ASTM D2166/D2166M-24 PDF

Full title and description

ASTM D2166/D2166M-24 — Standard Test Method for Unconfined Compressive Strength of Cohesive Soil. This test method describes a strain-controlled unconfined compression test used to determine the unconfined compressive strength (an index of undrained shear strength) of cohesive soils in intact, remolded, or reconstituted states. The method is intended for soils that retain intrinsic strength and do not expel water during the loading phase (typically clays and clayey soils).

Abstract

ASTM D2166/D2166M-24 provides procedures to prepare specimens and perform a strain-controlled axial compression test on unconfined cylindrical specimens of cohesive soil to obtain compressive strength and related parameters (axial strain, average cross-sectional area, sensitivity). The standard emphasizes applicability limits, units (SI and inch-pound treated independently), significance of drainage and saturation, and reporting/rounding conventions. It is an index test for undrained shear strength and is not a substitute for triaxial or other confined tests when lateral confinement or pore-pressure measurement is required.

General information

• Status: Active (current version)
• Publication date: June 1, 2024 (D2166/D2166M-24; last updated June 18, 2024)
• Publisher: ASTM International
• ICS / categories: 93.020 — Earthworks, excavations, foundation construction, underground works
• Edition / version: D2166/D2166M-24
• Number of pages: 8

Scope

This method covers determination of the unconfined compressive strength of cohesive soils (intact, remolded, or reconstituted) using strain-controlled axial loading. It yields an approximate value of strength expressed in total stresses and applies only to cohesive materials that will not expel or bleed water during loading and that retain intrinsic strength after removal of confining pressure. Materials not suitable for this test include highly fissured or varved clays, dry and crumbly soils, silts, peats, and sands. The method is intended as an index (undrained) test and does not replace confined triaxial tests for many design applications.

Key topics and requirements

• Specimen types: intact, remolded, or reconstituted cylindrical specimens.
• Strain-controlled axial loading to a failure condition (constant rate of axial deformation).
• Calculation and reporting of axial strain, average cross-sectional area, and unconfined compressive strength (peak axial stress).
• Applicability limited to soils that do not expel water during loading; unsuitable for sands, silts, peats, and varved/fissured materials.
• Provides an index of undrained shear strength; drainage and degree of saturation affect results.
• Guidance on units: SI and inch-pound systems are independent; do not mix unit systems.
• Requirements for reporting, significant digits, and rounding consistent with Practice D6026 (unless otherwise specified).
• Notes on sensitivity determination by comparing intact and remolded specimen results; alternative methods (D2850, D4648) for some materials.
• Laboratory competence and equipment suitability emphasized (see Practice D3740 for evaluating testing agencies).

Typical use and users

Used by geotechnical and civil engineers, soil testing laboratories, construction quality-control teams, researchers, and regulatory bodies to obtain a quick index of undrained shear strength for cohesive soils. Typical applications include preliminary site investigations, classification and screening of clayey materials, sensitivity testing (intact vs. remolded), and situations where rapid field/lab strength estimates are required. Not typically used where full stress‑path or pore‑pressure measurements are required for final design.

Related standards

Closely related and frequently referenced standards include: Test Method D2850 (Unconsolidated‑Undrained Triaxial Compression Test on Cohesive Soils), Test Method D4648/D4648M (Unconfined Compression Test for materials that cannot retain shape), Test Method D4767 (Consolidated Undrained Triaxial Compression Test), Practice D6026 (significant digits and rounding), and Practice D3740 (selection and qualification of testing agencies). These documents provide complementary procedures, precision statements, and guidance on applicability and reporting.

Keywords

unconfined compressive strength, cohesive soil, clay, unconfined compression test, undrained shear strength, strain-controlled loading, sensitivity, intact specimen, remolded specimen, SI units, inch‑pound units

FAQ

Q: What is this standard?

A: ASTM D2166/D2166M-24 is the ASTM standard test method for measuring the unconfined compressive strength of cohesive soils using a strain-controlled unconfined compression test on cylindrical specimens.

Q: What does it cover?

A: It describes specimen preparation (intact, remolded, reconstituted), test procedure (strain-controlled axial deformation), calculations (axial strain, average area, compressive strength), reporting requirements, unit system usage, and limitations on applicable soil types. It provides an index of undrained shear strength, not a full in-situ stress replication.

Q: Who typically uses it?

A: Geotechnical engineers, soil testing laboratories, consultants, construction QA/QC personnel, and researchers use it for quick strength estimation and comparative testing of cohesive soils.

Q: Is it current or superseded?

A: Current — the active version is D2166/D2166M-24 (published June 2024). It supersedes earlier editions (for example, D2166/D2166M-16).

Q: Is it part of a series?

A: Yes. It is part of the ASTM geotechnical test methods (committee D18) and is commonly used alongside related test methods and practices such as D2850, D4767, D4648/D4648M, D6026, and D3740.

Q: What are the key keywords?

A: Cohesive soil, unconfined compressive strength, unconfined compression, undrained shear strength, strain-controlled, intact specimen, remolded specimen, sensitivity.