The soil prepared and compacted to support a structure or a pavement system. Also sometimes called grade.
Found on http://www.pavement.com/glossary/A.html
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. ==Construction== Subgrades are commonly compacted before the construction of a road, pavement o
Found on http://en.wikipedia.org/wiki/Subgrade
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