Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 2: Measurement of displacements along a line: Extensometers (ISO 18674-2:2016)

This Standard applies to the measurement of displacements along a line by means of extensometers carried out for geotechnical monitoring. It is to be applied in conjunction with EN ISO 22474-1.
Specifically, this Standard applies to
–   investigating soils and rocks;
–   checking geotechnical design values in connection with the Observational Design method;
–   deriving geotechnical design values (e.g. pile load test; trial tunnelling);
–   evaluating stability ahead of, during or after construction (e.g. natural slopes, slope cuts, embankments, excavation walls, foundations, dams, refuse dumps, tunnels).

Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 2: Verschiebungsmessungen entlang einer Messlinie: Extensometer (ISO 18674-2:2016)

Dieser Teil der ISO 18674-2 gilt für geotechnische Verschiebungsmessungen entlang einer Messlinie mit Hilfe eines Extensometers. Die allgemeinen Regeln für die Qualitätsüberwachung des Baugrunds, der mit dem Baugrund interagierenden Strukturen, der geotechnischen Füllungen und geotechnischen Bauarbeiten sind in ISO 18674-1:2015 angegeben.
Wenn sie zusammen mit ISO 18674-3:2016 anzuwenden sind, erlaubt ISO 18674-2 die Bestimmung der in jede Richtung wirkenden Verschiebungen.
Diese Norm gilt für:
   Überwachung des Verhaltens von Böden, Schüttmaterial und Felsen
   die Prüfung geotechnischer Ausführungsvorschläge im Zusammenhang mit der Beobachtungsprozedur
   die Ableitung geotechnischer Schlüsselparameter (z. B. von Ergebnissen von Pfahlprobebelastungen oder Probestollen)
   die Beurteilung der Standsicherheit vor, während und nach dem Bau (z. B. Stabilität bei natürlichen Böschungen, Böschungseinschnitten, Aufschüttungen, Baugrubenwänden, Gründungen, Dämmen, Mülldeponien, Tunneln)
ANMERKUNG   Dieses Dokument erfüllt die Anforderungen für die Qualitätsüberwachung des Baugrunds, der mit dem Baugrund interagierenden Strkuturen und geotechnischen Bauarbeiten mit einem Extensometers als Teil der geotechnischen Untersuchung und Prüfung in Übereinstimmung mit den Verweisen [1] und [2].

Reconnaissance et essais géotechniques - Mesures géotechniques - Partie 2: Mesure de déplacement le long d‘une ligne par extensomètre (ISO 18674-2:2016)

Le présent document s'applique à la mesure des déplacements le long d'une ligne à l'aide d'extensomètres utilisés à des fins de surveillance géotechnique. Les règles générales d'exécution de la surveillance du terrain, des structures interagissant avec le terrain et des travaux géotechniques sont présentées dans l'ISO 18674‑1.
Appliqué en même temps que l'ISO 18674‑3, le présent document permet la détermination des déplacements dans n'importe quelle direction.
Le présent document s'applique à:
— la surveillance du comportement des sols, des remblais et des roches;
— la vérification des valeurs de calcul géotechnique rattaché à la méthode d'étude observationnelle;
— la déduction des valeurs de calcul géotechnique (p. ex.: essai de charge des pieux ou essai de percement de tunnel);
— l'évaluation de la stabilité avant, pendant ou après la construction (p. ex.: talus naturels, talus de remblai, remblais, parois d'excavation, fondations, barrages, décharges ou tunnels).
NOTE Le présent document répond aux exigences pour la surveillance du terrain, des structures interagissant avec le terrain et des travaux géotechniques aux moyens des extensomètres en tant qu'essai et reconnaissance géotechnique selon les Références [5] et [6].

Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 2. del: Meritve pomikov vzdolž merilne linije: ekstenzometer (ISO 18674-2:2016)

Ta standard se uporablja za merjenje iztisnin vzdolž merilne linije z ekstenzometri za namene geotehničnih meritev. Standard je treba uporabljati v povezavi s standardom EN ISO 22474-1.  Ta standard se uporablja zlasti za:  – preiskovanje zemljin in kamnin;  – preverjanje vrednosti geotehničnega projektiranja v povezavi z metodo opazovalnega projektiranja; – izpeljavo vrednosti geotehničnega projektiranja (npr. obremenilni preskus pilotov, gradnja testnega predora);  – ocenjevanje stabilnosti pred, med ali po gradnji (npr. naravna pobočja, rezi pobočij, nasipi, stene izkopa, temelji, jezovi, odlagališča odpadkov, predori).

