ISO 18674-4:2020
(Main)Geotechnical investigation and testing — Geotechnical monitoring by field instrumentation — Part 4: Measurement of pore water pressure: Piezometers
Geotechnical investigation and testing — Geotechnical monitoring by field instrumentation — Part 4: Measurement of pore water pressure: Piezometers
This document specifies the measurement of pore water pressures and piezometric levels in saturated ground by means of piezometers installed for geotechnical monitoring. General rules of performance monitoring of the ground, of structures interacting with the ground, of geotechnical fills and of geotechnical works are presented in ISO 18674‑1. If applied in conjunction with ISO 18674-5, the procedures described in this document allow the determination of effective stresses acting in the ground. This document is applicable to: — monitoring of water pressures acting on and in geotechnical structures (e.g. quay walls, dikes, excavation walls, foundations, dams, tunnels, slopes, embankments, etc.); — monitoring of consolidation processes of soil and fill (e.g. beneath foundations and in embankments); — evaluating stability and serviceability of geotechnical structures; — checking geotechnical designs in connection with the Observational Design procedure. NOTE This document fulfils the requirements for the performance monitoring of the ground, of structures interacting with the ground and of geotechnical works by the means of piezometers, installed as part of the geotechnical investigation and testing in accordance with References [4] and [5] This document relates to measuring devices, which are installed in the ground. For pore water pressure measurements carried out in connection with cone penetration tests, see ISO 22476-1.
Reconnaissance et essais géotechniques — Surveillance géotechnique par instrumentation in situ — Partie 4: Mesure de la pression interstitielle: Piézomètres
Le présent document spécifie la mesure des pressions interstitielles et des niveaux piézométriques dans un sol saturé, au moyen de piézomètres installés dans le cadre d'une surveillance géotechnique. Les règles générales de surveillance des performances du terrain, des structures en interaction avec le terrain, des remblais et des travaux géotechniques sont présentées dans l'ISO 18674‑1. Si elles sont appliquées conjointement à la norme ISO 18674‑5, les procédures décrites dans le présent document permettent de déterminer les contraintes effectives qui agissent dans le sol. Le présent document s'applique: — au suivi des pressions d'eau qui agissent sur et dans les structures géotechniques (par ex. parois de quais, digues, parois d'excavation, fondations, barrages, tunnels, talus, levées de terre, etc.); — au suivi des processus de consolidation du terrain et des remblais (par ex. sous des fondations et dans des levées de terre); — à l'évaluation de la stabilité et de l'aptitude à l'entretien des structures géotechniques; — au contrôle des calculs géotechniques en lien avec la procédure observationnelle. NOTE Le présent document satisfait aux exigences relatives à la surveillance des performances du terrain, des structures en interaction avec le terrain et des ouvrages géotechniques au moyen de piézomètres mis en œuvre dans le cadre des études et essais géotechniques conformément aux Références [4] et [5]. Le présent document se rapporte à des dispositifs de mesure, lesquels sont installés dans le sol. Pour les mesures de pression interstitielle réalisées en lien avec des essais de pénétration au cône, voir l'ISO 22476‑1.
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INTERNATIONAL ISO
STANDARD 18674-4
First edition
2020-06
Geotechnical investigation and
testing — Geotechnical monitoring by
field instrumentation —
Part 4:
Measurement of pore water pressure:
Piezometers
Reconnaissance et essais géotechniques — Surveillance géotechnique
par instrumentation in situ —
Partie 4: Mesure de la pression interstitielle: Piézomètres
Reference number
ISO 18674-4:2020(E)
©
ISO 2020
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ISO 18674-4:2020(E)
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© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO 18674-4:2020(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 7
5 Instruments . 7
5.1 General . 7
5.2 Open piezometer systems . 9
5.2.1 General. 9
5.2.2 Types of open piezometer systems .10
5.3 Closed piezometer systems .13
5.3.1 General.13
5.3.2 Types of closed piezometer systems .16
5.4 Absolute versus relative measurements and atmospheric compensation.17
5.5 Requirements for filters .19
5.5.1 Filters in open piezometer systems.19
5.5.2 Filters in closed piezometer systems .19
5.6 Measuring range and accuracy .20
6 Installation and measuring procedure .20
6.1 Installation .20
6.1.1 General.20
6.1.2 Installation of open piezometer systems .21
6.1.3 Installation of closed piezometer systems .23
6.1.4 Checks before, during and after installation .24
6.1.5 Maintenance .25
6.2 Carrying out the measurement .25
6.2.1 Instrumentation check and calibration .25
6.2.2 Measurement .26
7 Data processing and evaluation .26
8 Reporting .26
8.1 Installation report .26
8.2 Monitoring report .26
Annex A (normative) Measuring and evaluation procedure .27
Annex B (informative) Geo-engineering applications .34
Annex C (informative) Protection of piezometers at the ground level .36
Annex D (informative) Response time for pore water pressure measurements .39
Annex E (normative) Fully grouted piezometer installation.42
Annex F (normative) Measuring negative pore water pressure (soil suction) .44
Annex G (informative) Measuring examples .45
Bibliography .57
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ISO 18674-4:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 182, Geotechnics, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 341, Geotechnical
Investigation and Testing, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
A list of all parts in the ISO 18674 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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INTERNATIONAL STANDARD ISO 18674-4:2020(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 4:
Measurement of pore water pressure: Piezometers
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing
this document using a colour printer.
1 Scope
This document specifies the measurement of pore water pressures and piezometric levels in saturated
ground by means of piezometers installed for geotechnical monitoring. General rules of performance
monitoring of the ground, of structures interacting with the ground, of geotechnical fills and of
geotechnical works are presented in ISO 18674-1.
If applied in conjunction with ISO 18674-5, the procedures described in this document allow the
determination of effective stresses acting in the ground.
This document is applicable to:
— monitoring of water pressures acting on and in geotechnical structures (e.g. quay walls, dikes,
excavation walls, foundations, dams, tunnels, slopes, embankments, etc.);
— monitoring of consolidation processes of soil and fill (e.g. beneath foundations and in embankments);
— evaluating stability and serviceability of geotechnical structures;
— checking geotechnical designs in connection with the Observational Design procedure.
NOTE This document fulfils the requirements for the performance monitoring of the ground, of structures
interacting with the ground and of geotechnical works by the means of piezometers, installed as part of the
geotechnical investigation and testing in accordance with References [4] and [5] This document relates to
measuring devices, which are installed in the ground. For pore water pressure measurements carried out in
connection with cone penetration tests, see ISO 22476-1.
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 18674-1:2015, Geotechnical investigation and testing — Geotechnical monitoring by field
instrumentation — Part 1: General rules
ISO 22475-1, Geotechnical investigation and testing — Sampling by drilling and excavation methods and
groundwater measurements — Part 1: Technical principles for execution
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18674-1 and the following apply.
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ISO 18674-4:2020(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
piezometer
field instrument system for measuring pore water pressure (3.2) or piezometric level (3.4) where the
measuring point (3.15) is confined within the ground or geotechnical fill so that the measurement
responds to the fluid pressure around the measuring zone/point and not to fluid pressures at other
elevations
Note 1 to entry: The system consists of a sealed reservoir (3.1.2) filled with fluid, a filter (3.1.3) and a measuring
device (3.1.7).
Note 2 to entry: The system is either an open piezometer system (3.6) or a closed piezometer system (3.7).
3.1.1
intake zone
zone confined by seals (3.1.6), between which water in the ground can flow to the measuring device,
thus defining the measuring point (3.15)
Note 1 to entry: See Figure 1.
Note 2 to entry: It is assumed that a hydrostatic pore water pressure (3.2) distribution is established along the
intake zone.
