TS011-Test methods of Geotextiles

Test Methods of Geotextiles

Guddy Prajapati

Department of Textile Technology

Shri Vaishnav Vidhyapeeth Vishwavidyalaya ,Indore, India

ABSTRACT:

Geotextile are the permeable fabric which is used in association with soil. It’s have ability to separate, filter, reinforce, protect or drain.The four main polymers used for geotextile as a raw material are polyester , polyamide, polypropylene and polyethylene and the natural fibres are also used such as jute, coir etc. the applications areas for geotextiles related to material and numerous and are constantly growing. The typical application of the geotextile are retaining walls, steep slopes, land slide repairs, soft feel embankments, road ways, reinforcement, erosion control in sea embankments. The main functions of geotextile are separation, reinforcement, stabilization , filtration, drainage, protection and moisture barrier/water proofing. Performance parameters required for geotextiles are permeability, compressibility,and extensibility of fabric and toughness of the fabric. The application standard for testing geotextile materials are trapezoid tearing strength of geotextile (ASTM D4533), effects of temperature on geotextile (ASTM D4594), wide-width tensile test (ASTM D4595), tensile test of geomembrane (ASTM D6693), puncture testing for geotextile (ASTM D6241), tensile test of geomembrane (ASTM D7003), grab test for geotextile (ASTM D 4632).

Keyword : American Society for Testing and Materials (ASTM)

DEFINITION OF GEOTEXTILE

“The geotextile fabrics is a permeable, polymeric (synthetic or natural) textile material which may be nonwoven , knitted or woven, used in contact with soil and / or other materials in geotechnical and civil engineering application.”

WHY TESTING IS REQUIRED ?

Testing of geotextile material is done to know about the product quality.
For the compliance to regulatory requirements.
Design and development.
For special considerations.

GEOTEXTILE Fabric Performance Characteristics

Geometric parameters include:

Voluminosity :A reflection of the bulkiness of a fabric for a given areal density (mass per unit area).
Thickness of the fabric: Similar to voluminosity, fabric thickness is related to fiber and yarn diameter. The larger the fiber and yarn diameter, the thicker and bulkier the fabric.
Porosity: The amount of open space in a unit volume of the fabric.
Surface Texture:The smoothness of the surface, which in turn is governed by fiber and yarn diameter.
Permeability: The ease of air or liquid flow through a fabric.
Compressibility: The ability of a fabric to resist transverse (through the thickness ) compression.
Extensibility of a Fabric: A measure of the ability of a fabric to stretch and conform.
Toughness of a fabric: A measure of the durability of the fabric.

ASTM Test Method for Geotextiles:

HYDRAULIC PROPERTIES for testing materials

Apparent Opening Size [ASTM D 4751]

Apparent opening size is important parameter to determine the geotextiles soil filtration capability
In this Method a spherical solid glass beads are dry sieved through a sample for a specified time and at a specified time and at a specified frequency of vibration
After this the amount of beads retained by the sample is then measured
The test of sample is then carried out in a range of sizes of glass beads.
The apparent opening size is the pore size at which 90 % of the glass beads are retained on within the fabric.

Permittivity [ASTM D 4491]

This permittivity test method is the mechanism by which water moves through the fabric.
This test is used to measures the quantity of water which can pass through a geotextile perpendicular to the surface of the geotextile.
This permittivity test may be measured in a constant head or falling head test,
A constant head testing is more common due to the high flow rates through geotextiles
In this constant head test, a head of 50 mm water is maintained on the sample throughout the test.
The quantity of flow is measured with respect to time.
In the falling head test a column of water is allowed to flow through the sample and the reading of head changes versus time is taken.
The flow rate of water through the sample should be slow enough to get an accurate readings.

Permeability [ASTM D 4491]

This permeability test is derived from the permittivity test using the nominal thickness of the geotextile materials.
In this test permittivity is divided by the thickness to determine permeability.
This is generally used to compare the geotextile material permeability to the soil’s permeability
In this test the water flow rate the amount of water that travels through the geotextile material is expressed in gallons per minute per square foot.

Transmissivity [ASTM D 4716]

In this transmissivity test the volumetric flow rate of water per unit width of sample specimen per unit gradient in a direction parallel to the plane of the specimen
In this the sum of the open area of the sample of a geotextile material is then divided by the total area of the sample and expressed in percent (Areaof opening /Total area *100).
In this small piece of sample is held within a slide cover, inserted into a projector and the magnified image traced on a sheet of paper.
And using a planimeter, the magnified open spaces can be measured.

