prEN ISO 18674-8

Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 8: Measurement of forces: Load cells (ISO/DIS 18674-8:2022)

This standard is part 8 of the series ISO 18674, as described in ISO 18674-1: Part 1.
General rules for the methods and rules for measurement of normal forces and loads from tieback, bracing, struts and other elements like piles in geotechnical engineering or more general in foundation engineering are given

Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 8: Messung von Kräften: Kraftmessdosen (ISO/DIS 18674‑8:2022)

Reconnaissance et essais géotechniques - Surveillance géotechnique par instrumentation in situ - Partie 8: Mesure des forces : capteurs de force (ISO/DIS 18674-8:2022)

Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 8. del: Merjenje sil: obremenilne celice (ISO/DIS 18674-8:2022)

General Information

• Status: Not Published
• Publication Date: 20-Aug-2024
• ICS: 93.020 - Earthworks. Excavations. Foundation construction. Underground works
• Technical Committee: CEN/TC 341 - Geotechnical Investigation and Testing
• Drafting Committee: CEN/TC 341 - Geotechnical Investigation and Testing
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Start Date: 23-Mar-2023
• Due Date: 27-Aug-2023
• Completion Date: 23-Mar-2023
• Ref Project: oSIST prEN ISO 18674-8:2022 - Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation - Part 8: Measurement of forces: Load cells (ISO/DIS 18674-8:2022)

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 18674-8:2022
01-oktober-2022
Geotehnično preiskovanje in preskušanje - Geotehnične meritve - 8. del: Merjenje
sil: obremenilne celice (ISO/DIS 18674-8:2022)

Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation

- Part 8: Measurement of forces: Load cells (ISO/DIS 18674-8:2022)
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 8:
Messung von Kräften: Kraftmessdosen (ISO/DIS 18674‑8:2022)
Reconnaissance et essais géotechniques - Surveillance géotechnique par

instrumentation in situ - Partie 8: Mesure des forces : capteurs de force (ISO/DIS 18674-

8:2022)
Ta slovenski standard je istoveten z: prEN ISO 18674-8
ICS:
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
oSIST prEN ISO 18674-8:2022 en,fr,de

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

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oSIST prEN ISO 18674-8:2022
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oSIST prEN ISO 18674-8:2022
DRAFT INTERNATIONAL STANDARD
ISO/DIS 18674-8
ISO/TC 182 Secretariat: BSI
Voting begins on: Voting terminates on:
2022-07-28 2022-10-20
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 8:
Measurement of loads: Load cells

Reconnaissance et essais géotechniques — Surveillance géotechnique par instrumentation in situ —

Partie 8: Mesure des forces : capteurs de force
ICS: 93.020
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
ISO/CEN PARALLEL PROCESSING
THEREFORE SUBJECT TO CHANGE AND MAY
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ISO/DIS 18674-8:2022(E)
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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oSIST prEN ISO 18674-8:2022
ISO/DIS 18674-8:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 18674-8
ISO/TC 182 Secretariat: BSI
Voting begins on: Voting terminates on:
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 8:
Measurement of loads: Load cells

Reconnaissance et essais géotechniques — Surveillance géotechnique par instrumentation in situ —

Partie 8: Mesure des forces : capteurs de force
ICS: 93.020
This document is circulated as received from the committee secretariat.
COPYRIGHT PROTECTED DOCUMENT
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FOR COMMENT AND APPROVAL. IT IS
© ISO 2022
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NATIONAL REGULATIONS.
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RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
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© ISO 2022 – All rights reserved
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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oSIST prEN ISO 18674-8:2022
ISO/DIS 18674-8:2022(E)
Contents Page

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

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

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

3 Terms and definitions .................................................................................................................................................................................... 2

4 Symbols and abbreviated terms..........................................................................................................................................................3

5 Instruments............................................................................................................................................................................................................... 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 Electric load cells .................................................................................................................................................................................. 4

5.3 Hydraulic load cells ............................................................................................................................................................................ 5

5.4 Instruments for specific applications ................................................................................................................................ 6

5.4.1 Anchor load cells................................................................................................................................................................. 6

5.4.2 Load cell for cast-in-place concrete piles ...................................................................................................... 7

5.5 Measurement accuracy ................................................................................................................................................................... 9

6 Installation and measuring procedure ........................................................................................................................................ 9

6.1 Installation ................................................................................................................................................................................................. 9

6.1.1 General ........................................................................................................................................................................................ 9

6.1.2 Anchor load cells.............................................................................................................................................................. 10

6.1.3 Load cells at the base of cast-in-place concrete piles ...................................................................... 10

6.1.4 Load cells for struts across excavations ..................................................................................................... 11

6.2 Carrying out the measurement ......... .................................................................................................................................. .. 11

6.2.1 Instrumentation check and calibration ...................................................................................................... 11

