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:
“He who rides and keeps the beaten track studies the fences chiefly.”
—Henry David Thoreau (1817–1862)
“—My brother Toby, quoth she, is going to be married to Mrs. Wadman. “Then he will never,” quoth my father, “be able to lie diagonally in his bed again as long as he lives.””
—Laurence Sterne (1713–1768)
“The foundation of humility is truth. The humble man sees himself as he is. If his depreciation of himself were untrue,... it would not be praiseworthy, and would be a form of hypocrisy, which is one of the evils of Pride. The man who is falsely humble, we know from our own experience, is one who is falsely proud.”
—Henry Fairlie (1924–1990)