prENV 1046 - 51_e_stf

7/14/2019 prENV 1046 - 51_e_stf

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EUROPEAN PRESTANDARD

PRÉNORME EUROPÉENNE

EUROPÄISCHE VORNORM

FINAL DRAFTprENV 1046

February 2000

ICS 23.040.20; 23.040.45

English version

Plastics piping and ducting systems - Systems outside buildingstructures for the conveyance of water or sewage - Pratices for

installation above and below ground

Systèmes de canalisations et de gaines en plastique -Système d'adduction d'eau ou d'assainissement à

l'extérieur de la structure des bâtiments - Pratiques pour lapose en aérien et en enterré

Kunststoff-Rohrleitungs- und Schutzrohr-Systeme -Systeme außerhalb der Gebäudestruktur zum Transport

von Wasser oder Abwasser - Verfahren zur ober- undunterirdischen Verlegung

This draft European Prestandard is submitted to CEN members for formal vote. It has been drawn up by the Technical Committee CEN/TC155.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice andshall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION

COMIT É E UROPÉ E N DE NORMAL ISAT ION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Central Secretariat: rue de Stassart, 36 B-1050 Brussels

© 2000 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.

Ref. No. prENV 1046:2000 E

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Page 2prENV 1046:2000

Contents

Page

Foreword ................................................................................................................................................3

Introduction ...........................................................................................................................................4

1 Scope..................................................................................................................................................5

2 Normative references.......................................................................................................................5

3 Terms and definitions ......................................................................................................................5

3.1 Terminology.....................................................................................................................................5

3.2 Symbols...........................................................................................................................................6

4 Transport, handling and storage at depots and sites ..................................................................9

4.1 General............................................................................................................................................94.2 Transport .........................................................................................................................................9

4.3 Handling ........................................................................................................................................ 10

4.4 Storage..........................................................................................................................................10

5 Installation ......................................................................................................................................11

5.1 Pipes in trenches...........................................................................................................................11

5.2 Special installation techniques ......................................................................................................29

5.3 Laying of pipes above ground .......................................................................................................29

6 Methods of assembly (jointing) ....................................................................................................33

6.1 General..........................................................................................................................................336.2 Joints using an elastomeric seal ...................................................................................................34

6.3 Mechanical compression joints .....................................................................................................34

6.4 Other joints and jointing methods..................................................................................................35

7 Bends...............................................................................................................................................36

7.1 Cold bending .................................................................................................................................36

7.2 Hot bending ...................................................................................................................................36

8 Inspection and testing ...................................................................................................................36

8.1 Inspection ......................................................................................................................................36

8.2 Testing...........................................................................................................................................36Annex A (normative) Classification of soils......................................................................................38

Annex B (normative) Thermal considerations on laying of pipes above ground ......................... 41

Annex C (informative) Behaviour of buried flexible pipes...............................................................48

Annex D (normative) Joint and jointing examples...........................................................................50

Annex E (normative) Beam-column theory.......................................................................................58

Bibliography ........................................................................................................................................69

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Foreword

This European Prestandard has been prepared by Technical Committee CEN/TC 155 "Systèmes decanalisations et de gaines en plastiques", the secretariat of which is held by NNI.

This document is currently submitted to the Formal Vote.

This prestandard is based on the results of the work being undertaken in ISO/TC 138 "Plastics pipes,fittings and valves for the transport of fluids", which is a Technical Committee of the InternationalOrganization for Standardization (ISO) (see bibliography), modified as necessary to be applicable topiping systems of any plastics materials and any relevant application.

This prestandard is a guidance document only. It provides a set of guidelines which gives correct

practices for installation of plastics piping and ducting systems outside building structures above andbelow ground.

It relates to standards on general functional requirements and codes of practice.

CEN/TC 164 and CEN/TC 165 are preparing standards covering pipe laying and pipe design. Whenthese standards are published this prestandard will be revised to take account of those standards.

It includes the following:

Annex A, which is normative, gives criteria for classification of soils;

Annex B, which is normative, details calculation procedures for assessing thermal effects on pipingdesigns and/or layouts above ground;

Annex C, which is informative, describes the behaviour of buried flexible pipes;

Annex D, which is normative, describes joints and examples thereof;

Annex E, which is normative, details calculation procedures for assessing the need to apply thebeam-column theory and determining the maximum deflection of above ground pipes;

Bibliography.