Note 3 to entry: The constant of proportionality between flow into or out of a piezometer (3.1) and the change of
pore water pressure is called the intake factor F.
3.1.2
reservoir
space between the ground and the measuring device (3.1.7), occupied by a fluid, which allows the pore
water pressure (3.2) to act on the sensing element of the measuring device
Note 1 to entry: The pores within the filter (3.1.3) are an integral part of the reservoir.
Note 2 to entry: In open piezometer systems (3.6), the water-filled part of the standpipe is part of the reservoir.
3.1.3
filter
permeable section of a piezometer (3.1) defining the intake zone (3.1.1), which allows water to enter and
at the same time restricts soil particles entering the standpipe or measuring device (3.1.7)
Note 1 to entry: The filter can be a combination of elements, such as a sand pocket, a perforated pipe, a geotextile
sleeve, a filter tip (3.1.4) and grout backfill in specific cases.
3.1.4
filter tip
filter (3.1.3) element which is a common part of a closed piezometer system (3.7)
Note 1 to entry: Filter tips are formed of a material with purpose-designed pore diameters, i.e. HAE filter (3.1.4.1)
or LAE filter (3.1.4.2).
3.1.4.1
high air entry filter
HAE filter
filter tip (3.1.4) with comparatively small pores giving a higher resistance to the passage of air than to
the passage of water
Note 1 to entry: Commonly, high air entry filter tips have pore diameters of between 1 μm and 3 μm.
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ISO 18674-4:2020(E)
Note 2 to entry: HAE filter tips are used when it is intended to keep gas out of the measuring device (3.1.7).
Note 3 to entry: In unsaturated soil or when negative pore water pressures (3.2) are to be measured (i.e. suction;
see Annex F), the pressure of the gaseous phase is always higher than that of the pore water. The required pore
diameter of the HAE filter tip depends on the difference between the pore air pressure and the pore water
pressure.
3.1.4.2
low air entry filter
LAE filter
filter tip (3.1.4) with comparatively large pores giving a lower resistance to the passage of air readily
allowing the passage of both air and water
Note 1 to entry: Commonly, low air entry filter tips have pore diameters of between 20 μm and 50 μm.
3.1.5
filter pack
permeable material, placed around a slotted section of an open piezometer (3.1) or around the filter tip
(3.1.4), allowing water to reach the measuring device (3.1.7)
3.1.6
seal
layer in a borehole, made with a material that has a permeability suitable for hydraulical separation of
two aquifers (3.10)
Note 1 to entry: Seals are generally used to confine an intake zone (3.1.1).
3.1.7
measuring device
part of the piezometer (3.1) system used to measure the piezometric level (3.4) in an open system (3.6) or
the pore water pressure (3.2) in a closed system (3.7)
Note 1 to entry: For an open piezometer system (3.6), the measuring device is commonly a water level meter
(3.1.7.1) for manual measurements or a pressure transducer for automatic measurements.
Note 2 to entry: For a closed piezometer system (3.7), the measuring device is typically a diaphragm pressure
transducer (see 7b in Figure 1 b)). The diaphragm separates a reservoir (3.1.2) and an inner chamber in the
transducer. The deflection of the diaphragm is a function of the pore water pressure (3.2) (see Figure 3).
Note 3 to entry: For closed piezometer systems, the measuring device is often synonymously termed a piezometer
in a narrow sense.
3.1.7.1
water level meter
measuring device with a marked length measuring tape and a tip that activates a signal (light, sound)
when it comes into contact with water
Note 1 to entry: A water level meter is commonly used for manual measurements in open systems (3.6) or during
the installation procedure of piezometers (3.1).
3.1.7.2
electric piezometer
piezometer (3.1) where the measuring device (3.1.7) has a diaphragm and the deflection of the diaphragm
due to pore water pressure (3.2) is measured by an electric sensor
Note 1 to entry: Electric piezometers are commonly based on strain gauge, piezo-electric, vibrating wire or
capacitive sensors. Data acquisition devices exist which accommodate all types of electric piezometers.
Note 2 to entry: See Figure 3.
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ISO 18674-4:2020(E)
3.1.7.3
fibre optic piezometer
piezometer (3.1) where the pressure measuring device (3.1.7) has a diaphragm and the deflection of the
diaphragm is measured by an optical sensor
Note 1 to entry: Fibre optic piezometers do not require electrical connection between read-out unit and sensor.
Note 2 to entry: Fibre optic piezometers require a dedicated read-out unit.
3.1.7.4
pneumatic piezometer
piezometer (3.1) where the pressure measuring device (3.1.7) has a valve which is opened pneumatically
by a gas pressure, which is applied from the outside via gas-filled tubes and closed by the pore water
pressure (3.2)
Note 1 to entry: See Figure 4.
3.2
pore water pressure
u
pressure of the water in the voids of the ground or a fill, relative to the atmospheric pressure
Note 1 to entry: The pore water pressure is the difference between the total stress and the effective stress in
saturated ground (see References [6] and [7]).
Note 2 to entry: For rocks, the associated term is joint water pressure.
Note 3 to entry: The state of soil or fill where the pores are completely filled with water is referred to as
“saturated”.
Note 4 to entry: Pore water pressure measurements can yield positive or negative values (see Reference [8] and
Annex F). Instruments that directly measure negative pore pressures are sometimes termed ‘tensiometers’, but
are not within the scope of this document (see ISO 11276).
Note 5 to entry: Measurements of the pore water pressure can be affected by changes of the atmospheric pressure
(see 5.4.1 and Annex A).
3.3
pressure head
ψ
ratio u/γ of the pore water pressure u (3.2) and the specific weight of water γ , above a point
w w
Note 1 to entry: For an open piezometer system (3.6), it is proportional to the elevation difference between the
piezometric level (3.4) and the level of the measuring point (3.15) (see Figure 1).
3.4
piezometric level
z
w
elevation to which water will rise in an open standpipe piezometer (3.6.1) and at which the pressure of
the water in the ground is equal to that of the ambient atmosphere
Note 1 to entry: The piezometric level z is the sum of the geometric elevation z and the pressure head ψ (3.3):
w
z = z + u/γ .
w w
Note 2 to entry: See Figure 1.
3.5
groundwater table
water table
elevation at which pore water pressure u (3.2) is zero
Note 1 to entry: See Figure 1.
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ISO 18674-4:2020(E)
Note 2 to entry: An equivalent term is phreatic surface.
Note 3 to entry: The groundwater level is the level of the groundwater table at a geographical coordinate.
3.6
open system
open piezometer system
field instrument system in which the fluid is in direct contact with the atmosphere and the piezometric
level (3.4) at the measuring point (3.15) is measured
3.6.1
open standpipe piezometer
open piezometer system (3.6), consisting of a pipe (installed in the ground) which, at its upper end, is
open to the atmosphere and with a perforated section, located in the intake zone (3.1.1)
Note 1 to entry: See Figure 1 a).
Note 2 to entry: Typical inner diameters of the pipe are from 19 mm to 60 mm.
3.6.2
Casagrande piezometer
open standpipe piezometer (3.6.1) with one or two comparatively small inner diameter pipes and a
porous filter tip (3.1.4) at the measuring point (3.15)
Note 1 to entry: See 5.2.2.4, Figure 2 and Reference [9].
3.6.3
monitoring well
open standpipe piezometer (3.6.1) with a large inner diameter of the pipe (typically ≥100 mm)
Note 1 to entry: A monitoring well can be used as standpipe piezometer (3.1), if the response time (3.9) is
satisfactory (see Annex D).
Note 2 to entry: A monitoring well is often used for taking samples of the groundwater or for performing
pumping tests.
