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:
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“Birth control that really works: Every night before we go to bed we spend an hour with our kids.”
—Roseanne Barr Arnold (20th century)
“... in spite of everything, I still believe that people are really good at heart. I simply can’t build up my hopes on a foundation consisting of confusion, misery, and death. I see the world gradually being turned into a wilderness, I hear the ever approaching thunder, which will destroy us too, I can feel the sufferings of millions and yet, if I look up into the heavens, I think that it will all come right, that this cruelty too will end, and that peace and tranquillity will return again.”
—Anne Frank (1929–1945)