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Meaning of subgrade

sub•grade

Pronunciation: (sub'grād"), [key]
— Civ. Engin., Building Trades. Civ. Engin.,Building Trades.
—n.
  1. the prepared earth surface on which a pavement or the ballast of a railroad track is placed or upon which the foundation of a structure is built.
—adj.
  1. beneath the finished ground level of a project.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.