Tests related to filtering geotextiles

Basic tests are conducted to verify the suitability of geotextiles for their intended purpose. These tests are composed of the mass per unit area, thickness, permeability, tensile strength, opening size and others. To check the mechanical resistance to loads that apply during installation and service, additional tests can be performed. 

Laboratory test results have shown that geotextiles can be successfully employed as filters in most simations, even in some cases when available design criteria would not recommend their use. This highlights the need for more realistic filter design criteria where filters in service conditions are more accurately simulated. On the other hand, some experimental techniques also have to be improved and complementary tests may be needed if the range of application of geotextile filters is to be expanded, or 

The line fraction filtration test (Sansone and Koemer, 1992) can also provide valuable information about the long-term behaviour of filter fabric. In this test, the geotextile specimen is subjected to the flow of a mixture of water and soil. It may be particularly interesting for evaluating geotextile performance in silt fences in erosion control works. Palmeira and Farias (2000), eg, reported on test series in which slurries were used with soils from erosion in Brazil. The results showed that often the flow rate tended to stabilize even though conventional design would not recommend that use. 

To represent better conditions in situ, a test was established to take into account the abrasive load induced by hydraulic processes on the bank and bottom of waterways. The rotating dmm test (RPG, 1994) was developed for geotextile filter layers under riprap. The single armourstone always has some space that allows rocking movements under hydraulic loads which can abrade the fabric. This test also proved suitable for checking resistance against abrasion of geotextiles that are not protected by armour and are loaded by sediment and bed-load transport. Recovered samples proved the similarity to fabric that was tested in that device. 

In that test, a mixture of stone chippings and water passes over geotextile samples installed in a rotating drum. The standard test is composed of two abrasion phases at 16 rpm at 40,000 revolutions each, changing direction every 5000 revolutions. If the samples are not degraded after the first 40,000 revolutions (visual inspection), new stone chippings are filled in and the second phase is carried out. If the samples have not been destroyed after 80,000 revolutions, samples are taken and their tensile 

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