Subgrade

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title: "Subgrade" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["road-transport", "pavements", "transportation-engineering", "permanent-way"] description: "Material underneath a road or track" topic_path: "engineering" source: "https://en.wikipedia.org/wiki/Subgrade" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Material underneath a road or track ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d6/MortarlessPavement.jpg" caption="Pavers]] F.) Fine-grained [[sand"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/a/a5/Section_through_railway_track_and_foundation.png" caption="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, pavement or 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.

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.

References

References

1. http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com''
2. "Ruts Cause Hydroplaning Accidents".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::