ASTM D7702-14(R2021) pdf free download

ASTM D7702-14(R2021) pdf free download.Standard Guide for Considerations When Evaluating Direct Shear Results Involving Geosynthetics
1. Scope
1.1 This guide presents a summary of available information related to the evaluation of direct shear test results involving geosynthetic materials. 1.2 This guide is intended to assist designers and users of geosynthetics. This guide is not intended to replace education or experience and should only be used in conjunction with professional judgment. 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 ofa project’s many unique aspects. Not all aspects of this practice 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 This guide is applicable to soil-geosynthetic and geosynthetic-geosynthetic direct shear test results, obtained using either Test Method D5321/D5321M or D6243/D6243M. 1.4 This guide does not address selection of peak or large-displacement shear strength values for design. Refer- ences on this topic include Thiel (1), 2 Gilbert (2), Koerner and Bowman (3), and Stark and Choi (4). 1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.7 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions—For definitions of terms relating to soil and rock, refer to Terminology D653. For definitions of terms relating to geosynthetics and GCLs, refer to Terminology D4439. 3.2 Definitions ofTerms Specific to This Standard: 3.2.1 adhesion, c a or c, n—the y-intercept of the Mohr- Coulomb shear strength envelope; the component of shear strength indicated by the term c a , in Coulomb’s equation, τ = c a + σ tan δ. 3.2.2 failure envelope, n—curvi-linear line on the shear stress-normal stress plot representing the combination of shear and normal stresses that define a selected shear failure criterion (for example, peak and post-peak). Also referred to as shear strength envelope. 3.2.3 Mohr-Coulomb friction angle δ, n—angle of friction of a material or between two materials (degrees), the angle defined by the least-squares, “best-fit” straight line through a defined section of the shear strength-normal stress failure envelope; the component of the shear strength indicated by the term δ, in Coulomb’s equation, τ = c + σ tan δ. 3.2.4 Mohr-Coulomb shear strength envelope, n—the least- squares, “best-fit” straight line through a defined section of the shear strength-normal stress failure envelope described in the equation τ = c a + σ tan δ. The envelope can be described for any chosen shear failure criteria (for example, peak, post-peak, or residual). 3.2.5 secant friction angle, δ sec , n—(degrees) the angle defined by a line drawn from the origin to a data point on the shear strength-normal stress failure envelope. Intended to be used only at the shearing normal stress for which it is defined. 3.2.6 shear strength, τ, n—the shear force on a given failure plane. In the direct shear test it is always stated in relation to the normal stress acting on the failure plane. Two different types of shear strengths are often estimated and used in standard practice: 3.2.6.1 peak shear strength, n—the largest value of shear resistance experienced during the test under a given normal stress. 3.2.6.2 post-peak shear strength, n—the minimum, or steady-state value of shear resistance that occurs after the peak shear strength is experienced. 3.2.6.3 Discussion—Due to horizontal displacement limita- tions of many commercially available shear boxes used to determine interface shear strength, the post-peak shear strength is often specified and reported as the value of shear resistance that occurs at 75 mm [3 in.] of displacement. The end user is cautioned that the reported value of post-peak shear strength (regardless how defined) is not necessarily the residual shear strength. In some instances, a post-peak shear strength may not be defined before the limit of horizontal displacement is reached.