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Introduction

This prestandard contains guidance for installation procedures for plastics piping systems and theircomponents intended to be used above or below ground for pressure and non-pressure applicationsoutside building structures. It is intended to be used in conjunction with general standards forinstallation recommendations, for example those issued by CEN/TC 164 "Water supply" andCEN/TC 165 "Waste water engineering".

This prestandard includes recommendations for the pipe surround and backfilling procedures but notroad base and road sub-base details. Attention is drawn to any national regulations which may coverthese or other aspects of installation.

This prestandard does not cover matters relating to renovation of existing pipeline systems using liningtechniques, or replacement of existing pipeline systems using trenchless techniques.

This prestandard is intended to be used by authorities, design engineers, installation contractors andmanufacturers.

In this prestandard, much of the guidance is expressed as requirements, e.g. by use of "shall" or byinstructions in the imperative. It is strongly recommended that these be followed whenever applicable.

Other guidance is presented for consideration as a matter of judgement in each case, e.g. by use of"should".

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1 Scope

This prestandard is applicable to the installation of plastics piping systems to be used for theconveyance of water or sewage under gravity and pressure conditions above and below ground. It isintended to be used for pipes of nominal size up to and including DN 3000.

Where in this prestandard the term "pipe" is used then it serves also to cover any "fittings", "ancillary"products and "components".

NOTE 1 It is assumed that additional recommendations and/or requirements are detailed in theindividual materials System Standards. Instances where this is expected to apply include those indicatedin this prestandard as follows:

a) any special transportation requirements (see 4.2.6);

b) maximum storage height (see 4.4.3 and 4.4.4);

c) maximum storage period in direct sunlight (see 4.4.6);

d) any climatic conditions requiring special storage (see 4.4.7);e) limiting initial and/or long-term deflections (see 5.1.1 and 5.1.2);

f) information on mole ploughing and boring (see 5.2), if applicable;

g) longitudinal tensile modulus and strength (see 5.3.1.1);

h) coefficient of thermal linear expansion (see 5.3.2.2 and Annex B);

i) suitability for use in areas exposed to sunlight (see 5.3.3);

j) selection of appropriate jointing system (see clause 6);

k) recommended radii of curvature for cold bending (see 7.1);

l) permitted rates of loss of water under test (see 8.2.1);

m) if applicable the relationship between SDR and stiffness.

NOTE 2 Guidance and instructions concerning commissioning of systems can be found in thestandards prepared by CEN/TC 164 and by CEN/TC 165 and the relevant national and/or localregulations.

NOTE 3 Concerning the character of this document see Foreword and Introduction.

2 Normative references

This prestandard incorporates by dated or undated reference, provisions from other publications.These normative references are cited at the appropriate places in the text and the publications arelisted hereafter. For dated references, subsequent amendments to, or revisions of, any of thesepublications apply to this prestandard only when incorporated in it by amendment or revision. For

undated references the latest edition of the publication referred to applies (including amendments).

EN 1295-1:1997, Structural design of buried pipelines under various conditions of loading - Part 1:

General requirements

3 Terms and definitions

3.1 Terminology

See Figure 1 for an illustration of the meaning and limits of the terms used in this prestandard.

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key1 Trench width, b 2 Depth of cover3 100 mm to 300 mm4 Ground surface5 Native soil6 Embedment7 Main backfill8 Pipe zone9 Haunch zone10 Trench grade11 Trench bottom12 Foundation, if required13 Bedding, if required

Figure 1 — Trench cross-section showing terminology

3.2 Symbols

For the purposes of this prestandard, the following symbols apply:

A a specific type of U-shaped expansion joint (see Figure B.6);

a clearance between a pipe joint and an adjacent support (see Figure B.1);

Ap area of a pipe cross-section, π x - xe

d e e (see Annex E);

B a specific type of U-shaped expansion joint (see Figure B.7);

b width of a trench cross-section (see Figure 1);

b c bearing width of a cradle support (see Figure 17);

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b S horizontal clearance between the pipe or fitting and the trench sidewall or an adjacent pipe orfitting (see Figure 1);

c a factor for thermal expansion in relationships between fixed anchorages and compensationsection pipe lengths (see Annex B);

d e (mean) external diameter of a pipe (see Figure 1);

d i (mean) internal diameter of a pipe [see equation (E.5)];

DN nominal size of a pipe and associated fittings;

e pipe wall thickness;

