1. the prepared foundation layer of earth or other material that supports a road, railroad, or other structure
Usage: engineering; construction

Examples

• The engineers tested the subgrade before laying the asphalt.
• Poor drainage caused the subgrade to become unstable.
• The construction crew compacted the subgrade to the required density.
• Heavy rains damaged the subgrade beneath the highway.
• The railroad’s subgrade needed reinforcement after the flooding.
• Workers prepared the subgrade by removing all organic material.