🏗️ Unconsolidated undrained (UU) triaxial compression test — cylindrical soil specimen (undisturbed, recompacted, remoulded or reconstituted) in a membrane subjected in the cell to isotropic stress without drainage and then sheared without drainage; undrained shear strength cu equal to half the deviator stress at failure (peak deviator stress or e.g. 15 % vertical strain), stress–strain relationship in terms of total stresses, PN-EN ISO 17892-8

Construction PN-EN ISO 17892-8

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 17892-8:2018-05 (Polish version), in full (our translation): “This document describes the unconsolidated undrained triaxial compression test on specimens. This document applies to the laboratory determination of shear strength in triaxial compression of undrained specimens within geotechnical investigation. The cylindrical specimen, comprising undisturbed, recompacted, remoulded or reconstituted soil, is subjected to isotropic stress under undrained conditions and then sheared under the same conditions. The test allows the determination of shear strength and stress–strain characteristics in terms of total stresses. Non-standard procedures, such as tests with measurement of pore pressure in the soil and tests with filter drains, are not covered by this document. NOTE: This document fulfils the requirements for unconsolidated undrained triaxial compression tests of soil in geotechnical investigation and testing according to EN 1997-1 and EN 1997-2.” We read the text of the standard in the preview of ISO 17892-8:2018 from the cover to 5.2.4 (triaxial cell); we do not have the rest of Clause 5, Clauses 6–8 (procedure, results, test report) or Annex A.

ACCORDING TO THE TEXT OF ISO 17892-8:2018 (foreword, introduction, Clauses 1–5.2.4). The standard was prepared by CEN/TC 341 together with ISO/TC 182 (Vienna Agreement); the first edition replaces ISO/TS 17892-8:2004 and Cor.1:2006. Scope (1): unconsolidated undrained triaxial compression; laboratory determination of undrained shear strength in compression; cylindrical specimen of undisturbed, recompacted, remoulded or reconstituted soil, subjected to isotropic stress without drainage and sheared without drainage; strength and stress–strain relationship in total stresses; non-standard procedures (with pore pressure measurement, with filter drains) are not covered. References (2): ISO 14688-1, ISO 17892-1, -2 and -3. Definitions (3): cell pressure — pressure of the fluid in the cell; deviator stress — difference between vertical and horizontal total stress at mid-height of the specimen; undrained shear strength — equal to half the deviator stress at failure in the UU test; failure — peak deviator stress or, if not reached, a specified strain criterion, e.g. 15 % vertical strain. Symbols (4): among others cu, Ai and Acor (initial cross-section and during shearing), a (piston cross-section with an external load cell), Dm, Em (membrane modulus in tension), tm, Hi, Hs = Hi − ΔHi (height before shearing), W (weight of piston, top cap, any hanger and half the specimen), γ (unit weight of the cell fluid), (Δσv)m (membrane correction), εv, σc, σh, σv, ΔV. Apparatus (5): regular maintenance, checks and calibration according to Annex A; Figure 1 — load measuring device (alternative positions), air bleed, vertical displacement device, piston, top cap, specimen, rubber membrane, O-rings, control and measurement of cell pressure, cell; the cell must withstand the pressure without leakage (preferably transparent); the piston must run smoothly with minimal friction and in alignment; deformations of the top cap, pedestal and their connections must be negligible compared to those of the specimen; diameter of top cap and pedestal normally equal to the specimen diameter — smaller specimens are allowed if cavities under the membrane at the ends can be avoided.

STATUS (PKN catalogue cards as of 02.10.2026). The card of PN-EN ISO 17892-8:2018-05 (Polish version, published 27-09-2021, 20 pages, price group K) has no “Withdrawn” header: Building and Construction Sector, KT 254 Geotechnics, ICS 13.080.20 and 93.020, “Introduces: EN ISO 17892-8:2018 [IDT], ISO 17892-8:2018 [IDT]”; the card lists no additional elements. The PKN search for “PN-EN ISO 17892-8” (02.10.2026) shows the English and Polish versions 2018-05. The EVS catalogue (read 02.10.2026) lists ISO 17892-8:2018 as valid from 14.02.2018.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 17892-8 appears in 7 records at 6 laboratories: AB 283, AB 962, AB 1416, AB 1770, AB 1778, AB 1914. In the current scopes on the PCA website (read 02.10.2026, issues from 24.09.2024 to 17.07.2026) all give “PN-EN ISO 17892-8:2018-05”; AB 283 and AB 1778 add the national amendment “Ap1” (AB 1778: “/Ap1:2021-04”), which the card of the 2018-05 edition does not list — we have not checked its content. The “Laboratories” tab searches for entries STARTING WITH “PN-EN ISO 17892-8” and shows all 6 laboratories — checked with the tab query on the production server labcoda.pl on 02.10.2026.

