ISO 17892-8:2018 - Unconsolidated Undrained Triaxial Test (Summary & Applications)

Overview

ISO 17892-8:2018 specifies the laboratory method for the unconsolidated undrained (UU) triaxial compression test used in geotechnical investigation and testing. The standard applies to cylindrical soil specimens (undisturbed, re‑compacted, remoulded or reconstituted) that are first subjected to an isotropic cell pressure under undrained conditions and then sheared under undrained conditions. Results are reported in terms of total stresses, providing the undrained shear strength and stress‑strain relationships for geotechnical design and assessment. Non‑standard procedures (for example tests measuring pore pressure or using filter drains) are not covered.

Key topics and technical requirements

• Test scope: Determination of undrained triaxial shear strength under compression loading; fulfills requirements of EN 1997‑1 and EN 1997‑2.
• Specimen types: Undisturbed, re‑compacted, remoulded or reconstituted cylindrical specimens.
• Test stages: specimen preparation → application of isotropic cell pressure (undrained) → undrained shearing → dismounting and reporting.
• Measured outputs: deviator stress, vertical strain, corrected cross‑sectional area, bulk/dry density, water content, and undrained shear strength (defined as one half of the deviator stress at failure).
• Apparatus & accuracy:
  • Triaxial cell with leak‑proof design; transparent cells preferred.
  • Confining membrane requirements (e.g., elastic modulus ~1 400 kPa typical; unstretched diameter 95–100% of specimen after water storage; thickness ≤ 1% of specimen diameter).
  • Cell pressure stability to ±1 kPa or 1% (whichever greater).
  • Load measurement accuracy: 1 N or 1% (whichever greater).
  • Vertical displacement accuracy: 0.1 mm or 0.1% of initial height.
• Corrections & checks: Membrane correction for strength estimates, calibration and maintenance per Annex A, and mandatory/optional reporting elements.

Applications and users

Who benefits:

• Geotechnical engineers and consultants evaluating undrained strength for bearing capacity, slope stability and short‑term performance.
• Construction and foundation designers needing laboratory input for cohesive soils.
• Testing laboratories and QA/QC teams performing standardised soil strength testing.
• Research institutions studying undrained behaviour of natural and reconstituted soils.

Typical uses:

• Rapid strength assessment in soft cohesive soils where drainage is prevented during loading.
• Input to design models and limit‑state calculations under undrained conditions.
• Compliance testing for projects requiring alignment with ISO and Eurocode requirements.

Related standards

• ISO 17892 series (e.g., Part 1: water content; Part 2: bulk density; Part 3: particle density)
• ISO 14688‑1 (soil identification and description)
• EN 1997‑1 and EN 1997‑2 (geotechnical design standards referenced by the document)

Keywords: ISO 17892-8:2018, unconsolidated undrained triaxial test, triaxial compression test, undrained shear strength, laboratory testing of soil, geotechnical testing.