Subgrade
![Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand](/Images/godic/202502/13/MortarlessPavement5507.jpg")
In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway (US: railroad) track. It is also called formation level.
The term can also refer to imported material that has been used to build an embankment.