Tests on a two layered ballast system

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 track. Regular maintenance is required to keep track geometry within acceptable limits and to maintain ride quality of the track. The two layered ballast system proposes to replace the crib ballast by stone of smaller size. The aim is to fill the voids beneath the sleeper as soon as they become unacceptably large and to maintain ride quality of track without use of tamping or stone-blowing. Preliminary model tests have been carried out on the proposed system which 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 system is self maintaining and keeps track vertical profile within tolerable limits without use of Stone blowing or Tamping machines. Full scale live track trials on the proposed system are planned for, later this year.