3.6.4
observation well
open pipe within a borehole, where the intake zone (3.1.1) is unconfined
Note 1 to entry: Observation wells are often incorrectly termed open standpipe piezometers (3.6.1). Observation
wells do not classify as piezometers (3.1) as they do not have seals (3.1.6).
Note 2 to entry: See 5.2.2.3.2.
3.7
closed system
closed piezometer system
measuring system in which the reservoir (3.1.2) is not in direct contact with the atmosphere and in
which the pressure in the fluid is measured by a pressure measuring device (3.1.7)
Note 1 to entry: See Figure 1 b).
Note 2 to entry: Examples for pressure measuring devices, used in closed systems, are electric transducers, fibre
optic transducers and pressure valves.
3.7.1
diaphragm piezometer
closed system (3.7) with a filter tip (3.1.4), a small reservoir (3.1.2) and diaphragm which separates the
pore water from the measuring system
Note 1 to entry: The deflection of the diaphragm is measured and the signal is transported through a cable to an
accessible location.
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ISO 18674-4:2020(E)
Note 2 to entry: Possible diaphragm piezometers are electric piezometers (3.1.7.2) or fibre optic piezometers
(3.1.7.3).
Note 3 to entry: The pressure is measured adjacent to the filter tip.
3.7.2
closed hydraulic twin-tube piezometer
closed system (3.7) with a porous ceramic filter tip (3.1.4) located within an intake zone (3.1.1) and
connected to a remote location via twin fluid filled tubes
Note 1 to entry: The pressure measurement takes place at the remote location and not at the filter tip. The
measurements need to be adjusted for elevation differences between the filter tip and the remote location.
3.7.3
probe piezometer
closed system (3.7) where a moveable measuring device (3.1.7) is inserted into a pipe which is equipped
with one or more measuring ports, each located at an intake zone (3.1.1)
3.8
multi-level piezometer
system with several measuring points (3.15) permanently installed at different elevations in the ground,
where each measuring point has its own intake zone (3.1.1)
3.9
hydrodynamic time lag
response time
time span between a change of the pore water pressure (3.2) in the ground and the associated change in
the measurement
Note 1 to entry: The time lag depends primarily on the type and dimensions of the piezometer (3.1) (essentially
the size of the reservoir (3.1.2)), the permeability of the ground and the installation procedure (see Annex D).
Note 2 to entry: The term “slow response time” of the piezometer is synonymous with a long hydrodynamic
time lag.
3.10
aquifer
body of permeable rock or soil mass suitable for containing and transmitting groundwater
3.11
unconfined aquifer
aquifer (3.10) in which the groundwater surface forms the upper boundary
3.12
confined aquifer
aquifer (3.10) which is bounded above and below by aquicludes (3.14)
3.13
confining layer
aquitard
a low permeability layer of rock or soil that restricts groundwater flow and seperates aquifers (3.10)
3.14
aquiclude
body of soil or rock with extremely low transmissivity, which effectively prevents the flow of water
through the ground
3.15
measuring point
point in the ground where the pore water pressure (3.2) is referenced to
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ISO 18674-4:2020(E)
4 Symbols and abbreviated terms
Symbol Name Unit
2
A cross-sectional area of the standpipe m
d borehole diameter / diameter of intake zone m
D diameter of a standpipe m
F intake factor —
FS full scale —
GWT groundwater table —
HAE high air entry —
k hydraulic conductivity of soil m/s
s
k hydraulic conductivity of grout m/s
g
L length of intake zone m
LAE low air entry —
p pressure kPa
q unconfined compressive strength Pa
u
RL reference level —
t time s
u pore water pressure kPa
z geometric height m
z geometric height of the measuring point m
mp
z piezometric level m
w
3
γ unit weight of water kN/m
w
ψ pressure head m
5 Instruments
5.1 General
5.1.1 Open piezometer systems and closed piezometer systems should be distinguished from each
other (see Table 1 and Figure 1).
Table 1 — Piezometer types
No. Type Sub-type Feature
A filter and reservoir, installed in the ground and open
to the atmosphere.
— open standpipe
The measuring device is retrievable. Readings can be
piezometer
manual or automatic.
Open piezom-
1 eter system
An advantage of open systems is the possibility that
— monitoring well
(see 5.2)
automatic measurements can be checked against manual
measurements.
— Casagrande piezometer
Open piezometers may not have a suitable response time
in low permeability soils.
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ISO 18674-4:2020(E)
Table 1 (continued)
No. Type Sub-type Feature
A filter, a reservoir and a pressure transducer are in-
— electric, fibre optic or
stalled in the ground and are closed from the atmosphere.
Closed
probe piezometer
piezometer Retrievable pressure transducers are possible using
2
system (see — pneumatic piezometer special systems.
5.3)
Closed systems commonly have a shorter time lag than
— twin-tube piezometer
open systems.
5.1.2 The choice between open or closed systems should be made according to the monitoring plan
(see ISO 18674-1:2015, 4.3) and in consideration of the loading conditions and the hydrodynamic time
lag of the system.
NOTE 1 The choice between open or closed system is crucial and can be a decisive factor on success or failure
of the measurement. For example, in undrained conditions, an open system will not correctly follow the true
changes of pore water pressure (see Annex D).
NOTE 2 Climatic conditions play also an important role when choosing between an open and a closed system.
For example, when there is a risk of freezing conditions, a closed system is preferred.
5.1.3 The intake zone of the filter should be limited to an adequately short vertical section of the
aquifer.
NOTE Pore water pressures can vary with depth or in stratified aquifers or when vertical groundwater flow
is present.
5.1.4 All components and equipment intended for installation in the ground shall be sufficiently
resistant to mechanical loading and chemical attack by constituents in the groundwater. Any reactions
between the materials used and the ground, in particular consequences of diverse electrochemical
potential e.g. galvanic effects, shall be prevented.
NOTE Differences in electrochemical potential can cause modified pore water pressures. This effect
emanates from gases generated by electric curre
...
NORME ISO
INTERNATIONALE 18674-4
Première édition
2020-06
Reconnaissance et essais
géotechniques — Surveillance
géotechnique par instrumentation in
situ —
Partie 4:
Mesure de la pression interstitielle:
Piézomètres
Geotechnical investigation and testing — Geotechnical monitoring by
field instrumentation —
Part 4: Measurement of pore water pressure: Piezometers
Numéro de référence
ISO 18674-4:2020(F)
©
ISO 2020
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ISO 18674-4:2020(F)
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ISO 18674-4:2020(F)
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 2
4 Symboles et termes abrégés . 7
5 Instruments . 8
5.1 Généralités . 8
5.2 Systèmes de piézomètre ouverts . 9
5.2.1 Généralités . 9
5.2.2 Types de systèmes de piézomètre ouverts .10
5.3 Systèmes de piézomètre fermés .13
5.3.1 Généralités .13
5.3.2 Types de systèmes de piézomètre fermés .16
5.4 Mesures absolues et relatives et compensation de la pression atmosphérique .17
5.5 Exigences relatives aux filtres .19
5.5.1 Filtres des systèmes de piézomètre ouverts .19
5.5.2 Filtres des systèmes de piézomètre fermés.19
5.6 Étendue et exactitude des mesures .20
6 Mise en place et procédure de mesure .20
6.1 Mise en place .20
6.1.1 Généralités .20
6.1.2 Mise en place de systèmes de piézomètre ouverts .22
6.1.3 Mise en place de systèmes de piézomètre fermés .23
6.1.4 Contrôles avant, pendant et après la mise en place .25
6.1.5 Maintenance .26
6.2 Réalisation de la mesure .26
6.2.1 Vérification et étalonnage de l'instrumentation .26
6.2.2 Mesure .26
7 Traitement et évaluation des données .27
8 Compte rendu .27
8.1 Compte rendu d’installation .27
8.2 Compte rendu de surveillance .27
Annexe A (normative) Procédure de mesure et d'évaluation .28
Annexe B (informative) Applications géotechniques .35
Annexe C (informative) Protection des piézomètres au niveau du sol .37
Annexe D (informative) Temps de réponse des mesures de pression interstitielle .40
Annexe E (normative) Mise en place d’un piézomètre entièrement cimenté .43
Annexe F (normative) Mesure d’une pression interstitielle négative (succion du sol) .45
Annexe G (informative) Exemples de mesure .46
Bibliographie .59
© ISO 2020 – Tous droits réservés iii
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ISO 18674-4:2020(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes
nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est
en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.
