ISO 17892-8:2018

INTERNATIONAL ISO
STANDARD 17892-8
First edition
2018-02
Geotechnical investigation and
testing — Laboratory testing of soil —
Part 8:
Unconsolidated undrained triaxial test
Reconnaissance et essais géotechniques — Essais de laboratoire sur
les sols —
Partie 8: Essai triaxial non consolidé non drainé
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Apparatus . 3
6 Test procedure . 6
6.1 General requirements and equipment preparation . 6
6.2 Preparation of specimens . 6
6.3 Application of cell pressure and initial readings . 7
6.4 Shearing . 8
6.5 Dismounting . 8
7 Test results . 9
7.1 Bulk density, dry density and water content . 9
7.2 Stage prior to shearing . 9
7.3 Shearing . 9
7.3.1 Corrected cross-sectional area . 9
7.3.2 Deviator stress . 9
7.3.3 Vertical strain .10
7.3.4 Undrained shear strength .10
7.4 Correction for elastic membrane .10
8 Test report .10
8.1 Mandatory reporting .10
8.2 Optional reporting .11
Annex A (normative) Calibration, maintenance and checks .12
Bibliography .14
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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URL: www .iso .org/ iso/ foreword .html.
This document was prepared by the European Committee for Standardization (CEN) Technical
Committee CEN/TC 341, Geotechnical investigation and testing, in collaboration with ISO Technical
Committee TC 182, Geotechnics, in accordance with the Agreement on technical cooperation between
ISO and CEN (Vienna Agreement).
This first edition of ISO 17892-8 cancels and replaces ISO/TS 17892-8:2004 and ISO/TS 17892-
8:2004/Cor.1:2006.
A list of all the parts in the ISO 17892 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved

Introduction
This document covers areas in the international field of geotechnical engineering never previously
standardized. It is intended that this document presents broad good practice throughout the world and
significant differences with national documents is not anticipated. It is based on international practice
(see Reference [1]).
INTERNATIONAL STANDARD ISO 17892-8:2018(E)
Geotechnical investigation and testing — Laboratory
testing of soil —
Part 8:
Unconsolidated undrained triaxial test
1 Scope
This document specifies a method for unconsolidated undrained triaxial compression tests.
This document is applicable to the laboratory determination of undrained triaxial shear strength under
compression loading within the scope of geotechnical investigations.
The cylindrical specimen, which can comprise undisturbed, re-compacted, remoulded or reconstituted
soil, is subjected to an isotropic stress under undrained conditions and thereafter is sheared
under undrained conditions. The test allows the determination of shear strength and stress-strain
relationships in terms of total stresses.
Non-standard procedures such as tests with the measurement of pore pressure or tests with filter
drains are not covered in this document.
NOTE This document fulfils the requirements of unconsolidated undrained triaxial compression tests for
geotechnical investigation and testing in accordance with EN 1997-1 and EN 1997-2.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 14688-1, Geotechnical investigation and testing — Identification and classification of soil — Part 1:
Identification and description
ISO 17892-1, Geotechnical investigation and testing — Laboratory testing of soil — Part 1: Determination
of water content
ISO 17892-2, Geotechnical investigation and testing — Laboratory testing of soil — Part 2: Determination
of bulk density
ISO 17892-3, Geotechnical investigation and testing — Laboratory testing of soil — Part 3: Determination
of particle density
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
cell pressure
pressure applied to the cell fluid
3.2
deviator stress
difference between the applied vertical total stress and the horizontal total stress at the mid height of
the specimen
3.3
undrained shear strength
equal to one half of the deviator stress at failure in the unconsolidated undrained triaxial
compression test
3.4
failure
stress or strain condition at which one of the following criteria are met:
— peak deviator stress;
— a specified deformation criterion if a peak deviator stress has not been achieved, e.g., 15 %
vertical strain.
4 Symbols
A initial cross-sectional area of the specimen
i
A cross-sectional area of the specimen during shear
cor
a cross-sectional area of the piston if an external load cell is used
c undrained shear strength
u
D initial internal diameter of membrane (before it is placed on the specimen)
m
E elastic modulus for the membrane, measured in tension
m
f factor relating the vertical strain to the specimen volumetric strain
H initial height of the specimen prior to shearing (=H -ΔH )
s i i
H Initial height of specimen after preparation
i
h distance from the top of the top cap to the mid height of the specimen
P vertical load reading
t initial thickness of the unstressed membrane
m
V initial volume of the specimen after preparation
i
W gravity force acting on the sum of the deadweight hanger (if used), the piston, the top cap and
one half of the soil specimen
γ unit weight of the cell fluid
ΔH height change prior to shearing
i
ΔH height change during shearing
s
2 © ISO 2018 – All rights reserved

(Δσ ) correction to vertical total stress due to the membrane
v m
ε vertical strain
v
(ε ) vertical strain of the membrane
v m
σ cell pressure at the mid height of the specimen
c
σ horizontal total stress at the mid height of the specimen
h
σ vertical total stress at the mid height of the specimen
v
ΔV specimen volume change (with reduction in volume being a positive numerical value)
5 Apparatus
5.1 General
The apparatus shall undergo regular maintenance, checks and calibration as specified in Annex A.
A schematic diagram of a typical apparatus for triaxial compression testing is shown in Figure 1.
Key
1 alternative positions for load measuring device
2 air bleed
3 vertical displacement measuring device
4 piston
5 top cap
6 soil specimen
7 rubber membrane
8 O-rings
9 device for control and measurement of cell pressure
10 triaxial cell
P vertical load
Figure 1 — Schematic diagram of a typical unconsolidated undrained triaxial apparatus
5.2 Triaxial cell
5.2.1 The triaxial cell shall be able to withstand the applied cell pressure without leakage of cell fluid
out of the cell.
...