Types of geotextiles used in drainage

Geotextiles in conjunction with geonets, geospacers, etc. (GCDs) 

Geotextiles in conjunction with a strip drainage core of continuous drainage channels, typically forming prefabricated vertical drains (PVDs) 

Non woven geotextiles are sheet-type materials their in-plane drainage property is often expressed using a term called transmissivity (6), which is dehned as the planer coefficient of permeability (fep) times the thickness (f) of the geotextile at the particular stress under which it will function (Eq. [13.1])  

The value of fep can be measured by a device with parallel flow (ASTM D4716/ D4716M-14, 2013) or radial flow (ASTM D6574/D6574M-13el, 2013). The principles of the devices are illustrated in Fig. 13.1 for parallel and radial flow. Koerner et al. (1984) reported that although there are some differences for the results of parallel and the radial flow, basically the results are similar and comparable. 

Palmeira and Gardoni (2002) and Pak and Zahmatkesh (2011) reported that for nonwoven geotextiles, fep can be predicted with reasonable accuracy using the following equation (Giroud, 1996) (Eq. [13.2])  

---