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 joy when the insouciant
armadillo glances at us and doesn’t
quicken his trotting
across the track into the palm brush.
What is this joy? That no animal
falters, but knows what it must do?”
—Denise Levertov (b. 1923)
“even
The bed of love, that in the imagination
Had seemed to be the giver of all peace,
Is no more than a wine-cup in the tasting,
And as soon finished.”
—William Butler Yeats (1865–1939)
“Wonder is the foundation of all philosophy; research, the progress; ignorance, the end. There is, by heavens, a strong and generous kind of ignorance that yields nothing, for honour and courage, to knowledge: an ignorance to conceive which needs no less knowledge than to conceive knowledge.”
—Michel de Montaigne (1533–1592)