ASTM D6768/D6768M-20

Standard Test Method for Tensile Strength of Geosynthetic Clay Liners

SIGNIFICANCE AND USE
5.1 This test method may be used for the acceptance testing of commercial shipments of GCLs, but caution is advised since information about between-laboratory precision is incomplete. Comparative tests as directed in 5.1.1 may be advisable.  
5.1.1 In cases of a dispute arising from differences in reported test results when using this test method for acceptance of shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias. The two parties should take a group of test samples that are as homogeneous as possible and which are from the lot of material in question.  
5.2 Some modification of clamping techniques may be necessary for a given GCL, depending upon its structure. Specimen clamping may be modified as required at the discretion of the individual laboratory, provided a representative tensile strength is obtained. In any event, the procedure described in Section 10 of this test method for obtaining tensile strength must be maintained.  
5.3 This test method is applicable for testing GCLs as received. It is used with a constant rate of extension type tension apparatus.
SCOPE
1.1 This test method establishes the procedures for the measurement of tensile strength of a geosynthetic clay liner (GCL). This test method is strictly an index test method to be used to verify the tensile strength of GCLs. Results from this test method should not be considered as an indication of actual or long-term performance of the geosynthetic(s) in field applications.  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Apr-2020
• ICS: 59.080.70 - Geotextiles
• Technical Committee: D35 - Geosynthetics
• Drafting Committee: D35.04 - Geosynthetic Clay Liners

Relations

• Replaces: ASTM D6768/D6768M-19 - Standard Test Method for Tensile Strength of Geosynthetic Clay Liners
• Effective Date: 01-May-2020
• Refers: ASTM D4439-24 - Standard Terminology for Geosynthetics
• Effective Date: 01-Feb-2024
• Refers: ASTM D6072/D6072M-18 - Standard Practice for Obtaining Samples of Geosynthetic Clay Liners
• Effective Date: 01-Jun-2018
• Refers: ASTM D4439-18 - Standard Terminology for Geosynthetics
• Effective Date: 15-Apr-2018
• Refers: ASTM D4439-17 - Standard Terminology for Geosynthetics
• Effective Date: 01-Aug-2017
• Refers: ASTM D123-17 - Standard Terminology Relating to Textiles
• Effective Date: 01-Mar-2017
• Refers: ASTM D5889/D5889M-16 - Standard Practice for Quality Control of Geosynthetic Clay Liners
• Effective Date: 01-Jul-2016
• Refers: ASTM D123-15b - Standard Terminology Relating to Textiles
• Effective Date: 15-Sep-2015
• Refers: ASTM D4439-15a - Standard Terminology for Geosynthetics
• Effective Date: 01-Sep-2015
• Refers: ASTM D123-15a - Standard Terminology Relating to Textiles
• Effective Date: 01-Sep-2015
• Refers: ASTM D4439-15 - Standard Terminology for Geosynthetics
• Effective Date: 01-Jul-2015
• Refers: ASTM D123-15 - Standard Terminology Relating to Textiles
• Effective Date: 01-Apr-2015
• Refers: ASTM D6072/D6072M-09(2015) - Standard Practice for Obtaining Samples of Geosynthetic Clay Liners
• Effective Date: 01-Jan-2015
• Refers: ASTM D4439-14 - Standard Terminology for Geosynthetics
• Effective Date: 01-Mar-2014
• Refers: ASTM D123-13ae1 - Standard Terminology Relating to Textiles
• Effective Date: 15-Jun-2013

Overview

ASTM D6768/D6768M-20: Standard Test Method for Tensile Strength of Geosynthetic Clay Liners establishes a reliable procedure for measuring the tensile strength of geosynthetic clay liners (GCLs). GCLs are manufactured hydraulic barriers composed of clay bonded to one or more layers of geosynthetic material, widely used in civil engineering and environmental containment applications. This standard provides an index test method, ensuring consistent quality and performance verification of GCL materials, rather than direct field performance prediction. It is internationally recognized, following World Trade Organization principles for standards development.

Key Topics

• Purpose and Scope

  • Designed for the measurement and verification of tensile strength in GCLs.
  • Applicable for both SI and inch-pound units, with no mixing of the two systems.

• Testing Methodology

  • Utilizes a constant rate of extension (CRE) tensile testing machine.
  • Specifies sample preparation, clamping procedures, and handling during testing.
  • Recommendations for comparative testing between parties in case of disputes.

• Sampling and Test Conditions

  • Details on sample selection, positioning, and specimen preparation from GCL rolls.
  • Testing should take place in controlled laboratory conditions (21 ± 2°C, 50–70% relative humidity).

• Reporting and Documentation

  • Test results should include all specimen values, average tensile strength, standard deviations as requested, type of GCL, equipment used, and complete traceability details.
  • Notes potential adjustments for specimen clamping based on GCL structure.

• Precision and Bias

  • Recommendations to exercise caution in acceptance testing due to limited inter-laboratory precision data.
  • No inherent bias identified with the standard, as tensile strength is method-defined.