E H hoop tensile modulus of elasticity (see Annex E);

E x elasticity modulus of the pipe material in the longitudinal direction (see Annex B and Annex E);

F net sum of axial loads (see Annex E);

f 1 deflection multiplication factor (deflection) (see Annex E);

f 2 deflection multiplication factor (end rotation) (see Annex E);

f 3 deflection multiplication factor (moment) (see Annex E);

F H horizontal reaction force on a pipework anchorage or sleeve (see Figure B.4);

F

thermal load (see Annex E);

F

Poisson load (see Annex E);

F p load due to pressure (see Annex E);

F S factor of safety [see equation (5)];

F T reaction force on a fixed anchorage by thermal expansion or contraction of a pipe [seeequation (B.2)];

F V vertical reaction force on a pipework anchorage or sleeve (see Figure B.4);

h s depth of snow (see Annex E);

second axial moment of area (for a pipe) (see Annex B and Annex E);

L1 first pipe length along the span (La) of an expansion joint from a fixed point to the offset leg(see figures B.4, B.5 and B.6);

L1C the compensation portion of the first pipe length along the span of an expansion joint, i.e. fromthe offset pipe leg to the nearest preceding guide or anchorage (see figures B.4 to B.7);

L2 second pipe length along the span (La) of an expansion joint from the first offset leg to the nextoffset leg or fixed point (see figures B.5 and B.6);

L2C the compensation portion of the second pipe length along the span of an expansion joint, i.e.from the offset pipe leg to the next guide or anchorage (see Figure B.5);

L3 third pipe length along the span (La) of an expansion joint from the second offset leg to thenext fixed point;

L3C the compensation portion of the third pipe length along the span of an expansion joint, i.e. froma second offset pipe leg to the next guide or anchorage (see Figure B.6);

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La span of supported pipework between fixed anchorages;

l b buckling length (see Annex E);

LBC the compensation portion of a branch pipe, i.e. from the branch junction to the first guide or

anchorage along the branch (see Figure B.2);l d length of the pipe influencing the deflection (see Annex E);

Lf free length of a straight pipe (see Figure B.1);

LL free length from a fixed point of the second leg of an L-shaped expansion joint (seeFigure B.4);

LLC the compensation portion of the second leg of an L-shaped expansion joint, i.e. from the elbowto the next guide or anchorage (see Figure B.4);

LO offset length of an expansion joint (see figures B.5 and B.6);

LOC the compensation portion of the offset length of an expansion joint, i.e. from the first elbow tothe next guide, anchorage or elbow (see Figure B.3);

LS length of pipe span between support centres (see Annex B and Annex E);

LS,max maximum span width for pipe support (see Annex B);

M compaction classification: Moderate (see Table 5);

M b bending moment (see Annex E);

N compaction classification: Not (see Table 5);

p internal pressure (see Annex E);

P1, P2 fixed points associated with expansion joints in a piping system (see figures B.3 to B.6);

p crit critical negative pressure creating global buckling (see Annex E);

Q net sum of all axial loads acting on the pipe and in the liquid column (see Annex E);

q sum of laterally distributed loads (see Annex E);

q 0 linear load arising from the mass of the pipework itself (see Annex E);

Q crit critical buckling load for the pipe as a column (see Annex E);

q l linear load arising from the mass of liquid in a full pipe [see equation (E.8)];

q s linear load arising from snow supported by the pipe [see equation (E.9)];

R 0 ratio of offset to linear compensation piping lengths [see equation (B.9)];

R 1 ratio of linear to offset compensation piping lengths [see equation (B.10)];

S initial specific stiffness (see Tables 1 and 2);

SN stiffness number or classification (see Tables 1 and 2);

W compaction classification: Well (see Table 5);

L linear coefficient of thermal expansion;

deflection of pipe at midspan between supports;+l 2 thermal expansion;

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l 1 thermal contraction;

l variation in length;

L1,h thermal expansion of a pipe in horizontal direction [see equation (B.5a)];

LL,v thermal expansion of a pipe in vertical direction [see equation (B.5b)];

T temperature difference creating load;

correction factor (see Table E.5);

0 apparent specific weight of pipe wall material [see equation (E.7)];

l specific weight of liquid contained in pipe in service [see equation (E.8)];

s specific weight of snow (see Table E.5);

Poisson ratio (see Table E.5);

b axial bending stress (see Annex E); c,b axial compressive bending stress (see Annex E);

c,crit critical axial compressive stress (see Annex E);

c,max maximum axial compressive stress (see Annex E);

c,n axial compressive normal stress (see Annex E);

n axial normal stress (see Annex E);

x,d allowable longitudinal stress in the pipe wall;

x,p

longitudinal stress in the pipe wall induced by internal pressure;

x,q longitudinal stress in the pipe wall induced by distributed loads;

x,r remaining longitudinal design stress capability in the pipe wall [see equation (B.3)];

x,u,L longitudinal stress limit for long-term failure strength.

