Compaction Degree Calculator
Dry density and compaction degree from field density, with a pass/fail check.
Inputs
Result
Formula
| Dry density | ρd = wet density ÷ (1 + w) |
| Compaction | K = ρd ÷ ρd,max × 100% |
| Void ratio | e = Gs × ρw ÷ ρd − 1 |
| Verdict | Pass where K ≥ required |
Wet density 1.95 g/cm³ at 12% moisture with a 1.85 g/cm³ maximum: dry density 1.741 g/cm³ gives 94.1% compaction — a pass against 94%, but with only 0.1 point to spare.
Typical compaction requirements by location (design governs)
| Location | Required λc | Testing frequency |
|---|---|---|
| Ground slab subgrade | 0.90 | Every 100-200 m² |
| General backfill | 0.93 | Every layer, every 100 m² |
| Building footing backfill | 0.94 | Every layer, every 50 m² |
| Pipe trench backfill | 0.93 | Every layer, every 20 m |
| Retaining wall backfill | 0.94 | Every layer, every 50 m² |
| Road subgrade | 0.95 | Every 200 m per lane |
FAQ
Why not compare wet density directly?
Water occupies volume without adding strength. Water the same soil and the wet density rises while compaction has not changed, so wet-density checks pass falsely in the rainy season. Convert to dry density — water volume removed — to measure how densely the particles themselves are packed.
What if compaction fails?
Separate moisture from effort. More than ±2% from optimum and rolling simply will not work — dry or wet the soil, then re-roll. If moisture is right and density is low, the passes or roller weight were insufficient; add passes. Never cover a failing layer with the next one.
Where does the maximum dry density come from?
A laboratory Proctor test (standard or modified) on the same soil as the fill. Values cannot be borrowed from another job or replaced by rules of thumb — the same soil from different sources can differ by over 0.1 g/cm³, which is 5 points of compaction. Re-test when the borrow area changes.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.