General Information

Status
Published
Public Enquiry End Date
29-Sep-2015
Publication Date
19-Feb-2017
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
03-Jan-2017
Due Date
10-Mar-2017
Completion Date
20-Feb-2017

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SLOVENSKI STANDARD
SIST EN ISO 18674-2:2017
01-marec-2017
*HRWHKQLþQRSUHLVNRYDQMHLQSUHVNXãDQMH*HRWHKQLþQHPHULWYHGHO0HULWYH
SRPLNRYY]GROåPHULOQHOLQLMHHNVWHQ]RPHWHU ,62

Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation

- Part 2: Measurement of displacements along a line: Extensometers (ISO 18674-
2:2016)
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 2:
Verschiebungsmessungen entlang einer Messlinie: Extensometer (ISO 18674-2:2016)

Reconnaissance et essais géotechniques - Mesures géotechniques - Partie 2: Mesure

de déplacement le long d‘une ligne par extensomètre (ISO 18674-2:2016)
Ta slovenski standard je istoveten z: EN ISO 18674-2:2016
ICS:
13.080.20 Fizikalne lastnosti tal Physical properties of soils
17.040.30 Merila Measuring instruments
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
SIST EN ISO 18674-2:2017 en

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

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SIST EN ISO 18674-2:2017
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SIST EN ISO 18674-2:2017
EN ISO 18674-2
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2016
EUROPÄISCHE NORM
ICS 13.080.20; 93.020
English Version
Geotechnical investigation and testing - Geotechnical
monitoring by field instrumentation - Part 2: Measurement
of displacements along a line: Extensometers (ISO 18674-
2:2016)

Reconnaissance et essais géotechniques - Mesures Geotechnische Erkundung und Untersuchung -

géotechniques - Partie 2: Mesure de déplacement le Geotechnische Messungen - Teil 2:

long d'une ligne par extensomètre (ISO 18674-2:2016) Verschiebungsmessungen entlang einer Messlinie:

Extensometer (ISO 18674-2:2016)
This European Standard was approved by CEN on 11 September 2016.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, 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: Avenue Marnix 17, B-1000 Brussels

© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18674-2:2016 E

worldwide for CEN national Members.
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SIST EN ISO 18674-2:2017
EN ISO 18674-2:2016 (E)
Contents Page

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

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SIST EN ISO 18674-2:2017
EN ISO 18674-2:2016 (E)
European foreword

This document (EN ISO 18674-2:2016) 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 May 2017, and conflicting national standards shall be

withdrawn at the latest by May 2017.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN [and/or CENELEC] 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, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 18674-2:2016 has been approved by CEN as EN ISO 18674-2:2016 without any

modification.
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SIST EN ISO 18674-2:2017
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SIST EN ISO 18674-2:2017
INTERNATIONAL ISO
STANDARD 18674-2
First edition
2016-10-15
Geotechnical investigation and
testing — Geotechnical monitoring by
field instrumentation —
Part 2:
Measurement of displacements along
a line: Extensometers
Reconnaissance et essais géotechniques — Mesures géotechniques —
Partie 2: Mesure de déplacement le long d‘une ligne par extensomètre
Reference number
ISO 18674-2:2016(E)
ISO 2016
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 3

5 Instruments ............................................................................................................................................................................................................... 4

5.1 General ........................................................................................................................................................................................................... 4

5.2 In-place extensometer ...................................................................................................................................................................... 8

5.2.1 Measuring points ............................................................................................................................................................. 8

5.2.2 Connecting elements .................................................................................................................................................... 8

5.2.3 Measuring head and read-out device ............................................................................................................. 9

5.3 Probe extensometer ........................................................................................................................................................................10

5.3.1 Measuring points and guide tube ...................................................................................................................10

5.3.2 Probe .......................................................................................................................................................................................11

5.5 Tape extensometer (convergence tape) .........................................................................................................................12

5.6 Measuring range and accuracy ..............................................................................................................................................12