L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www
.iso .org/ directives).
L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l'élaboration du document sont indiqués dans l'Introduction et/ou dans la liste des déclarations de
brevets reçues par l'ISO (voir www .iso .org/ brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion
de l'ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir www .iso .org/ avant -propos.
Ce document a été élaboré par le Comité technique ISO/TC 182, Géotechnique, en collaboration avec
le comité technique CEN/TC 341, Investigations et essais géotechniques, du Comité européen de
normalisation (CEN), conformément à l'accord de coopération technique entre l'ISO et le CEN (Accord
de Vienne).
Une liste de toutes les parties de la série ISO 18674 est disponible sur le site web de l’ISO.
Tout commentaire ou toute question à propos du présent document doit être adressé à l’organisme de
normalisation national de l’utilisateur. Une liste complète de ces organismes est disponible à l’adresse
www .iso .org/ members .html.
iv © ISO 2020 – Tous droits réservés
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NORME INTERNATIONALE ISO 18674-4:2020(F)
Reconnaissance et essais géotechniques — Surveillance
géotechnique par instrumentation in situ —
Partie 4:
Mesure de la pression interstitielle: Piézomètres
IMPORTANT — Le présent document spécifie la mesure des pressions interstitielles et des
niveaux piézométriques dans un sol saturé, au moyen de piézomètres installés dans le cadre
d’une surveillance géotechnique. Les règles générales de surveillance des performances du
terrain, des structures en interaction avec le terrain, des remblais et des travaux géotechniques
sont présentées dans l'ISO 18674-1.
1 Domaine d’application
Le présent document spécifie la mesure des pressions interstitielles et des niveaux piézométriques
dans un sol saturé, au moyen de piézomètres installés dans le cadre d’une surveillance géotechnique.
Les règles générales de surveillance des performances du terrain, des structures en interaction avec le
terrain, des remblais et des travaux géotechniques sont présentées dans l'ISO 18674-1.
Si elles sont appliquées conjointement à la norme ISO 18674-5, les procédures décrites dans le présent
document permettent de déterminer les contraintes effectives qui agissent dans le sol.
Le présent document s’applique:
— au suivi des pressions d'eau qui agissent sur et dans les structures géotechniques (par ex. parois de
quais, digues, parois d’excavation, fondations, barrages, tunnels, talus, levées de terre, etc.);
— au suivi des processus de consolidation du terrain et des remblais (par ex. sous des fondations et
dans des levées de terre);
— à l’évaluation de la stabilité et de l’aptitude à l'entretien des structures géotechniques;
— au contrôle des calculs géotechniques en lien avec la procédure observationnelle.
NOTE Le présent document satisfait aux exigences relatives à la surveillance des performances du terrain,
des structures en interaction avec le terrain et des ouvrages géotechniques au moyen de piézomètres mis en
œuvre dans le cadre des études et essais géotechniques conformément aux Références [4] et [5]. Le présent
document se rapporte à des dispositifs de mesure, lesquels sont installés dans le sol. Pour les mesures de pression
interstitielle réalisées en lien avec des essais de pénétration au cône, voir l’ISO 22476-1.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s'applique (y compris les
éventuels amendements).
ISO 18674-1:2015, Reconnaissance et essais géotechniques — Surveillance géotechnique par
instrumentation in situ — Partie 1: Règles générales
EN ISO 22475-1, Reconnaissance et essais géotechniques — Méthodes de prélèvement et mesurages
piézométriques — Partie 1: principes techniques des travaux
© ISO 2020 – Tous droits réservés 1
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ISO 18674-4:2020(F)
3 Termes et définitions
Pour les besoins du présent document, les termes et les définitions de l’ISO 18674-1 ainsi que les
suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/
3.1
piézomètre
système d'instrument de terrain destiné à mesurer la pression interstitielle (3.2) ou le niveau
piézométrique (3.4) à l'endroit où le point de mesure (3.15) est confiné dans le sol ou le remblai de telle
sorte que la mesure répond à la pression du fluide autour de la zone ou du point de mesure et non aux
pressions du fluide à d'autres élévations
Note 1 à l'article: Le système consiste en un réservoir (3.1.2) étanche rempli de fluide, un filtre (3.1.3) et un
dispositif de mesure (3.1.7).
Note 2 à l'article: Le système est soit un système de piézomètre ouvert (3.6), soit un système de piézomètre fermé (3.7).
3.1.1
zone de prise
zone confinée par des bouchons (3.1.6), entre lesquels l’eau dans le sol peut s’écouler vers le dispositif de
mesure (3.1.7), délimitant ainsi le point de mesure (3.1.5)
Note 1 à l'article: Voir la Figure 1.
Note 2 à l'article: On suppose qu’une distribution de pression interstitielle (3.2) hydrostatique est établie le long
de la zone de prise.
Note 3 à l'article: La constante de proportionnalité entre le débit entrant ou sortant d’un piézomètre (3.1) et le
changement de pression interstitielle (3.2) est appelé facteur de prise F.
3.1.2
réservoir
espace entre le terrain et le dispositif de mesure (3.1.7), occupé par un fluide, qui permet à la pression
interstitielle (3.2) d’agir sur l’élément de détection du dispositif de mesure
Note 1 à l'article: Les pores du filtre (3.1.3) font partie intégrante du réservoir.
Note 2 à l'article: Dans les systèmes de piézomètre ouverts (3.6), la partie remplie d’eau du tube piézométrique fait
partie du réservoir.
3.1.3
filtre
section perméable d’un piézomètre (3.1) délimitant la zone de prise (3.1.1), qui permet l’entrée de l’eau,
et dans le même temps empêche l’entrée des particules du sol dans le tube piézométrique ou le dispositif
de mesure (3.1.7)
Note 1 à l'article: Le filtre peut être constitué d’une combinaison d’éléments, tels qu’une poche de sable, un tube
crépiné, un manchon de géotextile, une pointe filtrante (3.1.4) et un remplissage de coulis dans certains cas
particuliers.
3.1.4
pointe filtrante
élément filtrant ( filtre (3.1.4)) qui est une partie commune d’un système de piézomètre fermé (3.1.7)
Note 1 à l'article: Les pointes filtrantes sont formées d’un matériau dont la porosité est choisie en fonction des
besoins, i.e. filtre HCEA (3.1.4.1) ou filtre BCEA (3.1.4.2).
2 © ISO 2020 – Tous droits réservés
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ISO 18674-4:2020(F)
3.1.4.1
filtre à haut coefficient d’entrée d’air
filtre HCEA
pointe filtrante (3.1.4) dont la taille des pores est comparativement petite, ce qui lui confère une
résistance élevée au passage de l’air par rapport au passage de l’eau
Note 1 à l'article: Couramment, les pointes filtrantes à haut coefficient d’entrée d’air ont des diamètres de pores
situés entre 1 µm et 3 µm.
Note 2 à l'article: Les pointes filtrantes HCEA sont utilisées lorsqu’on souhaite maintenir le gaz à l’extérieur du
dispositif de mesure (3.1.7).
