SIST EN ISO 18674-5:2019

SLOVENSKI STANDARD
oSIST prEN ISO 18674-5:2019
01-januar-2019
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Geotechnical investigation and testing - Geotechnical monitoring by field instrumentation
- Part 5: Stress change measurements by Total Pressure Cells (TPC) (ISO/DIS 18674-
5:2018)
Geotechnische Erkundung und Untersuchung - Geotechnische Messungen - Teil 5:
Spannungsänderungsmessungen mittels Druckmessdosen (ISO/DIS 18674 5:2018)
Reconnaissance et essais géotechniques - Surveillance géotechnique par
instrumentation in situ - Partie 5: Mesures avec capteurs hydrauliques (ISO/DIS 18674-
5:2018)
Ta slovenski standard je istoveten z: prEN ISO 18674-5
ICS:
13.080.20 Fizikalne lastnosti tal Physical properties of soils
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
oSIST prEN ISO 18674-5:2019 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 18674-5:2019

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oSIST prEN ISO 18674-5:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 18674-5
ISO/TC 182 Secretariat: BSI
Voting begins on: Voting terminates on:
2018-09-25 2018-12-18
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 5:
Stress change measurements by Total Pressure Cells (TPC)
Reconnaissance et essais géotechniques — Surveillance géotechnique par instrumentation in situ —
Partie 5: Mesures avec capteurs hydrauliques
ICS: 13.080.20; 93.020
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 18674-5:2018(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2018

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oSIST prEN ISO 18674-5:2019
ISO/DIS 18674-5:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
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
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Email: copyright@iso.org
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Published in Switzerland
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Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 5
5 Instruments . 5
5.1 General . 5
5.2 Deformation measuring method . 7
5.3 Compensation measuring method . 7
5.4 Stiffness of the pressure pad . 8
5.5 Shape of pressure pad . 8
5.6 Accuracy . 9
6 Installation and measuring procedure .10
6.1 Installation .10
6.1.1 Installation in the ground .10
6.1.2 Installation in fill .11
6.1.3 Installation in concrete / shotcrete .12
6.1.4 Installation in contact planes .13
6.2 Carrying out the measurement .14
6.2.1 Instrumentation check and calibration .14
6.2.2 Measurement .14
7 Data processing and evaluation .14
8 Reporting .14
8.1 Installation report .14
8.2 Monitoring report .14
Annex A (normative) Evaluation procedure .15
Annex B (informative) Geo-engineering applications .17
Annex C (informative) Measuring examples .18
Bibliography .27
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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 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 parts 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.
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oSIST prEN ISO 18674-5:2019
DRAFT INTERNATIONAL STANDARD ISO/DIS 18674-5:2018(E)
Geotechnical investigation and testing — Geotechnical
monitoring by field instrumentation —
Part 5:
Stress change measurements by Total Pressure Cells (TPC)
1 Scope
This document specifies the measurement of stress changes by means of total pressure cells (TPC). It
refers to cells which are permanently installed either in the ground, in adjacent engineered structures
or in contact planes between any two media. 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.
If applied in conjunction with ISO 18674-4:2019, this document allows the determination of effective
stress acting in the ground.
Indirect stress monitoring methods (see 18674-1:2015, Table B.2) are not subject of this document.
This document is applicable to:
— monitoring changes of the state of stress in the ground and in geo-engineered structures (e.g. in
earth fill dams or tunnel lining);
— monitoring contact pressures at the interface between two media (e.g. earth pressure on retaining
wall; contact pressure at the base of a foundation);
— checking geotechnical designs and adjustment of construction in connection with the Observational
Design procedure;
— evaluating stability during or after construction.
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 total pressure cells as part of the
geotechnical investigation and testing according to EN 1997-1 and EN 1997-2, see 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
EN ISO 18674-1:2015, Geotechnical investigation and testing — Geotechnical monitoring by field
instrumentation — Part 1: General rules
ISO 18674-4:2019, Geotechnical investigation and testing — Geotechnical monitoring by field
instrumentation — Part 4: Measurement of pore water pressure: Piezometer
ISO 22475-1:2006, Geotechnical investigation and testing — Sampling methods and groundwater
measurements — Part 1: Technical principles for execution
ISO 22476-1:2012, Geotechnical investigation and testing — Field testing — Part 1: Electrical cone and
piezocone penetration test
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3 Terms and definitions
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/
For the purposes of this document the terms and definitions given in ISO 18674-1:2015 and the
following apply:
3.1
total pressure cell
TPC
field instrument for stress change measurements where a total pressure cell is the sensing element of
the system
Note 1 to entry: A total pressure cell consists of a pressure pad (1), a pressure tubing (2) and a pressure measuring
device (3) (see Figure 1 and Reference [3]).
