ISO 21052:2021
(Main)Restrained joint systems for ductile iron pipelines — Calculation rules for lengths to be restrained
Restrained joint systems for ductile iron pipelines — Calculation rules for lengths to be restrained
This document specifies a computation method used to determine the length of the ductile iron pipes to be restrained, when used for conveying raw water, drinking water, sewerage under pressure. This computation method takes into account all common pipeline route changes, including changes in the diameter of the pipeline itself and dead ends at the extremity of the pipeline, the outside diameter of the pipe, the system test pressure (to estimate the thrust), depth of cover, the characteristics of the soil surrounding the pipe and trench backfilling methods for a worldwide usage. The characteristics of the restrained joint are not covered by this document but can also be considered to determine the restraining length using any appropriate method. The computation method defined in this document is applicable to all types of restrained joint systems, with their operating pressure ratings of ductile iron pipelines complying with ISO 2531, ISO 7186 and ISO 16631. NOTE 1 ISO 10804 deals with actual design of the joint for various operating pressures of the pipeline. NOTE 2 National standards or established calculation methods can be used instead of this ISO standard.
Systèmes d'assemblages verrouillés pour canalisations en fonte ductile — Règles de calcul pour les longueurs à verrouiller
Le présent document spécifie une méthode de calcul utilisée pour déterminer la longueur des tuyaux en fonte ductile à verrouiller, lorsque ceux-ci sont utilisés pour le transport d’eau brute, d’eau potable, d’eaux usées sous pression. Cette méthode de calcul tient compte de tous les changements de direction courants des canalisations, y compris des changements de diamètre de la canalisation à proprement parler et des plaques pleines à l’extrémité de la canalisation, du diamètre extérieur du tuyau, de la pression d’épreuve du réseau (pour estimer la force de poussée), de la hauteur de couverture, des caractéristiques du sol entourant le tuyau et des méthodes de remblayage des tranchées pour un usage à l’échelle mondiale. Les caractéristiques de l’assemblage verrouillé ne sont pas abordées par le présent document, mais elles peuvent également être prises en compte pour déterminer la longueur à verrouiller à l’aide d’une quelconque méthode appropriée. La méthode de calcul définie dans le présent document est applicable à tous les types de systèmes d’assemblages verrouillés, avec les classes de pression de fonctionnement des canalisations en fonte ductile selon l’ISO 2531, l’ISO 7186 et l’ISO 16631. NOTE 1 L’ISO 10804 traite de la conception réelle de l’assemblage pour différentes pressions de fonctionnement de la canalisation. NOTE 2 Les normes nationales ou les méthodes de calcul établies peuvent être utilisées à la place de cette Norme ISO.
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21052
First edition
2021-11
Restrained joint systems for ductile
iron pipelines — Calculation rules for
lengths to be restrained
Systèmes d'assemblages verrouillés pour canalisations en fonte
ductile — Règles de calcul pour les longueurs à verrouiller
Reference number
ISO 21052:2021(E)
© ISO 2021
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ISO 21052:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
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Published in Switzerland
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ISO 21052:2021(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 3
4 Thrust restraint principles, calculation rules and general specification .4
4.1 Thrust forces . 4
4.2 Calculation rules and general specification . 4
4.3 Standard jointing systems offer no longitudinal restraint . 5
4.4 Restrained joint systems . 5
4.5 Length to be restrained . 5
4.6 Restrained design method . 5
4.7 Gravity thrust blocks . 6
5 Thrust force . . 6
5.1 Internal hydrostatic pressure in straight pipes . 6
5.2 Internal hydrostatic pressure in bends . 6
5.3 Internal hydrostatic pressure in other configurations . 7
6 Restrained joints . 8
6.1 Principle . 8
6.2 Conservative design . . 8
6.3 Required prevailing site conditions . 8
7 Unit frictional force, F . 8
s
7.1 Static frictional force. 8
7.2 Values of soil cohesion . 9
8 Polyethylene encasement and PU coating and other extruded organic coatings.10
9 Unit bearing resistances, R .10
s
9.1 Lateral resistance, passive soil pressure . 10
9.2 Design value of passive soil pressure . 10
9.3 Empirical values of passive soil pressure . 11
10 Application to common situations .14
10.1 Horizontal bends . 14
10.2 Vertical down bends . 15
10.3 Vertical up bends . 15
10.4 Tees . 16
10.5 Reducers . 17
10.6 Dead ends . 17
10.7 Encroaching restrained lengths . 17
10.8 Equal angle vertical offset (θ) . 18
10.9 Combined horizontal equal angle bends (θ) . 19
10.10 Combined horizontal unequal angle bends . . 20
10.11 Combined vertical equal angle offsets (θ) . 21
10.11.1 Pipeline under obstruction . 21
10.11.2 Pipeline over obstruction . 22
11 Restrained lengths .22
12 Installation and laying instruction .22
12.1 Select backfill considerations . .22
12.1.1 Backfill material versus native soil support characteristics .22
12.1.2 Swamps or marshes . 22
12.2 Combining thrust blocks/anchor blocks and restrained joints .22
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ISO 21052:2021(E)
12.3 Pipe in a casing .23
12.3.1 Restrained lengths inside casing . 23
12.3.2 Balancing the thrust force with restraining lengths outside the casing .23
12.4 Future excavations . 23
Annex A (informative) Dimensions and unit weights of pipes filled with water for preferred
class . .24
Annex B (informative) Soil classification chart .25
Bibliography .26
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ISO 21052:2021(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 5, Ferrous metal pipes and metallic fittings,
Subcommittee SC 2, Cast iron pipes, fittings and their joints.
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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INTERNATIONAL STANDARD ISO 21052:2021(E)
Restrained joint systems for ductile iron pipelines —
Calculation rules for lengths to be restrained
1 Scope
This document specifies a computation method used to determine the length of the ductile iron pipes to
be restrained, when used for conveying raw water, drinking water, sewerage under pressure.
This computation method takes into account all common pipeline route changes, including changes in
the diameter of the pipeline itself and dead ends at the extremity of the pipeline, the outside diameter
of the pipe, the system test pressure (to estimate the thrust), depth of cover, the characteristics of the
soil surrounding the pipe and trench backfilling methods for a worldwide usage. The characteristics
of the restrained joint are not covered by this document but can also be considered to determine the
restraining length using any appropriate method.
The computation method defined in this document is applicable to all types of restrained joint systems,
with their operating pressure ratings of ductile iron pipelines complying with ISO 2531, ISO 7186 and
ISO 16631.
NOTE 1 ISO 10804 deals with actual design of the joint for various operating pressures of the pipeline.
