TS007-Test Methods of Geotextiles



Test Methods of Geotextiles
Palak Solanki
Department of Textile Technology
DKTE Engineering College ,Icchalkaranji, India
Abstract
Geotextiles are polymer fabric used in the construction of roads, drains, harbor works, and for land reclamation and many other civil engineering purposes. Testing of geotextile material is important so as to determine if a particular geotextile material is suitable for a particular application. Geotextiles are kind of geosynthetic material that has become more and more popular over past fifteen years. The material owes its success in more than 80 applications to a large extent to its resistance to biodegradation. EDANA Association says that, “By being lighter, thinner and more resource efficient than gravel, nonwoven geotextiles offer both an environmental benefit and cost savings to the user.

Introduction 
Geotextile is typically defined as any permeable textile material used to increase soil stability, provide erosion control or aid in drainage. More simply put if it is made of textile and buried in the ground it is probably a geotextile! Due to global infrastructure projects in emerging markets of Asia Pacific, the Middle East and Latin America, along with governmental policies and environmental standards, demand for geotextiles is expected to grow.

HISTORY
Geotextiles were originally intended to be an alternative to granular soil filters. The original, and still sometimes used, term for geotextiles is filter fabrics. Work originally began in the 1950s with R.J. Barrett using geotextiles behind precast concrete seawalls, under precast concrete erosion control blocks, beneath large stone riprap, and in other erosion control situations. He used different styles of woven monofilament fabrics, all characterized by a relatively high percentage open area. He discussed the need for both adequate permeability and soil retention, along with adequate fabric strength and proper elongation and set the tone for geotextile use in filtration situations.

Properties of geotextiles
Three main characteristics required and specified for a geotextile are
  • Mechanical responses
  • Filtration ability
  • Chemical resistance

These are the properties that produce require working effect. They are developed from the combination of the physical form of the polymer fibers, their textile construction and the polymer chemical characteristics.
For example – the mechanical response of a geotextile will depend upon the orientation and regularity of the fibers as well as the type of polymer from which it is made. Also, the chemical resistance of a geotextile will depend upon the size of the individual component fibers in the fabric, as well as their chemical composition – fine fibers with a large specific surface area are subject to more rapid chemical attack than coarse fibers of the same polymer.

Testing methods of geotextiles
Mechanical properties
ASTM D4533 Trapezoid Tearing Strength of Geotextiles:
ASTM D4533 is an index test used to measure the force required to continue or propagate a tear in woven or non-woven geotextiles by the trapezoid method. The trapezoid tear method is a test that produces tension along a reasonably defined course such that the tear propagates across the width of the specimen. Specimens are 3 inches wide by 8 inches long and marked with an isosceles trapezoid. A preliminary 0.625 inch long cut is made on the specimen. The specimen is clamped along the marked trapezoid and then pulled in tension at a constant crosshead speed. The maximum force is recorded and reported as the tearing strength.



ASTM D4632 Grab Test for Geotextiles
ASTM D4632 is an index test which provides a procedure for determining the breaking load (grab strength) and elongation (grab elongation) of geotextiles using the grab method. ASTM D4632 covers the determination of breaking load (grab strength) and elongation (grab elongation) of geotextiles using the grab method.The grab method is a modified tensile test in which the specimen is pulled in tension at a constant crosshead rate and continues until specimen rupture. The specimen size is 4 inches wide by 8 inches long. Edge effects are eliminated by clamping the specimen with 1 inch wide by 2 inch long clamps, therefore leaving the specimen unclamped on the edges.


ASTM D4595 Wide-Width Tensile Test Equipment for Geotextiles

ASTM D4595 measures the tensile properties of geotextiles using a wide-width strip specimen tensile method. ASTM D4595 is applicable to most geotextiles that include woven fabrics, nonwoven fabrics, layered fabrics, knit fabrics, and felts that are used for geotextile application. The determination of the wide-width strip force elongation properties of geotextiles provides design parameters for reinforcement type applications. Wide width specimen may be prepared wet or dry. A Universal Testing Machine which can pull at a Constant Rate of Extension (CRE) is required as well as the necessary grips with wide-width jaws to secure the sample.


ASTM D6241 Puncture Testing for Geotextiles
ASTM D6241 is a standard used to measure the force required to puncture a geotextile or geotextile-related product. For this test method, a geotextile test specimen is clamped with grips without tension between circular plates on a compression or tensile testing machine. A force is exerted against the center of the unsupported portion of the test specimen by a steel plunger attached to the load indicator. The relatively large size of the plunger provides a multidirectional force on the geotextile until a break occurs. The maximum force is the value of puncture strength.


Hydraulic properties
Water Permeability of Geotextiles-Permittivity Method
This test measures the quantity of water which can pass through a geotextile (normal to the plane) in an isolated condition. The permeability may be measured either in a constant head or falling head test, although constant head testing is more common due to the high flow rates through geotextiles. Since there are geotextiles of various thicknesses available it is better to evaluate them in terms of permittivity, which relates the quantity of water passing through a geotextile under a given head over a particular cross-sectional area. This test is useful in classifying geotextiles and for comparing the in-isolation water permeability of geotextiles. However, in drainage and filtration applications, the influence of in-soil confinement should be established prior to selecting a geotextile.



Constant Head Hydraulic Transmissivity
This method may be used to estimate the in-plane permeability of a geotextile or a composite drain. The sample is confined, at varying normal stresses, and the flow under a constant head is measured. This test is useful for classifying geotextiles and geocomposite drains and will provide information to allow comparisons of in- plane permeability to be made. However, in drainage applications, the influence of in-soil confinement should be established.


Durability properties
Temperature Stability
This test method provides a procedure for the determination of shrinkage of geotextile fabrics when exposed to elevated temperatures. The effect of the temperature is expressed as a percentage decrease in area of the geotextile. A specimen of geotextile is subjected to heat exposure for a pre-determined time period. The factor of shrinkage is determined after exposure by physical measurement.


AS 3706 Exposure to Light and Heat

This standard sets out a method for determining the durability of geotextiles when subjected to degradation due to exposure to light and heat by artificial means. A geotextile specimen is exposed to the heat and light generated by a high capacity incandescent light bulb. The tensile strength of the specimen after exposure is compared to the parent strength and the resultant loss in strength recorded.

ASTM D5970 Exposure to Natural Elements

This test method covers evaluating the deterioration in tensile strength and strain after outdoor exposure.  The deterioration is assessed as a reduction in strength and strain at failure from the unexposed geotextile.  The specific location of the light and weather exposure is made on the basis of a site specific decision between the parties involved. Geotextile specimens are exposed to the natural elements for a predetermined period of time. After exposure, the tensile strength of the specimens are determined and compared to the parent strength.



Applications of geotextiles:
  • Roadways, parking lots and construction sites
  • River canals and costal works
  • Filtration
  • Drainage
  • Reinforcement
  • Separation
  • Protection

Conclusion
Test methods are a means to understand the end use of any product. Test results give a true picture of the product. It is very important to conduct tests according to the given standards so as to ensure exact results and hence interpretate the quality of the product along with its end uses.
References:


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25 Comments

  1. Amazingly presented! Well done

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  2. Very well presented & its very informative...well done

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  3. Good one Palak 💯

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  4. This comment has been removed by the author.

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  5. great������

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  6. Informative! Very well presented ��

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  7. Impressive work.

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  8. Very informative well done

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  9. Very impressive good

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  10. Excellent work well done

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