Note 2 to entry: The pressure pad (1) consists of two steel platens, welded together around their peripheries,
where the intervening cavity is filled with a liquid. The cavity is connected to the inner chamber (3a) of the
pressure measuring device via a liquid-filled pressure tubing (2). Inner and outer chambers (3a and 3b) of the
pressure measuring device are separated by a flexible diaphragm (3c).
Note 3 to entry: Total pressure cells are stationary instruments which are embedded in a medium (see 3.2),
placed at the interface between any two media (see 3.3) or installed in boreholes (see 3.4).
Note 4 to entry: The target of the measurement is the change of the total normal stress Δσ of the medium acting
n
onto the flat side of the pad.
Key
1 pressure pad
2 pressure tubing
3 pressure measuring device
3a inner chamber
3b outer chamber
3c diaphragm
4 height of the pressure pad cavity
5 height of the pressure pad
6 measuring line (electric cable or twin hydraulic tubing)
7 control and readout unit
8 medium investigated
Figure 1 — Principal components of a TPC measuring system
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3.2
embedment pressure cell
total pressure cell which is fully embedded within a medium
EXAMPLE Push-in cell in soft soil; embedment cell in fill, “tangential cell” (see 3.10) in shotcrete tunnel lining.
3.3
contact pressure cell
total pressure cell which is placed in the contact plane between two media
EXAMPLE Cell at the base of a slab foundation; “radial cell” (see 3.9) in shotcrete tunnel lining.
3.4
borehole pressure cell
total pressure cell which is installed in a borehole
Note 1 to entry: See 2 in Figure 2.
3.5
aspect ratio
height to the smallest lateral dimension ratio of the pressure pad.
Note 1 to entry: For rectangular pads, the smallest lateral dimension is the width, for circular pads the diameter.
Note 2 to entry: Typical aspect ratios are of the order of 1:20 to 1:40.
3.6
total stress state
state of the ground where the internal forces acting in the ground are carried by the solid portion
(skeleton) of the ground and the pore water
Note 1 to entry: One only stress component can be monitored by a total pressure cell (which is the change of the
total normal stress Δσ ; see 3.1).
n
Note 2 to entry: Changes of 2-D and 3-D stress states can be monitored by a cluster of a sufficient number of
independently oriented TPCs installed at a measuring location: Three (3) TPCs for a 2-D stress state, and six (6)
TPCs for a 3-D stress state.
Note 3 to entry: By placing a TPC pad with its sensing side towards the vertical, the vertical normal stress
component σ can be directly monitored.
v
3.7
effective stress state
state of the ground where the internal forces acting in the ground are carried by the solid portion
(skeleton) of the ground
Note 1 to entry: It is {σ’} = {σ} - u
where
{σ’} = effective stress tensor;
{σ} = total stress tensor;
u = porewater pressure.
3.8
contact stress
stress component which acts normal to a contact plane
EXAMPLE Normal stress acting in the interface between a slab foundation and the ground.
Note 1 to entry: Shear stresses acting within the contact plane cannot be measured by a TPC.
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3.9
radial stress
specific contact stress between the ground and a tunnel lining
Note 1 to entry: Radial TPCs (“radial cells”) are especially designed for monitoring radial stresses.
Note 2 to entry: See 3 in Figure 2.
3.10
tangential stress
hoop stress monitored within shotcrete or concrete tunnel linings
Note 1 to entry: Tangential TPCs (“tangential cells”) are especially designed for monitoring tangential stresses in
tunnel linings. An alternative term is “concrete TPC”.
Note 2 to entry: See 4 in Figure 2.
