Subsoil Movements ~ these are due primarily to changes in volume
when the subsoil becomes wet or dry and occurs near the upper
surface of the soil. Compact granular soils such as gravel suffer very
little movement whereas cohesive soils such as clay do suffer volume
changes near the upper surface. Similar volume changes can occur
due to water held in the subsoil freezing and expanding † this is called
Frost Heave.
Foundations---Subsoil Movements