway ballast and its maintenance

A clean and homogeneous ballast bed is an essential pre-requisite for the wheel-on-rail system to function smoothly. To fulfil its load distribution function, the gradation of railway ballast has to be kept in relatively tight limits. Too uniform gradation or too many fines in the ballast both reduce the maintainability of track geometry significantly. The quality of track geometry is not only defined by the prevailing quality index, but even more important also by the ability to produce a high initial quality and to achieve a low rate of degradation. One of the most important factors for both is the state of the ballast. A new research project of the Technical University of Graz[1] reveals by statistical analysis of thousands of track quality data that even on new ballast there are significant differences in track quality deterioration rates. For ballast that has been in service over a longer period, fines and blocked drainage are main problems. When track geometry maintenance becomes frequently necessary due to fouled ballast, maintenance of the ballast by ballast cleaning is the most economical solution. By correct application of ballast undercutter cleaners the resulting ballast quality can be assessed as being superior to the placement of new ballast. In particular, reviews of the sieve analysis of cleaned ballast shows the excellent gradation results that can be attained through ballast cleaning. The achievement of low track geometry degradation rates compensates for the cost of the ballast cleaning operations.