Earthwork
Proctor Test
A laboratory test that determines the optimum moisture content and maximum dry density for a specific soil, used as the benchmark for field compaction.
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In the Field
The Proctor test gives you the target — field density testing tells you if you hit it. Soil at optimum moisture compacts best. Too dry and it won't compact; too wet and it pumps. Add water or dry out the soil as needed.
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Rule of Thumb
95% Proctor compaction is the standard for most structural fills under slabs and pavements. Granular base under roads is sometimes spec'd to 100% of modified Proctor.