Note 3 à l'article: Dans un sol non-saturé ou lorsqu’on doit mesurer des pressions interstitielles (3.2) négatives
(c.-à-d. une succion, voir l’Annexe F), la pression de la phase gazeuse est toujours supérieure à celle de l’eau
interstitielle. Le diamètre de pore requis pour une pointe filtrante HCEA dépend de la différence entre la pression
de l’air interstitiel et la pression interstitielle.
3.1.4.2
filtre à bas coefficient d’entrée d’air
filtre BCEA
pointe filtrante (3.1.4) dont la taille des pores est comparativement grande, ce qui lui confère une
résistance moindre et permet facilement le passage de l’air et de l’eau
Note 1 à l'article: Couramment, les pointes filtrantes à bas coefficient d’entrée d’air ont des diamètres de pores
situés entre 20 µm et 50 µm.
3.1.5
massif filtrant
matériau perméable, placé autour d’une section crépinée (fentes ou trous) d’un piézomètre (3.1) ouvert,
ou autour de la pointe filtrante (3.1.4), permettant à l’eau d’atteindre le dispositif de mesure (3.1.7)
3.1.6
bouchon
couche dans un trou de forage, constituée d'un matériau de perméabilité appropriée et permettant une
séparation hydraulique de deux aquifères (3.10)
Note 1 à l'article: Les bouchons servent généralement à confiner une zone de prise (3.1.1).
3.1.7
dispositif de mesure
partie du système de piézomètre (3.1) utilisée pour mesurer le niveau piézométrique (3.4) dans un
système ouvert (3.6), ou la pression interstitielle (3.2) dans un système fermé (3.7)
Note 1 à l'article: Pour un système ouvert (3.6), le dispositif de mesure est couramment un dispositif de mesure
de niveau d’eau (3.1.7.1) dans le cas de mesures manuelles, ou un capteur de pression dans le cas de mesures
automatiques.
Note 2 à l'article: Pour un système fermé (3.7), le dispositif de mesure est généralement un capteur de pression à
membrane (voir 7b à la Figure 1.b). La membrane sépare un réservoir (3.1.2) et une chambre interne située dans
le capteur. La déflexion de la membrane dépend de la pression interstitielle (3.2) (voir la Figure 3).
Note 3 à l'article: Pour les systèmes fermés, le dispositif de mesure est souvent appelé piézomètre, au sens strict
du terme.
3.1.7.1
dispositif de mesure de niveau d’eau
dispositif de mesure comportant un ruban de mesure dont la longueur est graduée et une extrémité qui
active un signal (lumineux ou sonore) lorsqu’elle entre en contact avec l’eau
Note 1 à l'article: On utilise couramment un dispositif de mesure de niveau d’eau pour les mesures manuelles
dans les systèmes ouverts (3.6) ou lors de la procédure d'installation des piézomètres (3.1).
© ISO 2020 – Tous droits réservés 3
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ISO 18674-4:2020(F)
3.1.7.2
piézomètre électrique
piézomètre (3.1) dans lequel le dispositif de mesure (3.1.7)comporte une membrane dont la déformation
sous l’effet de la pression interstitielle (3.2) est mesurée par un capteur électrique
Note 1 à l'article: Les piézomètres électriques reposent couramment sur des capteurs à jauge de contrainte,
piézo-électriques, à corde vibrante ou capacitifs. Certains dispositifs d’acquisition des données prennent en
charge tous les types de piézomètre électrique.
Note 2 à l'article: Voir la Figure 3.
3.1.7.3
piézomètre à fibre optique
piézomètre (3.1) dans lequel le dispositif de mesure (3.1.7) de la pression comporte une membrane dont
la déformation est mesurée par un capteur optique
Note 1 à l'article: Les piézomètres à fibre optique ne nécessitent pas de liaison électrique entre le dispositif
d’affichage et le capteur.
Note 2 à l'article: Les piézomètres à fibre optique nécessitent un dispositif d’affichage dédié.
3.1.7.4
piézomètre pneumatique
piézomètre (3.1) dans lequel le dispositif de mesure (3.1.7) comporte une vanne qui est ouverte de
manière pneumatique par la pression d'un gaz, laquelle est exercée depuis l’extérieur par l’intermédiaire
de tubes remplis de gaz, et fermée par la pression interstitielle (3.2)
Note 1 à l'article: Voir la Figure 4.
3.2
pression interstitielle
u
pression de l’eau dans les vides du terrain ou d’un remblai, par rapport à la pression atmosphérique
Note 1 à l'article: La pression interstitielle est la différence entre la contrainte totale et la contrainte effective
dans un terrain saturé (voir les Références [6] et [7]).
Note 2 à l'article: Dans le cas des roches, le terme associé est pression de l’eau des fissures.
Note 3 à l'article: Un sol ou un remblai dont les pores sont entièrement remplis d’eau est dit «saturé».
Note 4 à l'article: Les mesures de pression interstitielle peuvent donner des valeurs positives ou négatives (voir
la Référence [8] et l’Annexe F). Les instruments qui mesurent directement des pressions interstitielles négatives
sont parfois appelés «tensiomètres», mais ils n’entrent pas dans le champ d’application du présent document
(voir ISO 11276).
Note 5 à l'article: Les mesures de la pression interstitielle peuvent être affectés par les changements de la
pression atmosphérique (voir 5.4.1 et Annexe A).
3.3
hauteur de charge
ψ
rapport u/γ de la pression interstitielle u (3.2) et du poids spécifique de l’eau γ , au-dessus d’un point
e e
Note 1 à l'article: Pour un système ouvert (3.6), elle est proportionnelle à la différence de hauteur entre le niveau
piézométrique (3.4) et le niveau du point de mesure (3.15) (voir Figure 1).
4 © ISO 2020 – Tous droits réservés
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ISO 18674-4:2020(F)
3.4
niveau piézométrique
z
e
hauteur à laquelle l’eau s’élèvera dans un piézomètre à tube ouvert (3.6.1) et à laquelle la pression de
l’eau dans le terrain est égale à celle de l’atmosphère ambiante
Note 1 à l'article: Le niveau piézométrique z est la somme de la hauteur géométrique z et de la hauteur de charge
e
ψ (3.3): z = z + u/γ .
e e
Note 2 à l'article: Voir la Figure 1.
3.5
surface de la nappe phréatique
hauteur à laquelle la pression interstitielle u (3.2) est nulle
Note 1 à l'article: Voir la Figure 1.
Note 2 à l'article: On parle également de «surface phréatique».
Note 3 à l'article: Le niveau de la nappe phréatique est le niveau de la surface de la nappe phréatique à la
coordonnée géographique considérée.
3.6
système ouvert
système de piézomètre ouvert
système d’instrument de terrain dans lequel le fluide est en contact direct avec l’atmosphère et dans
lequel est mesuré le niveau piézométrique (3.4) au niveau du point de mesure (3.15)
3.6.1
piézomètre à tube ouvert
système de piézomètre ouvert (3.6), consistant en un tube (installé dans le terrain) qui, au niveau de son
extrémité supérieure, est ouvert à l’atmosphère et comporte une section crépinée, située dans la zone
de prise (3.1.1)
Note 1 à l'article: Voir la Figure 1 a)
Note 2 à l'article: Le diamètre interne du tube est généralement compris entre 19 mm et 60 mm.
3.6.2
piézomètre Casagrande
piézomètre à tube ouvert (3.6.1) comportant un ou deux tubes de diamètre interne comparativement
plus petit et une pointe filtrante (3.1.4) poreuse au niveau du point de mesure (3.15)
Note 1 à l'article: Voir 5.2.2.4, la Figure 2 et la Référence [9].
