Soil Compaction Testing
CSI Division 31, Earthwork
Field and laboratory testing that verifies compacted fill soil has reached a specified percentage of its maximum density, typically established in the lab through a Proctor test and confirmed in the field with a nuclear density gauge or sand cone test, required before a foundation, slab, or pavement can be built on top of that fill.
Why it matters
Fill soil that hasn't been compacted to spec keeps settling under load after construction is complete, showing up later as a cracked slab or a settled foundation, which is exactly why compaction testing exists as a required checkpoint before building on top of fill rather than an optional quality check.
On a real project
A geotechnical testing firm runs a nuclear density gauge test on each lift of compacted fill beneath a new slab, verifying it meets the specified 95 percent of the laboratory's maximum dry density before the contractor is allowed to place the next lift.
Who this matters most to
A Civil Engineer specifies the required compaction percentage based on the geotechnical report. A QA/QC Inspector or geotechnical testing firm verifies each lift meets that requirement before construction proceeds.
Where this goes wrong
A contractor places several lifts of fill without waiting for compaction test results between each one, assuming the soil is compacting adequately based on how it looks and feels underfoot. A later test reveals a lower lift never actually met the required density, and the contractor has to remove and recompact several completed lifts to reach the one that failed.