6 Installation and measuring procedures ....................................................................................................................................13

6.1 Installation ...............................................................................................................................................................................................13

6.1.1 Surface components ........................................................................................................................................... ........13

6.1.2 Installation in boreholes and in fill ...............................................................................................................13

6.1.3 In-place extensometer .............................................................................................................................................14

6.1.4 Probe extensometer ...................................................................................................................................................14

6.1.5 Tape extensometer ......................................................................................................................................................15

6.2 Carrying out the measurement ..............................................................................................................................................15

6.2.1 Instrumentation check and calibration .....................................................................................................15

6.2.2 Measurement ...................................................................................................................................................................15

7 Data processing and evaluation .........................................................................................................................................................15

8 Reporting ...................................................................................................................................................................................................................16

8.1 Installation report .............................................................................................................................................................................16

8.2 Monitoring report ..............................................................................................................................................................................16

Annex A (normative) Measuring and evaluation procedure ....................................................................................................17

Annex B (informative) Backfill materials .....................................................................................................................................................26

Annex C (informative) Geo-engineering applications .....................................................................................................................27

Annex D (informative) Measuring examples .............................................................................................................................................28

Bibliography .............................................................................................................................................................................................................................46

© ISO 2016 – All rights reserved iii
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(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 on 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 the following URL: www.iso.org/iso/foreword.html.

The committee responsible for this document is ISO/TC 182, Geotechnics.

A list of all part in the ISO 18674 series, published under the general title Geotechnical investigation and

testing – Geotechnical monitoring by field instrumentation, can be found on the ISO website.

iv © ISO 2016 – All rights reserved
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SIST EN ISO 18674-2:2017
INTERNATIONAL STANDARD ISO 18674-2:2016(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 2:
Measurement of displacements along a line:
Extensometers
1 Scope

This document specifies the measurement of displacements along a line by means of extensometers

carried out 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 18674-3, this document allows the determination of displacements

acting in any direction.
This document is applicable to:
— monitoring the behaviour of soils, fills and rocks;

— checking geotechnical designs in connection with the Observational Design procedure;

— deriving geotechnical key parameters (e.g. from results of pile load tests or trial tunnelling);

— evaluating stability ahead of, during or after construction (e.g. stability of natural slopes, slope cuts,

embankments, excavation walls, foundations, dams, refuse dumps, tunnels).

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 extensometers as part of the geotechnical

investigation and testing in accordance with References [5] and [6].
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. 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
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 18674-1 and the following apply.

3.1
extensometer

field instrument for monitoring changes of distance between two or more measuring points located

along a measuring line

Note 1 to entry: Monitoring of such changes allows the determination of displacements of measuring points

acting in the direction of the measuring line.
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)

Note 2 to entry: At a measuring point, the movements of the medium (e.g. soil, rock, concrete and steel structures)

being investigated are transferred to the measuring point by devices such as anchors, rings or bolts (see 5.1.6).

Note 3 to entry: In the ground, the measuring points are typically installed in boreholes. The measuring line then

coincides with the axis of the borehole.
3.2
in-place extensometer

permanently installed extensometer, essentially consisting of anchor(s), connecting element(s) and at

least one measuring head

Note 1 to entry: Each connecting element is affixed to an anchor and free to move along the measuring line.

Note 2 to entry: Measuring heads are commonly located at one end of the measuring line. When carrying out the

measurements, they function as reference measuring points.
Note 3 to entry: For in-place extensometers in boreholes, see Reference [7].
Note 4 to entry: See Figure 1.
3.3
rod extensometer
in-place extensometer where the connecting element is a rod
Note 1 to entry: Common rod materials are steel or fibreglass.
Note 2 to entry: See Figure 1 a).
3.4
wire extensometer
in-place extensometer where the connecting element is a wire
Note 1 to entry: See Figure 1 b).
3.5
single extensometer
in-place extensometer with one anchor only
Note 1 to entry: See Figure 1 b).
3.6
multiple-point extensometer
in-place extensometer with more than one anchor
Note 1 to entry: Up to six anchor points are common in geo-engineering practice.
Note 2 to entry: See Figure 1 a).
3.7
chain extensometer
in-place extensometer formed of a series of single extensometer elements
Note 1 to entry: See Figure 1 c).
3.8
probe extensometer
extensometer where the connecting element is a moveable unit

Note 1 to entry: Probe extensometers can be developed as single-point probe extensometer (3.9) or double-point

probe extensometer (3.10).
Note 2 to entry: See Figure 2.
2 © ISO 2016 – All rights reserved
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
3.9
single-point probe extensometer

extensometer, essentially consisting of a measuring probe and a guiding tube with measuring marks

and in which, at the measuring position, only one measuring mark interacts with the probe

Note 1 to entry: The connecting element is the unit consisting of a measuring cable and a probe. The measured

value is the distance between the measuring mark and the reference mark at the head of the guiding tube.

