What is Geotextile? Purposes of Use

Geotextile

Geotextile is the most widely used type of geosynthetic. Geotextile is often referred to as fabric. For example, common construction terminology for geotextiles includes geo fabric, filter fabric, construction fabric, synthetic fabric, and road reinforcing fabric.geotextiles are usually categorized as either woven or nonwoven, depending on the type of manufacturing
process.

Purposes of Geotextile use

1. Soil Reinforcement : Used for subgrade stabilization, slope reinforcement, and mechanically stabilized earth retaining walls. Also used to strengthen the junction between the top of soft clays and overlying embankments.

2. Sediment Control: Used as silt fences to trap sediment on-site.
3. Erosion Control: Installed along channels, under riprap, and used for shore and beach protection.
4. Asphalt Overlay: Used in asphalt overlays to reduce reflective cracking.
5. Separation: Used between two dissimilar materials, such as an open-graded base and a clay subgrade, in order to prevent contamination.
6. Filtration and Drainage: Used in place of a graded filter where the flow of water occurs across (perpendicular to) the plane of the geotextile. For drainage applications, the water flows within the geotextile.

Probably the most common usage of geotextiles is for filtration (flow of water through the geotextile). For filtration, the geotextile should be at least 10 times more permeable than the soil. In addition, the geotextile must always be placed between a less permeable (i.e., the soil) and a more permeable (i.e., the open graded gravel) material.

Inappropriate use of a geotextile would be to wrap it around a drainage pipe and then cover the geotextile with open-graded gravel. This is because the geotextiles would then have more permeable material on both sides of the geotextiles and it would tend to restrict flow.

Two important design properties for geotextiles used as filtration devices are that they have an adequate flow capacity and a proper soil retention capability:

1. Flow Capacity: Although specifications have been developed that limit the open area of the filtration geotextile to 10% or even 5%, it is best to have a larger open area to develop an adequate flow capacity.
2. Soil Retention Capability: The apparent opening size (AOS), also known as the equivalent opening size (EOS), determines the soil retention capability. The AOS is often expressed in terms of opening size (mm) or equivalent sieve size. Obviously, if the geotextiles openings are larger than the largest soil particle diameter, then all of the soil particles will migrate through the geotextiles and clog the drainage system.

Some of the limitations of geotextile are as follows:

Laboratory testing of Geotextiles

1. Unit weight, gm/m²
2. Thickness, mm (ASTM D5199-2012)
3. Tensile Strength, KN/M – ASTM D4595-2017 –
   (a) Machine direction
   (b) Cross-machine direction
4. Grab Strength, N ASTM D4632-2008
   (a) Machine direction
   (b) Cross-machine direction
5. Elongation at failure, ASTM D4632-2008
   (a) Machine direction
   (b) Cross-machine direction
6. Puncture Strength,
7. Apparent opening size, mm
8. Puncture Strength,N
9. Trapezoidal Tear Strength,N ASTM D4533-1991
   (a) Machine direction
   (b) Cross-machine direction
10. Burst strength, N
11. Water permittivity, per sec.

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