Earthwork
Subbase
A layer of granular material (typically crushed stone or gravel) placed between the subgrade and the base course or pavement to distribute loads and improve drainage.
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In the Field
Subbase material is typically #57 stone or processed gravel. It provides drainage and a stable working platform. Don't skip it to save money — poor subbase is the #1 cause of premature pavement failure.
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Rule of Thumb
A minimum 4-inch compacted subbase is typical for residential driveways; 6–8 inches for commercial pavements, depending on traffic loading.