Cross-plane permeability

Rawal A. A cross-plane permeability model for needlepunched nonwoven structures. J Textile Institute 2007 97 527-32. 

From the above description of the basic geo-filtration mechanism, it becomes evident that the performance of geotextiles as filter media depends largely on two properties the material s cross-plane permeability and pore-size characteristics. 

Schematic for cross-plane permeability measurements of geotextiles. 

Both the V20 and y/ values can be plotted against the Ah values to represent the cross-plane permeability characteristics of the geotextile. 

Filtration can be defined as a soil—geotextile system in equilibrium that allows for adequate liquid flow with hmited soil loss across the plane of the geotextile over a lifetime of service compatible with the application under consideration (Koerner, 2005). Therefore, the filter function refers to geotextile pore size distribution (PSD) or filtration opening size and to the geotextile cross-plane permeability (or permittivity). 

If theoretical equations (Giroud, 1996) are used to evaluate the cross-plane permeability and filtration opening size of a nonwoven geotextile, the porosity and thickness must be known (see the section on cross-plane permeability). 

The permeability criterion of the filter system refers to the capacity of the geotextile filter to guarantee free liquid flow across the filter s plane. For this function, geotextile cross-plane permeability or permittivity is necessary for the design, and sometimes also thickness and porosity. 

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