SIST EN ISO 18674-4:2020

SLOVENSKI STANDARD
01-september-2020
Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 4. del: Meritve
tlaka porne vode: piezometri (ISO 18674-4:2020)
Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation
- Part 4: Measurement of pore water pressure: Piezometers (ISO 18674-4:2020)
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 4:
Porenwasserdruckmessungen: Piezometer (ISO 18674-4:2020)
Reconnaissance et essais géotechniques - Surveillance géotechnique par
instrumentation in situ - Partie 4: Mesure de la pression interstitiell (ISO 18674-4:2020)
Ta slovenski standard je istoveten z: EN ISO 18674-4:2020
ICS:
13.080.05 Preiskava tal na splošno Examination of soils in
general
17.100 Merjenje sile, teže in tlaka Measurement of force,
weight and pressure
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 18674-4
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2020
EUROPÄISCHE NORM
ICS 13.080.20; 93.020
English Version
Geotechnical investigation and testing - Geotechnical
monitoring by field instrumentation - Part 4: Measurement
of pore water pressure: Piezometers (ISO 18674-4:2020)
Reconnaissance et essais géotechniques - Surveillance Geotechnische Erkundung und Untersuchung -
géotechnique par instrumentation in situ - Partie 4: Geotechnische Messungen - Teil 4:
Mesure de la pression interstitiell (ISO 18674-4:2020) Porenwasserdruckmessungen: Piezometer (ISO
18674-4:2020)
This European Standard was approved by CEN on 23 June 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
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United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18674-4:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 18674-4:2020) has been prepared by Technical Committee ISO/TC 182
"Geotechnics" in collaboration with Technical Committee CEN/TC 341 “Geotechnical Investigation and
Testing” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2021, and conflicting national standards shall
be withdrawn at the latest by January 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 18674-4:2020 has been approved by CEN as EN ISO 18674-4:2020 without any
modification.
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
ISO 18674-4:2020(E)
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
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Published in Switzerland
ii © ISO 2020 – All rights reserved

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
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
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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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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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any patent rights identified during the development of the document will be in the Introduction and/or
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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.
iv © ISO 2020 – All rights reserved

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.
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.
2 © ISO 2020 – All rights reserved

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.
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.
4 © ISO 2020 – All rights reserved

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.
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
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
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.
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
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 currents created by using different metals or alloys in the piezometer
tip and/or filter material.
8 © ISO 2020 – All rights reserved

ISO 18674-4:2020(E)
a) Open system b) Closed system
Key
GL Ground Level A zone above GWT B zone below GWT
I unconfined aquifer II aquiclude or aquitard III confined aquifer
z piezometric level in III GWT groundwater table in I RL reference level (e. g. sea level)
w
1a water level meter 1b readout unit with barometer 2a vented top cap with base plate
2b base plate 3a standpipe 3b signal cable
4 backfill 5 borehole wall 6 seal
7a perforated or slotted section 7b pressure measuring device 7b1 reservoir with filter tip
7b2 inner chamber of transducer 7e end cap 8 filter pack
9 intake zone 10 pressure head 11 elevation of measuring point
relative to RL
Figure 1 — Types of piezometer systems
5.2 Open piezometer systems
5.2.1 General
5.2.1.1 An open piezometer system shall include the following components: a filter around the
measuring point, a seal above the filter and an open pipe which extends from the filter through the seal
up to the ground surface.
EXAMPLE See Figure 1 a).
ISO 18674-4:2020(E)
NOTE 1 The water pressure at the piezometric level is in equilibrium with the atmospheric pressure.
NOTE 2 If the borehole extends deeper than the intake zone, a seal is placed below the filter. It is also good
practice to include a seal below the filter if horizontal flow is required (e.g. for performing rising or falling
head tests).
5.2.1.2 The measuring point of an open piezometer is defined as the midpoint of the intake zone.
NOTE 1 The piezometric level, measured at the measuring point of an open piezometer is influenced by the
intake zone. A hydrostatic pressure distribution is assumed over the height of the intake zone.
NOTE 2 For an open piezometer, the measuring point is not related to the position of the measuring device.
For example, when using a pressure transducer in an open piezometer, the measuring point remains the centre of
the intake zone, which is usually not the position of the pressure transducer.
5.2.1.3 The top cap of the standpipe shall be equipped with a vent to permit unrestricted variations of
the water level inside the pipe.
5.2.1.4 Measurements can be conducted either by determining the piezometric level (e.g. by a
water level meter) or by measuring the water pressure in the standpipe at a specified depth below the
piezometric level (e.g. by using a pressure transducer). When a pressure transducer is used to determine
the piezometric level, compensation for atmospheric variations should be considered (see 5.4).
5.2.1.5 In case of artesian conditions and an overflow of the standpipe, the standpipe can be extended
to a level above the highest piezometric level or the open system can be converted to a closed system (see
5.3), e.g. by sealing a pressure gauge onto the top end of the standpipe.
5.2.2 Types of open piezometer systems
5.2.2.1 General
Open piezometer systems can be of the following types:
— Open standpipe piezometer
— Monitoring well
— Casagrande piezometer
5.2.2.2 Open standpipe piezometer
An open standpipe piezometer shall include the following components:
— a straight pipe with a minimum inner diameter of 12 mm;
NOTE 1 The minimum inner diameter is related to self-de-airing of open standpipe systems.
NOTE 2 Main considerations in the selection of the inner diameter are the ground conditions and the
hydrodynamic time lag. Larger diameter pipes have longer hydrodynamic time lags.
— a slotted or perforated section of the lower part of the standpipe;
NOTE 3 When used in highly permeable ground with large and rapid water variations, the openings in
the perforated or slotted pipe need to be sufficiently large to minimise flow resistance.
— a filter pack around the slotted or perforated section of the standpipe according to 5.5.1.1 and
5.5.1.2;
— a sealing plug of at least 1 m above the filter pack to confine the intake zone and to avoid rain water
directly entering the piezometer system;
10 © ISO 2020 – All rights reserved

