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Test Methods

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).

Descriptive properties

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.

Mechanical porperties

   Wide-width tensile test EN ISO 10319

This test is performed for all kinds of geotextiles and geogrids on a specimen of 200 mm width and 100mm length. A longitudinal force is applied to the specimen until it ruptures while the maximum tensile strength,the elongation and the energy absorption is measured. The main difference between this method and others such as DIN 53857, ASTM D1682 etc.is the width of the specimen or the rate of strain.
   
   Static puncture test (CBR) EN ISO 12236

A steel plunger (50 mm diameter) is pushed at a constant rate on the centre of the specimen which is clamped between two steel rings. Maximum push-through force and displacement at maximum force are measured.
   
   Puncture Resistance (US Rod) ASTM D4833

This test is similar to the static puncture test (CBR) but a different plunger (ø 8 mm) is used and the specimen is smaller. Koerner though recommends the CBR test as it gives more consistent results*.
   
Dynamic perforation test (cone drop test) EN 918

A steel cone is dropped from a distance of 50 cm onto the centre of a fixed geotextile specimen. The degree of penetration is measured by the hole diameter.

Grab Strength ASTM D4632A

A continually increasing load is applied longitudinally to the specimen and the test is carried to rupture. Values for the maximum grab strength and elongation of the test specimen are measured. This test simulates the geotextile being subjected to tensile stress as surface pressure is applied and the stone base attempts to move sideways.
Trap Tear Strength ASTM D4533

A pre-cut specimen is subjected to a tensile force to continue or propagate a tear.
Mullen burst test ASTM D3786

An inflatable rubber membrane is used to deform the geotextile into a shape of a hemisphere of 30 mm diameter until it bursts. Due to the small sample size and high variation in the test procedure, the results of this test vary widely.

Hydraulic properties

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