Note 2 to entry: Because of its design, function and usual geotechnical application, the single-point probe

extensometer is commonly designated as a “magnetic extensometer,” a “magnet settlement probe” or an

“inductance probe.”
Note 3 to entry: See Figure 2 a).
3.10
double-point probe extensometer

extensometer, essentially consisting of a measuring probe and a guiding tube with measuring marks

and in which, at the measuring position, two measuring marks interact with the probe

Note 1 to entry: The connecting element is the measuring probe. The measured value is the distance between the

two measuring marks which are in interaction with the probe.

Note 2 to entry: Because of its design and function, the double-point probe extensometer is commonly designated

as an “incremental extensometer” or a “sliding micrometer.”
Note 3 to entry: See Figure 2 b).
3.11
gauge length

nominal distance between the contact points of the double-point extensometer probe

Note 1 to entry: L is commonly 1,0 m.

Note 2 to entry: L is commonly verified in a calibration of the probe prior to the measurement.

3.12
tape extensometer

extensometer for distance measurements between two accessible measuring points by means of a

measuring tape, essentially consisting of a device for tensioning of the tape with a reproducible pulling

force, two end pieces for connecting the device to bolts (3.13) and of a read-out unit

Note 1 to entry: Traditionally, tape extensometers were used in tunnelling. By means of follow-up measurements,

the change of the distances of two tunnel wall measuring points (in tunnelling, termed “convergence”) is

determined. For this reason, tape extensometers are commonly designated as “convergence tapes.”

Note 2 to entry: See Figure 3.
3.13
convergence bolts
measuring bolts fitting to the type of tape extensometer used
4 Symbols
Symbol Name Unit
d depth of borehole m
d distance between measuring point i and measuring head m
F subscript for follow-up measurement —
h height of measuring head above sea level m
i number of a measuring point —
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
Symbol Name Unit
K temperature correction term —
L gauge length of a double-point probe extensometer m

L length of the connecting element between measuring head and measuring point i m

l distance between measuring points m
l length of a measuring ring for probe extensometer m
n total number of measuring points along a measuring line —
P pulling force of wire extensometer kN
R subscript for reference measurement —
s displacement reading m
T temperature °C
t elapsed time s
u, v, w displacement component in x-, y-, z-direction, respectively m

w displacement component of measuring point i in z-direction relative to the measuring head m

i rel
w absolute displacement component of the measuring head in z-direction m
w absolute displacement component of measuring point i in z-direction m

Δw relative displacement between adjacent measuring points i and i-1 in z-direction m

x, y, z local coordinates of measuring points on a guide tube or in a borehole m
α coefficient of linear thermal expansion K
ε strain in direction of the z coordinate —
5 Instruments
5.1 General

5.1.1 The following types of extensometer in-place, probe and tape should be distinguished from each

other (see Table 1 and Figures 1 to 3).
Table 1 — Extensometer types
Extensometer
Automatic data
Feature
acquisition
No. Type Subtype
Single-point/multiple-point in-place
all instrument components are per-
in-place
extensometer
1 manently installed in the ground or possible
(see 5.2)
at accessible surfaces
rod/wire extensometer
probe single-point/double-point probe
(see 5.3) extensometer
measuring unit sequentially moved
not common
into measuring positions
tape
3 steel/wire tape extensometer
(see 5.4)

5.1.2 Changes of the distances between measuring points shall be monitored by comparison of the

measured values with those of the reference measurement. Displacements of the measuring points along

the measuring line shall be deduced in accordance with Annex A.

5.1.3 An increase of the distance between two measuring points (=extension) shall be assigned a

positive value.

