Hydraulic properties of geotextiles

Hydraulic properties of geotextiles are especially important for applications in which the geotextile has the function of a filter or drain. In these cases hydraulic requirements must be met. These requirements are typically retention, clogging, and hydraulic conductivity for filters and the transmissivity for drains, in addition to other specrhc requirements of the project. 

The properties of geotextiles can be classified in three ways mechanical, hydraulic, and chemical. Some of the important geotextile properties are discussed below. 

The dimension of the fibre, yam or filament has a direct impact on the mechanical and hydraulic properties of the geotextile. Fibre dimension is expressed according to its diameter, described in deniers or dtex, depending on the measuring system used (American or International System). Thread dimension is generally defined by its yam density. In the case of nonwoven geotextiles made from short staple fibres, fibre dimension is completed by the length of the cut fibres. 

Geotextiles offer various properties that we can categorize into three main families the physical properties refer to the dimensional characteristics of the product. Mechanical properties refer to the behaviour of the geotextile when it is subjected to mechanical constraints. Hydraulic properties describe the behaviour of the geotextile in the presence of liquids or gases. The key properties of geotextiles are defined in Table 3.2. 

The key properties of geotextiles used in reinforced soil applications are introduced with short explanations. For details about the tests mentioned here, see chapters Hydraulic properties, behavior and testing of geotextiles Long-term geotextile degradation mechanisms and exposed lifetime predictions and Geotextiles used in separation. 

Additional to the criteria for particle retention, the permeability requirements of the geotextile filter for various soil types must be considered. The permeability of a geotextile filter in severe soil and hydraulic conditions can be reduced by an order of magnitude over its fife. To ameliorate this, it is important that the geotextile maintain or exceed its index permeability while under load i.e. any re-orientation of the fibres should not decrease or increase the permeability. Criteria against clogging have also been recommended for the permeability as well as for the retention properties of a geotextile filter. 

With the needle-punched nonwoven geotextiles, the water can move in both the vertical and horizontal directions. The nonwoven geotextiles can provide a drainage function by transmitting liquid within the plane of their structure. This means the flow is predominant in the lateral direction, and this is important in assessing the in-plane hydraulic properties (Kopitar, Skenderi, Rukavina, 2014). 

Pak, A., Zahniatkesh, Z. (2011). Experimantal study of geotextiles drainage filtration properties under different hydraulic gradients confining pressures. International Journal of Civil Engineering, 9(2), 97—102. 

After bonding of the geotextile using mechanical means, some thermal or chemical processes, as shown in Section 3.2.1, can be applied to give the product its final physical, mechanical and hydraulic properties. Once the product has attained its final characteristics, it will be inspected, cut and packaged. These procedures can be more or less automated, as was explained in the previous section. 

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