A cubic yard of earth measured in its natural position swells to more than a cubic yard after it is excavated. This occurs because of an increase in voids.
Swell is expressed as a percentage of natural volume, for example, if 10 yd3 in the ground becomes 13 yd3 after excavation, the swell factor is 30%.
The following table lists swell factors for various engineering materials.
Material | Swell (%) |
---|---|
Clay | |
Dry | 40 |
Wet | 40 |
Clay and gravel | |
Dry | 40 |
Wet | 40 |
Coal, anthracite | 35 |
Coal, bituminous | 35 |
Earth, loam | |
Dry | 25 |
Wet | 25 |
Gravel | |
Dry | 12 |
Wet | 12 |
Gypsum | 74 |
Hardpan | 50 |
Limestone | 67 |
Rock, well blasted | 65 |
Sand | |
Dry | 12 |
Wet | 12 |
Sandstone | 54 |
Shale and soft rock | 65 |
Slate | 65 |
Traprock | 65 |