4 Transport, handling and storage at depots and sites

4.1 General

Plastics pipes may be supplied in straight lengths or coiled forms (either free standing or on drums).

NOTE Attention is drawn to the need for consideration of personnel safety during the transport,handling and storage, especially in wet and cold weather conditions. Particular care should be exercisedwhen decoiling coiled pipes as considerable forces can be released.

Additional information should be given in the System Standards, if applicable.

4.2 Transport

NOTE Attention is drawn to the need to conform to national and/or local transport regulations.

4.2.1 When transporting pipes, use either flat-bed or purpose made vehicles. The bed shall be freefrom nails and other protuberances.

4.2.2 Secure the pipes effectively before transporting them. Any side support post shall be flat andfree from sharp edges.

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4.2.3 When loading socket-ended pipes, stack the pipes so that the sockets are not in contact withadjacent pipes.

4.2.4 The largest diameter pipes should be placed on the bed of the vehicle.

4.2.5 Pipes should not be allowed to overhang the vehicle by more than five times the nominal size,DN, expressed in metres or 2 m, whichever is the smaller. These recommendations may not applywhen rigid bundles of pipes are being transported.

4.2.6 When pipes and/or fittings require special transportation practices the manufacturer shall notifythe customer of the procedures to be used.

4.3 Handling

4.3.1 When handling the pipes, take care to prevent damage.

4.3.2 Plastics pipes can be damaged when in contact with sharp objects.

They shall not be dropped, thrown or dragged along the ground.

4.3.3 It is preferable to use fabric slings or rope to lift the pipe. Metal bars, slings, hooks or chains willdamage the pipe if they are used incorrectly. When loading or unloading pipes with fork lift equipment,then only fork lift trucks with smooth forks should be used. Care should be taken to ensure that forksdo not strike the pipe when lifting.

4.3.4 The impact resistance of plastics pipes is reduced at very low temperatures and under theseconditions, take more care during handling.

4.4 Storage

4.4.1 Although plastics pipes are light, durable and resilient, take reasonable precautions duringstorage.

4.4.2 Stack the pipes or coils on surfaces free from sharp objects, stones or projections. For themaximum stacking height, see the referring standard.

When storing pipes in racks, ensure that any sockets lie alternately within the pile and projectsufficiently for the pipes to be correctly supported.

4.4.3 Where the pipes are supplied in coils, store them either vertically or stacked flat one on top ofthe other, taking care to protect the pipes from extremes of temperature. For further information, seethe referring standard.

Each coil of pipe of nominal size greater than DN 90 should be stored vertically in purpose-built racksor cradles. For further information, see the referring standard.

4.4.4 When straight pipes are stored on racks, these shall provide sufficient support to preventpermanent deformation.

4.4.5 Do not place pipes or rubber seals in close proximity to fuels, solvents, oils, greases, paints orheat sources.

4.4.6 For the recommended maximum storage period for pipes in direct sunlight, see the referringstandard.

4.4.7 In extreme climatic conditions special storage requirements may be necessary. Follow theadvice given in the manufacturer's technical data accordingly.

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4.4.8 If pipes are supplied in a bundle or other packaging, the restraints and/or packaging should beremoved as late as possible prior to installation.

5 Installation

5.1 Pipes in trenches

5.1.1 Behaviour of flexible pipes under load

The behaviour of a pipe when subject to a load depends upon whether it is flexible or rigid. Plasticspipes are flexible. When loaded a flexible pipe deflects and presses into the surrounding material. Thisgenerates a reaction in the surrounding material which controls deflection of the pipe. The amount ofdeflection which occurs is limited by the care exercised in the selection and laying of the bedding andsidefill materials. Hence flexible pipes rely for their load-bearing properties on the bedding and sidefillmaterials.

