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1.1 This guide presents a description of how to use test results from reduction factor test reports for reinforcement geosynthetics. It is based solely on testing and reporting requirements as established in American Association of State Highway and Transportation Officials (AASHTO) standard AASHTO R 69-15, Standard Practice for Determination of Long-Term Strength for Geosynthetic Reinforcement. AASHTO R 69-15 is used to determine the long-term allowable material strength, T_al, that is solely product property performance dependant.

1.2 This guide is intended to assist designers and users of reinforcement geosynthetics when reviewing reports of reduction factor testing efforts. This guide is not intended to replace education or experience, or other alternative design procedures. This guide is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project’s many unique aspects. Not all aspects of this guide may be applicable in all circumstances. The word “standard” in the title of this document means only that the document has been approved through the ASTM consensus process.

1.3 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.

1.4 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.

1.5 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.

4.1 The long-term material strength of geosynthetic reinforcement material is a critical design parameter for many civil engineering projects including, but not limited to, reinforced wall structures and reinforced slopes. Geosynthetic reinforcement products are produced using a variety of polymeric materials and using a variety of manufacturing procedures. Accordingly, product-specific testing using representative produced products is recommended for establishment of long-term material strength for products used as reinforcement in structures.

4.2 The primary use of the test results obtained from a reinforcement testing program is to determine the available long-term (that is, end of design life, typically 75 years) material strength, T_al, of the reinforcement. The available long-term strength, T_al, is calculated as follows:

4.3 This long-term geosynthetic reinforcement strength concept is illustrated in Fig. 1. As shown in the figure, some strength losses occur immediately upon installation, and others occur throughout the design life of the reinforcement. Much of the long-term strength loss does not begin to occur until near the end of the reinforcement design life.

FIG. 1 Long-Term Geosynthetic Strength Concepts

4.4 The value selected for T_ult, for design purposes, is the minimum average roll value (MARV) for the product. This minimum average roll value, denoted as T_MARV, accounts for statistical variance in the material strength. Other sources of uncertainty and variability in the long-term strength result from installation damage, creep extrapolation, and the chemical degradation process. It is assumed that the observed variability in the creep rupture envelope is 100 % correlated with the short-term tensile strength, as the creep strength is typically directly proportional to the short-term tensile strength within a product line. Therefore, the MARV of T_ult adequately takes into account variability in the creep strength.

4.5 In accordance with AASHTO R 69-15, the test program results provided in geosynthetic reinforcement design reduction factor test reports are focused on characterization of the product line, specifically testing representative products within the product line to accomplish that characterization.

4.6 The guidelines provided in this document explain how to use the test data to characterize the entire product line with regard to long-term strength and durability properties.