5.1 The Aperture Stability Modulus is a measure of the in-plane shear modulus, which is a function of other geogrid characteristics, most notably junction stability, flexural rib stiffness, and rib tensile modulus.

5.2 The test data can be used in conjunction with interpretive methods to evaluate the geogrid aperture stability at various traffic loads and base/subgrade conditions.

Note 1: Aperture stability modulus is referenced in the FHWA Geosynthetics Design and Construction Guidelines (2008) as an input parameter for the design of geogrid-reinforced unpaved roads using punched and drawn biaxial geogrids. Geogrids of different manufacturing process and material composition may use this property in calibration and validation of their material within the associated design.

5.3 This test method is not intended for routine acceptance testing of geogrid. This test method should be used to characterize geogrid intended for use in applications in which aperture stability is considered relevant.

1.1 This test method covers the procedure for measuring the “Aperture Stability Modulus” of a geogrid. (The terms “Secant Aperture Stability Modulus,” “Torsional Rigidity Modulus,” “In-plane Shear Modulus,” and “Torsional Stiffness Modulus” have been used in the literature to describe this same property.)

1.2 This test method is intended to determine the in-plane stability of a geogrid by clamping a center node and measuring the stiffness over an area of the geogrid. This test method is applicable for various types of geogrid.

1.3 This test method is intended to provide characteristic properties for design. The test method was developed for pavement and subgrade improvement calibrated design methods requiring input of aperture stability modulus.

1.4 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 non-conformance with the standard.

1.5 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.