NOTE 2 National standards or established calculation methods can be used instead of this ISO standard.
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 2531, Ductile iron pipes, fittings, accessories and their joints for water applications
ISO 7186, Ductile iron products for sewerage applications
ISO 10804, Restrained joint systems for ductile iron pipelines — Design rules and type testing
ISO 16631, Ductile iron pipes, fittings, accessories and their joints compatible with plastic (PVC or PE)
piping systems, for water applications and for plastic pipeline connections, repair and replacement
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2531, ISO 10804 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 http:// www .electropedia .org/
3.1.1
mechanical flexible joint
flexible joint in which sealing is obtained by applying pressure to the gasket by mechanical means
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ISO 21052:2021(E)
3.1.2
push-in flexible joint
flexible joint assembled by pushing the spigot through the gasket into the socket of the mating
component
3.1.3
restrained joint
joint in which a means is provided to prevent longitudinal separation of the assembled joint
3.1.4
maximum design pressure
MDP
P
MD
maximum operating pressure of the system or of the pressure zone fixed by the designer considering
future developments and including surge
Note 1 to entry: It is the maximum pressure considering the design pressure and surge together, where:
— MDP is designated MDPa, P , fixed allowance for surge (secondary distribution networks);
MDa
— MDP is designated MDPc, P , surge is calculated (pumping & water mains).
MDc
[SOURCE: ISO 10802:2020, 3.6]
3.1.5
system test pressure
STP
P
ST
pressure to which a pipeline or a pipeline section is subjected for testing purposes
Note 1 to entry:
— PST = 1,5 × PD (when PMD ≤ 10 bar), or
— PST = PD + 5 (when PMD > 10 bar)
where P is the design pressure.
D
Note 2 to entry: 1 bar is equivalent to 0,1 MPa.
[SOURCE: ISO 10802:2020, 3.7, modified — The original note 2 to entry has been replaced by a new one.]
3.1.6
thrust force
unbalanced hydrostatic force developed at the locations of a pipeline, changing diameter or direction
3.1.7
bearing resistance
passive pressure that is generated as the pipeline attempts to separate and move into the soil
3.1.8
frictional resistance
resisting force resulting from the interaction of the pipeline with the soil encountered on the project
site and the pipeline laying conditions
3.1.9
passive soil pressure
maximum pressure that the soil imparts on a structure at the prescribed depth
Note 1 to entry: The passive soil pressure is dependent upon the compaction of the soil.
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ISO 21052:2021(E)
3.1.10
restrained length
minimum length to be restrained in order to balance thrust forces (3.1.6) and prevent disassembly or
separation of the pipeline
3.2 Symbols
2
A cross-sectional area of pipe, in m
2
A surface area of the pipe bearing on the soil, in m /m
p
2
C pipe-soil cohesion, equals f C , in kN/m ;
c s
2
C soil cohesion, in kN/m (see Table 2)
s
D outside diameter of pipe spigot, in m (see Annex A)
e
f ratio of pipe-soil cohesion to soil cohesion (see Table 2)
c
F unit frictional resistance, in kN/m
f
F unit frictional force assuming 1/2 the pipe circumference bears against the soil, in kN/m
s
(F ) unit frictional force assuming the entire pipe circumference contacts the soil, in kN/m
s b
f ratio of pipe-soil friction angle to soil friction angle (see Table 2)
φ
h thrust block height, in m
H depth of cover to top of pipe, in m
H depth of cover to pipe centreline, in m
c
K trench condition modifier (see Table 2)
n
L minimum required restrained pipe length, in m
2
N = tan (45° +φ/2)
φ
2
P system test pressure, in kN/m
2
P passive soil pressure, in kN/m
p
R unit bearing resistance, in kN/m
s
T resultant thrust force, in kN
3
γ backfill soil density, in kN/m (see Table 2)
W unit normal force on pipe = 2 W + W + W , in kN/m
e p w
W earth prism load = γ HD , in kN/m
e e
W unit weight of pipe, in kN/m (see Annex A)
p
W unit weight of water, kN/m (see Annex A)
w
θ bend angle, in degrees
δ pipe-soil friction angle, equals f φ, in degrees;
φ
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ISO 21052:2021(E)
φ soil internal friction angle, in degrees (see Table 2)
S safety factor (see 4.2)
f
4 Thrust restraint principles, calculation rules and general specification
4.1 Thrust forces
When underground or above-ground pipelines are in operation, unbalanced hydrostatic or
hydrodynamic forces are developed at many locations under the internal pressure of the fluid in the
pipeline, this is known as thrust forces. Unless the pipe joints in these areas are restrained against
longitudinal movement, joint separation can result. These thrust forces are developed at locations
where the pipeline changes either in diameter or in direction. Such locations include horizontal and
vertical bends, tees, wyes, reducers, offsets, pipe bifurcations and valves.
At these locations the thrust forces are resisted with thrust blocks at the focus of the thrust force, or by
installing a group of restrained joint pipes, in such a way that the unbalanced force is transmitted to the
surrounding soil or pedestals (above-ground installation, without overstressing the pipeline wall and
without subjecting the pipeline to joint separation).
The present standard studies and provides formulae which enable to balance thrust forces with the
adequate quantity of restrained joint pipes.
Proper care shall be taken by the designer when chambers are installed within the restrained length of
the pipeline.
The manufacturer’s recommendations for selecting the type of restrained joint shall also be taken into
account.
4.2 Calculation rules and general specification
The following parameters shall be taken into account: the cross-sectional area of the pipe (Table A.1),
the pipeline changes generating the thrust force (Clause 5), the outside diameter of the pipe (Table A.1),
the depth of cover of the pipe (see Figure 6), the characteristics of the soil surrounding the pipe and the
trench backfilling methods (Clauses 7 and 9), the pipeline external coating system (bituminous, epoxy
and acrylic paints or polyethylene encased pipe, PU and other extruded coatings - Clause 8).
The system test pressure (STP) of the pipeline is calculated from the maximum design pressure (MDP)
and shall be used to estimate the thrust forces (Clause 5); and a safety factor of 2 is recommended.