Key
1 Borehole (vertically down-dipping; back-filled).
2 Array of three differently oriented borehole TPCs for monitoring horizontal ground stresses.
3 Radial TPCs at the ground/shotcrete lining interface.
4 Tangential TPCs in the shotcrete lining.
5 shotcrete lining
6 tunnel excavation contour
Figure 2 — Example of TPC layout in near-surface tunnelling
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Key
A clay core 1 TPC (single or cluster)
B filter zone 2 piezometer
C rock fill 3 routing for measuring cable
 4 terminal
Figure 3 — Example (schematic) of a TPC layout in an earth dam
4 Symbols
Symbol Name Unit
C TPC edge correction factor -
E Young’s modulus MPa
p pressure in the outer chamber of the measuring device MPa
a
p hydrostatic pressure difference between the external measuring station and TPC MPa
h
p pressure loss in measuring tube MPa
L
p pre-tensioning pressure MPa
p-t
p pressure in the inner chamber of the measuring device MPa
i
p pressure in a follow-up measurement MPa
F
p pressure in reference measurement MPa
R
3
γ specific weight of compensation fluid N/m
fluid
σ σ ’ normal stress (total; effective) MPa
n n
Δσ difference of total normal stress MPa
n
σ vertical stress MPa
v
σ maximum horizontal stress MPa
H
σ minimum horizontal stress MPa
h
5 Instruments
5.1 General
5.1.1 It shall be noted that TPC measurements are prone to substantial errors as the presence of
the cell in the medium tends to create significant changes in the stress field which is the target of the
measurement.
NOTE 1 See Figure 4 (Reference [5]).
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NOTE 2 The selection of appropriate instruments, adherence to their range of application and adequate
installation procedures are critical to reduce these errors to acceptable levels (see 5.4 and 5.6).
  a)  TPC stiffer than medium     b)  TPC softer than medium
  (over-registering TPC)     (under-registering TPC)
Key
I Stress trajectories around a TPC 1 Total pressure cell embedded in a medium.
II Normal stress profile A — A’
Figure 4 — Registering effect of embedded TPCs
5.1.2 Deformation and compensation measuring methods should be distinguished from each other
(see Table 1).
Table 1 — Monitoring features associated with TPC measuring methods
Long-term sta-
Measuring TPC stiff- Atmospheric pressure Automatic
bility of sensor Logging speed
method ness compensation data acquisition
signal
Deformation tends to be depends, amongst independent barometric amenable comparatively
(see 5.2) soft others, on the pressure monitoring may quick
type of electrical be needed
sensors used
vented TPC tend to be
unreliable
Compensation tends to be tends to be long- vented TPC tend to be cumbersome; comparatively
(see 5.3) stiff term stable reliable comparatively slow
costly
5.1.3 Any change of the total normal stress Δσ acting onto the flat side of a pressure pad (1 in Figure 1)
n
shall be uniquely associated with a change of the pressure of the liquid in the intervening cavity of the TPC.
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NOTE A change of the total normal stress Δσ acting onto the pad causes a change in the deflection of the
n
platens thus triggering a flow of the liquid through the cavity of the interconnected components (1), (2) and (3a)
which results in a deflection of the diaphragm (3c) between (3a) and (3b) (see Figure 1).
5.1.4 The stiffness of the pressure pad in sensing direction should be low in comparison with the
stiffness of the pressure tubing und the housing of the pressure measuring device.
5.1.5 The shape and location of the pressure measuring device shall not affect the total normal stress
σ of the medium acting onto the pressure pad.
n
NOTE A common technical solution is a TPC where the measuring device (3) is located sufficiently far away
from the pressure pad (1), and where (1) and (3) are interconnected by a stiff pressure tubing (2).
5.1.6 The pressure measuring device (3 in Figure 1) shall consist of an inner chamber (3a) and an
outer chamber (3b) which are separated by a flexible diaphragm (3c). The cavity of the interconnected
components (1), (2) and (3a) shall be completely filled with an, in engineering terms, incompressible
and de-aired liquid.
5.1.7 The housing of the pressure measuring device should be sufficiently stiff so that even high
ground pressures acting onto the outer side of the device do not affect the mechanical behaviour of the
diaphragm, in particular its calibration characteristics.
NOTE Experience In high embankments has shown that the earth pressure, acting on the housing of a
pressure transducer, can cause a substantial shift of the zero-point and a change in the linearity of the transducer.
5.2 Deformation measuring method
5.2.1 The measurement of the deflection of the diaphragm of the pressure measuring device (see 3c in
Figure 1) should be used as a method for measuring the pressure of the liquid in the intervening cavities.
NOTE Commonly, the diaphragm (3c) separating (3a) and (3b) coincides with the measuring diaphragm of
an electric pressure transducer.
5.2.2 The pressure in the outer chamber of the measuring device (see 3b in Figure 1) shall be either
constant or atmospheric.
NOTE If TPC measurements are influenced by changes of the atmospheric pressure that changes should be
monitored separately. Attempts to circumvent this issue by integrating a small venting tube into the measuring
line (see 6 in Figure 1) are often marred with difficulties; as such tubes tend to become blocked by condensed
water. This feature is in contrast to the compensation measuring method (see 5.3 and Table 1).
