Soil-geotextile systems are often subject to water infiltration due to natural weather variations. When the water penetration resistance of the geotextile leads to accumulation of water at the soil-geotextile interface, a serious problem of instability in the geotechnical structure can occur. Most nonwoven geotextiles have a water penetration resistance greater than 5 mm when completely cleaned and composed only of hydrophobic filaments/yarns. Geotextiles porous structure is of great complexity and a series of factors involving the hydraulic properties of the geotextile, as well as some microscopic-scale phenomena, such as the effects of capillarity, must be considered.

The migration of the water from the soil to the geotextile is affected by the type of polymer that composes the fibers of the geotextile. Polyester and polypropylene are the most common polymers used in the manufacture of nonwoven geotextiles and they are both hydrophobic materials. In addition to the differences inherent to the polymer itself and to the manufacturing process, the surfaces of the fibers and filaments may be covered by additives such as lubricating oils, surface-active and antistatic materials during the manufacturing process that alter the geotextile-water angle of contact and impart hydrophobic or hydrophilic characteristics to the material, and this feature is often ignored in projects.

In the literature, there are several procedures for determining water penetration resistance of geotextiles, which is a useful feature to the understanding of the interaction between water and geotextiles under unsaturated conditions. The purpose of the present article is to discuss the different test procedures found in the literature for the determination of water penetration resistance of geotextiles. Experimental data are presented to illustrate the affinity of geotextiles with water under different conditions. This paper also presents an evaluation of the current state of knowledge regarding the hydrophobic/hydrofilic properties of geotextiles under unsaturated conditions.

Often, geotextiles are used as filters or drains without proper verification of some of the basic principles for selecting and installing the product and thus some minimum and important requirements may be ignored. Although in the majority of cases there are no serious problems, sometimes the accumulation of a few centimeters of water over drainage systems may compromise the stability of geotechnical structures if this condition is not considered in the design. It has been observed that some of the test procedures reviewed do not take into account the hydrophobic/hydrophilic characteristics of the geotextiles, and therefore, the tests did not produce consistent results.