In the case of rigid pipes, the load on a pipe is borne primarily by the inherent strength of the pipematerial and when this load exceeds a limiting value the pipe breaks. Standards for rigid pipes,therefore, usually include ultimate crushing strength tests to determine this limiting value and thusassess the loadings which may be allowed above the installed pipe.

Flexible pipes on the other hand deflect under load and can be deflected to a high degree withoutfracture. The level of deflection reached by a buried pipe depends on the properties of the surroundingmaterial and to a much less extent on the stiffness of the pipe but not on its strength properties. Hencefor flexible pipes the crushing strength test and design procedures applied to rigid pipes are notappropriate.

When a flexible pipe is installed and backfilled it will be deflected. This is called the initial deflection.The pipe continues slowly to have an increase in deflection but reaches a limiting value within areasonable period of time. The use of the installation procedures detailed in this prestandard willminimize the levels of both the initial and final deflections. If the pipeline is pressurized then areduction in the amount of deflection will occur. A more detailed description of this behaviour is givenin Annex C.

5.1.2 Limiting deflection

There are several methods of structural design (see EN 1295-1:1997) that are used to estimate thedeflection of a pipe under load but, though they are capable of being in reasonable agreement, they do

not give exactly the same answers for a given condition. The values calculated are usually theexpected average deflections.

Pipes made from different materials have different limiting deflection levels. For the applicablemaximum permissible initial and, if appropriate, long-term deflection see the relevant SystemStandard. If this installation prestandard is followed it is expected that the deflections will be less thanthe limiting values given in the relevant System Standards.

Where it can be expected that a product covered by the System Standard may be delivered with somedistortion, e.g. pipes delivered in coils, then this should be stated. The average deflection is to beassumed to be in addition to this distortion.

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5.1.3 Design considerations

5.1.3.1 General

If it is essential to determine the soil conditions that relate to trench construction and pipe installationprior to construction, the native soil and the backfill material shall be classified in accordance withAnnex A. The classification shall be used to choose a suitable pipe stiffness in accordancewith 5.1.3.2.

NOTE The classification will also indicate the areas of suitable materials for pipe zone backfill, so thatimportation of material may be minimized. Native materials conforming to 5.1.6.3 and group 1, 2, 3 and 4are all suitable as backfill in the pipe zone. If backfill materials have to be imported it is suggested thatgroup 1 or 2 materials are used.

5.1.3.2 Choice of pipe stiffness

The choice of pipe stiffness shall be made either using the tables in this prestandard or on the basis of

calculations in accordance with EN 1295-1:1997 or on the basis of previous experience.

Where calculations show that a pipe stiffness lower than that given in Table 1 or Table 2 isappropriate, then pipes with this lower stiffness may be used. Where pipes are intended to be used inconditions where they have by previous experience proved to be satisfactory it is not necessary toverify this by detailed calculation even though their stiffness may be lower than the appropriate valuegiven in Table 1 or Table 2.

If such experience is not available then the minimum stiffness required shall be selected from Table 1or Table 2. These tables have been prepared to cover the following conditions:

a) non-trafficked areas with depths of cover between 1 m and 3 m and between 3 m and 6 m see

Table 1);b) trafficked areas with depths of cover between 1 m and 3 m and between 3 m and 6 m (see

Table 2).

In the absence of prior satisfactory experience, where pipes have a depth of cover less than 1 m ormore than 6 m the pipe stiffness and the installation shall be designed by calculation.

Where a System Standard uses SDR for classification purposes instead of stiffness it shall also givethe equivalent stiffness values in its relevant part.

Generally the choice of pipe stiffness depends upon the native soil, the pipe zone backfill material andits compaction, the depth of cover, the loading conditions and the limiting properties of the pipes.

In order to make a choice of pipe stiffness possible, the native soil and backfill materials have beenclassified into six main groups as described in Annex A.

Based on the native soil, backfill details and depth of cover, the minimum pipe stiffness is selectedfrom Tables 1 or 2. Using a pipe of this stiffness installed in an embedment formed from theappropriate backfill material compacted to the specified degree of compaction should result indeflections of not more than the limiting values given in the relevant System Standard.

NOTE Whenever a common structural design method for buried pipelines (at least one for plasticsmaterials) becomes available, Tables 1 and 2 will be reviewed.

