Home

Volume changes in soil

Unsaturated soil consists of individual soil particles held together by water and air pockets between the particles. The air and water combination pulls the soil particles together by surface tension. This results in a force called 'soil suction'.

Diagram of soil particles and air pockets bound together with water in a sphere.

Wetting the soil reduces this soil suction force. This causes the soil particles to separate and the soil volume to increase. Drying the soil revives the suction force which pulls particles together causing the soil volume to decrease.

Two cubes illustrating volume change up to 20%. The smaller of the two is labelled 'Dry clay shrinks' and the larger is labelled 'Wet clay swells'.