16. Swelling and Shrinking Soils

Soils containing clay minerals (illite, montmorillonite) changing their volumes with soil-water content variation. Soil-water content decreases are followed by soil shrinkage, and increases in soil-water content is followed by swelling. These phenomena are expressed by the creation or closing of soil cracks, and the soil surface decreases/increases simultaneously. Soil cracks can be characterized by crack porosity, by their specific volume and by the specific surface; nets of cracks on the soil surface can be characterized by their specific length. An equilibrium relationship of crack porosity to soil-water content is typical of any particular soil. Soil cracks characterised by their volume and surface play an important role in water infiltration into dry, heavy soils; they significantly increase the retention volume of such soils and the infiltration surface of water-filling soil cracks. The importance of water infiltration into the soil matrix from cracks surface is demonstrated.