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Table 1 — Recommended minimum stiffness for non-trafficked areas

Values in newtons per square metres

Backfill Compaction- Pipe stiffness 1)

material class 2) For depth of cover 1 m et 3 m

group 3) Undisturbed native soil group 3)

1 2 3 4 5 6

1WMN

125012502000

125020002000

200020002000

200040004000

400050008000

5000630010000

2WMN

200020004000

200040006300

400050008000

500063008000

50006300

**

3WMN

40006300

**

63008000

**

800010000

**

8000****

4WMN

6300****

8000****

8000****

For depth of cover > 3 m et 6 m

1WM

20002000

20004000

25004000

40005000

50006300

63008000

2WM

40005000

40005000

50008000

800010000

8000**

3 WM 6300** 8000** 10000** ****

4WM

****

****

****

1) Initial specific stiffness, S , determined in accordance with the relevant System Standards2) See Table 5.3) See Annex A.**) Structural design is necessary to determine trench details and pipe stiffness.

NOTE 1 If a pipe of given stiffness is intended to be used under more severe loading conditions(than originally envisaged), it may be possible to achieve this by the use of a higher class of installation.It is essential that this is verified by structural design.

NOTE 2 Attention is drawn to the limitations that may apply due to negative pressure in service anddue to mechanical compaction requirements during installation for pipe stiffness up to and includingSN 2500.

NOTE 3 In cases of combined loading conditions (such as soil load plus internal pressure) specialconsiderations and possibly precautions should be taken.

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Table 2 — Recommended minimum stiffness for trafficked areas

Values in newtons per square metres

Backfill Compaction Pipe stiffness 1)

material class 2) For depth of cover 1 m et 3 m

group 3) Undisturbed native soil group 3)

1 2 3 4 5 6

1 W 4000 4000 6300 8000 10000 **

2 W 6300 8000 10000 ** **

3 W 10000 ** ** **

4 W ** ** **

For depth of cover > 3 m et 6 m

1 W 2000 2000 2500 4000 5000 6300

2 W 4000 4000 5000 8000 8000

3 W 6300 8000 10000 **

4 W ** ** **

1) Initial specific stiffness, S , determined in accordance with the relevant System Standards2) See Table 5.3) See Annex A.**) Structural design is necessary to determine trench details and pipe stiffness.

NOTE 1 If a pipe of given stiffness is intended to be used under more severe loading conditions(than originally envisaged), it may be possible to achieve this by the use of a higher class of installation. Itis essential that this is verified by structural design.

NOTE 2 Attention is drawn to the limitations that may apply due to negative pressure in service anddue to mechanical compaction requirements during installation for pipe stiffness up to and includingSN 2500.

NOTE 3 In cases of combined loading conditions (such as soil load plus internal pressure) specialconsiderations and possibly precautions should be taken.

5.1.3.3 Types of installation

The two most commonly used practices for the installation of plastics pipes are either to surround thepipe with the same material (see Figure 2) or splitting the surround into two materials or degrees ofconsolidation (see Figure 3). The use of such a split embedment is normally only found to be practicalwith pipes of nominal sizes greater than DN 600.

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Key

1 Pipe zone

2 Bedding

Figure 2 — Trench with full surround pipe zone

Key

1 Split level

2 Secondary pipe zone backfill3 Primary pipe zone backfill:

0,5d e height 0,7d e

4 Bedding

5 Invert

Figure 3 — Trench with split surround pipe zone

If a split embedment is used it is important that the split level between the lower and upper materialshould occur at between 50 % and 70 % of the pipe diameter above the bedding (see Figure 3). Thisis to prevent the possibility of generating high stresses/strains at the split level when the pipe deflects.

To ensure that the split surround provides the same degree of support to the pipe as the full surroundthe following rules shall be applied:

a) the material in the primary pipe zone (see Figure 3) of a split surround should be at least onegrade stiffer than that required in the pipe zone of a full surround, where a grade is a particularcombination of material group and a compaction class, a change by one step in either of whichcomprises a one-step-change of grade. Thus the one grade change may be achieved by eitherincreasing the compaction class or using a higher group of material (see Table 5). Forinstance, if an application using a full surround requires backfill material group 2 moderatelycompacted, then a split surround would require either a well compacted group 2 material or agroup 1 material with moderate compaction;

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b) the material in the secondary pipe zone (see Figure 3) of a split surround may be up to twogrades less stiff than that in the pipe zone of a full surround. But care shall be taken that themaximum total difference between primary and secondary pipe zone is not more than twogrades. This also may be achieved by changing either the material group and/or the

compaction class. In any case the lowest soil stiffness which is allowed is achieved using anuncompacted material of group 4. For instance, for the case described in item a) therequirements would be fulfilled in the secondary pipe zone by using uncompacted group 2 (onegrade lower) or moderately compacted group 3 (also one grade lower) or uncompactedgroup 3 (three grades lower) material. The last option is not allowed because in this case themaximum two grades difference would be exceeded.

