Subgrade
In transport engineering, subgrade is the native material underneath a constructed road,[1] pavement or railway track (US: railroad track). It is also called formation level.
![](../I/MortarlessPavement.jpg.webp)
Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand
![](../I/Section_through_railway_track_and_foundation.png.webp)
Section through railway track and foundation showing the sub-grade
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
References
- http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance highwaysmaintenence.com
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