For each pipeline changes and their combination, a specific formula is provided to calculate the length of
pipes to be restrained. The list of common situations is provided in Table 1 together with the subclause
number:
Table 1 — Type of common situation
Subclause
Description
number
Horizontal bends 10.1
Vertical down bends 10.2
Vertical up bends 10.3
Tees 10.4
Reducers 10.5
Dead ends 10.6
Encroaching restrained lengths 10.7
Equal angle vertical offset (θ) 10.8
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ISO 21052:2021(E)
Table 1 (continued)
Subclause
Description
number
Combined horizontal equal angle bends (θ) 10.9
Combined horizontal unequal angle bends 10.10
Combined vertical equal angle offsets (θ) 10.11
Pipeline under obstruction 10.11.1
Pipeline over obstruction 10.11.2
4.3 Standard jointing systems offer no longitudinal restraint
Ductile iron pipes and fittings are most often joined with push-in or mechanical flexible joints
(Figure 1). Neither of these joints provide significant restraint against longitudinal separation other
than the friction, between the gasket and the plain end of the pipe or fitting. Tests have shown that
this frictional resistance of these joints are unpredictable. Thus, these joints should be considered as
offering no longitudinal restraint for design purposes.
4.4 Restrained joint systems
The primary objective of the restrained joint system is to design a system to transmit the unbalanced
forces to the surrounding soil without overstressing the pipeline wall and without subjecting the
pipeline to joint separation. In order to accomplish the transfer of the unbalanced forces, the friction
and passive resistance have been relied upon.
4.5 Length to be restrained
The length of the pipe, with restrained joints on each side of the focus of a thrust force, is calculated
using the sum of the components of the unbalanced forces in the direction of the corresponding leg. The
objective of the thrust restraint design using a restrained joint system is to extend the side of the fitting
with inseparable joints so that the fitting can transmit the unbalanced forces to the surrounding soil.
a) Push-in flexible joint b) Mechanical flexible joint
Key
1 nominal laying length
Figure 1 — Push-in and mechanical flexible joints
4.6 Restrained design method
This document shows the method to calculate the quantum of thrust forces for the most common
situations and the approaches to the design of restrained joint systems for balancing these forces. The
suggested design approaches are conservatively based on accepted principles of soil mechanics.
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ISO 21052:2021(E)
4.7 Gravity thrust blocks
The design of gravity thrust blocks to counter the thrust forces in pipeline systems is not covered by
this document. Thrust blocks/anchor blocks should not interfere with the angular deflection and axial
movement of restrained joints as prescribed by the manufacturer.
5 Thrust force
5.1 Internal hydrostatic pressure in straight pipes
The internal hydrostatic pressure acts perpendicularly on any plane with a force equal to the
pressure (P) times the area (A) of the plane. All components of these forces acting radially within a
pipe are balanced by circumferential tension in the wall of the pipe. Axial components acting on a plane
perpendicular to the pipe through a straight section of the pipe are balanced internally by the force
acting on each side of the plane (Figure 2).
Figure 2 — Internally balanced force
5.2 Internal hydrostatic pressure in bends
In the case of a bend as shown in Figure 3, the forces PA acting axially along each side of the bend are
not balanced. The vector sum of these forces is shown as T. This is the thrust force. In order to prevent
separation of the joints, a reaction equal to and in the opposite direction of T, shall be established.
θ
TP=2 Asin (1)
2
where
T is the resultant thrust force, in kN;
2
P is the system test pressure, in kN/m ;
2
A is the cross-sectional area of pipe, in m ;
θ is the bend angle, in degrees.
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ISO 21052:2021(E)
Figure 3 — Thrust force
5.3 Internal hydrostatic pressure in other configurations
Figure 4 depicts the net thrust force at various other configurations. In each case the expression for T
can be derived by the vector addition of the axial forces.
b) Reducer
a) Tee c) Dead end
d) Closed valve e) Wye
Key
2
A is the cross-sectional area of the pipe a, in m
a
2
A is the cross-sectional area of the pipe b, in m
b
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ISO 21052:2021(E)
2
A is the cross-sectional area of the pipe n°1, in m
1
2
A is the cross-sectional area of the pipe n°2, in m
2
2
P is the system test pressure of the pipe section n°1, in kN/m
1
2
P is the system test pressure of the pipe section n°2, in kN/m
2
Figure 4 — Thrust force for various configurations
6 Restrained joints
6.1 Principle
The method of providing thrust restraint in the pipe itself is by the use of restrained joints. Restrained
joint systems function, in a manner similar to thrust blocks, in so far as the reaction of the entire
restrained lengths of piping with the soil balances the thrust forces.
6.2 Conservative design
A practical design procedure has been adopted in this document, based on valid assumptions. The
assumptions considered in the design procedure are on the conservative side.
6.3 Required prevailing site conditions
Attention is drawn to the fact that all parameters considered in the formulae shall be validated by the
prevailing site conditions as taken into consideration by the project designer/owner.
The thrust force shall be restrained or balanced by the reaction of the restrained pipe lengths with the
surrounding soil, taking into account:
a) the static friction between the pipe length and the soil;
b) the restraint provided by the pipe as it bears against the side fill soil along each side of the fitting.
The use of restrained joint pipes, adjacent to the fittings, actually increases the lengths of all the arms
of the fitting.
7 Unit frictional force, F
s
7.1 Static frictional force
The static frictional force acting on a body is equal in magnitude to the applied force, up to a maximum
value. In the conventional analysis, the maximum static friction is proportional to the normal force
between the surfaces which provide the friction. The constant of proportionality, in this case called the
coefficient of friction, depends upon the nature of the surfaces. Experimental work indicates that for
friction between pipes and soils, the force is also dependent upon the cohesion of the soil.
Thus,
FA=+CW tanδ (2)
sp
where
2
A is the surface area of the pipe bearing on the soil, in m /m:
p
π D /2 (for bends, assume 1/2 the pipe circumference bears against the soil);
e
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...
