Dirtwork term
Compaction
also called: lift compaction, soil compaction
Mechanical pressing of soil to reduce air voids, increase density, and provide a stable surface.
Compaction is the step that turns loose dumped dirt into dirt that won't settle under load. Done with vibratory rollers, sheepsfoot rollers, plate compactors, or jumping jacks depending on the material and the access. The goal is a measurable density, usually expressed as a percentage of the maximum a Proctor lab test established for that soil.
Earthwork is placed and compacted in lifts, single layers of 6 to 12 inches at a time. You can't dump 4 feet of fill and roll the top, the bottom stays loose and the whole thing settles unevenly within a year. Each lift gets placed at the right moisture content, then compacted to the spec before the next lift goes on.
For structural fill under a slab or behind a retaining wall, density testing is usually required. For ranch road base or residential sub-grade, visual compaction with the right equipment is sometimes enough. We match the method to the spec.
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Related terms
Other words that come up alongside this one
Sub-grade
The natural soil surface that supports everything you build on top of it, pad, road base, slab.
Lift
A single layer of dirt placed and compacted before the next layer is added on top of it.
Select Fill
Imported soil chosen for known compaction and stability properties, used where native soil isn't suitable.
Pad
Prepared, compacted area of ground sized and elevated for a structure to be built on top of it.
Mass Grading
Large-scale cutting and filling to reshape an entire site to a planned set of elevations.
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