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.
|Clay and gravel|
|Rock, well blasted||65|
|Shale and soft rock||65|