5.1.4 The point onto which the extensometer measurements are related shall be denoted the

“reference point.”
4 © ISO 2016 – All rights reserved
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)

5.1.5 For absolute measurements, the coordinates of the reference point shall be independently

determined or assumed and verified as fixed.

NOTE If the reference point is assumed to be at the deepest anchor, surveying of the measuring head can

serve as a check.

5.1.6 Extensometer measuring points shall be marked by devices such as anchors, rings or bolts. The

measuring points of these devices shall be specified as follows:
— for anchors, the centre of an anchor;
— for rings, the centre of a ring;

— for bolts, the centre of a contact butt (for screwed couplings) or the centre of an eye (for eye/hook

couplings).

5.1.7 It shall be secured that the device, marking a measuring point, is set in such a way that it is

solidly connected to the medium so that any movement of the medium at the measuring point is fully

transferred to the device.

5.1.8 Instruments shall not significantly affect the conditions of the medium under investigation

and, in turn, shall not be significantly affected in their functionality by the medium (in accordance with

ISO 18674-1:2015, 5.1 and 5.2).
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
a) Rod extensometer b) Wire extensometer c) Chain extensometer
Key
1 anchor
1 anchors 1 to 3
1..3
2 connecting element (wire)
2 connecting elements 1 to 3
1..3
3 measuring head
3 local measuring heads 1 to 3
1..3
4 borehole wall
5 read-out device
6 pulling device
P tension force

EXAMPLE 1 For subfigure a), triple-point rod extensometer with electrical displacement transducers.

EXAMPLE 2 For subfigure b), single-point wire extensometer with dial gauge read-out.

EXAMPLE 3 For subfigure c), triple-point chain extensometer with electrical displacement transducers.

Figure 1 — Examples of in-place extensometer types
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
a) Single-point probe extensometer b) Double-point probe extensometer
Key
1 measuring tube 6 probe (in measuring position with rings No. 2 and 3)

2 anchor plates 1 to 3 (with external measuring rings) 7 setting rods (or pulling rope)

1..3
2 measuring rings 1 to 5 8 read-out unit
1..5
3 probe (in measuring position with anchor Plate No.2) 9 backfill
4 measuring tape 10 borehole wall
5 measuring head with reference mark
EXAMPLE 1 For subfigure a), magnetic probe extensometer in telescopic tubing.
EXAMPLE 2 For subfigure b), sliding micrometer.
Figure 2 — Examples of probe extensometer types
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SIST EN ISO 18674-2:2017
ISO 18674-2:2016(E)
Key
1 convergence bolt
2 measuring tape (or measuring wire)
3 device for tensioning of tape (or wire) and read-out
4 coupling element
Figure 3 — Principal sketch of a tape extensometer
5.2 In-place extensometer
5.2.1 Measuring points

The measuring points should be similar in their function to those common in rock nailing and

anchoring works.

EXAMPLES Wedge, straddle packer, spring-activated clamp, cement- or resin-grouted borehole packer, anchor

grouting with non-shrinking cement.

NOTE The movement of a measuring point is also transferred to the attached connecting element.

5.2.2 Connecting elements

5.2.2.1 For rod extensometers, a string of interconnected steel rods or a continuous glass fibre-

reinforced resin rod should be used, and for wire extensometers, steel wires should be used.

5.2.2.2 The selection of the material and that of the cross sectional area of the connecting elements

should be guided by the measuring task, environmental conditions, measuring accuracy and the length

of the measuring section (see Table 2).

5.2.2.3 If a connecting element can be disconnected temporarily from its fixing device at the measuring

point, it shall be established that the coupling tolerance does not exceed the intended measuring accuracy

of the system.

EXAMPLE Screw couplings or bayonet locks of the connecting element at the anchors.

NOTE Movements across the borehole axis or closure of the borehole can block the connecting element

and can affect the functionality of the extensometer. The functionality of an extensometer can be checked by

intermittently uncoupling a connecting element.

5.2.2.4 The coefficient of thermal expansion of the connecting elements shall be specified. Temperature

variations within the system should be taken into account.

NOTE Temperature-induced changes of the length of the connecting elements can have a substantial

influence on the accuracy of an extensometer system. The measurement of thermal gradients by a series of

temperature sensors along the extensometer can be useful in developing a suitab
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