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.
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Famous quotes containing the words track, bed and/or foundation:
“What is the use of going right over the old track again? There is an adder in the path which your own feet have worn. You must make tracks into the Unknown.”
—Henry David Thoreau (1817–1862)
“It would surpass the powers of a well man nowadays to take up his bed and walk, and I should certainly advise a sick one to lay down his bed and run.”
—Henry David Thoreau (1817–1862)
“The poet needs a ground in popular tradition on which he may work, and which, again, may restrain his art within the due temperance. It holds him to the people, supplies a foundation for his edifice; and, in furnishing so much work done to his hand, leaves him at leisure, and in full strength for the audacities of his imagination.”
—Ralph Waldo Emerson (1803–1882)