1. 
   Subgrade
   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 compa...
   Found op http://en.wikipedia.org/wiki/Subgrade
   
   
2. 
   Subgrade
   The soil prepared and compacted to support a structure or a pavement system. Also sometimes called grade.
   Found op http://www.pavement.com/glossary/A.html
   
   

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