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.

Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand
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.


Subgrades are commonly compacted before the construction of a road, pavement or railway track

See alsoEdit


  1. ^ The Idiots' Guide to Highways Maintenance