Track Bed and Foundation
Railway tracks are generally laid on a bed of stone track ballast or track bed, in turn is supported by prepared earthworks known as the track formation. The formation comprises the subgrade and a layer of sand or stone dust (often sandwiched in impervious plastic), known as the blanket, which restricts the upward migration of wet clay or silt. This may also be layers of waterproof fabric to prevent water penetrating to the subgrade. The track and ballast form the permanent way. The term foundation may be used to refer to the ballast and formation, i.e. all man-made structures below the tracks.
Additional measures are required where the track is laid over permafrost, such as on the Qingzang Railway in Tibet. For example, transverse pipes through the subgrade allow cold air to penetrate the formation and prevent that subgrade from melting.
The sub-grade layers are slightly sloped to one side to help drainage of water. Rubber sheets may be inserted to help drainage and also protect iron bridgework from being affected by rust.
Read more about this topic: Track (rail Transport)
Famous quotes containing the words track, bed and/or foundation:
“The weary sun hath made a golden set,
And by the bright track of his fiery car
Gives token of a goodly day tomorrow.”
—William Shakespeare (1564–1616)
“Romeo. I dreamt a dream tonight.
Mercutio. And so did I.
Romeo. Well, what was yours?
Mercutio. That dreamers often lie.
Romeo. In bed asleep, while they do dream things true.
Mercutio. O then I see Queen Mab hath been with you.
She is the fairies’ midwife, and she comes
In shape no bigger than an agate stone
On the forefinger of an alderman,
Drawn with a team of little atomi
Over men’s noses as they lie asleep.”
—William Shakespeare (1564–1616)
“The foundation of empire is art & science. Remove them or degrade them, & the empire is no more. Empire follows art & not vice versa as Englishmen suppose.”
—William Blake (1757–1827)