Railroad Track Structures

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Railroad Track Structures

 

Geogrids can be used effectively to reinforce ballast and sub-ballast layers. When a geogrid is placed within one of these layers, mechanical interlock occurs whereby coarse aggregate particles partially penetrate through the geogrid’s apertures and become confined both laterally and vertically. The result is a layer with enhanced stiffness characteristics which is able to more efficiently transfer the dynamic loads imposed by the cross-ties.

For a given set of loading conditions (axle load, speed of train, etc.), the overall thickness of a roadbed structure (ballast + sub-ballast) is mostly determined by the stiffness of the underlying soil (subgrade). When weaker foundation soils are encountered, it may be necessary to increase the thickness of the overall section in order to limit the pressure imposed under dynamic loading and reduce the rate of track settlement. The inclusion of a geogrid within the sub-ballast layer will normally lead to a significant reduction in the required overall roadbed thickness.

When more competent foundation soils are encountered, the settlement rate of the track is mostly determined by movement within the ballast layer itself. Extensive research in the laboratory and on working rail lines has demonstrated that by including a geogrid within the ballast layer, the track settlement rate can be reduced significantly leading to an extension of the period between ballast maintenance events.

Scope

  • Mainline tracks
  • Sidings and classification yards
  • Intermodal yards
  • Class 1 railroads, transit rail and high speed rail (HSR)

Benefits

  • Reduce initial roadbed construction costs by 50%
  • Increase period between ballast maintenance events by 2 to 5 times
  • Resolve issues associated with local soft spots beneath the track