🚧 Civil · 6 min read
Swell and Shrinkage Factors — Bank, Loose, and Compacted Soil
Soil changes volume when you dig it and again when you compact it. Estimating earthworks means always knowing which state your number is in.
The three states
- Bank (BCM) — in place, undisturbed. What the survey measures.
- Loose (LCM) — excavated, in a truck or stockpile. Larger than bank (it has bulked).
- Compacted (CCM) — placed and compacted as fill. Smaller than bank.
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Conversions
LCM = BCM × (1 + swell%)
CCM = BCM × (1 − shrinkage%)
Load factor = 1 / (1 + swell%) (multiply LCM by this to get BCM)
CCM = BCM × (1 − shrinkage%)
Load factor = 1 / (1 + swell%) (multiply LCM by this to get BCM)
Typical values
| Material | Swell | Shrinkage |
|---|---|---|
| Sand / gravel | 10–15% | 3–7% |
| Common earth / loam | 20–30% | 8–12% |
| Stiff clay | 30–40% | 12–18% |
| Blasted rock | 50–60% | −10 to 0% (bulks permanently) |
Where each state is used
| Quantity | State |
|---|---|
| Excavation payment | Bank (BCM) |
| Haul / truck counts | Loose (LCM) |
| Fill / import required | Compacted (CCM) |
| Spoil disposal volume | Loose (LCM) |
Cut-fill balance
Import required (BCM) = Fill needed (CCM) / (1 − shrinkage%) − usable cut (BCM)
If the result is negative, you have surplus to dispose of — convert to loose for haulage.
🚧 Using EngEst Pro
EngEst Pro’s Civil Calculator applies swell and shrinkage factors per soil type automatically, so the earthworks BOQ shows excavation in bank volume, haulage in loose volume, and fill in compacted volume — no manual conversion.
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