Applications

The ASTM D6768/D6768M-20 standard is critical across industries and sectors relying on GCLs for containment and environmental protection. Key applications include:

• Quality Control in Manufacturing:
  Utilized during production and pre-delivery testing of geosynthetic clay liners to ensure consistency and mechanical integrity.

• Acceptance Testing:
  Applied for acceptance of commercial shipments, providing a benchmark for tensile strength compliance before GCLs are used in projects.

• Project Specification and Procurement:
  Enables project designers and engineers to specify and verify material requirements for landfill liners, mining containment, wastewater lagoons, and other environmental or civil works.

• Research and Product Development:
  Essential for product comparison, R&D, and development of new geosynthetic clay liner technologies.

Related Standards

For comprehensive evaluation and quality assurance of geosynthetic clay liners, ASTM D6768/D6768M-20 is often used in conjunction with the following standards:

• ASTM D76/D76M: Specification for Tensile Testing Machines for Textiles
• ASTM D123: Terminology Relating to Textiles
• ASTM D4439: Terminology for Geosynthetics
• ASTM D5889/D5889M: Practice for Quality Control of Geosynthetic Clay Liners
• ASTM D6072/D6072M: Practice for Obtaining Samples of Geosynthetic Clay Liners

These standards help support robust quality control, consistent terminology, and reliable sampling methods in geosynthetic materials testing.

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Keywords: ASTM D6768, tensile strength, geosynthetic clay liner, GCL, index test, quality control, environmental containment, laboratory testing, civil engineering standards, geosynthetics

