Question

why are sleeper used in rails below ​

Answer 1

Sleepers are laid below the rails so that the weight of passing train is spread over a large area (which decreases pressure) and the track may not sink into the ground.

Answer 2

Railway sleepers are made up concrete and help in absorbing enormous stresses produced by the weight of the train on the railway tracks. They are generally made broader in size which make them absorb stress better.