FILTER CRITERIA OF GEOTEXTILES

Geotextiles are synthetic woven or non-woven materials which can be used for the de-watering of soil instead of natural filters. After a description of the criteria for natural filters, the criteria for geotextiles are derived. The design diagram according to Cistin/Ziems is recast with reference to the mesh width or opening size of the geotextile; the characteristic values are easily determined. Permeability is determined as a dependent of the normal stress. The theoretical derivations were confirmed by filter tests. Filter criteria which are valid for geotextiles as wovens, thin non-wovens and needle punched non-wovens and take into consideration laminated or turbulent flow patterns are provided, and reference is made to long term proving tests. (TRRL)