The effects of volume changes in soil
Volume changes result in possible serious damage to the footings or to the building they support. The footing system must be selected to suit the anticipated volume change of the foundation soil.
Wet soil - volume increases
Dry soil - volume decreases
Footings laid on clay soil are liable to subside or lift as the clay's volume decreases with drying and increases with wetting. The pressure of a building on that soil can limit this volume change. However, small buildings of three or less storeys do not exert the necessary pressure to prevent expansion of the foundation material. Therefore, small buildings, like houses, are the most often damaged by soil volume changes.