TS010-Test Methods of Geotextiles

Test Methods of Geotextiles

Chinmayee Chandorkar

Department of Textile Technology

DKTE Engineering College, Icchalkaranji,India

ABSTRACT:
The geosynthetics industry has expanded rapidly in recent years and technical textiles can be categorized in various parts and has wide range of products. Among various types of technical textiles, geotextiles are permeable geosynthetic material made of textile materials which are ideal materials for infrastructure works such as roads, harbors and many others.
This paper provides an overview of all the essential test methods of geotextile and thus there application.

INTRODUCTION :
Geotextiles were one of the first textile products in human history. Excavation of ancient Egyptian sites show the use of mats made from grass and linen. These early geotextiles were made of natural fibres, fabrics or vegetation mixed with soil to improve road quality, particularly when roads were made of unstable soil.

Geotextile have been used very successfully in road construction for over 30years. Their primary function is to separate the sub base from the sub grade resulting in stronger road construction. The geotextile perform this function by providing a dense mass of fibres at the interface of two layers.

Geotextiles have proven to be amongst the most versatile and cost-effective ground modification materials. Their use has expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal and hydraulic engineering.

TYPES OF GEOTEXTILE:

• Woven Monofilament
• Woven Multifilament
• Woven slit-film monofilament
• Woven slit-film multifilament
• Non-woven continuous filament heat bonded
• Non-woven continuous filament needle punched
• Non-woven staple needle-punched
• Non-woven resin bonded
• Other woven and nonwoven combinations
• Knitted

FUNCTIONS:

SEPERATION:

A flexible porous geotextile is used.

Placed between dissimilar material.

The integrity and functioning of dissimilar material remains intact.

FILTRATION:

Allows for adequate liquid flow with limited soil loss.

DRAINAGE: (Transmissivity):

Provides an avenue for flow of water through the plane of geotextile.

SEALING:

Geotextile acts as a liquid barrier.

Minimizes vertical flow of water into the pavement structure.

REINFORCEMENT :
Improves strength and deformation properties.

Reinforcement provided by geotextiles allow embankments and roads to be built over very weak soils and allows for steeper embankments to be built.

ESSENTIAL PARAMETERS:

MASS PER UNIT AREA (UNIT WEIGHT):

• Usually given in unit of g/m^2
• Determined by weighing specimens.
• Linear dimensions measured without any tension

PUNCTURE STRENGTH:

• To measure puncture strength.
• Measured in Newton

BURST STRENGTH:

Calculates strength of geotextile to a continuous hydraulic load.

Unit – Pounds per Square inch kilo Pascal

DYNAMIC PUNCTURE:

• To measure strength to falling objects.
• Expressed in mm.

PERMEABILITY:

• Measures the rate at which liquids can pass through the geotextile.
• Expressed in litres per square meters per second.

APPARENT OPENING SIZE:

• Largest opening dimension through which the soil may pass.

GRAB TENSILE STRENGTH AND ELONGATION:

• Measures by loading it continuously.
• Breaking load expressed in Newton.
• Elongation at break expressed in percent.

TEST METHODS:

Geotextile properties are generally categorized in the following groups: physical, mechanical, hydraulic, endurance, and degradation. Each group encompasses testing that characterizes different aspect of geotextiles and their performance. In addition to these property groups, geotextile testing may be characterized as either index or performance. Index tests are used for general characterization of a geotextile product and do not provide values that can be directly used for design purposes, while performance testing provides information about the expected behavior of a geotextile in an engineered system. Index testing is performed on the geotextile alone or in isolation, while performance testing often involves both the geotextile and soil to be placed in an engineered system.

Physical properties are used to characterize the geotextile in the as received, manufactured condition, and are obtained with Index testing. Common physical properties include specific gravity, mass per unit area, thickness and stiffness.

Mechanical properties provide an understanding of geotextile strength and compressibility under varying loads. Common mechanical properties include compressibility, tear strength, tensile strength, puncture strength and seam strength.

The ability of water to flow through or within a geotextile is a function of geotextile hydraulic properties. Common hydraulic properties include porosity, percent open area, Apparent Opening Size(AOS), permittivity and transmissivity.

