The granular material i.e. broken stones, shingles, gravels, etc., placed below and around the sleepers, to transmit wheel load from sleepers to formation and also to provide proper drainage, is called ballast.
What Are the Functions Ballast in Railway Track bed?
The primary reasons for using ballast are as follow:
It provides a hard and level bed for the sleepers.
It holds the sleepers in proper place during the passage o moving trains.
It provides to some extent elastic bed for the track.
It transmits and distributes the load from the sleepers to formation uniformly.
It provides an easy means for maintain the correct levels of two rails of the track, without disturbing the rail road bed.
It protects the surface of formation from direct exposure to frost, rain and sun.
It provides a proper drainage to the track and keeps the sleepers in dry conditions.
It obstructs the growth of vegetation at formation.
It prevents lateral longitudinal and vertical movement of the track.
It provides proper super elevation to the outer rail on curves.