Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 4: Measurement of pore water pressure: Piezometers (ISO 18674-4:2020)

This standard forms part 4 of the series ISO 18674, as described in ISO 18674-1: Part 1. General rules the methods and gives rules for measurement of pore water pressures in geotechnical engineering or more general in foundation engineering. Pore pressures are needed to obtain effective stresses and play a key role in the analysis of engineered construction in and on ground.

Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 4: Porenwasserdruckmessungen: Piezometer (ISO 18674-4:2020)

Dieses Dokument legt die Messung von Porenwasserdrücken und piezometrischen Höhen in gesättigten Böden mit Hilfe von Piezometern fest, die zur geotechnischen Überwachung installiert werden. Die allgemeinen Regeln für die messtechnische Überwachung des Baugrunds, der mit dem Baugrund in Wechselwirkung stehenden Bauwerke, geotechnischer Auffüllungen und geotechnischer Bauarbeiten sind in ISO 18674 1 angegeben.
In Verbindung mit ISO 18674 5 erlauben die in diesem Dokument beschriebenen Verfahren die Bestimmung der im Baugrund wirkenden effektiven Spannungen.
Dieses Dokument ist anzuwenden für:
- die Überwachung von auf und in geotechnischen Bauwerken (z. B. Kaimauern, Deiche, Baugrubenwände, Gründungen, Dämme, Tunnel, Böschungen, Aufschüttungen usw.) wirkenden Wasserdrücken;
- die Überwachung von Konsolidierungsprozessen von Böden und Schüttmaterial (z. B. unterhalb von Gründungen und in Aufschüttungen);
- die Bewertung der Stabilität und Gebrauchstauglichkeit von geotechnischen Bauwerken;
- die Überprüfung geotechnischer Entwürfe im Zusammenhang mit der Beobachtungsmethode.
ANMERKUNG Dieses Dokument erfüllt die Anforderungen für die messtechnische Überwachung des Baugrunds, der mit dem Baugrund in Wechselwirkung stehenden Bauwerke und geotechnischer Bauarbeiten, die mittels Piezometern durchgeführt wird, die im Rahmen der geotechnischen Erkundung und Untersuchung nach Verweisung [4] und [5] eingebaut werden. Dieses Dokument bezieht sich auf Messgeräte, die im Baugrund eingebaut werden. Für Informationen zu im Zusammenhang mit Drucksondierungen durchgeführten Porenwasserdruckmessungen siehe ISO 22476 1.

Reconnaissance et essais géotechniques - Surveillance géotechnique par instrumentation in situ - Partie 4: Mesure de la pression interstitiell (ISO 18674-4:2020)

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.

Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 4. del: Meritve tlaka porne vode: piezometri (ISO 18674-4:2020)

General Information

Status
Published
Public Enquiry End Date
09-Oct-2019
Publication Date
13-Aug-2020
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
28-Jul-2020
Due Date
02-Oct-2020
Completion Date
14-Aug-2020

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SLOVENSKI STANDARD
SIST EN ISO 18674-4:2020
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
SIST EN ISO 18674-4:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 18674-4:2020
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SIST EN ISO 18674-4:2020
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

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of 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

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.
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SIST EN ISO 18674-4:2020
EN ISO 18674-4:2020 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 18674-4:2020
EN ISO 18674-4:2020 (E)
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.
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SIST EN ISO 18674-4:2020
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SIST EN ISO 18674-4:2020
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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SIST EN ISO 18674-4:2020
ISO 18674-4:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© 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

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
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SIST EN ISO 18674-4:2020
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 2020 – All rights reserved iii
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SIST EN ISO 18674-4:2020
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

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

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.
iv © ISO 2020 – All rights reserved
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SIST EN ISO 18674-4:2020
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 2020 – All rights reserved 1
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SIST EN ISO 18674-4:2020
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
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SIST EN ISO 18674-4:2020
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 2020 – All rights reserved 3
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SIST EN ISO 18674-4:2020
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

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

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

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):

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
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SIST EN ISO 18674-4:2020
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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SIST EN ISO 18674-4:
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