3.6.3
puits de contrôle
piézomètre à tube ouvert (3.6.1) comportant un tube de grand diamètre interne (généralement
≥ 100 mm)
Note 1 à l'article: Sous réserve que le temps de réponse (3.9) soit satisfaisant, un puits de contrôle peut être utilisé
comme piézomètre (3.1) à tube ouvert (voir l'Annexe D)
Note 2 à l'article: Un puits de contrôle est souvent utilisé pour prélever des échantillons d’eau souterraine ou
pour effectuer des essais de pompage.
3.6.4
puits d’observation
tube ouvert à l’intérieur d'un trou de forage, dans lequel la zone de prise (3.1.1) n’est pas confinée
Note 1 à l'article: Les puits d’observation sont souvent incorrectement appelés piézomètres à tube ouvert (3.6.1). Ne
comportant pas de bouchon (3.1.6), les puits d'observation ne peuvent pas être classés comme des piézomètres (3.1).
© ISO 2020 – Tous droits réservés 5
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ISO 18674-4:2020(F)
Note 2 à l'article: Voir 5.2.2.3.2.
3.7
système fermé
système de piézomètre fermé
système de mesure dans lequel le réservoir (3.1.2) n’est pas en contact direct avec l’atmosphère et dans
lequel la pression au sein du fluide est mesurée à l’aide d'un dispositif de mesure (3.1.7) de la pression
Note 1 à l'article: Voir la Figure 1 b)
Note 2 à l'article: Exemples de dispositif de mesure de la pression, utilisés dans des systèmes fermés: capteurs
électriques, capteurs à fibre optique et à vanne à membrane.
3.7.1
piézomètre à membrane
système fermé (3.7) pourvu d'une pointe filtrante (3.1.4), d'un petit réservoir (3.1.2) et d’une membrane
qui sépare l’eau interstitielle du système de mesure
Note 1 à l'article: La déformation de la membrane est mesurée et le signal est conduit par un câble jusqu’à un
endroit accessible
Note 2 à l'article: Les piézomètres à membrane peuvent être des piézomètres électriques (3.1.7.2) ou des
piézomètres à fibre optique (3.1.7.3).
Note 3 à l'article: La pression est mesurée à proximité de la pointe filtrante.
3.7.2
piézomètre à tubes hydrauliques jumelés fermés
système fermé (3.7) comportant une pointe filtrante (3.1.4) en céramique poreuse située dans une zone
de prise (3.1.1) et reliée à un site distant par l’intermédiaire de tubes jumelés remplis de fluide
Note 1 à l'article: La mesure de pression a lieu au niveau du site distant, pas au niveau de la pointe filtrante. Les
mesures doivent être ajustées pour tenir compte des différences d’élévation entre la pointe filtrante et le site
distant.
3.7.3
piézomètre à sonde
système fermé (3.7) dans lequel un dispositif de mesure (3.1.7) amovible est inséré dans un tube, lequel
est équipé d’un ou plusieurs orifices de mesure, chacun étant situé au niveau d'une zone de prise (3.1.1)
3.8
piézomètre multi-niveau
système comportant plusieurs points de mesure (3.15) placés de manière permanente à différentes
hauteurs dans le sol, chaque point de mesure ayant sa propre zone de prise (3.1.1)
3.9
retard hydrodynamique
temps de réponse
durée qui s’écoule entre un changement de la pression interstitielle (3.2) dans le sol et le changement
correspondant de la mesure
Note 1 à l'article: Le retard dépend en premier lieu du type et des dimensions du piézomètre (3.1) (en particulier
de la taille du réservoir (3.1.2)), de la perméabilité du sol et de la procédure d’installation (voir l'Annexe D).
Note 2 à l'article: L’expression «temps de réponse lent» associé à un piézomètre, est synonyme d’un retard
hydrodynamique long.
3.10
aquifère
masse de roche ou de sol perméable apte à contenir et à transmettre les eaux souterraines
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ISO 18674-4:2020(F)
3.11
aquifère non confiné
aquifère (3.10) dans lequel la surface de l'eau souterraine correspond à sa limite supérieure
3.12
aquifère confiné
aquifère (3.10) qui est délimité au-dessus et au-dessous par des aquicludes (3.14)
3.13
couche de confinement
couche de roche ou de sol peu perméable qui restreint l'écoulement des eaux souterraines et sépare les
aquifères (3.10)
3.14
aquiclude
masse de sol ou de roche de très faible transmissivité, qui empêche efficacement l'eau de s'écouler dans
le terrain
3.15
point de mesure
point dans le sol auquel fait référence la pression interstitielle (3.2)
4 Symboles et termes abrégés
Symbole Nom Unité
2
A est l’aire de la section du tube piézométrique m
d diamètre du trou de forage / diamètre de la zone de prise m
D diamètre d’un tube piézométrique m
F facteur de prise —
PE Pleine échelle
SNP surface de la nappe phréatique m
HCEA haut coefficient d’entrée d’air —
k conductivité hydraulique du sol m/s
s
k conductivité hydraulique du coulis m/s
g
L longueur de la zone de prise m
BCEA bas coefficient d’entrée d’air —
P pression kPa
q résistance à la compression non confinée Pa
u
NR niveau de référence —
t temps s
u pression interstitielle kPa
z haut
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 18674-4
ISO/TC 182
Geotechnical investigation and
Secretariat: BSI
testing — Geotechnical monitoring by
Voting begins on:
2020-03-27 field instrumentation —
Voting terminates on:
Part 4:
2020-05-22
Measurement of pore water pressure:
Piezometers
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ISO/FDIS 18674-4:2020(E)
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ISO/FDIS 18674-4:2020(E)
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ISO/FDIS 18674-4:2020(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 7
5 Instruments . 7
5.1 General . 7
5.2 Open piezometer systems . 9
5.2.1 General. 9
5.2.2 Types of open piezometer systems .10
5.3 Closed piezometer systems .13
5.3.1 General.13
5.3.2 Types of closed piezometer systems .16
5.4 Absolute versus relative measurements and atmospheric compensation.17
5.5 Requirements for filters .19
5.5.1 Filters in open piezometer systems.19
5.5.2 Filters in closed piezometer systems .19
5.6 Measuring range and accuracy .20
6 Installation and measuring procedure .20
6.1 Installation .20
6.1.1 General.20
6.1.2 Installation of open piezometer systems .21
6.1.3 Installation of closed piezometer systems .23
6.1.4 Checks before, during and after installation .24
6.1.5 Maintenance .25
6.2 Carrying out the measurement .25
6.2.1 Instrumentation check and calibration .25
6.2.2 Measurement .26
7 Data processing and evaluation .26
8 Reporting .26
8.1 Installation report .26
8.2 Monitoring report .26
Annex A (normative) Measuring and evaluation procedure .27
Annex B (informative) Geo-engineering applications .34
Annex C (informative) Protection of piezometers at the ground level .36
Annex D (informative) Response time for pore water pressure measurements .39
Annex E (normative) Fully grouted piezometer installation.42
Annex F (normative) Measuring negative pore water pressure (soil suction) .44
Annex G (informative) Measuring examples .45
Bibliography .57
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ISO/FDIS 18674-4:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
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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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 182, Geotechnics, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 341, Geotechnical
Investigation and Testing, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
A list of all parts in the ISO 18674 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv © ISO 2020 – All rights reserved
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 18674-4:2020(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 4:
Measurement of pore water pressure: Piezometers
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing
this document using a colour printer.
1 Scope
This document specifies the measurement of pore water pressures and piezometric levels in saturated
ground by means of piezometers installed for geotechnical monitoring. General rules of performance
monitoring of the ground, of structures interacting with the ground, of geotechnical fills and of
geotechnical works are presented in ISO 18674-1.
