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Section through railway track and foundation showing the ballast and formation layers. The track bed or trackbed is the groundwork onto which a railway track is laid. Trackbeds of disused railways are sometimes used for recreational paths or new light rail links.
Commonly used when measuring the flat surfaces of a hex drive, such as a hex nut. AFF above finished floor A dimension that establishes a distance away from the finished floor. Example would be the top of a coffee table to the shag of the carpet, not where the bottom of the tables feet dig in. AISI: American Iron and Steel Institute
Grooved rail, used when track is laid in places traversed by other vehicles or pedestrians. A grooved rail, groove rail, or girder rail is a special rail with a groove designed for tramway or railway track in pavement or grassed surfaces (grassed track or track in a lawn). The head on the right-hand side of the rail bears the vehicle's weight.
In the 1830s Robert L. Stevens invented the flanged 'tee' rail (actually a distorted I beam), which had a flat bottom and required no chair; a similar design was the contemporary bridge rail (of inverted U section with a bottom flange and laid on longitudinal sleepers); these rails were initially nailed directly to the sleeper.
The London Underground continued to use bullhead rail after it had been phased out elsewhere in Britain but, in the last few years, there has been a concerted effort to replace it with flat-bottom rail. [15] However, the process of replacing track in tunnels is a slow one, due to the difficulty of using heavy plant and machinery.
In geology, a bed is a layer of sediment, sedimentary rock, or volcanic rock "bounded above and below by more or less well-defined bedding surfaces". [1] A bedding surface is three-dimensional surface, planar or curved, that visibly separates each successive bed (of the same or different lithology) from the preceding
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Track relaying, using 30-foot section flat-bottom steel rail (BS 30 m) secured by Pandrol clips, [5] was well-underway in September 1989, with one-and-a-half miles of the track relaid and claims that the new railway would create about 60 jobs. [8]