Significance of unsaturated behaviour of geotextiles in earthen structures

The unsaturated hydraulic characterisation of nonwoven geotextiles presented in this paper shows that they only require suctions between 0.8 kPa and 1.2 kPa to induce a rapid drop, of several orders of magnitude, in hydraulic conductivity. This implies that the inclusion of geotextiles in unsaturated earthen systems, for drainage or separation/filtration purposes, can potentially impede the flow of water and lead to a redistribution of the water content profile in the system. This latter aspect is the focus of this study. Geosynthetic drainage layers in contact with unsaturated soils were investigated using soil-geosynthetic columns where clay was in contact with a sand drainage material as well as with a drainage geocomposite layer (a geonet sandwiched between nonwoven geotextiles). The unsaturated drainage layers were found to impede downward flow of moisture consistent with the formation of a capillary break at the drainage layer-clay interface. Accumulation of moisture associated with an increase in moisture storage in the clay was observed, which progressed with depth until breakthrough of flow occurred into the drainage layer. Despite having significantly lower thickness than the sand capillary break, the geocomposite capillary break exhibited similar performance to the capillary break.