6.2.2 Measurement ......................................................................................................................................................................12

7 Data processing and evaluation .......................................................................................................................................................12

8 Reporting ..................................................................................................................................................................................................................13

8.1 Installation report ............................................................................................................................................................................ 13

8.2 Monitoring report ............................................................................................................................................................................. 13

Annex A (informative) Geo-engineering applications ...................................................................................................................14

Annex B (informative) Measuring examples............................................................................................................................................15

Bibliography .............................................................................................................................................................................................................................34

iii
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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.
A list of all parts in the ISO 18674 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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oSIST prEN ISO 18674-8:2022
DRAFT INTERNATIONAL STANDARD ISO/DIS 18674-8:2022(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 8:
Measurement of loads: Load cells

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 forces by means of load cells carried out for geotechnical

monitoring. For measuring forces by means of strain or displacement gauges, see ISO 18674-7.

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 18674-1:2015.
This document is applicable to:

— performance monitoring of geotechnical structures such as anchors, end-anchored rock bolts,

tiebacks, piles, struts, props and steel linings;

— checking geotechnical designs and adjustment of construction in connection with the Observational

Design procedure;
— evaluating stability during or after construction.

Not subject of this document are devices where the load is purposely applied to geotechnical structures

in the wake of geotechnical field tests such as calibrated hydraulic jacks for pull-out tests of anchors or

load tests of piles.

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 load cells as part of the geotechnical

investigation and testing in accordance with References [1] and [2].
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 7500-1:2018, Metallic materials — Calibration and verification of static uniaxial testing machines —

Part 1: Tension/compression testing machines — Calibration and verification of the force-measuring system

ISO 18674-1:2015, Geotechnical investigation and testing — Geotechnical monitoring by field

instrumentation — Part 1: General rules

ISO 18674-7:2023, Geotechnical investigation and testing – Geotechnical monitoring by field

instrumentation – Part 7: Measurement of strain: Strain

ISO 22477-5:2018, Geotechnical investigation and testing — Testing of geotechnical structures — Part 5:

Testing of grouted anchors
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3 Terms and definitions

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

apply.

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 https:// www .electropedia .org/
3.1
load cell
field instrument for monitoring forces acting in geotechnical structures

Note 1 to entry: Load cells are commonly placed at an end of a structural member where forces are transmitted

from one member to another.

EXAMPLE Load cell at the anchor head where the force acting in the anchor tendon is transmitted to a

retaining wall.

Note 2 to entry: Common are electric (see 3.2) and hydraulic (see 3.3) measuring principles.

Note 3 to entry: Indispensable components of load cells are a load bearing element and load distribution plates

for transmitting forces between structural members.
3.2
electric load cell

instrument with an elastically-behaving body which deforms under the applied force, where the

resulting deformation is measured by electric sensors
Note 1 to entry: An example of such body is a steel cylinder (see Figure 2).
Note 2 to entry: For typical electric sensors, see 5.2.4.
3.3
hydraulic load cell

instrument with a flat liquid-filled compartment where the force to be monitored acts normal to the

flat distribution plates on the sides of the compartment and where the pressure in the liquid of the

compartment is measured by a pressure measuring device.
Note 1 to entry: See Figure 3.

Note 2 to entry: The compartment is formed by two steel plates, welded together around their peripheries, where

the intervening cavity is filled with a liquid (de-gassed fluid).
3.4
anchor load cell

purpose-designed load cell with a centric passage to accommodate the anchor tendon.

Note 1 to entry: See Figure 4.
Note 2 to entry: The tendon typically comprises a bar, strands or wires.
3.5
nominal range
the range over which the load cell is calibrated

Note 1 to entry: Other terms which are used in practice are, for example, load range, nominal load, capacity, full-

scale capacity or measuring range.

Note 2 to entry: Outside of the nominal range, the load cell is not calibrated and therefore the measurements are

not reliable.
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3.6
over range

the maximum load that can be applied on the load cell, without damaging the load cell.

Note 1 to entry: Other terms which are used in practice are, for example, “overrange capacity” or “overload”.

Note 2 to entry: Typically, the over range of commercially available load cells is up to 1,5 times the nominal range.

4 Symbols and abbreviated terms
Symbol Name Unit
A largest dimension in cross section of structural member m
B smallest dimension in cross section of structural member m
D outer diameter m
F axial force acting in a member N
FS Full scale -
H height m
P installation load N
P effective axial load N
F reaction force in the anchor head N
P axial load N
R pile shaft resistance N
R pile toe resistance N
S shear force N
t elapsed time day
z depth m
α angle between the tendon at the anchor head and the anchor axis degree
5 Instruments
5.1 General
5.1.1 A load cell can be either electric (see 5.2) or hydraulic (see 5.3).

NOTE Other types of load cells, such as mechanical or photo-elastic are not considered in this document.