WHAT THE LABORATORIES TEST (PCA entries). Soils — “Undrained shear strength, unconsolidated undrained triaxial compression test method (UU)” (AB 283); “Shear strength, … unconsolidated and undrained (UU)” (AB 1770, two entries); “Shear strength”, load range from 0 to 25 kN (AB 1778); “Compressive strength”, cell pressure from 0 to 3000 kPa, UU (AB 1914); “Tests of soils in the triaxial compression apparatus without saturation with water and without consolidation”, cell pressure from 0 to 3500 kPa (AB 962, AB 1416).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Quantity: cu is HALF the deviator stress at failure — reporting the whole deviator stress as shear strength doubles the result; “compressive strength” in the AB 1914 entry is a different name from the quantity defined in the standard. Failure criterion: when the deviator stress does not reach a peak, a strain criterion is adopted (e.g. 15 %) — in Part 9 (consolidated test) the example strain criterion is 10 %, so results of the two tests are compared only with the criterion named. Stresses: UU gives the result in TOTAL stresses, without pore pressure measurement — it does not give effective parameters (Part 9 serves for those). Name of the test: AB 962 and AB 1416 describe it as “without saturation with water and without consolidation”, while the standard defines it as a test without consolidation and WITHOUT DRAINAGE — its scope says nothing about saturation. Apparatus: top cap and pedestal normally of the specimen diameter — the standard allows smaller specimens only if cavities under the membrane at the ends can be avoided (5.2.4); the membrane correction enters the calculation (symbol (Δσv)m).

WHAT WE DO NOT STATE. We do not have 5.2.5–8 or Annex A: requirements for membranes, transducers and frame, rate of compression, specimen dimensions, cell pressure, formulae for the corrected cross-section, deviator stress and membrane correction or the content of the test report; nor do we know the content of the national amendment Ap1 — we therefore give none of these figures.

Method principle

A cylindrical soil specimen in a rubber membrane is subjected in the triaxial cell to isotropic stress without drainage and without consolidation, and then compressed axially without drainage to failure; the undrained shear strength cu is half the deviator stress at failure (total stresses).

Applications

• Cohesive soils in geotechnical investigation — undrained shear strength cu; 6 laboratories in PCA scopes
• Stability analyses under undrained (short-term) conditions according to EN 1997-1 and EN 1997-2
• Stress–strain relationship in terms of total stresses

Key parameters

Standard

Standard number

PN-EN ISO 17892-8:2018-05 (wersja polska; EN ISO 17892-8:2018 IDT, ISO 17892-8:2018 IDT)

Title (PL)

Rozpoznanie i badania geotechniczne — Badania laboratoryjne gruntów — Część 8: Badania trójosiowe bez konsolidacji i bez odpływu

Title (EN)

Geotechnical investigation and testing — Laboratory testing of soil — Part 8: Unconsolidated undrained triaxial test

Step-by-step procedure

1. Specimen

   Cylinder of undisturbed, recompacted, remoulded or reconstituted soil in a membrane; water content and density according to ISO 17892-1 and -2. PN-EN ISO 17892-8:2018-05 current (PKN cards as of 02.10.2026).

2. Cell pressure

   Isotropic stress without drainage, without consolidation (details in Clause 6 — outside the part we read).

3. Shearing

   Axial compression without drainage to failure: peak deviator stress or strain criterion (e.g. 15 %).

4. Results

   Deviator stress from force and corrected cross-section with membrane correction; cu = ½ deviator stress at failure (we do not have the formulae).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard contains no safety warnings in the part we read; the cell operates under pressure — safety rules are set by the laboratory
• TECHNICAL NOTE: cu is half the deviator stress at failure, in total stresses; effective parameters are given by the consolidated test (PN-EN ISO 17892-9)

Frequently asked questions