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In transport engineering
Transportation engineering or transport engineering is the application of technology and scientific principles to the planning, functional design, operation and management of facilities for any mode of transportation to provide for the safe, ...
, subgrade is the native material underneath a constructed road
A road is a thoroughfare used primarily for movement of traffic. Roads differ from streets, whose primary use is local access. They also differ from stroads, which combine the features of streets and roads. Most modern roads are paved.
Th ...
,http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com'' pavement or railway track
Railway track ( and UIC terminology) or railroad track (), also known as permanent way () or "P way" ( and Indian English), is the structure on a railway or railroad consisting of the rails, fasteners, sleepers ( railroad ties in American ...
(US: railroad track). It is also called formation level.
The subgrade provides support to the subbase level and acts as an integral load-bearing layer. Failure of the subgrade can cause depressions and rutting of the upper base and surface courses. These in turn can lead to water pooling in deformations and cause vehicle aquaplaning
Aquaplaning or hydroplaning by the tires of a road vehicle, aircraft or other wheeled vehicle occurs when a layer of water builds between the wheels of the vehicle and the road surface, leading to a loss of traction that prevents the vehicle ...
among other issues.
The term can also refer to imported material that has been used to build an embankment.
Construction
Subgrades are commonly compacted before the construction of a road, pavement or railway track. This is to ensure their ability to absorb the loads being transferred down from the upper layers, increasing the life and wear of the surface courses.See also
*Subsoil
Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus. The su ...
* Track bed
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. Background
According to Network Rail
Network Rail Limited is t ...
References
{{Geotechnical engineering Road transport Pavements Transportation engineering Permanent way