The Shrink-swell capacity of clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 refers to the extent to which a clay will expand when wet and retract when dry. Soil that is problematic due to high capacity is known as shrink-swell soil, or expansive soil.

Description

Due to the physical and chemical properties of some clays (such as the Lias Group

Lias Group

The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...

) large swelling occurs when water is absorbed. Conversely when the water dries up these clays contract (shrink).

Problems

Clay groups with a high shrink-swell capacity tend to damage crops during dry spells, as the soil contracts, pulling roots apart. Additionally in wet periods expansion of the clay can lead to ground heave, which can damage the foundations of buildings.