Since geotextiles have been developed by the textile industry, geotextile properties were first measured by textile tests.It soon became evident that these tests were not related to the real behaviour of the geotextile, especially once it is placed in contact with the soil. Institutes in different countries developed new test equipment and test methods more appropriate to the geotextile end-uses. But this also made it more difficult to compare the various products from different countries. Since several years the European Standard Tests provide a common basis and are accepted not only throughout the European Union but throughout Europe and have widely been adopted by ISO (International Standard Organisation).
Mass per Unit Area EN ISO 9864 – The mass is determined by the weight of small samples of known size which have been taken along the full width and length of the sample. Thickness at specified pressures EN ISO 9863-1. The thickness of the geotextile is determined at pressures from 2 kPa to 200 kPa, which simulates the geotextile being in service.
|Characteristic opening size EN ISO 12956
A defined graded granular material is washed through a single layer of the geotextile sample used as a sieve and the particle size distribution is determined. The characteristic opening size corresponds to a specified size (i.e.D90) of the material passed.
Water permeability (Velocity Index) EN ISO 11058
Constant head method: A single layer of the geotextile specimen is subjected to a unidirectional flow of water normal to the plane under a range of constant water heads.Falling head method: Like the constant head method but with falling water head. The result is the velocity index (VH50) in m/s corresponding to a head loss of 50 mm across a specimen, expressed to the nearest 1 mm-1.
Permeability under load DIN 60500-4
The permeability perpendicular to the plane is measured under a constant water head and a range of different loads. This is particularly interesting when comparing geotextiles of different thickness.
* R.M.Koerner,Designing with Geotextiles,p.110,Fourth Edition, 1999,Prentice Hall