ASTM D5321/D5321M-21 PDF

Full title and description

ASTM D5321/D5321M-21 — Standard Test Method for Determining the Shear Strength of Soil‑Geosynthetic and Geosynthetic‑Geosynthetic Interfaces by Direct Shear. The method defines a direct‑shear test procedure for measuring total shear resistance between a geosynthetic and soil or between two geosynthetics under controlled normal stress and constant shear rate; results are used to derive design values such as interface friction and adhesion for geotechnical design and acceptance testing.

Abstract

This test method describes specimen preparation, test apparatus (large direct shear box), normal stress selection, shear displacement rate, and result presentation (shear stress vs. displacement; Mohr‑Coulomb envelope to obtain interface friction and adhesion). It is intended as a performance test to provide design values representative of the tested conditions; it is applicable to most geosynthetics but not to geosynthetic clay liners (GCLs), which are covered by Test Method D6243/D6243M.

General information

• Status: Superseded by a later revision (see notes below).
• Publication date: Approved June 1, 2021 (designated D5321/D5321M‑21).
• Publisher: ASTM International (formerly American Society for Testing and Materials).
• ICS / categories: Geotextiles and related products — ICS 59.080.70 (geotextiles).
• Edition / version: D5321/D5321M‑21 (2021 edition).
• Number of pages: 12 pages (typical published PDF).

Scope

Specifies a laboratory direct‑shear procedure to determine the shear resistance of interfaces formed by a geosynthetic and soil, or two geosynthetics, under a constant rate of deformation and prescribed normal stresses. The method is intended to simulate field interface behavior for design and acceptance testing, but results are specific to the tested materials and conditions (soil type, compaction/moisture, normal stress, drainage, shear rate, specimen mounting). GCLs are explicitly excluded and are covered by D6243/D6243M.

Key topics and requirements

• Direct shear apparatus configuration and specimen mounting (large shear box to accommodate geosynthetic specimens).
• Selection of normal stresses representative of design conditions (typically multiple normal loads to define a shear envelope).
• Controlled shear displacement rate and guidance on rates for geosynthetic/soil versus geosynthetic/geosynthetic interfaces.
• Measurement and reporting of peak and post‑peak shear stress versus displacement; derivation of interface friction angle and adhesion (Mohr‑Coulomb parameters).
• Limitations and cautions: results are sensitive to test conditions, and inter‑laboratory precision data are incomplete — experienced laboratories and agreed test conditions are recommended for acceptance testing.

Typical use and users

Used by geotechnical and civil engineers, materials and quality control laboratories, geosynthetic manufacturers, and designers for slope stability, reinforced earth, landfill liners and caps, base course and pavement systems, and overlap/slip‑resistance evaluations. Commonly used in specification, design verification, product development, and dispute resolution when interface shear behavior is critical.

Related standards

Commonly referenced and complementary standards include: ASTM D6243/D6243M (GCL shear by direct shear), ASTM D3740 (laboratory qualification/practice), ASTM D4439 (geosynthetics terminology), ASTM D6706 (geosynthetic pullout test), and international standards such as ISO 12957 (geosynthetic friction assessment). Users should consult related standards for sampling, mounting, and laboratory qualification practices.

Keywords

direct shear; interface shear; geosynthetic; geotextile; soil‑geosynthetic friction; shear strength; adhesion; Mohr‑Coulomb; performance test; interface friction angle.

FAQ

Q: What is this standard?

A: ASTM D5321/D5321M‑21 is a laboratory direct‑shear test method for measuring the shear resistance of soil‑geosynthetic and geosynthetic‑geosynthetic interfaces to derive design parameters like interface friction and adhesion.

Q: What does it cover?

A: It covers specimen preparation, test apparatus and box size, selection of normal stresses, shear displacement rates, data acquisition (shear stress vs. displacement), and derivation of interface strength parameters; it warns that results depend strongly on test conditions and are intended to represent the tested conditions. GCLs are excluded (see D6243/D6243M).

Q: Who typically uses it?

A: Geotechnical and civil engineers, testing laboratories, geosynthetic product developers and manufacturers, contractors, and regulatory agencies involved in design and acceptance of geosynthetic systems.

Q: Is it current or superseded?

A: D5321/D5321M‑21 was approved June 1, 2021. A later revision (D5321/D5321M‑26) was issued in early 2026; therefore the 2021 edition has been superseded by the 2026 revision — consult ASTM or your standards provider for the latest edition and for redline/changes.

Q: Is it part of a series?

A: Yes — it is part of ASTM Committee D35 geosynthetics documents and is commonly used alongside related D35 series standards (sampling, terminology, GCL test methods, pullout tests, laboratory practice). Revisions are issued periodically under the D5321 work items.

Q: What are the key keywords?

A: Direct shear, interface shear, geosynthetic, friction angle, adhesion, Mohr‑Coulomb envelope, performance test, interface strength.