Soil suction
Water in unsaturated soils

Capillarity phenomena occur at the interface between two fluids, because molecules there are subject to a set of unbalanced interaction forces, unlike a molecule located within the fluid. A water molecule within a body of water is subject to actions of the same nature (figure 1 b ), whereas one at the interface between two fluids, water-air for example, is subject to different actions: actions due to water and actions due to air (figure 1 a ). Water molecules at the water-air interface are therefore attracted to the water mass, and the water surface is subjected to a force perpendicular...