NORME ISO
INTERNATIONALE 21052
Première édition
2021-11
Systèmes d'assemblages verrouillés
pour canalisations en fonte ductile —
Règles de calcul pour les longueurs à
verrouiller
Restrained joint systems for ductile iron pipelines — Calculation rules
for lengths to be restrained
Numéro de référence
ISO 21052:2021(F)
© ISO 2021
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ISO 21052:2021(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2021
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut
être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
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Publié en Suisse
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ISO 21052:2021(F)
Sommaire Page
Avant-propos .v
1 Domaine d’application . 1
2 Références normatives .1
3 Termes, définitions et symboles . 1
3.1 Termes et définitions . 1
3.2 Symboles . 3
4 Principes de retenue des forces de poussée, méthodes de calcul et spécifications
générales . 4
4.1 Forces de poussée . 4
4.2 Méthodes de calcul et spécifications générales . 4
4.3 Les assemblages standards ne permettent pas une retenue longitudinale . 5
4.4 Assemblages verrouillés . 5
4.5 Longueur à verrouiller . 5
4.6 Méthode de calcul du verrouillage . 6
4.7 Massifs de butée gravitaires . 6
5 Force de poussée . 6
5.1 Pression hydrostatique interne dans des tuyaux installés en ligne droite . 6
5.2 Pression hydrostatique interne dans les coudes. 7
5.3 Pression hydrostatique interne dans d’autres configurations . 7
6 Assemblages verrouillés.8
6.1 Principe . 8
6.2 Méthode conservatrice . 8
6.3 Conditions requises sur le site. 9
7 Force de frottement unitaire, F . 9
s
7.1 Force de frottement statique . 9
7.2 Valeurs de cohésion du sol . 9
8 Gaine en polyéthylène et revêtement en polyuréthane et autres revêtements
organiques extrudés .10
9 Résistances à l’appui unitaires, R .10
s
9.1 Résistance latérale, pression passive du sol . 10
9.2 Valeur de calcul de la pression passive du sol . 11
9.3 Valeurs empiriques de la pression passive du sol . 11
10 Application aux situations courantes .15
10.1 Coudes horizontaux. 15
10.2 Coudes verticaux vers le bas . 16
10.3 Coudes verticaux vers le haut . 16
10.4 Tés . 17
10.5 Cônes . 18
10.6 Plaques pleines . 18
10.7 Chevauchement des longueurs verrouillées. 19
10.8 Coudes successifs verticaux à angles égaux (θ) (baïonnette). 19
10.9 Coudes successifs horizontaux à angles égaux (θ) . 20
10.10 Coudes successifs horizontaux à angles inégaux . 21
10.11 Double baïonnette verticale à angles égaux (θ) . 22
10.11.1 Canalisation en dessous d’un obstacle . 22
10.11.2 Canalisation au-dessus d’un obstacle . 24
11 Longueurs verrouillées .24
12 Instructions de mise en place et de pose .24
12.1 Considérations relatives au remblai spécifique . 24
12.1.1 Caractéristiques de soutènement du matériau de remblayage et du sol natif . 24
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ISO 21052:2021(F)
12.1.2 Marécages ou marais . 25
12.2 Association des massifs de butée/massifs d’ancrage et des assemblages verrouillés .25
12.3 Tuyau dans un fourreau. 25
12.3.1 Longueurs verrouillées à l’intérieur d’un fourreau . 25
12.3.2 Équilibrage de la force de poussée avec les longueurs verrouillées à
l’extérieur du fourreau . 25
12.4 Futures excavations . 25
Annexe A (informative) Dimensions et poids unitaires des tuyaux de classe
préférentielleremplis d’eau .26
Annexe B (informative) Tableau de classification des sols.27
Bibliographie .28
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ISO 21052:2021(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes
nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est
en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.
L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document a
été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir
www.iso.org/directives).
L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l'élaboration du document sont indiqués dans l'Introduction et/ou dans la liste des déclarations de
brevets reçues par l'ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion
de l'ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 5, Tuyauteries en métaux ferreux et
raccords métalliques, sous-comité SC 2, Tuyaux en fonte, raccords et leurs joints.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
v
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NORME INTERNATIONALE ISO 21052:2021(F)
Systèmes d'assemblages verrouillés pour canalisations
en fonte ductile — Règles de calcul pour les longueurs à
verrouiller
1 Domaine d’application
Le présent document spécifie une méthode de calcul utilisée pour déterminer la longueur des tuyaux
en fonte ductile à verrouiller, lorsque ceux-ci sont utilisés pour le transport d’eau brute, d’eau potable,
d’eaux usées sous pression.
Cette méthode de calcul tient compte de tous les changements de direction courants des canalisations,
y compris des changements de diamètre de la canalisation à proprement parler et des plaques pleines à
l’extrémité de la canalisation, du diamètre extérieur du tuyau, de la pression d’épreuve du réseau (pour
estimer la force de poussée), de la hauteur de couverture, des caractéristiques du sol entourant le tuyau
et des méthodes de remblayage des tranchées pour un usage à l’échelle mondiale. Les caractéristiques
de l’assemblage verrouillé ne sont pas abordées par le présent document, mais elles peuvent également
être prises en compte pour déterminer la longueur à verrouiller à l’aide d’une quelconque méthode
appropriée.
La méthode de calcul définie dans le présent document est applicable à tous les types de systèmes
d’assemblages verrouillés, avec les classes de pression de fonctionnement des canalisations en fonte
ductile selon l’ISO 2531, l’ISO 7186 et l’ISO 16631.
NOTE 1 L’ISO 10804 traite de la conception réelle de l’assemblage pour différentes pressions de fonctionnement
de la canalisation.
NOTE 2 Les normes nationales ou les méthodes de calcul établies peuvent être utilisées à la place de cette
Norme ISO.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s'applique (y compris les
éventuels amendements).
ISO 2531, Tuyaux, raccords et accessoires en fonte ductile et leurs assemblages pour l'eau
ISO 7186, Produits en fonte ductile pour l'assainissement
ISO 10804, Assemblages verrouillés pour canalisations en fonte ductile — Règles de conception et essais de
type
ISO 16631, Tuyaux, raccords et accessoires en fonte ductile et leurs assemblages compatibles avec les
canalisations plastiques (PVC ou PE) pour la distribution d'eau et pour les connexions, réparations et
remplacements des canalisations en plastiques
3 Termes, définitions et symboles
3.1 Termes et définitions
Pour les besoins du présent document, les termes et définitions de l’ISO 2531, de l’ISO 10804 ainsi que
les suivants, s’appliquent.
1
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ISO 21052:2021(F)
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp;
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/ .
3.1.1
assemblage flexible mécanique
assemblage flexible dans lequel l’étanchéité est obtenue en appliquant une pression sur la bague de joint
par des moyens mécaniques
3.1.2
assemblage flexible automatique
assemblage flexible qui se monte en poussant le bout uni d’un composant dans la bague de joint située
dans l’emboîture du composant adjacent
3.1.3
assemblage verrouillé
assemblage dans lequel est inclus un moyen d’éviter que l’assemblage ne se déboîte longitudinalement
3.1.4
pression maximale de calcul en régime permanent
MDP
P
MD
pression maximale de fonctionnement du réseau ou de la zone de pression fixée par le concepteur en
tenant compte des développements à venir et en incluant le coup de bélier
Note 1 à l'article: Il s’agit de la pression maximale qui considère ensemble la pression de calcul en régime
permanent et le coup de bélier, où:
— la MDP est désignée MDPa, P , tolérance définie pour le coup de bélier (réseaux de distribution secondaires);
MDa
— la MDP est désignée MDPc, P , le coup de bélier est calculé (canalisations de pompage et d’eau).
