The tensile creep and creep rupture behavior of geosynthetic materials is an important factor in evaluating their long-term performance, particularly when geosynthetics are used as reinforcement or load-bearing components in geotechnical and civil engineering structures. Under sustained tensile loads, geosynthetic materials may undergo progressive deformation over time and, in some cases, eventually experience creep rupture. Therefore, standardized tensile creep testing is essential for assessing their long-term strength, deformation characteristics, and structural reliability.

This article introduces the specimen preparation, test procedure, and test report requirements for tensile creep and creep rupture testing of geosynthetic materials. It provides practical guidance on specimen preparation, loading conditions, data collection, test result evaluation, and report preparation, helping laboratories and engineers conduct reliable and repeatable tests in accordance with relevant testing standards.

I. Specimen Preparation

1. Sampling: Sampling shall be carried out in accordance with the provisions of this specification T 1101—2006.

2. Specimen Quantity

(1) For determination of tensile creep properties: 4 specimens;

(2) For determination of tensile creep rupture: 12 specimens;

(3) For determination of tensile strength: In accordance with the provisions of this specification T1121.

Note: If specimens of representative width are used for determination of tensile creep properties and tensile creep rupture, the number of specimens should be considered when cutting the specimens.

3. Specimen Dimensions

3.1 Determination of Specimen Dimensions

(1)The specimen dimensions shall be compatible with the dimensions of the testing apparatus.

(2)The specimen dimensions shall be appropriate for the accuracy of the measuring device used.

(3)The specimen dimensions shall be determined according to the representative technical width.

(4)Ensure that the distance between each of the two reference points marking the gauge length and the grips is not less than 20 mm.

3.2 Minimum Marking Length of Specimens

(1) Not less than 200 mm;

(2) For geogrids, not less than two complete grids;

(3) For all samples, the measurement accuracy of the marking length must be ±0.1%.

3.3 Specimen Width

(1) For products exhibiting significant lateral shrinkage (≥10%) when tested according to this specification T 1121, the specimen width shall be 200 mm;

(2) For geogrids: at least 3 complete units;

(3) For all other products: one technical representative width.

Note: Specimen size primarily affects the feasibility and accuracy of the test; the required load depends on the specimen width.

4. Sample conditioning and condition setting: Perform in accordance with Article 5 of this specification T 1101—2006.

II. Test Procedure

1. Determination of Tensile Creep Properties

Under specified temperature and humidity conditions, a constant static load is applied to the specimen. The load is uniformly distributed across the entire width of the specimen. The elongation of the specimen is recorded continuously or at specified time intervals, and the load is maintained for 1000 hours. If the specimen fractures in less than 1000 hours, the fracture time is recorded.

1.1 Determine the tensile properties of the specimen for its width according to the provisions of this specification T 1121, including tensile strength, elongation at break, and reduction of diameter in the transverse direction.

1.2 Determine the tensile strength and elongation at break of a specimen of representative width according to the provisions of this specification T 1121. If necessary, evaluate the validity of the representative width specimen used, as detailed in the calculation examples in the explanatory notes.

1.3 After marking reference points on the specimen according to the marking length required in 3.2 of this method, mount the specimen on the fixture.

1.4 Apply a pretension equal to 1% of the tensile strength, expressed in kN/m.

1.5 Determine the mark length as the initial mark length, accurate to ±0.1%.

1.6 If applicable, install and fix the elongation meter, and set the initial elongation value to 0.

1.7 Select four loads from the following range for testing:

Tensile strength of 10%, 20%, 30%, 40%, 50%, and 60% was applied to four specimens. Four different loads were applied to each specimen, with a loading time not exceeding 60 seconds.

1.8 Measurement Time

The end of loading shall be taken as the zero time point of the test. Measure the change in gauge length at the following specified time intervals, with an accuracy of ±1%:

1, 2, 4, 8, 15, 30, and 60 min

2, 4, 8, and 24 h

3, 7, 14, 21, and 42 days

2. Determination of Tensile Creep Rupture

Under the specified temperature and humidity conditions, a constant static load is applied to the specimen and distributed uniformly across its entire width. The load is maintained until the specimen ruptures. The timing system records the time to rupture, and timing stops when the specimen breaks.

2.1 Determine the wide-width tensile properties of the sample in accordance with T 1121 of this test specification, including tensile strength, elongation at break, and transverse contraction of the specimen.

2.2 Determine the tensile strength and elongation at break of the specimen with the representative technical width in accordance with T 1121 of this test specification. If necessary, evaluate the validity of the specimen at the representative technical width used.

2.3 Mount the specimens on the fixture.

2.4 Select four load levels from 30% to 90% of the specimen's tensile strength for testing. Apply one load level to three specimens, for a total of 12 specimens tested. The zero-point time of the test is the end of the loading period.

Note: Select four equally spaced logarithmic time intervals, such as 100h, 500h, 2000h, and 10000h. Estimate the load level that might cause the three parallel tests to fail at 100h. Based on this result, estimate the load that might cause failure at 500h. Then estimate the other two load levels.

2.5 Record the time when creep rupture occurs.

3. Requirements for Using Specimens with Representative Technical Width

When specimens with a representative technical width of less than 200 mm are used, it is important to properly determine the specimen width.

3.1 Specimens for Geogrids and Geonets

Specimens with a representative technical width for geogrids and geonets shall meet the following requirements:

Determine the wide-width tensile strength and elongation of the specimen in accordance with T 1121 of this test specification. Prepare reduced-width specimens and measure their tensile strength and elongation. A reduced-width specimen may be considered to have the representative technical width when both of the following conditions are satisfied:

The deviation in tensile strength does not exceed ±5%;

The deviation in elongation does not exceed ±20%.

When calculating tensile strength, the number of tensile elements per meter of width shall also be determined. Place as much of the full roll width of the sample as possible on a flat surface. Using a ruler with a length of at least 1.5 m, measure the width corresponding to the tensile elements within a length of approximately 1 m, denoted as W. Calculate the number of tensile elements per meter of width based on the measured number of elements, to the nearest 0.1 element. The number of tensile elements on the specimen shall also be recorded. (See Example 1 in the explanatory notes for details.)

3.2 Determination of the Technical Representative Width of Geotextiles

Prepare widened specimens with a width less than 200 mm and greater than 50 mm. Determine the tensile strength and elongation of both wide and narrowed specimens according to the provisions of this specification T 1121, and calculate the tensile strength and elongation of specimens of both widths. If the widened specimen simultaneously meets the requirements that the tensile strength deviation does not exceed ±5% and the elongation deviation does not exceed ±20%, it can be determined as the technical representative width (see Example 2 in the explanatory notes for details).

III. Test Report The test report shall include the following

(1) Sample name, specifications, and condition description;

(2) Start and end dates of the test;

(3) Test apparatus;

(4) Conditioning of the specimen and atmospheric conditions used in the test;

(5) Average tensile strength, elongation, and transverse shrinkage of the specimen in the wide strip tensile test;

(6) If required, provide detailed information supporting the determination of whether specimens with the representative technical width are suitable for creep testing.

(7) If required, perform creep testing using specimens with the dimensions specified by the sample submitter, and calculate the average tensile strength and elongation.

(8) Description of the loading method.

(9) Express the tensile creep load as a percentage of the tensile strength specified in Item (5).

(10) Present the results showing the relationship between creep elongation and time.

(11) Nominal gauge length.

(12) A logarithmic relationship curve between deformation and time for each specimen under each load level, including all data points.

(13) The tensile creep rupture time for each specimen.

(14) A detailed description of any deviations from the specified test procedure.