Compaction: Density & Quality Control
Why Compaction Matters
Compacted soil supports structures better and prevents settling. Poor compaction = buildings sink, roads crack, pavement fails. Specification requires 90-95% Standard Proctor density.
Compaction Process
- Spread soil in 6-12" lifts (thin layers, easier to compact)
- Water if soil is dry (optimal moisture for compaction)
- Operate compactor in overlapping passes (2-4 passes typical)
- Test density (see methods below)
- Repeat until target density reached (usually takes 4-6 passes)
- Move to next lift
Density Testing Methods
| Method | How It Works | Cost | Speed |
|---|
| Sand Cone | Dig hole, weigh, measure volume | $200-400/test | 30 min |
| Nuclear | Radioactive gauge measures density | $300-600/test | 5 min |
| eDensometer | Electrical probe, requires calibration | $200-400/test | 10 min |
Common Mistakes
- Thick lifts: 12"+ layers don't compact evenly. Keep to 6-8".
- Wrong moisture: Too wet or too dry compacts poorly. Test optimal moisture.
- Not enough passes: One pass doesn't achieve spec. Typical: 4-6 passes per lift.
- Skipping tests: Assume compaction is good (it's not). Test to verify.