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:
“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)
“So ‘a bade me lay more clothes on his feet. I put my hand into the bed and felt them, and they were as cold as any stone; then I felt to his knees, and so upward and upward, and all was as cold as any stone.”
—William Shakespeare (1564–1616)
“The Bermudas are said to have been discovered by a Spanish ship of that name which was wrecked on them.... Yet at the very first planting of them with some sixty persons, in 1612, the first governor, the same year, “built and laid the foundation of eight or nine forts.” To be ready, one would say, to entertain the first ship’s company that should be next shipwrecked on to them.”
—Henry David Thoreau (1817–1862)