Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Research and intercomparison tests necessary for the harmonisation of standards in geotextiles

The project comprised a series of investigations and intercomparison tests on nine specific test methods for geotextiles, in which 31 organisations from 11 European Union countries plus Switzerland took part. The principal benefits are that significant contributions have been made to 13 different draft European standards which are at various stages of progress in CEN TC 189. Many should subsequently become international standards.

The results of the work are summarised as follows:

Hydraulic permeability:
Tests using a reference screen demonstrated that the concept of the draft standard is sound. The repeatability and reproducibility are less satisfactory when the method is applied to geotextiles.

Filtration opening size:
The former German wet sieving method is now accepted throughout Europe. The coefficient of variation lies between 8% and 14%. Progressive tests using reference screens, reference soils, local soils and sample geotextiles identified the contributions made by each to the variability.

Hydraulic transmissivity:
Quality of foam, holding time and water quality were found to influence the test result significantly, while temperature did not. Agreement between laboratories is within 20%.

Compressive creep:
The method was shown to be relatively insensitive to specimen shape and size, and a duration of 1000 hour was satisfactory. Polyamide and polyester should be tested wet. Reproducibility is between 3% (for low creep) and 20% (for substantial creep).

The inclined plane test is suitable for normal pressures of less than 5 kPa with particular application to complex geosynthetic structures, the shear box test for 50 to 150 kPa, with the two tests agreeing to within 10%.

Tensile creep:
The proposed test method is in principle satisfactory, with a reproducibility of between 0.63% for a woven material and 6.75% for a nonwoven.

When normalised to the radiant exposure (quantity of ultraviolet radiation received), all three methods of artificial weathering agree satisfactorily. A radiant exposure of 50 MJ/sq.m was agreed as standard.

Biological resistance:
The test method was modified and is now acceptable, but only needs to be applied to geotextiles of doubtful quality or those thought to contain vegetable fibre.

Chemical resistance:
Methods were defined for screening the resistance to alkaline and aerobic acid aqueous environments, and for the resistance of polyesters to hydrolysis. Oven ageing preceded by a leaching treatment was found to give inconclusive results for the determination of resistance to oxidation, and an alternative approach using pressurized oxygen was found to be promising.


John GREENWOOD, (Technical Executive)
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