Question

You direct a contractor to excavate a 3-foot by 3-foot area, 3 feet deep (one cubic yard of earth, or about 3/4 of a cubic meter). Yet when loaded into a pick-up truck that holds exactly one cubic yard, the earth spills over the edges. In dry earth, what is the swell (percent of expansion of undisturbed medium-density soil when excavated) that should have been planned for? Would clay or gravel have a lesser swell?

Answer

The swell of dry earth is about 29 percent; for wet earth, it's 23 percent. Clay is similar but sands and gravels expand less and have a swell factor in the low teens.