Shrinkage in soil

The soil shrinkage is defined as the specific volume change of soil relative to its water content and is mainly due to clay swelling properties. It can be measured in most soils with more than 10% clay content and shows a typical S-shape. This process is reversible with changes in water content and the reverse to shrinkage is swelling.
Due to the physical and chemical properties of some clays  large swelling occurs when water is absorbed. Conversely when the water dries up these clays contract (shrink). The presence of these clay minerals is what allows soils to have the capacity to shrink and swell. Some of these clay minerals are: smectite, nontronite, bentonite, chlorite, montmorillonite, beidellite, attapulgite, illite and vermiculite. The amount of these minerals in a particular soil will also determine the severity of the shrink-swell capacity. For instance, soils with a small amount of expansive clay minerals will not expand as much when exposed to moisture as a soil with a large amount of the same clay minerals. If a soil is composed of at least 5 percent of these clay minerals by weight, it could have the ability to shrink and swell. This property is measured using coefficient of linear extensibility (COLE) values. If a soil has a COLE value greater than 0.06, then it can cause structural damage. A COLE value of 0.06 means that 100 inches of soil will expand by 6 inches when wet. Soils with this shrink-swell capacity fall under the soil order of Vertisols. As these soils dry, deep cracks can form on the surface, which then allows water to penetrate to deeper levels of the soil. This can cause the swelling of these soils to become cyclical, with periods of both shrinking and swelling.