5.1.2 The maximum load anticipated in the lifetime of the monitoring project plus a margin of 10 to

30 % shall not exceed the nominal range of the load cell.
NOTE 1 Too large a margin reduces the accuracy of the measurements.

NOTE 2 The measurement in the lower end (5 % to 10 %) of the nominal range is often less accurate.

5.1.3 At the measuring location, the force acting in a structural member shall be transmitted through

the load cell via load distribution plates. Spherical distribution plates may be used to improve an aligned

load distribution.
NOTE See Figure 1 for an example of a spherical distribution plate.
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ISO/DIS 18674-8:2022(E)
Key
d, d , D,D , T, B dimensions of the spherical load distribution plate
1 1
Figure 1 — Spherical load distribution plate (example)
5.1.4 The load cell shall have a specified load bearing element.
EXAMPLES See 1 in Figure 2 and 2 to 4 in Figure 3.

5.1.5 The material of the load bearing element (1 in Figure 2) of the cell should be mechanically

stable.
EXAMPLE Heat-treated steel grade S355J2+N according to EN 10027-1.

5.1.6 The influence of temperature on the load measurement shall be considered and documented.

Exposure of the load cell to direct sunlight or other heat sources should be avoided or minimised. The

load cells should be designed to minimize temperature errors.

NOTE 1 The readings of load cells are affected by temperature changes. The use of temperature-compensated

sensors decreases the influence of temperature changes on the measurements. Information for temperature

correction of the load cell may be provided by the manufacturer.

NOTE 2 Independent temperature measurements in the vicinity of the load cell assist in the evaluation of the

load measuring results.

NOTE 3 Temperature changes can also affect the loads within the structural members, see ISO 18674-1:2015,

5.3.1.
5.2 Electric load cells
5.2.1 Electric load cells should have features as shown in Figure 2.

NOTE The load bearing element is usually either a solid cylinder or a hollow cylinder, see 1 in Figure 2.

5.2.2 Cylindrical load bearing elements should have a height H to outer diameter D ratio within the

range of 0,1 ≤ H/D ≤ 2.
NOTE 1 H/D > 2 tends to decrease the stability of the load cell assembly.

NOTE 2 The quality of the measurements of load cells with low ratios of H/D may be more sensitive to

imperfections on alignment, placement and load distribution plates.
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oSIST prEN ISO 18674-8:2022
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a) Top view b) Side view
Key
D outer diameter of load bearing element (1) 3 O-ring
P load 4 electric sensor (here: full-bridge strain gauges)
H height of load bearing element (1) 5 electric cable
1 load bearing element (here: hollow cylinder) 6 control and readout unit
2 protective cylindrical cover 7 upper load distribution plate
7 lower load distribution plate
Figure 2 — Features of an electric load cell (example, see Reference [4])

5.2.3 The deformation of the load bearing element shall be measured by electrical sensors.

5.2.4 The sensor can be based on either strain gauge, piezo-electric, vibrating wire or capacitive

measuring principles, configured in such a way that the influence of eccentric loading is minimised.

NOTE 1 The influence of eccentric loading is typically minimised by using multiple sensors spaced evenly

around the cylinder and at equal distance from the axis.

NOTE 2 The output signal of an electrical strain gauge load cell might depend on the power supply of the

logging device, when not properly designed.
5.3 Hydraulic load cells
5.3.1 Hydraulic load cells should have features as shown in Figure 3.

NOTE Elements 2, 3 and 4 of Figure 3 form a liquid-filled compartment. Any change in the magnitude of the

load P results in a change of the pressure of the liquid in the compartment (4 in Figure 3).

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oSIST prEN ISO 18674-8:2022
ISO/DIS 18674-8:2022(E)
Key
P load 4 liquid-filled compartment
1 upper load distribution plate 5 lower load distribution plate/bearing plate
2/3 load cell plates 6 pressure measuring unit (here: electric pressure
transducer)
Figure 3 — Features of a hydraulic load cell

5.3.2 The pressure measuring unit (6 in Figure 3) should be positioned as close as practically feasible

to the liquid-filled compartment.

NOTE An increased spacing between the liquid-filled compartment (4) and the pressure measuring unit (6)

results in a decreased stiffness of the load measuring system influencing the measurement.

5.3.3 The pressure measuring unit can be either a Bourdon Gauge or an electric pressure transducer.

5.4 Instruments for specific applications
5.4.1 Anchor load cells

5.4.1.1 Anchor load cells shall have an axial centric passage to accommodate the anchor tendon.

NOTE See Figures 1 and 4.

5.4.1.2 Anchor load cells can be of an electric (see 5.2) or hydraulic type (see 5.3).

5.4.1.3 At the measuring location, the anchor load shall be transmitted through the load cell via load

distribution plates. The load distribution plates shall be designed to withstand yielding at capacity load

and to limit distortions when distributing the load to the structure.
NOTE 1 See 7 and 7 in Figure 2 and 1 and 5 in Figure 3.
1 2

NOTE 2 Common are heat-treated steel load distribution plates of a H/D-ratio of about 0,22 to 0,30.