If applied in conjunction with ISO 18674-5, the procedures described in this document allow the
determination of effective stresses acting in the ground.
This document is applicable to:
— monitoring of water pressures acting on and in geotechnical structures (e.g. quay walls, dikes,
excavation walls, foundations, dams, tunnels, slopes. embankments, etc.);
— monitoring of consolidation processes of soil and fill (e.g. beneath foundations and in embankments);
— evaluating stability and serviceability of geotechnical structures;
— checking geotechnical designs in connection with the Observational Design procedure.
NOTE This document fulfils the requirements for the performance monitoring of the ground, of structures
interacting with the ground and of geotechnical works by the means of piezometers, installed as part of the
geotechnical investigation and testing in accordance with References [4] and.[5] This document relates to
measuring devices, which are installed in the ground. For pore water pressure measurements carried out in
connection with cone penetration tests, see ISO 22476-1.
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 18674-1:2015, Geotechnical investigation and testing — Geotechnical monitoring by field
instrumentation — Part 1: General rules
ISO 22475-1, Geotechnical investigation and testing — Sampling by drilling and excavation methods and
groundwater measurements — Part 1: Technical principles for execution
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18674-1 and the following apply.
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ISO/FDIS 18674-4:2020(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
piezometer
field instrument system for measuring pore water pressure (3.2) or piezometric level (3.4) where the
measuring point (3.15) is confined within the ground or geotechnical fill so that the measurement
responds to the fluid pressure around the measuring zone/point and not to fluid pressures at other
elevations
Note 1 to entry: The system consists of a sealed reservoir (3.1.2) filled with fluid, a filter (3.1.3) and a measuring
device (3.1.7).
Note 2 to entry: The system is either an open piezometer system (3.6) or a closed piezometer system (3.7).
3.1.1
intake zone
zone confined by seals (3.1.6), between which water in the ground can flow to the measuring device,
thus defining the measuring point (3.15)
Note 1 to entry: See Figure 1.
Note 2 to entry: It is assumed that a hydrostatic pore water pressure (3.2) distribution is established along the
intake zone.
Note 3 to entry: The constant of proportionality between flow into or out of a piezometer (3.1) and the change of
pore water pressure is called the intake factor F.
3.1.2
reservoir
space between the ground and the measuring device (3.1.7), occupied by a fluid, which allows the pore
water pressure (3.2) to act on the sensing element of the measuring device
Note 1 to entry: The pores within the filter (3.1.3) are an integral part of the reservoir.
Note 2 to entry: In open piezometer systems (3.6), the water-filled part of the standpipe is part of the reservoir.
3.1.3
filter
permeable section of a piezometer (3.1) defining the intake zone (3.1.1), which allows water to enter and
at the same time restricts soil particles entering the standpipe or measuring device (3.1.7)
Note 1 to entry: The filter can be a combination of elements, such as a sand pocket, a perforated pipe, a geotextile
sleeve, a filter tip (3.1.4) and grout backfill in specific cases.
3.1.4
filter tip
filter (3.1.3) element which is a common part of a closed piezometer system (3.7)
Note 1 to entry: Filter tips are formed of a material with purpose-designed pore diameters, i.e. HAE filter (3.1.4.1)
or LAE filter (3.1.4.2).
3.1.4.1
high air entry filter
HAE filter
filter tip (3.1.4) with comparatively small pores giving a higher resistance to the passage of air than to
the passage of water
Note 1 to entry: Commonly, high air entry filter tips have pore diameters of between 1 μm and 3 μm.
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ISO/FDIS 18674-4:2020(E)
Note 2 to entry: HAE filter tips are used when it is intended to keep gas out of the measuring device (3.1.7).
Note 3 to entry: In unsaturated soil or when negative pore water pressures (3.2) are to be measured (i.e. suction;
see Annex F), the pressure of the gaseous phase is always higher than that of the pore water. The required pore
diameter of the HAE filter tip depends on the difference between the pore air pressure and the pore water
pressure.
3.1.4.2
low air entry filter
LAE filter
filter tip (3.1.4) with comparatively large pores giving a lower resistance to the passage of air readily
allowing the passage of both air and water
Note 1 to entry: Commonly, low air entry filter tips have pore diameters of between 20 μm and 50 μm.
3.1.5
filter pack
permeable material, placed around a slotted section of an open piezometer (3.1) or around the filter tip
(3.1.4), allowing water to reach the measuring device (3.1.7)
3.1.6
seal
layer in a borehole, made with a material that has a permeability suitable for hydraulical separation of
two aquifers (3.10)
Note 1 to entry: Seals are generally used to confine an intake zone (3.1.1).
3.1.7
measuring device
part of the piezometer (3.1) system used to measure the piezometric level (3.4) in an open system (3.6) or
the pore water pressure (3.2) in a closed system (3.7)
Note 1 to entry: For an open piezometer system (3.6), the measuring device is commonly a water level meter
(3.1.7.1) for manual measurements or a pressure transducer for automatic measurements.
Note 2 to entry: For a closed piezometers system (3.7), the measuring device is typically a diaphragm pressure
transducer (see 7b in Figure 1 b)). The diaphragm separates a reservoir (3.1.2) and an inner chamber in the
transducer. The deflection of the diaphragm is a function of the pore water pressure (3.2) (see Figure 3).
Note 3 to entry: For closed piezometers systems, the measuring device is often synonymously termed a
piezometer in a narrow sense.
3.1.7.1
water level meter
measuring device with a marked length measuring tape and a tip that activates a signal (light, sound)
when it comes into contact with water
Note 1 to entry: A water level meter is commonly used for manual measurements in open systems (3.6) or during
the installation procedure of piezometers (3.1).
3.1.7.2
electric piezometer
piezometer (3.1) where the measuring device (3.1.7) has a diaphragm and the deflection of the diaphragm
due to pore water pressure (3.2) is measured by an electric sensor
Note 1 to entry: Electric piezometers are commonly based on strain gauge, piezo-electric, vibrating wire or
capacitive sensors. Data acquisition devices exist which accommodate all types of electric piezometers.
Note 2 to entry: See Figure 3.
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ISO/FDIS 18674-4:2020(E)
3.1.7.3
fibre optic piezometer
piezometer (3.1) where the pressure measuring device (3.1.7) has a diaphragm and the deflection of the
diaphragm is measured by an optical sensor
Note 1 to entry: Fibre optic piezometers do not require electrical connection between read-out unit and sensor.
Note 2 to entry: Fibre optic piezometers require a dedicated read-out unit.
3.1.7.4
pneumatic piezometer
piezometer (3.1) where the pressure measuring device (3.1.7) has a valve which is opened pneumatically
by a gas pressure, which is applied from the outside via gas-filled tubes and closed by the pore water
pressure (3.2)
Note 1 to entry: See Figure 4.
3.2
pore water pressure
u
pressure of the water in the voids of the ground or a fill, relative to the atmospheric pressure
Note 1 to entry: The pore water pressure is the difference between the total stress and the effective stress in
saturated ground (see References [6] and [7]).
Note 2 to entry: For rocks, the associated term is joint water pressure.
Note 3 to entry: The state of soil or fill where the pores are completely filled with water is referred to as
“saturated”.
Note 4 to entry: Pore water pressure measurements can yield positive or negative values (see Reference [8] and
Annex F). Instruments that directly measure negative pore pressures are sometimes termed ‘tensiometers’, but
are not within the scope of this document (see ISO 11276).
Note 5 to entry: Measurements of the pore water pressure can be affected by changes of the atmospheric pressure
(see 5.4.1 and Annex A).
