ASTM D7556-10

Test Methods A, B, and C provide a means of evaluating the tensile modulus of geogrids and geotextiles for applications involving small-strain cyclic loading. The test methods allow for the determination of cyclic tensile modulus at different levels of prescribed or permanent strain, thereby accounting for possible changes in cyclic tensile modulus with increasing permanent strain in the material. These test methods shall be used for research testing and to define properties for use in specific design methods.

In cases of dispute arising from differences in reported test results when using these test methods for acceptance testing of commercial shipments, the purchaser and supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens which are as homogeneous as possible and which are from a lot of material of the type in question. The test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using Student’s t-test for unpaired data and an acceptable probability level chosen by the two parties before the testing began. If a bias is found, either its cause shall be found and corrected or the purchaser and supplier shall agree to interpret future test results in light of the known bias.

All geogrids can be tested by Test Methods A or B. Some modification of techniques may be necessary for a given geogrid depending upon its physical make-up. Special adaptations may be necessary with strong geogrids, multiple layered geogrids, or geogrids that tend to slip in the clamps or those which tend to be damaged by the clamps.

Most geotextiles can be tested by Test Method C. Some modification of clamping techniques may be necessary for a given geotextile depending upon its structure. Special clamping adaptations may be necessary with strong geotextiles or geotextiles made from glass fibers to prevent them from slipping in the clamps or being damaged as a result of being gripped in the clamps.

These test methods are applicable for testing geotextiles either dry or wet. It is used with a constant rate of extension type tension apparatus.

These test methods may not be suited for geogrids and geotextiles that exhibit strengths approximately 100 kN/m (600 lbf/in.) due to clamping and equipment limitations. In those cases, 100 mm (4 in.) width specimens may be substituted for 200 mm (8 in.) width specimens.

1.1 These test methods cover the determination of small-strain tensile properties of geogrids and geotextiles by subjecting wide-width specimens to cyclic tensile loading.

1.2 These test methods (A, B, and C) allow for the determination of small-strain cyclic tensile modulus by the measurement of cyclic tensile load and elongation.

1.3 This test method is intended to provide properties for design. The test method was developed for mechanistic-empirical pavement design methods requiring input of the reinforcement tensile modulus. The use of cyclic modulus from this test method for other applications involving cyclic loading should be evaluated on a case-by-case basis.

1.4 Three test methods (A, B, and C) are provided to determine small-strain cyclic tensile modulus on geogrids and geotextiles.

1.4.1 Test Method A—Testing a relatively wide specimen of geogrid in cyclic tension in kN/m (lbf/ft).

1.4.2 Test Method B—Testing multiple layers of a relatively wide specimen of geogrid in cyclic tension in kN/m (lbf/ft).

1.4.3 Test Method C—Testing a relatively wide specimen of geotextile in cyclic tension in kN/m (lbf/ft).

1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard.

1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.