Nonwoven Testing Methods for Geotextiles

Research reference: ASTM test methods and practices for geotextiles and geomembranes

Engineers buy geotextiles and geomembranes by test numbers. This reference article, in the collection contributed by Professor Kermit Duckett, lists the ASTM test methods and practices used to specify and verify geosynthetic materials: tensile and puncture tests for the fabrics, seam and stress-crack tests for the membranes, and exposure tests that estimate how buried materials age. Each entry gives the standard's number and what it determines, making the page a checklist that ties the geotextiles unit of this collection to procurement practice.

Tensile testing diagrams, specimen samples and a standards list on a research desk, no people

Testing Methods for Geotextiles    (Educational Research)

Education   Nonwoven Research

The Educational information in this section has been graciously donated to the Apparel Search Company by Professor Kermit Duckett.

 

Praveen Jana, Rammohan Nanjundappa & Hong Yin

INTRODUCTION

A geotextile is (as given in the terminology used for geosynthetics in ASTM Standard D 4439-87) "any permeable textile material used with foundation, soil, rock, earth, or any other geotechnical engineering material, as an integral part of manmade product, structure or system."

The various standards for testing the geotextiles are listed in Annual Book of ASTM Standards, volume 4.08 (geosynthetics) and volume 4.09 (geotextiles and geomembranes). A few important test methods are described in this paper and the rest are listed with the test number at the end of this paper.

TEST METHODS

1. Standard Test Method for Deterioration of Geotextiles from Exposure to Ultraviolet Light and Water (Xenon-Arc Type Apparatus) : ASTM Test Method D 4355-84.
This method determines the deterioration in tensile strength of geotextiles by exposure to ultraviolet light and water using an apparatus that employs a xenon-arc light source. This procedure compares five specimens (2 x 6 in.) of geotextiles in MD and CD under a standard set of conditions of humidity and temperature for three exposure times (0, 150, 300 and 500 hours), against unexposed specimens. The exposure consists of 120 min of light only, followed by 18 min or water spray and light. After being exposed to UV light, the specimens are subjected to cut or ravel strip tensile test. These results are compared to test results of unexposed specimens to give an indication of the deterioration in tensile strength of geotextiles by exposure to ultraviolet light and water. This method is not recommended for acceptance testing of commercial shipments.

2. Standard Test Method for Effects of Temperature on Stability of Geotextiles : ASTM Test Method D 4594-86.
This method measures the effects of temperature on the tensile strength and elongation properties of geotextiles. In this test, specimens of geotextile are conditioned at selected temperatures (typical of temperature that geotextiles are exposed to in actual usage) in an environmental chamber (capable of maintaining a temperature range from -40 to +100
C and able to regulate the test temperature within 2 C). While the selected temperatures are being maintained, two-inch cut or ravel strip tensile tests of five specimens (in MD and CD) are carried out. The same tests are carried out as control under the standard laboratory test conditions. Changes in strength and elongation as a result of exposure to different temperatures are thus determined. This test method is capable of evaluating the effects of temperature on geotextiles made from different polymers, different manufacturing processes, or both. This method can be used to test geotextiles made from nonwoven, woven, and composite fabrics (up to fabric strength of less than 1000 lb/in. width). But it cannot be used for knitted fabrics. This method is not recommended for testing of commercial shipments.

3. Standard Test Method for Tensile Properties of Geotexitles by Wide-width Strip Method : ASTM Test Method D 4595-86.
This method measures the tensile properties of geotextiles using a wide-width (8 x 8 in.) strip specimen tensile method. The width (which is greater than the length) of the specimen is the basic distinction between this method and other methods determining tensile properties. The greater width is to minimized the tendency of geotextiles to contract and also to provide a closer relationship to the expected behavior of geotextiles in actual usage. The dimensions of jaw faces need to be wider than 200 mm (8 in.) and the length needs to be a minimum of 50 mm (2 in.) in the direction of the applied force.

This procedure provides parameters for reinforcement applications. This method can be used for acceptance testing of commercial shipments.

4. Standard Test Method for Breaking Load and Elongation of Geotextiles (Grab Method): ASTM Test Method D 4632-86.
This method determines the breaking load (grab) and elongation (grab) of geotextiles using the grab method (only a part of the width of the specimen is gripped by the clamps). A continually increasing load is applied longitudinally to the test specimen until it ruptures. This method can be used if the effective strength of the fabric in use (that is, the strength of the material in a specific width together with the additional strength contributed by adjacent material) needs to be determined. Rectangular specimens (4 x 8 in.) must be cut in taking care that the longer dimension is parallel to the machine direction or cross machine direction depending on whether it is a MD or CD sample, respectively.