NOTE 3 The plate between the bearing element and the load cell (7 in Figure 2 and 5 in Figure 3) is commonly

referred to as bearing plate.
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5.4.1.4 The hole for feeding the anchor tendon through a load distribution plate shall be in the centre

of the plate.

5.4.1.5 For anchor tendons, spherical seats or wedges may be used to improve aligned load

distribution.
NOTE 1 See Figures 4a and b.

NOTE 2 Deviations from the perpendicular alignment between the load distribution plates and the anchor

tendon generate a force component which acts in transverse direction of the load cell. This effect, which affects

the accuracy of the anchor load measurement, cannot be avoided by a spherical nut or wedges, see 6.1.1.4 to

6.1.1.6.
a) Spherical seat for a bar tendon b) Wedges for two strand tendons
Key
1a nut 5 load bearing element 10 bearing plate
1b wedge 6 protection sleeve 11 ground surface
2a spherical seat 7 potting 12a bar tendon
2b head plate 8 electric sensor 12b strand tendon
3 upper load distribution plate 9 electric cable to readout 13 borehole wall
4 lower load distribution plate

Figure 4 — Schematic layout of anchor head devices for aligning different types of tendons

5.4.2 Load cell for cast-in-place concrete piles

5.4.2.1 When monitoring the performance of a cast-in-place concrete pile, a load cell may be located

at the toe of the pile. The layout of the load cell should be as in Figure 5.

NOTE 1 The load at the top of the pile is commonly measured by means of strain gauges, see ISO 18674-7.

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NOTE 2 A load cell at the head or at another location between toe and head is commonly associated with

pile testing procedures where a load is actively applied and systematically varied and where the deformational

response of the pile is considered in dependency of the applied load.

NOTE 3 Outside of pile testing, the use of a load cell at the head of the pile is limited to situations where only

axial loads are expected during the lifetime of the pile, as the presence of the load cell might influence the load

transfer to the pile.
Key
1 hydraulic load cell embedded in (5)
2 weld ring
3 reinforcement cage
4 ring of compressible material
(e.g. synthetic rubber)
5 conical plug (e.g. mortar)
6 concrete / mortar bed
7 borehole wall
8 bottom of borehole
9 casing inner wall (where applicable)

Figure 5 — Schematic layout of a hydraulic load cell at the base of a cast-in-place concrete pile

[5]
(after )

5.4.2.2 In case of a pile diameter greater than 1,00 m, an array of at least three load cells can be used.

Number and position (layout / geometry) of the load cells shall be designed to minimize eccentricity.

Distribution plates shall be designed to equally distribute the load into the load cells.

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5.5 Measurement accuracy

It should be realised that the measurement accuracy is predominately controlled by the design of the

mounting devices, the quality of the installation of these devices with regard to axiality (see 6.1.1.5)

and eccentricity (see 6.1.1.6) and changes of the ambient temperature at the measuring location.

NOTE 1 For anchor load cells, the central hole of the cell has to be large enough to avoid a contact of the cell

with the anchor tendon and, thus, the development of transverse loads to the cell resulting in reduced overall

accuracy and possible damage to the cell.

NOTE 2 For strand tendons, the angle formed by the cables at the anchor head with respect to the anchor

axis produces a transverse effect that is absorbed by the (upper) distribution plate. The measured axial load

component is smaller than the actual strand load (see 7.4).
6 Installation and measuring procedure
6.1 Installation
6.1.1 General
6.1.1.1 Load cells should be installed concurrently with the structural member.

NOTE This simplifies the placement and alignment of the cells and the associated load distribution plates. It

also ensures that there will be a full record of the load history.

6.1.1.2 The forces shall be transmitted from the structural member through the cell only.

6.1.1.3 Load distribution plates shall be placed outside the load bearing element and on the structural

member to distribute the load evenly.

6.1.1.4 The load cell shall be installed taking into consideration the orientation as well as the location

of the axis of the structural member.
NOTE 1 For the orientation requirement, see 6.1.1.5.
NOTE 2 For the location requirement, see 6.1.1.6.

6.1.1.5 The axis of the load cell shall be aligned parallel to the axis of the structural member and the

distribution plates should be perpendicular to the axis of the load cell and the structural member. A

deviation of ±5° is permissible.

NOTE Any non-parallelity leads to a transverse loading of the load cell which affects the quality of the

measurement.

6.1.1.6 Load cells and distribution plates shall be centred in the axis of the structural member. An

eccentricity of < 3 % of the diameter of the load bearing element of the cell is permissible.

EXAMPLE If the ou
...