Swell factor is the increase in soil volume when excavated. Soil expands 12-50% when dug up because air pockets form between loose particles. Clay swells ~30%, sand ~12%, and rock ~50%. Always calculate loose volume for truck loads.
- Sand/gravel: 12–15% swell factor (multiply bank volume by 1.12–1.15)
- Loam/topsoil: 20–25% swell factor (multiply bank volume by 1.20–1.25)
- Clay: 25–35% swell factor (multiply bank volume by 1.25–1.35)
- Rock/shale: 40–50% swell factor (multiply bank volume by 1.40–1.50)
- Ignoring swell factor can underestimate truck loads by 12–50%, causing project delays
| Soil Type | Swell Factor | 100 Bank yd³ Becomes |
|---|---|---|
| Sand/Gravel | 12–15% | 112–115 loose yd³ |
| Loam/Topsoil | 20–25% | 120–125 loose yd³ |
| Clay | 25–35% | 125–135 loose yd³ |
| Rock/Shale | 40–50% | 140–150 loose yd³ |