MDc
[SOURCE: ISO 10802:2020, 3.6]
3.1.5
pression d’épreuve du réseau
STP
P
ST
pression à laquelle une canalisation ou une section de canalisation est soumise à des fins d’essai
Note 1 à l’article:
— P = 1,5 × P (si P ≤ 10 bar), ou
ST D MD
— P = P + 5 (si P > 10 bar)
ST D MD
où P est la pression de calcul en régime permanent.
D
Note 2 à l'article: 1 bar équivaut à 0,1 MPa.
[SOURCE: ISO 10802:2020, 3.7, modifié — La Note 2 à l’article d’origine a été remplacée par une nouvelle
note.]
3.1.6
force de poussée
force hydrostatique non équilibrée développée aux emplacements d’une canalisation comportant un
changement de diamètre ou de direction
2
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ISO 21052:2021(F)
3.1.7
résistance à l’appui
pression passive qui est produite lorsque la canalisation tente de se déboîter et de s’enfoncer dans le sol
3.1.8
résistance de frottement
force de résistance résultant de l’interaction de la canalisation avec le sol du site du projet et les
conditions de pose de la canalisation
3.1.9
pression passive du sol
pression maximale transmise par le sol sur une structure à la profondeur spécifiée
Note 1 à l'article: La pression passive du sol dépend de la cohésion du sol.
3.1.10
longueur verrouillée
longueur minimale à verrouiller afin d’équilibrer les forces de poussée (3.1.6) et d’empêcher le
désassemblage ou le déboîtement de la canalisation
3.2 Symboles
2
A aire de la section transversale du tuyau, en m
2
A aire du tuyau en appui sur le sol, en m /m
p
2
C cohésion tuyau-sol, égale à f C , en kN/m
c s
2
C cohésion du sol, en kN/m (voir Tableau 2)
s
D diamètre extérieur du fût du tuyau, en m (voir Annexe A)
e
f rapport de la cohésion tuyau-sol à la cohésion du sol (voir Tableau 2)
c
F résistance de frottement unitaire, en kN/m
f
F force de frottement unitaire en présumant que la moitié de la circonférence du tuyau est en appui
s
contre le sol, en kN/m
(F ) force de frottement unitaire en présumant que toute la circonférence du tuyau est en contact
s b
avec le sol, en kN/m
f rapport de l’angle de frottement tuyau-sol à l’angle de frottement du sol (voir Tableau 2)
φ
h hauteur de la butée, en m
H hauteur de couverture jusqu’à la génératrice supérieure du tuyau, en m
H hauteur de couverture jusqu’à la ligne médiane du tuyau, en m
c
K modificateur de condition de la tranchée (voir Tableau 2)
n
L longueur de tuyau verrouillée minimale requise, en m
2
N = tan (45° + φ/2)
φ
2
P pression d’épreuve du réseau, en kN/m
2
P pression passive du sol, en kN/m
p
3
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ISO 21052:2021(F)
R résistance à l’appui unitaire, en kN/m
s
T force de poussée résultante, en kN
3
γ densité du remblai, en kN/m (voir Tableau 2)
W force normale unitaire sur le tuyau = 2 W + W + W , en kN/m
e p w
W charge du prisme de terre = γ HD , en kN/m
e e
W poids unitaire du tuyau, en kN/m (voir Annexe A)
p
W poids unitaire de l’eau, en kN/m (voir Annexe A)
w
θ angle du coude, en degrés
δ angle de frottement tuyau-sol, égal à f φ, en degrés
φ
φ angle de frottement interne du sol, en degrés (voir Tableau 2)
S coefficient de sécurité (voir 4.2)
f
4 Principes de retenue des forces de poussée, méthodes de calcul et
spécifications générales
4.1 Forces de poussée
Lorsque des canalisations enterrées ou en surface sont en service, la pression interne du liquide qui
s’écoule dans la canalisation produit à de nombreux emplacements des forces hydrostatiques ou
hydrodynamiques non équilibrées, appelées forces de poussée. À moins que les assemblages de tuyaux
dans ces zones soient verrouillés contre le mouvement longitudinal, un déboîtement des assemblages
peut se produire. Ces forces de poussée se développent dans les emplacements où la canalisation change
de diamètre ou de direction. Ces emplacements comprennent les coudes horizontaux et verticaux, les
tés, les raccords en Y, les cônes, les coudes successifs, les bifurcations de tuyaux et les vannes.
À ces emplacements, les forces de poussée sont contrées par des massifs de butée au niveau des
points d’application de la force de poussée, ou par l’installation d’un groupe de tuyaux à assemblages
verrouillés, de sorte que la force non équilibrée est transmise dans le sol environnant ou dans les
massifs d’ancrage (installation en surface, sans surcharger la paroi de la canalisation et sans soumettre
la canalisation à un déboîtement de l’assemblage).
La présente norme étudie et fournit des formules qui permettent d’équilibrer les forces de poussée avec
une quantité adéquate de tuyaux à assemblages verrouillés.
Le concepteur doit prendre les précautions appropriées lorsque des chambres sont installées sur la
longueur verrouillée de la canalisation.
Les recommandations du fabricant concernant le choix du type d’assemblage verrouillé doivent
également être prises en compte.
4.2 Méthodes de calcul et spécifications générales
Les paramètres suivants doivent être pris en compte: l’aire de la section transversale du tuyau
(Tableau A.1), les changements au niveau de la canalisation générant la force de poussée (Article 5),
le diamètre extérieur du tuyau (Tableau A.1), la hauteur de couverture du tuyau (voir Figure 6), les
caractéristiques du sol entourant la canalisation et les méthodes de remblayage de la tranchée
(Articles 7 et 9), le type de revêtement extérieur de la canalisation (peintures bitumineuses, époxy
et acryliques ou tuyau gainé de polyéthylène, revêtement en polyuréthane et autres revêtements
extrudés - Article 8).
4
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ISO 21052:2021(F)
La pression d’épreuve du réseau (STP) de la canalisation est calculée à partir de la pression maximale
de calcul en régime permanent (MDP) et doit être utilisée pour estimer les forces de poussée (Article 5);
un coefficient de sécurité de 2 est recommandé.