While all the tests describes thus far have focused on the short term behavior of geotextiles, the performance of a given geotextile in an engineered system will vary over the geotextile’s lifetime. This is commonly due to damage of the geotextile during installation, the affects of sustained loading on the geotextile structure and strength, and the effects of migrating soil particles on the hydraulic properties of the geotextile. Endurance testing focuses on long term textile behavior. Common testing addresses creep response, stress relaxation, long term clogging, abrasion and installation damage.

Long term performance of geotextile is also affected by geotextile degradation via different mechanisms including ultraviolet light (sunlight), chemical reactions with geotextile polymers, and thermal degradation. Degradation testing is important in determining the ultimate lifetime of geotextile in an engineered system.

Property	Reporting Units	Standard Test Designation
Grab Strength	lbf ( kN )	ASTM D 4632
Sewn Seam Strength	lbf ( kN )	ASTM D 4632
Tear Strength	lbf ( kN )	ASTM D 4533
Puncture Strength	lbf ( kN )	ASTM D 6241/ ASTM D 4833
Permittivity	sec-1	ASTM D 4411
AOS	US Sieve No. (mm)	ASTM D 4751
Ultraviolet stability	%	ASTM D 4355

MASS PER UNIT AREA : (ASTM D 5261)

• It should be measured to the accuracy nearest to 0.01% of total specimen weight.
• Fabric cost is directly related to mass per unit area.
• Important for economy of project.
• In this testing, the specimen is kept on the weighing machine and the weight is noted.

PUNCTURE STRENGTH:

• Used to determine the puncture or rupture characteristics of a material.
• This is generally a compressive test where a material is compressed by a probe or other type of device until the material ruptures or until an elongation limit is achieved.
• It is commonly used to determine the strength of a material.

In this method, the material is placed between two clamps or discs at bottom and the dowel is lowered gradually. The moment at which the material punctures is noted as the puncture strength.

BURST STRENGTH:

• It determines the strength or force required to rupture or burst the fabric.
• It is essential to maintain the gripping force to ensure reproducible test results.

In this method the material is placed between two discs and the air pressure is applied from bottom, a bulb shaped equipment is placed on top and vaccum is created. Thus after a certain point, the material bursts.

Dynamic Puncture Strength :

• Denotes the relative ability of a material or object to inhibit the intrusion of  foreign object.

In this method the dowel is not lowered gradually and made to fall suddenly on the fabric specimen that is clamped. And the weight of the dowel is different for different specimen depending on the strength.

Permeability :

• Used to determine the permeability of granular soils like sands and gravels containing little or no silt.
• This testing method is made for testing reconstituted or disturbed granular soil samples.

Apparent Opening Size:

This test method indicates the apparent opening size in a geotextile, which reflects the approximate largest opening dimension available for soil to pass through.

Any of the two methods are used for this testing:
DRY METHOD:

WET METHOD:

GRAB TENSILE STRENGTH AND ELONGATION :

• Used for geotextile fabrics to determine the breaking load and elongation.
• This test method measures the ultimate strength and elongation.
• In this method, the specimen is clamped between two jaws. One is stationary and the other is movable jaw, the movable jaw moves gradually and the specimen starts to elongate. After a certain point the specimen breaks.

APPLICATIONS:

Every textile product applied under the soil is a geotextile. The products are used for reinforcements of streets, embankments, ponds, pipelines, and similar applications. Depending on the required function, they are used in open-mesh versions, such as woven or, rarely, warp knitted structure, or with a closed fabric surface, such as a non-woven. The mode of operation of a geotextile in any application is defined by six discrete functions: separation, filtration, drainage, reinforcement, sealing and protection. Depending on the application the geotextile performs one or more of the these function simultaneously.

CONCLUSION :
Geotextile is a newly emerging field, and they are used worldwide. Textile are not only in clothing the human body but also on our motherland in order to protect her. Thus they have a bright future due to their multifunctional characteristics. It has become an integral part of civil engineering project, structure or system. Thus, taking into consideration their performance, it is essential to perform various tests in order to control the quality and decide their end usage depending on the test results. Extensive awareness should be created among the people about the test methods and application of geotextile.

REFERENCES :

• Jorge G. Zornberg, Nathan Thompson, Application Guide and Specifications for Geotextiles in Roadway Application. [Online] 2012
• Dr. Bipin J Agrawal, Geotextile: It’s Application to Civil Engineering- Overview. [Online] 2011