This method can be used for acceptance testing of commercial shipments. This procedure cannot be used for knitted geotextile materials.

5. Standard Test Method for Determining Apparent Opening Size of a Geotextile: ASTM Test Method D 4751-87.
Apparent Opening Size (AOS) for a geotextile is a property "which indicates the approximate largest particle that would effectively pass through the geotextile."

This method determines the AOS of a geotextile by sieving glass beads through a geotextile. A specimen is placed by sieve frame with sized glass beads on top of it. The frame with the geotextile is shaken laterally so that the jarring motion induces the beads to pass through the geotextile test specimen. This procedure is repeated with varius size glass beads on the same test specimen until the AOS of the geotextile is determined.

This method is useful because a geotextile and the adjacent soil need to be compatible. The apparent opening size (AOS) of a geotextile is a reflection of the approximate largest opening dimension testing of commercial shipments

6. Standard Test Method for Index Puncture Resistance of Geotextiles, Geomembranes, and Related Products: ASTM Test Method D 4833 - 88
Geomembranes are "very low permeability synthetic membrane liners or barriers used with any geotechnical engineering related material so as to control fluid migration in a man-made project, structure, or system.

Puncture resistance is "a test procedure which may contain a known bias but which may be used to establish an order for a set of specimens with respect to the property of interest."

The Index Puncture Resistance test is "a test procedure which may contain a known bias but which may be used to establish an order of a set of specimens with respect to the property of interest."

A test specimen (minimum specimen diameter is 100 mm) is clamped between circular plates of a ring clamp attachment secured in a tensile testing machine. A solid steel rod attached to the load indicator exerts force against the center of the specimen until it ruptures. The maximum force recorded is the puncture resistance of the specimen.

This method can be used for acceptance testing of commercial shipments.

7. Standard Test Method for Abrasion Resistance of Geotextiles (Sand Paper/sliding Block Method): ASTM Test Method D 4833 - 88. This test method determines the resistance of geotextiles to abrasion using an abrasion tester.

In this procedure, an abradant (with specified surface characteristics) is used to rub a test specimen (five specimens in MD and CD, 3 x 8
1/16 in.) that is mounted on a stationary surface. Under controlled conditions of pressure and abrasive action, the abradant is rubbed on a horizontal axis using a uniaxial motion. Resistance to abrasions is expressed as a percentage of original strength before abrading.

This method can be used for acceptance testing of commercial shipments, but cannot be used for geomembranes and grids.

Following are the listed test methods in the Annual Book of ASTM Standards: * the number in the brackets indicate the Volume number

GEOSYNTHETICS

GEOTEXTILES

GEOMEMBRANES

 

Reading the List

The standards group naturally by the question they answer. Strength questions are covered by the tensile methods — including the wide-strip tensile method for geomembranes (ASTM D 4885) — because a buried fabric fails by wide-width tension, not by the narrow-strip behavior of apparel tests. Damage questions are covered by puncture methods such as the pyramid puncture resistance test for unprotected and protected geomembranes (D 5494), which models the angular stone a liner must survive. Seam questions, unique to geomembranes, are covered by practices such as the pressurized air channel evaluation of dual-seamed geomembranes (D 5820), which tests a seam without cutting it.

Time is the third axis: D 4355 determines the deterioration in tensile strength of geotextiles from exposure to ultraviolet light, temperature and humidity in a xenon-arc apparatus — the installation-exposure risk — while D 5397 measures the stress-crack resistance of polyolefin geomembranes using a notched constant tensile load, the slow-crack failure mode that durability design must exclude. Used with the durability article in this unit, the list shows how a specification is actually assembled: index tests to qualify a product, performance tests to verify the design, and conformance tests to check what arrives on site.

Common Questions

What does ASTM D 4355 determine?

The deterioration in tensile strength of geotextiles from exposure to ultraviolet light, temperature and humidity, using a xenon-arc type apparatus.

Which standards address geomembrane seams and stress cracking?

D 5820 evaluates dual-seamed geomembranes by pressurized air channel, and D 5397 measures stress-crack resistance of polyolefin geomembranes using a notched constant tensile load test.

Which test covers puncture by angular material?

D 5494, the pyramid puncture resistance test for unprotected and protected geomembranes; tensile behavior is covered by methods such as the wide-strip test D 4885.

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