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6768/D6768M − 20
Standard Test Method for
Tensile Strength of Geosynthetic Clay Liners
This standard is issued under the fixed designation D6768/D6768M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D6072/D6072MPractice for Obtaining Samples of Geosyn-
thetic Clay Liners
1.1 This test method establishes the procedures for the
measurement of tensile strength of a geosynthetic clay liner
3. Terminology
(GCL). This test method is strictly an index test method to be
3.1 Definitions:
used to verify the tensile strength of GCLs. Results from this
3.1.1 geosynthetic clay liner, n—a manufactured hydraulic
test method should not be considered as an indication of actual
barrier consisting of clay bonded to a layer or layers of
or long-term performance of the geosynthetic(s) in field
geosynthetic material(s). D4439
applications.
3.2 For terminology of other terms used in this test method,
1.2 The values stated in either SI units or inch-pound units
refer to Terminologies D123 and D4439.
are to be regarded separately as standard. The values stated in
each system may not be exact equivalents; therefore, each
4. Summary of Test Method
system shall be used independently of the other. Combining
4.1 A 100-mm [4-in.] wide specimen is gripped across its
values from the two systems may result in nonconformance
entirewidthintheclampsofaconstantrateofextension(CRE)
with the standard.
type tensile testing machine operated at a prescribed rate of
1.3 This standard does not purport to address all of the
extension, applying a longitudinal force to the specimen until
safety concerns, if any, associated with its use. It is the
the specimen ruptures.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
5. Significance and Use
mine the applicability of regulatory limitations prior to use.
5.1 This test method may be used for the acceptance testing
1.4 This international standard was developed in accor-
ofcommercialshipmentsofGCLs,butcautionisadvisedsince
dance with internationally recognized principles on standard-
information about between-laboratory precision is incomplete.
ization established in the Decision on Principles for the
Comparative tests as directed in 5.1.1 may be advisable.
Development of International Standards, Guides and Recom-
5.1.1 In cases of a dispute arising from differences in
mendations issued by the World Trade Organization Technical
reportedtestresultswhenusingthistestmethodforacceptance
Barriers to Trade (TBT) Committee.
of shipments, the purchaser and the supplier should conduct
comparative tests to determine if there is a statistical bias. The
2. Referenced Documents
two parties should take a group of test samples that are as
2.1 ASTM Standards:
homogeneous as possible and which are from the lot of
D76/D76MSpecification for Tensile Testing Machines for
material in question.
Textiles
5.2 Some modification of clamping techniques may be
D123Terminology Relating to Textiles
necessary for a given GCL, depending upon its structure.
D4439Terminology for Geosynthetics
Specimen clamping may be modified as required at the
D5889/D5889MPractice for Quality Control of Geosyn-
discretion of the individual laboratory, provided a representa-
thetic Clay Liners
tive tensile strength is obtained. In any event, the procedure
describedinSection10ofthistestmethodforobtainingtensile
This test method is under the jurisdiction of ASTM Committee D35 on
strength must be maintained.
Geosynthetics and is the direct responsibility of Subcommittee D35.04 on Geosyn-
thetic Clay Liners.
5.3 This test method is applicable for testing GCLs as
Current edition approved May 1, 2020. Published May 2020. Originally
received. It is used with a constant rate of extension type
approved in 2002. Last previous edition approved in 2019 as D6768/D6768M–19.
DOI: 10.1520/D6768_D6768M-20. tension apparatus.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6768/D6768M − 20
6. Atmospheric Conditions 10.3 Insertion of Specimen in Clamps—Mountthespecimen
centrally in the clamps. The specimen must be visually
6.1 Atmospheric Conditions:
observed25mm[1in.]extendedpasttheclamp.Thespecimen
6.1.1 The atmospheric conditions of the laboratory deter-
lengthinthemachinedirectionmustbeparalleltothedirection
mining tensile strength of geosynthetic clay liners shall be:
of application of force.
relative humidity between 50 to 70% and a temperature of 21
6 2°C [70 6 4°F]. 10.4 Measurement of Tensile Strength—Start the tensile
testing machine.
7. Apparatus 10.4.1 Continuetestingthespecimenuntilcompleterupture
and record the maximum tensile force of the GCL.
7.1 Tensile Testing Machine—A constant rate of extension
(CRE) type of testing machine described in Specification
NOTE1—Insomeinstances,itmayberequiredtodetermineelongation.
In these cases, the user should indicate the criteria at which elongation is
D76/D76Mshallbeusedwithaminimumprecisionmeasuring
–4
required.
capability of 0.1 N/m [5.71 × 10 lbf/in.].
10.4.2 Readings of force and time shall be taken at a
7.2 Clamps—The clamps shall be a minimum 25 by
minimum rate of 20 readings per second.
100mm [1 by
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6768/D6768M − 19 D6768/D6768M − 20
Standard Test Method for
Tensile Strength of Geosynthetic Clay Liners
This standard is issued under the fixed designation D6768/D6768M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method establishes the procedures for the measurement of tensile strength of a geosynthetic clay liner (GCL). This
test method is strictly an index test method to be used to verify the tensile strength of GCLs. Results from this test method should
not be considered as an indication of actual or long-term performance of the geosynthetic(s) in field applications.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in nonconformance with the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D76/D76M Specification for Tensile Testing Machines for Textiles
D123 Terminology Relating to Textiles
D4439 Terminology for Geosynthetics
D5889/D5889M Practice for Quality Control of Geosynthetic Clay Liners
D6072/D6072M Practice for Obtaining Samples of Geosynthetic Clay Liners
3. Terminology
3.1 geosynthetic clay liner, n—a manufactured hydraulic barrier consisting of clay bonded to a layer or layers of geosynthetic
material(s). D4439
3.1 Definitions:
3.1.1 geosynthetic clay liner, n—a manufactured hydraulic barrier consisting of clay bonded to a layer or layers of geosynthetic
material(s). D4439
3.2 For terminology of other terms used in this test method, refer to Terminologies D123 and D4439.
4. Summary of Test Method
4.1 A 100-mm [4-in.] wide specimen is gripped across its entire width in the clamps of a constant rate of extension (CRE) type
tensile testing machine operated at a prescribed rate of extension, applying a longitudinal force to the specimen until the specimen
ruptures.
5. Significance and Use
5.1 This test method may be used for the acceptance testing of commercial shipments of GCLs, but caution is advised since
information about between-laboratory precision is incomplete. Comparative tests as directed in 5.1.1 may be advisable.
This test method is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.04 on Geosynthetic Clay
Liners.
Current edition approved May 1, 2019May 1, 2020. Published May 2019May 2020. Originally approved in 2002. Last previous edition approved in 20182019 as
D6768/D6768M – 18.D6768/D6768M – 19. DOI: 10.1520/D6768_D6768M-19.10.1520/D6768_D6768M-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6768/D6768M − 20
5.1.1 In cases of a dispute arising from differences in reported test results when using this test method for acceptance of
shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias. The two parties
should take a group of test samples that are as homogeneous as possible and which are from the lot of material in question.
5.2 Some modification of clamping techniques may be necessary for a given GCL, depending upon its structure. Specimen
clamping may be modified as required at the discretion of the individual laboratory, provided a representative tensile strength is
obtained. In any event, the procedure described in Section 10 of this test method for obtaining tensile strength must be maintained.
5.3 This test method is applicable for testing GCLs as received. It is used with a constant rate of extension type tension
apparatus.
D6768/D6768M − 20
6. Atmospheric Conditions
6.1 Atmospheric Conditions:
6.1.1 The atmospheric conditions of the laboratory determining tensile strength of geosynthetic clay liners shall be: relative
humidity between 50 to 70 % and a temperature of 21 6 2 °C [70 6 4 °F].
7. Apparatus
7.1 Tensile Testing Machine—A constant rate of extension (CRE) type of testing machine described in Specification D76/D76M
–4
shall be used with a minimum precision measuring capability of 0.1 N/m [5.71 × 10 lbf/in.].
7.2 Clamps—The clamps shall be a minimum 25 by 100 mm [1 by 4 in.] and with appropriate clamping power to prevent
slipping or crushing (damage).
7.3 Die or Template, 100 by 200 mm (61 mm) [4 by 8 in. (60.04 in.)].
7.4 Miscellaneous—Knives, razor, etc., as required.
8. Sampling Sampling, Test Specimens, and Test SpecimensUnits
8.1 Lot Sample—For the lot sample, take rolls of GCLs as directed in an applicable material specification, Practice
D5889/D5889M, or as agreed upon between the purchaser and the supplier.
8.2 Laboratory Sample—For the laboratory
...