3.3
pressure head
ψ
ratio u/γ of the pore water pressure u (3.2) and the specific weight of water γ , above a point
w w
Note 1 to entry: For an open piezometer system (3.6), it is proportional to the elevation difference between the
piezometric level (3.4) and the level of the measuring point (3.15) (see Figure 1).
3.4
piezometric level
z
w
elevation to which water will rise in an open standpipe piezometer (3.6.1) and at which the pressure of
the water in the ground is equal to that of the ambient atmosphere
Note 1 to entry: The piezometric level z is the sum of the geometric elevation z and the pressure head ψ (3.3):
w
z = z + u/γ .
w w
Note 2 to entry: See Figure 1.
3.5
groundwater table
water table
elevation at which pore water pressure u (3.2) is zero
Note 1 to entry: See Figure 1.
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ISO/FDIS 18674-4:2020(E)
Note 2 to entry: An equivalent term is phreatic surface.
Note 3 to entry: The groundwater level is the level of the groundwater table at a geographical coordinate.
3.6
open system
open piezometer system
field instrument system in which the fluid is in direct contact with the atmosphere and the piezometric
level (3.4) at the measuring point (3.15) is measured
3.6.1
open standpipe piezometer
open piezometer system (3.6), consisting of a pipe (installed in the ground) which, at its upper end, is
open to the atmosphere and with a perforated section, located in the intake zone (3.1.1)
Note 1 to entry: See Figure 1 a).
Note 2 to entry: Typical inner diameters of the pipe are from 19 mm to 60 mm.
3.6.2
Casagrande piezometer
open standpipe piezometer (3.6.1) with one or two comparatively small inner diameter pipes and a
porous filter tip (3.1.4) at the measuring point (3.15)
Note 1 to entry: See 5.2.2.4, Figure 2 and Reference [9].
3.6.3
monitoring well
open standpipe piezometer (3.6.1) with a large inner diameter of the pipe (typically ≥100 mm)
Note 1 to entry: A monitoring well can be used as standpipe piezometer (3.1), if the response time (3.9) is
satisfactory (see Annex D).
Note 2 to entry: A monitoring well is often used for taking samples of the groundwater or for performing
pumping tests.
3.6.4
observation well
open pipe within a borehole, where the intake zone (3.1.1) is unconfined
Note 1 to entry: Observation wells are often incorrectly termed open standpipe piezometers (3.6.1). Observation
wells do not classify as piezometers (3.1) as they do not have seals (3.1.6).
Note 2 to entry: See 5.2.2.3.2.
3.7
closed system
closed piezometer system
measuring system in which the reservoir (3.1.2) is not in direct contact with the atmosphere and in
which the pressure in the fluid is measured by a pressure measuring device (3.1.7)
Note 1 to entry: See Figure 1 b).
Note 2 to entry: Examples for pressure measuring devices, used in closed systems, are electric transducers, fibre
optic transducers and pressure valves.
3.7.1
diaphragm piezometer
closed system (3.7) with a filter tip (3.1.4), a small reservoir (3.1.2) and diaphragm which separates the
pore water from the measuring system
Note 1 to entry: The deflection of the diaphragm is measured and the signal is transported through a cable to an
accessible location.
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ISO/FDIS 18674-4:2020(E)
Note 2 to entry: Possible diaphragm piezometers are electric piezometers (3.1.7.2) or fibre optic piezometers
(3.1.7.3).
Note 3 to entry: The pressure is measured adjacent to the filter tip.
3.7.2
closed hydraulic twin-tube piezometer
closed system (3.7) with a porous ceramic filter tip (3.1.4) located within an intake zone (3.1.1) and
connected to a remote location via twin fluid filled tubes
Note 1 to entry: The pressure measurement takes place at the remote location and not at the filter tip. The
measurements need to be adjusted for elevation differences between the filter tip and the remote location.
3.7.3
probe piezometer
closed system (3.7) where a moveable measuring device (3.1.7) is inserted into a pipe which is equipped
with one or more measuring ports, each located at an intake zone (3.1.1)
3.8
multi-level piezometer
system with several measuring points (3.15) permanently installed at different elevations in the ground,
where each measuring point has its own intake zone (3.1.1)
3.9
hydrodynamic time lag
response time
time span between a change of the pore water pressure (3.2) in the ground and the associated change in
the measurement
Note 1 to entry: The time lag depends primarily on the type and dimensions of the piezometer (3.1) (essentially
the size of the reservoir (3.1.2)), the permeability of the ground and the installation procedure (see Annex D).
Note 2 to entry: The term “slow response time” of the piezometer is synonymous with a long hydrodynamic
time lag.
3.10
aquifer
body of permeable rock or soil mass suitable for containing and transmitting groundwater
3.11
unconfined aquifer
aquifer (3.10) in which the groundwater surface forms the upper boundary
3.12
confined aquifer
aquifer (3.10) which is bounded above and below by aquicludes (3.14)
3.13
confining layer
aquitard
a low permeability layer of rock or soil that restricts groundwater flow and seperates aquifers (3.10)
3.14
aquiclude
body of soil or rock with extremely low transmissivity, which effectively prevents the flow of water
through the ground
3.15
measuring point
point in the ground where the pore water pressure (3.2) is referenced to
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ISO/FDIS 18674-4:2020(E)
4 Symbols and abbreviated terms
Symbol Name Unit
2
A cross-sectional area of the standpipe m
d borehole diameter / diameter of intake zone m
D diameter of a standpipe m
F intake factor —
FS full scale —
GWT groundwater table —
HAE high air entry —
k hydraulic conductivity of soil m/s
s
k hydraulic conductivity of grout m/s
g
L length of intake zone m
LAE low air entry —
p pressure kPa
q unconfined compressive strength Pa
u
RL reference level —
t time s
u pore water pressure kPa
z geometric height m
z geometric height of the measuring point m
mp
z piezometric level m
w
3
γ unit weight of water kN/m
w
ψ pressure head m
5 Instruments
5.1 General
5.1.1 Open piezometer systems and closed piezometer systems should be distinguished from each
other (see Table 1 and Figure 1).
Table 1 — Piezometer types
No. Type Sub-type Feature
A filter and reservoir, installed in the ground and open
to the atmosphere.
— open standpipe
The measuring device is retrievable. Readings can be
piezometer
manual or automatic.
Open piezom-
1 eter system
An advantage of open systems is the possibility that
— monitoring well
(see 5.2)
automatic measurements can be checked against manual
measurements.
— Casagrande piezometer
Open piezometers may not have a suitable response time
in low permeability soils.
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ISO/FDIS 18674-4:2020(E)
Table 1 (continued)
No. Type Sub-type Feature
A filter, a reservoir and a pressure transducer are in-
— electric, fibre optic or
stalled in the ground and are closed from the atmosphere.
Closed
probe piezometer
piezometer Retrievable pressure transducers are possible using
2
system (see — pneumatic piezometer special systems.
5.3)
Closed systems commonly have a shorter time lag than
— twin-tube piezometer
open systems.
5.1.2 The choice between open or closed systems should be made according to the monitoring plan
(see ISO 18674-1:2015, 4.3) and in consideration of the loading conditions and the hydrodynamic time
lag of the system.
NOTE 1 The choice between open or closed system is crucial and can be a decisive factor on success or failure
of the measurement. For example, in undrained conditions, an open system will not correctly follow the true
changes of pore water pressure (see Annex D).
NOTE 2 Climatic conditions play also an important role when choosing between an open and a closed system.
For example, when there is a risk of freezing conditions, a closed system is preferred.
5.1.3 The intake zone of the filter should be limited to an adequately short vertical section of the
aquifer.
NOTE Pore water pressures can vary with depth or in stratified aquifers or when verti
...
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