Tests on a two-layered ballast system

Abstract

Considerable evidence suggests that ballast is the main cause of uniform and non-uniform settlement of railway track, provided the subgrade is adequately specified. Over a period of time uneven settlement of the ballast will cause voids to form under the sleepers, leading to unacceptable ride quality of the track. Regular maintenance is required to keep the track geometry within acceptable limits and to maintain ride quality. The proposed two-layered ballast system described in this paper would replace the crib ballast by stone of smaller size. The aim is to fill the voids beneath the sleepers as soon as they become unacceptably large and thus to maintain ride quality without the use of tamping or stone-blowing. Preliminary model tests carried out on the system indicate good potential for it. The results of the model tests have been validated by full-scale tests in the laboratory. The tests have shown that by replacing crib ballast by stone of smaller size a void beneath the sleeper will be filled up to less than the void size minus the average particle size of crib ballast. The next logical step is to go for full-scale live track trials, and it is anticipated that these will take place in the near future.