Which statement about swell factor is true?

• A. Swell factor is the ratio of dry density to moist density.
• B. It is the weight of material per unit volume.
• C. Swell factor is the volume increase of excavated material.
• D. Swell factor is the angle of repose.

Answer: (C)

Swell factor is about how much volume increases when excavated material is loosened from its in-situ state. When soil or rock is dug up and becomes loose, the grains create more space between them, so the material takes up more space. This volume increase is the swell factor, typically expressed as the swollen (loose) volume divided by the original in-situ volume, a value greater than 1. This concept is why describing the volume increase of excavated material is the correct statement. It’s not about density (which is weight per unit volume) or the angle of repose (a slope property); those are different properties. In practice, understanding swell factor helps estimate how much material must be moved or stored and how to convert between in-situ and loose volumes for earthwork calculations.