Pour tous les changements au niveau d’une canalisation et leurs combinaisons, une formule spécifique
est fournie pour calculer la longueur des tuyaux à verrouiller. La liste des situations courantes est
fournie dans le Tableau 1 avec le numéro du paragraphe correspondant:
Tableau 1 — Types de situations courantes
Numéro du
Description
paragraphe
Coudes horizontaux 10.1
Coudes verticaux vers le bas 10.2
Coudes verticaux vers le haut 10.3
Tés 10.4
Cônes 10.5
Plaques pleines 10.6
Chevauchement des longueurs verrouillées 10.7
Coudes successifs verticaux à angles égaux (θ) (baïonnette) 10.8
Coudes successifs horizontaux à angles égaux (θ) 10.9
Coudes successifs horizontaux à angles inégaux 10.10
Double baïonnette verticale à angles égaux (θ) 10.11
Canalisation en dessous d’un obstacle 10.11.1
Canalisation au-dessus d’un obstacle 10.11.2
4.3 Les assemblages standards ne permettent pas une retenue longitudinale
Les canalisations et raccords en fonte ductile sont généralement assemblés à l’aide d’assemblages
flexibles automatiques ou mécaniques (Figure 1). Aucun de ces assemblages ne permet une retenue
significative contre le déboîtement longitudinal autre que le frottement, entre la bague de joint et le bout
uni du tuyau ou du raccord. Les essais ont montré que la résistance de frottement de ces assemblages est
imprévisible. Il convient donc de considérer que ces assemblages n’offrent pas de retenue longitudinale
à des fins de conception.
4.4 Assemblages verrouillés
Le principal objectif d’un assemblage verrouillé est de concevoir un système qui transmet les forces
non équilibrées au sol environnant sans surcharger la paroi de la canalisation et sans soumettre la
canalisation à un déboîtement de l’assemblage. Pour permettre le transfert des forces non équilibrées,
la résistance de frottement et la résistance passive ont été prises en compte.
4.5 Longueur à verrouiller
La longueur de tuyau, avec les assemblages verrouillés sur chaque côté du point d’application d’une
force de poussée, est calculée en utilisant la somme des composantes des forces non équilibrées dans la
direction du tronçon correspondant. L’objectif du calcul de la retenue des forces de poussée à l’aide d’un
assemblage verrouillé est de prolonger le côté du raccord par des assemblages inséparables de sorte
que le raccord peut transmettre les forces non équilibrées au sol environnant.
5
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ISO 21052:2021(F)
a)Assemblage flexible automatique b)Assemblage flexible mécanique
Légende
1 longueur de pose nominale
Figure 1 — Assemblages flexibles automatiques et mécaniques
4.6 Méthode de calcul du verrouillage
Le présent document décrit la méthode permettant de calculer le quantum des forces de poussée
pour les situations les plus courantes ainsi que les méthodes de calcul des assemblages verrouillés
permettant d’équilibrer ces forces. La méthode de calcul suggérée est généralement conservatrice,
basée sur des principes reconnus en mécanique des sols.
4.7 Massifs de butée gravitaires
Le dimensionnement des massifs de butée gravitaires servant à contrer les forces de poussée dans les
réseaux de canalisations n’est pas abordé par le présent document. Il convient que les massifs de butée/
massifs d’ancrage n’interfèrent pas avec la déviation angulaire et le mouvement axial des assemblages
verrouillés, conformément aux spécifications du fabricant.
5 Force de poussée
5.1 Pression hydrostatique interne dans des tuyaux installés en ligne droite
La pression hydrostatique interne agit perpendiculairement sur tout plan avec une force égale à la
pression (P) multipliée par l’aire (A) du plan. Toutes les composantes de ces forces agissant radialement
dans un tuyau sont équilibrées par la tension circonférentielle dans la paroi du tuyau. Les composantes
axiales agissant sur un plan perpendiculaire au tuyau dans une section droite de ce dernier sont
équilibrées au niveau interne par la force agissant sur chaque côté du plan (Figure 2).
Figure 2 — Force équilibrée au niveau interne
6
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ISO 21052:2021(F)
5.2 Pression hydrostatique interne dans les coudes
Dans le cas d’un coude tel qu’illustré à la Figure 3, les forces PA agissant axialement le long de chaque
côté du coude ne sont pas équilibrées. La somme vectorielle de ces forces est représentée par T. Il s’agit
de la force de poussée. Pour éviter le déboîtement des assemblages, une réaction similaire et dans la
direction opposée de T doit être établie.
θ
TP=2 Asin (1)
2
où
T est la force de poussée résultante, en kN;
2
P est la pression d’épreuve du réseau, en kN/m ;
2
A est l’aire de la section transversale du tuyau, en m ;
θ est l’angle du coude, en degrés.
Figure 3 — Force de poussée
5.3 Pression hydrostatique interne dans d’autres configurations
La Figure 4 illustre la force de poussée nette dans d’autres configurations. Dans chaque cas
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 21052
ISO/TC 5/SC 2
Restrained joint systems for ductile
Secretariat: AFNOR
iron pipelines — Calculation rules for
Voting begins on:
20210806 lengths to be restrained
Voting terminates on:
Systèmes d'assemblages verrouillés pour canalisations en fonte
20211001
ductile — Règles de calcul pour les longueurs à verrouiller
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
ISO/FDIS 21052:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 21052:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
CH1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 21052:2021(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 3
4 Thrust restraint principles, calculation rules and general specification .4
4.1 Thrust forces . 4
4.2 Calculation rules and general specification . 4
4.3 Standard jointing systems offer no longitudinal restraint . 5
4.4 Restrained joint systems . 5
4.5 Length to be restrained . 5
4.6 Restrained design method . 5
4.7 Gravity thrust blocks . 6
5 Thrust force . 6
5.1 Internal hydrostatic pressure in straight pipes . 6
5.2 Internal hydrostatic pressure in bends . 6
5.3 Internal hydrostatic pressure in other configurations . 7
6 Restrained joints . 8
6.1 Principle . 8
6.2 Conservative design . 8
6.3 Required prevailing site conditions . 8
7 Unit frictional force, F . 8
s
7.1 Static frictional force . 8
7.2 Values of soil cohesion . 9
8 Polyethylene encasement and PU coating and other extruded organic coatings .10
9 Unit bearing resistances, R .10
s
9.1 Lateral resistance, passive soil pressure.10
9.2 Design value of passive soil pressure .11
9.3 Empirical values of passive soil pressure .11
10 Application to common situations .15
10.1 Horizontal bends .15
10.2 Vertical down bends .16
10.3 Vertical up bends .16
10.4 Tees .17
10.5 Reducers .18
10.6 Dead ends .18
10.7 Encroaching restrained lengths .18
10.8 Equal angle vertical offset (θ) .19
10.9 Combined horizontal equal angle bends (θ) .20
10.10 Combined horizontal unequal angle bends .21
10.11 Combined vertical equal angle offsets (θ) .22
10.11.1 Pipeline under obstruction .22
10.11.2 Pipeline over obstruction .23
11 Restrained lengths .23
12 Installation and laying instruction .23
12.1 Select backfill considerations .23
12.1.1 Backfill material versus native soil support characteristics .23
12.1.2 Swamps or marshes .24
12.2 Combining thrust blocks/anchor blocks and restrained joints .24
© ISO 2021 – All rights reserved iii
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ISO/FDIS 21052:2021(E)
12.3 Pipe in a casing .24
12.3.1 Restrained lengths inside casing .24
12.3.2 Balancing the thrust force with restraining lengths outside the casing .24
12.4 Future excavations .24
Annex A (informative) Dimensions and unit weights of pipes filled with water for preferred
class .25
Annex B (informative) Soil classification chart .26
Bibliography .27
iv © ISO 2021 – All rights reserved
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ISO/FDIS 21052:2021(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 5, Ferrous metal pipes and metallic fittings,
Subcommittee SC 2, Cast iron pipes, fittings and their joints.
