6. Conclusion

The attraction exerted by an unsaturated soil on the water it contains is described quite simply, in the case of granular soils, by capillarity. In the case of fine soils, however, it is necessary to take into account the physico-chemical interactions between water and clay minerals, which are quantified macroscopically by Atterberg limits. The state of water in an unsaturated soil is characterized by a potential, or suction, although the terms negative pressure or capillary pressure are sometimes used.

The measurement and control of suction in soils is based on a variety of techniques, some more direct than others, and is generally rather delicate, which explains the delay in acquiring experimental results for unsaturated soils, both in terms of fluid transfer (water and air) and mechanical behavior. While suction control techniques, which originate in soil science,...