subgrade
nounUK /ˈsʌbɡreɪd/
US /ˈsʌbɡreɪd/
The layer of ground under a road or path that holds it up.
Workers packed the subgrade tightly before pouring the concrete for the new road.
RELATED WORDS
OTHER MEANINGS
2. A grade or level that is below the normal or required standard.
The inspector rejected the subgrade materials because they were too weak.
3. In education, a level of schooling below a standard grade, such as a pre-kindergarten class.
The school added a subgrade class for the youngest children.
4. The prepared soil surface beneath a railway track or building foundation.
Engineers tested the subgrade to make sure it could support the heavy train.