5.2.3 A deformation measurement carried out directly at the pressure pad platens, e.g. by means of
strain gauges or built-in vibrating wire sensors, should be avoided as this measuring procedure will
typically result in pad dimensions with high aspect ratios (see 3.5) leading to unfavourable embedment
conditions (see 6.1) and ill-defined edge correction factors (see A.1).
5.3 Compensation measuring method
5.3.1 In TPC compensation measuring systems, any changes of the distance between the platens of the
pressure pad caused by Δσ shall be compensated by an externally applied pressure p .
n a
NOTE Common practice is hydraulic application of p at comparatively high pressure levels and pneumatic
a
application of p at comparatively low pressure levels.
a
5.3.2 Compensation should be carried out at the diaphragm (3c in Figure 1) of the pressure measuring
device (3 in Figure 1). Any deflection of the diaphragm, as described in 5.2.1, shall be compensated by a
pressure p acting in the outer chamber (3b) of the device.
a
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5.3.3 The compensation point shall be clearly defined and well identifiable when making the
measurement. Pressure valve or electric diaphragm switch techniques may be employed.
5.4 Stiffness of the pressure pad
In sensing direction, the stiffness of the pressure pad should conform to the stiffness of the medium.
NOTE 1 Stress concentration effects influence the measuring results yielding either systematically too low or
too high values (see Figure 4).
NOTE 2 Amongst the factors which influence the stiffness of the TPC system are the following:
—   measuring principle (deformation, see 5.2, versus compensation, see 5.3; see also Table 1);
—   aspect ratio (see 3.5);
—   height of liquid-filled cavity (4 in Figure 1);
—   volume and compressibility of the liquid in the closed inner system;
—   deformability of the housing of the closed inner system (see 5.1.7).
NOTE 3 Further difficulties arise when the stiffness of the medium is changing in course of the monitoring
project, e.g. consolidation of fill or curing of shotcrete. For further influencing factors, see Reference [4].
5.5 Shape of pressure pad
5.5.1 The shape of the pressure pad can be rectangular, square, oval or circular. If not affected by other
constraints (e.g. construction; shape and dimension of medium or contact), circular shapes should be
preferred.
NOTE 1 Common pad dimensions are diameters, respectively edge lengths, of the order of 100 to 400 mm.
NOTE 2 Common for soils and fine-grained fill are circular pads with a diameter of about 120 to 300 mm; for
ground / concrete contacts rectangular pads of 200 mm × 300 mm; for ground / tunnel lining contacts radial
pads of 150 mm × 250 mm and for tunnel lining embedment tangential pads of 100 mm × 200 mm.
5.5.2 The aspect ratio (see 3.5) should not be higher than 1:15 for soil and fill and not be higher than
1:25 for rock and concrete. Pads with small aspect ratios shall be preferred, provided that the pad platens
will not touch each other across the liquid-filled cavity.
NOTE Commonly, TPCs are about 4 to 12 mm thick.
5.5.3 The selection of the pads should be made in consideration of the influence which edges and
corners of the pressure pads can have onto the stress distribution around the pad (Figure 5) and thus
onto the measurement. Figure 6 shows two technical solutions which are reducing the edge effect. These
solutions should be considered in the TPC selection.
NOTE Edges and corners of pressure pads are commonly stiffer than the sensing area of the pads and, thus,
are attracting over-proportionally high stresses. This effect is particularly relevant for high aspect ratios.
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Key
1 weld seam
2 top platen
3 liquid-filled cavity
4 bottom platen
Figure 5 — Edge effect of pressure pads: Stress concentration at comparatively stiff edge
(schematic)
I   flexible edge solution II   edge groove solution
Key
1 weld seam 1 weld seam
2 stiff bearing plate 2 top plate
3 liquid-filled cavity 3 liquid-filled cavity
4a flexible cover plate 4b bottom plate
5 groove
Figure 6 — Examples of technical solutions for reducing edge effects
5.5.4 In aggressive media, e.g. in sulphatic rock or groundwater, the TPC material should be corrosion-
resistant.
5.5.5 In the case that, after the completion of the monitoring project, TPCs are left in the ground
attention shall be paid to the compatibility of the material, in particular of the cell liquid, to the
environment.
EXAMPLE Use of bio-degradable hydraulic oil.
5.6 Accuracy
5.6.1 It shall be realised that the degree of conformity between the embedded TPC and the surrounding
medium is critical for the accuracy of the TPC system.
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