View source for Subgrade

{{Short description|Material underneath a road or track}}
[[Image:MortarlessPavement.jpg|thumb|right|Layers in the construction of a mortarless pavement: A.) Subgrade B.) [[Subbase (pavement)|Subbase]] C.) [[Base course]] D.) [[Paver base]] E.) [[Paver (flooring)|Pavers]] F.) Fine-grained [[sand]]]]
[[File:Section through railway track and foundation.png|450px|thumb|right|Section through railway track and foundation showing the sub-grade]]
In [[transport engineering]], '''subgrade''' is the term used in the US for the native material underneath a constructed [[road]],<ref name="idiot">http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com''</ref> [[Road surface|pavement]] or [[Track (rail transport)|railway track]] (US: railroad track). In British English it is 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]] among other issues.<ref>{{Cite web |title=Ruts Cause Hydroplaning Accidents |url=https://www.atlantaeng.com/ruts_cause_hydroplaning.html |access-date=2024-02-09 |website=www.atlantaeng.com}}</ref>

The term can also refer to imported material that has been used to build an [[Embankment (transportation)|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]]
* [[Track bed]]

==References==
{{reflist}}

{{Geotechnical engineering}}

[[Category:Road transport]]
[[Category:Pavements]]
[[Category:Transportation engineering]]
[[Category:Permanent way]]