PHYSICAL PROPERTIES for testing materials:

Weight (Mass per Unit Area) [ASTM D 5261]:

The mass per unit area is determined by cutting a minimum of 10 specimens.
The cutted specimen should be atleast 100 mm square, and then weighing them on accurate scale.

Thickness [ASTM D 5199]

The average thickness of geotextile material is measured using a thickness guage (electronic micrometer) under a specified applied pressure.
This is measured usually by a dead weight mechnanism.
The pressure requirement used is 20 kPa applied through a circular loading tip with a diameter of 6.35 mm.

Grab strength (Grab tensile) and Elongation [ASTM D 4632]:

This method is the standard strength test used in geotextile industry. This method is used to determine the force or load at which the geotextile breaks and how far it stretches before it breaks.
In this a sample is placed in clamps and mechanically pulled at a constant rate until it ruptures.
Sample size is 4” wide* 8” long.
The clamps is 1”*2”. The clamp is buried 1” deep.
The 1” of the sample is left unclamped on each side of the 2” section of the clamp.
In this, the force is not applied to the whole sample and the result is reported in”pounds of force”

Wide Width strength (ww Tensile) and Elongation[ASTM D 4595]:

This test Provides a more reliable assessment of geotextile strength . This method is used to calculate the required tensile strength .
This is typically only done with only woven (reinforcement) geotextiles.
This method requires the full width of the sample be clamped.
The clamps size are 8”*2”.
The sample size is 8” wide*8”long (minimum). It is a true tensile test.
Then the “pounds of force” is then divided by 8, multiplied by 12. And then the test result is reported as pounds per inch.

Tensile Creep [ASTM D5262 and D6992]:

This test method is used to geosynthetics (including geogrids) used in steepened slopes and retaining walls.
This test is performed by placing a load on a sample materials for up to 10,000 hours
Then the samples materials are gripped across their full width. And the elongation (strain) of the sample is monitored over the test period.
From these results, the time to rupture at various load level will cause rupture at a given time can be determined.
The sample size of 8”*8” sample with an 8”*2” clamp size is used.

Mullen Burst (Diaphragm Burst) [ASTM D3786]:

This test is used to determine the puncture strength of paper and was then adopted to textiles
The mullen burst determines the force required to rupturebthe geotextile as it is distended
In this a inflatable rubber membrane is used to deform the geotextile sample into the shape of a hemisphere through a 30mm diameter ring until it bursts.
The result is then reported in pounds per square inch (psi).

Puncture Strength [ASTM D4833]:

This test method is also used to determine the puncture resistance of geotextiles.
A sample is clamped without tension between circular plates of a slip- free ring clamp.
The force is exerted by a metal puncture rod attached to a load indicator against the center of the unsupported portion of the sample until break occurs.
The used puncture rod is made solid steel rod having diameter of 8mm and a 45 degree beveled edge.
The maximum force required is then recorded as a test result and used to report.

Trapezoidal Tear [ASTM D4533]:

In this trapezoidal tear test the samples is cut in shape of isosceles trapezoid and then small cut is done on one side of the trapezoid.
After cutting in small cuts the 2 non –parallel sides of the geotextile is gripped in parallel flat faced clamps in such a way that it allows the tear to propagate as the jaws move apart and then the required strain rate is applied.
A continuous tearing is applied and in this way maximum force used is recorded
This procedure requires the jaw faces to be atleast 2”*3”.

Friction [ASTM D 5321]

This test is direct adaptation of shear test.
In this test a fabric is fixed to the top half of the shear box and a standard laboratory soil is used in the bottom half.
The force causes a sliding between the fabric and the soil is used to determined for different normal stresses and the shear strength parameters are obtained.

UV Resistance [ASTM D 4355]

This test is a measure of the potential for the deterioration of tensile strength in the fabric due to exposure to ultraviolet light and water.
This is typically expressed at 500 hours exposure .
For some products, such as ground cover, it is expressed in specified as high as 25,000 hours exposure.

CONCLUSION

Test methods are a means to understand the product.
Test results give a true pictureof the product.
Test results are dependable when conducted exactly as per the standard test methods.

REFERENCES