ISO 18674-4:2020(E)
NOTE 4 When using clay pellets to form a seal, it is good practice to have at least 1 m of the seal below the
groundwater level in order to allow the pellets to swell. When this is not possible, it is good practice to use a
grout mixture as the seal.
— a sealing plug of at least one meter length in each confining layer. The location and length of the plug
should be adjusted to the local ground conditions.
5.2.2.3 Monitoring well
5.2.2.3.1 A monitoring well (see 3.6.3) with appropriate seals may be used as an open standpipe
piezometer (see 5.2.2.2) as long as the response time is acceptable for purpose.
5.2.2.3.2 Monitoring wells should be clearly distinguished from observation wells. As the groundwater
regime cannot be known a priori, the use of observation wells is strongly discouraged.
NOTE Observation wells (see 3.6.4) do not classify as piezometers as they do not have seals and thus can
create connections between different aquifers and disturb the groundwater regime. The use of observation wells
is limited to the measurement of the groundwater level in the uppermost layer of the ground in which, from the
groundwater table, the water pressure increases uniformly with depth.
5.2.2.4 Casagrande piezometer
5.2.2.4.1 A Casagrande piezometer shall include the following components:
— a low air entry filter made from appropriate material such as quartz sand, ceramic material, sintered
metal or porous plastic, placed in a borehole;
— one or two standpipes of a comparatively small inner diameter attached to the filter coming up to
the surface.
NOTE 1 See Figure 2.
NOTE 2 A typical inner diameter of the standpipes is 12 mm. Smaller inner diameters can be used, but it is
possible that they are not self-de-airing.
5.2.2.4.2 With dual pipes the piezometer can be flushed to remove air and/or soil particles out of
the system.
NOTE 1 With dual pipes (see Figure 2 b)), the diameter of the pipes can be smaller than 12 mm.
NOTE 2 The use of a larger diameter pipe (see Figure 2 c)) allows the installation of a pressure measuring
device within the standpipe. The device can be retrieved and replaced.
NOTE 3 Using a special tip connection (see 9 in Figure 2 c)), a Casagrande piezometer can be converted to
a closed piezometer system. The pipe(s) can be closed by a device which includes a pressure transducer and a
suitable solution to seal the casing(s).
ISO 18674-4:2020(E)
a) Single standpipe b) Double standpipes c) Single standpipe
(with common D ) (with small D ) (with large D )
i i i
Key
1 porous filter 4 seal 7 second pipe allowing flushing
2 filter pack (filter sand) 5 backfill 8 larger diameter pipe allowing
3 borehole wall 6 small diameter pipe installation of pressure
transducer
9 filter tip connection (optional)
Figure 2 — Casagrande piezometer, showing different connections to the surface
12 © ISO 2020 – All rights reserved

ISO 18674-4:2020(E)
5.3 Closed piezometer systems
5.3.1 General
5.3.1.1 Closed piezometer systems shall include the components shown in Table 2. The components of
the system are a function of the installation method.
Table 2 — Piezometer components as a function of the installation method
Piezometer component
Installation
Filter tip at the Filter pack around Seal above
method
Measuring device
measuring point the filter tip the filter
traditional + + + +
a
fully grouted + + +
b
push-in + - + +
embedded + + - +
Key
+ essential
-   absent
a
The grout acts as a filter pack and as a seal, see 6.1.3.
b
The filter tip is pushed into the ground and is in direct contact with the ground, see 6.1.3.
EXAMPLE  For traditionally installed closed systems, see Figure 1 b).
NOTE  The water pressure at the pressure measuring device is not necessarily in equilibrium with the atmospheric
pressure.
5.3.1.2 The measuring point is the location of the diaphragm, adjacent to the filter tip.
NOTE When a filter pack is present around the filter tip, the pressure measured at the diaphragm is influenced
by the intake zone and does not necessarily represent the pressure at the measuring point in the ground.
5.3.1.3 Pressure measuring devices, or components thereof, shall be located either directly near the
filter tip or at the ground surface. The device located near the filter tip can be either a diaphragm pressure
transducer (see Figure 3) or a pressure valve (see Figure 4). Measuring devices at the ground surface can
be pressure gauges (see Figure 5), readout units and/or control panels.
ISO 18674-4:2020(E)
a) Diaphragm piezometer b) Types of possible diaphragm
transducer (schematic) transducers
Key
u pore water pressure 5 signal cable
1 filter tip 5a  electric cable
2 r
...