Geotextiles are often included in engineered earth systems, where they are used as a filter material to reduce the movement of soil particles into drains, and as a reinforcing material to increase the strength of soils subjected to loads. In both instances, the ability of the material to transmit water is of importance since soil strength tends to decrease as moisture content increases. If the inclusion of geotextiles reduce the ability for moisture to migrate as planned, they may not be accomplishing their intended purpose and, instead, may be worsening rather than improving the system. Conversely, in systems that are designed to prevent water movement, the inclusion of a fabric that attracts moisture may be undesirable and counter to the design. A series of tests were conducted on three geotextiles to evaluate their ability to conduct water under unsaturated conditions. It was found that the geotextiles tended to be hydrophobic and did not begin wetting until pore suctions were near zero or positive. It was found that the unsaturated hydraulic conductivity of the geotextiles was high when nearly saturated, but that the conductivity decreases rapidly as saturation fell. The fabrics also tended to exhibit a very high level of hysteresis that results in significantly different abilities to conduct water depending on whether the fabric is drying or wetting. A series of three tests, transmissivity, moisture content versus matric potential and unsaturated hydraulic conductivity, were conducted on the materials evaluated. This required the development of a suitable TDR methodology for use on a very thin material.
Geotextiles are increasingly being applied in a large variety of engineering uses, such as in the separation, drainage and reinforcement of soils. These uses are in roads, landfill covers and liners, and in embankments and foundations.