Examples from the Web for subgrade
The pavement laid was bitulithic and the subgrade was an old macadam road built by the County.Third Biennial Report of the Oregon State Highway Commission|S. Benson, W. L. Thompson, R. A. Booth, Herbert Nunn
When the work was finished, a subgrade reversed-grade drain carried the water to the shaft sump by gravity.
The side-walls and subgrade electric conduits were water-proofed with felt and pitch.
In each grade and subgrade date of commission, appointment, or warrant determines the order of precedence.
Some engineers advocate that in preparing the subgrade, the earth be thoroughly rolled; others prefer not to roll the subgrade.American Rural Highways|T. R. Agg