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.
© ISO 2021 – All rights reserved v
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 21052:2021(E)
Restrained joint systems for ductile iron pipelines —
Calculation rules for lengths to be restrained
1 Scope
This document specifies a computation method used to determine the length of the ductile iron pipes to
be restrained, when used for conveying raw water, drinking water, sewerage under pressure.
This computation method takes into account all common pipeline route changes, including changes in
the diameter of the pipeline itself and dead ends at the extremity of the pipeline, the outside diameter
of the pipe, the system test pressure (to estimate the thrust), depth of cover, the characteristics of the
soil surrounding the pipe and trench backfilling methods for a worldwide usage. The characteristics
of the restrained joint are not covered by this document but can also be considered to determine the
restraining length using any appropriate method.
The computation method defined in this document is applicable to all types of restrained joint systems,
with their operating pressure ratings of ductile iron pipelines complying with ISO 2531, ISO 7186 and
ISO 16631.
NOTE 1 ISO 10804 deals with actual design of the joint for various operating pressures of the pipeline.
NOTE 2 National standards or established calculation methods can be used instead of this ISO standard.
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 2531, Ductile iron pipes, fittings, accessories and their joints for water applications
ISO 7186, Ductile iron products for sewerage applications
ISO 10804, Restrained joint systems for ductile iron pipelines — Design rules and type testing
ISO 16631, Ductile iron pipes, fittings, accessories and their joints compatible with plastic (PVC or PE)
piping systems, for water applications and for plastic pipeline connections, repair and replacement
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2531, ISO 10804 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 http:// www .electropedia .org/
3.1.1
mechanical flexible joint
flexible joint in which sealing is obtained by applying pressure to the gasket by mechanical means
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ISO/FDIS 21052:2021(E)
3.1.2
push-in flexible joint
flexible joint assembled by pushing the spigot through the gasket into the socket of the mating
component
3.1.3
restrained joint
joint in which a means is provided to prevent longitudinal separation of the assembled joint
3.1.4
maximum design pressure
MDP
P
MD
maximum operating pressure of the system or of the pressure zone fixed by the designer considering
future developments and including surge
Note 1 to entry: It is the maximum pressure considering the design pressure and surge together, where:
— MDP is designated MDPa, P , fixed allowance for surge (secondary distribution networks);
MDa
— MDP is designated MDPc, P , surge is calculated (pumping & water mains).
MDc
[SOURCE: ISO 10802:2020, 3.6]
3.1.5
system test pressure
STP
P
ST
pressure to which a pipeline or a pipeline section is subjected for testing purposes
Note 1 to entry: to entry:
— P = 1,5 × P (when P ≤ 10 bar), or
ST D MD
— P = P + 5 (when P > 10 bar)
ST D MD
where P is the design pressure.
D
Note 2 to entry: 1 bar is equivalent to 0,1 Mpa.
[SOURCE: ISO 10802:2020, 3.7, modified — The original note 2 to entry has been replaced by a new one.]
3.1.6
thrust force
unbalanced hydrostatic force developed at the locations of a pipeline, changing diameter or direction
3.1.7
bearing resistance
passive pressure that is generated as the pipeline attempts to separate and move into the soil
3.1.8
frictional resistance
resisting force resulting from the interaction of the pipeline with the soil encountered on the project
site and the pipeline laying conditions
3.1.9
passive soil pressure
maximum pressure that the soil imparts on a structure at the prescribed depth
Note 1 to entry: The passive soil pressure is dependent upon the compaction of the soil.
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ISO/FDIS 21052:2021(E)
3.1.10
restrained length
minimum length to be restrained in order to balance thrust forces (3.1.6) and prevent disassembly or
separation of the pipeline
3.2 Symbols
2
A crosssectional area of pipe, in m
2
A surface area of the pipe bearing on the soil, in m /m
p
2
C pipe-soil cohesion, equals f C , in kN/m ;
c s
2
C soil cohesion, in kN/m (see Table 2)
s
D outside diameter of pipe spigot, in m (see Annex A)
e
f ratio of pipesoil cohesion to soil cohesion (see Table 2)
c
F unit frictional resistance, in kN/m
f
F unit frictional force assuming 1/2 the pipe circumference bears against the soil, in kN/m
s
(F ) unit frictional force assuming the entire pipe circumference contacts the soil, in kN/m
s b
f ratio of pipesoil friction angle to soil friction angle (see Table 2)
φ
h thrust block height, in m
H depth of cover to top of pipe, in m
H depth of cover to pipe centreline, in m
c
K trench condition modifier (see Table 2)
n
L minimum required restrained pipe length, in m
2
N = tan (45° +φ/2)
φ
2
P system test pressure, in kN/m
2
P passive soil pressure, in kN/m
p
R unit bearing resistance, in kN/m
s
T resultant thrust force, in kN
3
γ backfill soil density, in kN/m (see Table 2)
W unit normal force on pipe = 2 W + W + W , in kN/m
e p w
W earth prism load = γ HD , in kN/m
e e
W unit weight of pipe, in kN/m (see Annex A)
p
W unit weight of water, kN/m (see Annex A)
w
θ bend angle, in degrees
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ISO/FDIS 21052:2021(E)
δ pipe-soil friction angle, equals f φ, in degrees;
φ
φ soil internal friction angle, in degrees (see Table 2)
S safety factor (see 4.2)
f
4 Thrust restraint principles, calculation rules and general specification
4.1 Thrust forces
When underground or above-ground pipelines are in operation, unbalanced hydrostatic or
hydrodynamic forces are developed at many locations under the internal pressure of the fluid in the
pipeline, this is known as thrust forces. Unless the pipe joints in these areas are restrained against
longitudinal movement, joint separation can result. These thrust forces are developed at locations
where the pipeline changes either in diameter or in direction. Such locations include horizontal and
vertical bends, tees, wyes, reducers, offsets, pipe bifurcations and valves.
