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