By Glenn McDowell, Nottingham Centre for Geomechanics, School of Civil Engineering, University of Nottingham, and Peter Stickley, BWB Consulting. This paper was first published in GE’s January 2006 issue.
It has been shown (McDowell et al, 2004a) that the behaviour of different ballasts varies enormously.
McDowell et al (2004a) examined the performance of each of four different ballasts in a box test simulating train loading and rearrangement caused by tamping and were able to correlate the results in terms of settlement and degradation with simple index tests such as the Los Angeles Abrasion value and the Micro-Deval Attrition value (as defined in BS EN 13450: 2002 (British Standards Institution, 2002)).
In that paper, one ballast was clearly inferior to the others in terms of performance. In a subsequent paper, McDowell et al (2004b) investigated using the same box test method, as to whether a weak ballast could be mixed with a strong ballast to give a ballast mixture which meets current specifications, and how much weak ballast could be included without adversely affecting the performance of the mixture to a significant extent. This would allow the selection of an appropriate amount of weaker, cheaper aggregate for inclusion in rail trackbeds, reducing ballast cost.