At these locations the thrust forces are resisted with thrust blocks at the focus of the thrust force, or by
installing a group of restrained joint pipes, in such a way that the unbalanced force is transmitted to the
surrounding soil or pedestals (aboveground installation, without overstressing the pipeline wall and
without subjecting the pipeline to joint separation).
The present standard studies and provides formulae which enable to balance thrust forces with the
adequate quantity of restrained joint pipes.
Proper care shall be taken by the designer when chambers are installed within the restrained length of
the pipeline.
The manufacturer’s recommendations for selecting the type of restrained joint shall also be taken into
account.
4.2 Calculation rules and general specification
The following parameters shall be taken into account: the cross-sectional area of the pipe (Table A.1),
the pipeline changes generating the thrust force (Clause 5), the outside diameter of the pipe (Table A.1),
the depth of cover of the pipe (see Figure 6), the characteristics of the soil surrounding the pipe and the
trench backfilling methods (Clauses 7 and 9), the pipeline external coating system (bituminous, epoxy
and acrylic paints or polyethylene encased pipe, PU and other extruded coatings - Clause 8).
The system test pressure (STP) of the pipeline is calculated from the maximum design pressure (MDP)
and shall be used to estimate the thrust forces (Clause 5); and a safety factor of 2 is recommended.
For each pipeline changes and their combination, a specific formula is provided to calculate the length of
pipes to be restrained. The list of common situations is provided in Table 1 together with the subclause
number:
Table 1 — Type of common situation
Subclause
Description
number
Horizontal bends 10.1
Vertical down bends 10.2
Vertical up bends 10.3
Tees 10.4
Reducers 10.5
Dead ends 10.6
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ISO/FDIS 21052:2021(E)
Table 1 (continued)
Subclause
Description
number
Encroaching restrained lengths 10.7
Equal angle vertical offset (θ) 10.8
Combined horizontal equal angle bends (θ) 10.9
Combined horizontal unequal angle bends 10.10
Combined vertical equal angle offsets (θ) 10.11
Pipeline under obstruction 10.11.1
Pipeline over obstruction 10.11.2
4.3 Standard jointing systems offer no longitudinal restraint
Ductile iron pipes and fittings are most often joined with push-in or mechanical flexible joints
(Figure 1). Neither of these joints provide significant restraint against longitudinal separation other
than the friction, between the gasket and the plain end of the pipe or fitting. Tests have shown that
this frictional resistance of these joints are unpredictable. Thus, these joints should be considered as
offering no longitudinal restraint for design purposes.
4.4 Restrained joint systems
The primary objective of the restrained joint system is to design a system to transmit the unbalanced
forces to the surrounding soil without overstressing the pipeline wall and without subjecting the
pipeline to joint separation. In order to accomplish the transfer of the unbalanced forces, the friction
and passive resistance have been relied upon.
4.5 Length to be restrained
The length of the pipe, with restrained joints on each side of the focus of a thrust force, is calculated
using the sum of the components of the unbalanced forces in the direction of the corresponding leg. The
objective of the thrust restraint design using a restrained joint system is to extend the side of the fitting
with inseparable joints so that the fitting can transmit the unbalanced forces to the surrounding soil.
a) Push-in flexible joint b) Mechanical flexible joint
Key
1 nominal laying length
Figure 1 — Push-in and mechanical flexible joints
4.6 Restrained design method
This document shows the method to calculate the quantum of thrust forces for the most common
situations and the approaches to the design of restrained joint systems for balancing these forces. The
suggested design approaches are conservatively based on accepted principles of soil mechanics.
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ISO/FDIS 21052:2021(E)
4.7 Gravity thrust blocks
The design of gravity thrust blocks to counter the thrust forces in pipeline systems is not covered by
this document. Thrust blocks/anchor blocks should not interfere with the angular deflection and axial
movement of restrained joints as prescribed by the manufacturer.
5 Thrust force
5.1 Internal hydrostatic pressure in straight pipes
The internal hydrostatic pressure acts perpendicularly on any plane with a force equal to the
pressure (P) times the area (A) of the plane. All components of these forces acting radially within a
pipe are balanced by circumferential tension in the wall of the pipe. Axial components acting on a plane
perpendicular to the pipe through a straight section of the pipe are balanced internally by the force
acting on each side of the plane (Figure 2).
Figure 2 — Internally balanced force
5.2 Internal hydrostatic pressure in bends
In the case of a bend as shown in Figure 3, the forces PA acting axially along each side of the bend are
not balanced. The vector sum of these forces is shown as T. This is the thrust force. In order to prevent
separation of the joints, a reaction equal to and in the opposite direction of T, shall be established.
θ
TP=2 Asin (1)
2
where
T is the resultant thrust force, in kN;
2
P is the system test pressure, in kN/m ;
2
A is the crosssectional area of pipe, in m ;
θ is the bend angle, in degrees.
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ISO/FDIS 21052:2021(E)
Figure 3 — Thrust force
5.3 Internal hydrostatic pressure in other configurations
Figure 4 depicts the net thrust force at various other configurations. In each case the expression for T
can be derived by the vector addition of the axial forces.
b) Reducer
a) Tee c) Dead end
d) Closed valve e) Wye
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ISO/FDIS 21052:2021(E)
Key
2
A is the crosssectional area of the pipe a, in m
a
2
A is the crosssectional area of the pipe b, in m
b
2
A is the crosssectional area of the pipe n°1, in m
1
2
A is the crosssectional area of the pipe n°2, in m
2
2
P is the system test pressure of the pipe section n°1, in kN/m
1
2
P is the system test pressure of the pipe section n°2, in kN/m
2
Figure 4 — Thrust force for various configurations
6 Restrained joints
6.1 Principle
The method of providing thrust restraint in the pipe itself is by the use of restrained joints. Restrained
joint systems function, in a manner similar to thrust blocks, in so far as the reaction of the entire
restrained lengths of piping with the soil balances the thrust forces.
6.2 Conservative design
A practical design procedure has been adopted in this document, based on valid assumptions. The
assumptions considered in the design procedure are on the conservative side.
6.3 Required prevailing site conditions
Attention is drawn to the fact that all parameters considered in the formulae shall be validated by the
prevailing site conditions as taken into consideration by the project designer/owner.
The thrust force shall be restrained or balanced by the reaction of the restrained pipe lengths with the
surrounding soil, taking into account:
a) the static friction between the pipe length and the soil;
b) the restraint provided by the pipe as it bears against the side fill soil along each side of the fitting.
The use of restrained joint pipes, adjacent to the fittings, actually increases the lengths of all the arms
of the fitting.
7 Unit frictional force, F
s
7.1 Static frictional force
The static frictional
...
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