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Sitework & Earthworkaka: Proctor testaka: density testaka: compaction testingaka: nuclear density test

Soil Compaction Test

In Plain English

A test that checks whether soil has been packed tightly enough to meet the strength and density required by the project specifications.

Definition

A field or laboratory test performed to verify that compacted fill material meets the specified density requirements for the project. The standard Proctor test (ASTM D698) or modified Proctor test (ASTM D1557) establishes the maximum dry density and optimum moisture content in the lab; field testing uses a nuclear density gauge or sand cone to measure actual density. Results are expressed as a percentage of maximum Proctor density.

Why It Matters in Bidding

Compaction testing is a hold point that controls schedule and rework risk on earthwork and site packages. Failed tests stop the placement of slabs, pavements, and structures until the fill is reworked and re-tested, so estimators must budget for testing rounds, moisture conditioning, and the labor to re-compact, and they need to confirm whether testing costs fall to the owner's lab or the contractor.

Example

After placing structural fill under a building pad, the grading sub calls for a nuclear density gauge test; the result comes back at 92 percent of Proctor against a 95 percent spec, so the crew re-rolls and moisture-conditions the lift before the slab subcontractor is allowed to start.

Related Terms

CompactionBackfillSubgradeFill Material

Frequently Asked Questions

Typically the owner retains an independent testing agency for acceptance testing, but the contractor pays to re-test any fill that fails. Bid documents should specify who carries testing costs, so estimators confirm this in the specs and carry their own quality-control testing and rework allowance where the contractor is responsible.
It compares the field density of placed soil to the maximum dry density established in the lab Proctor test. A spec of 95 percent means the compacted fill must reach at least 95 percent of that lab maximum. Higher requirements demand more passes, tighter moisture control, and often thinner lifts, all of which add labor cost.
Tests are inspection hold points; follow-on work cannot proceed until results pass. Failed lifts require re-compaction, moisture adjustment, and re-testing, each adding days. Estimators build float into the grading sequence and budget for multiple test rounds rather than assuming every lift passes on the first attempt.

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