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The surface prepared to receive the ballast, sleepers, rails, etc.. for constructing the railway track is called Formation or sub grade.

Function of formation

  • The formation has the following functions
  • It provides a smooth and uniform bed on which the track is laid.
  • It bears the entire load transmitted from the moving loads to it through the ballast.
  • It provides drainage facilities.
  • It provides stability to the track.



  • The width of the formation depends upon
  • Numbers of tracks to be laid over it.
  • Gauge of the track.
  • Width of ballast layer.
  • Width of drains provided.



  • The height of the formation depends upon the topography of the alignment and the gradients adopted.

Slide Slopes

  • The slide slopes of the formation depends upon the characteristics of the soil, as shear strength, angle of repose etc.
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