5.1.3.4 Parallel piping systems

Parallel piping systems laid within a common trench shall be spaced sufficiently far apart to allowcompaction equipment if used to compact the pipe zone backfill material between the pipes. A

clearance of at least 150 mm greater than the width of the widest piece of compaction equipment usedis considered as a practical clearance between the pipes.

The pipe zone backfill material between the pipes shall be compacted to the same compaction classas the material between the pipe and the trench wall.

In cases of parallel piping systems laid within a stepped trench (see Figure 4) the pipe zone backfillmaterial shall be granular and shall be compacted to compaction class W.

Key

1 Well compacted (class W)

Figure 4 — Parallel pipes in a stepped trench

5.1.4 Trench construction

5.1.4.1 Safety

Operations in trenches are carried out in potentially hazardous conditions.

Where appropriate shore, sheet, brace, slope or otherwise support the trench walls to protect any

person in the trench. Take precautions to prevent objects falling into the trench, or its collapse causedby the position or movements of adjacent machinery or equipment, whilst the trench is occupied.

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Excavated material should be deposited at a distance of not less than 0,5 m from the edge of thetrench, and the proximity and height of the spoil bank should not be allowed to endanger the stability ofthe excavation.

NOTE Attention is drawn to any local and/or national safety regulations.

5.1.4.2 Trench width

The width of the trench at the springline of the pipe need not be greater than necessary to provideadequate room for jointing the pipe in the trench and compacting the pipe zone backfill at thehaunches. Typical values for b S (see figures 1 and 2) are given in Table 3.

Wider trenches may be necessary for installations involving, e.g., relatively deep burial or unstablenative soils. Narrower trenches may be used when the system design permits or access by persons isnot required.

Table 3 — Typical values for b S

Nominal sizeDN

b Smm

DN 300300 < DN 900900 < DN 1600

1600 < DN 24002400 < DN 3000

200300400600900

5.1.4.3 Trench depth

Determine the trench depth by the pipeline design, intended service, pipe properties, size of pipe andlocal conditions such as the properties of soil and combination of static and dynamic loading.

In general, care should be taken that the depth of cover above the crown of the pipe for pipes passingunder traffic areas should usually be a minimum of 600 mm, although shallower depths may be usedwhen the installation is designed accordingly. When determining the trench depth, allowance for asuitable bedding should be incorporated.

Take care to ensure that the burial depth is sufficient to prevent the conveyed fluids from beingaffected by frost.

Sufficient cover should be provided to prevent accidental pipe flotation in potentially high ground waterareas. Generally it is recommended not to dig the trench too far in advance of pipe laying and tobackfill as soon as possible after pipe laying. In frost conditions it may be necessary to protect thetrench bottom so that frozen layers are not left under the pipe.

5.1.4.4 Trench bottom

5.1.4.4.1 Trench grade

The surface at the trench grade (see Figure 1) shall be continuous, uniform and free of boulders.

5.1.4.4.2 Over-excavation

Where rock, cobbles or hardpan are encountered, over-excavate the trench bottom.

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Quicksands or similar soils, organic soils or soils that exhibit a volume change with a change inmoisture content may be encountered in the bottom of the trench. In such cases the engineer canspecify that further excavation be carried out and a foundation zone be provided. Each such situationshall be evaluated, on a case-by-case basis during construction, to determine the extent of over-

excavation and the type of foundation material to be used.

Where over-excavation is performed, including accidental over-excavation during construction, it isrecommended that the material for the foundation zone shall be the same as for the primary pipe zoneand shall be compacted to class W (see 5.1.6.3).

Compact the foundation material uniformly in accordance with 5.1.6.2 and 5.1.6.3.

5.1.4.4.3 Special conditions

When settlement of the soil can be expected, such as when a pipe passes through a soil transition,then the use of geotextiles as shown in Figure 7 can provide a solution. However, where large-scale

soil movements are anticipated then this solution may not be effective. In such cases it isrecommended that expert advice is sought.

Among special conditions which may be encountered during laying, is running or standing wateroccurring in the bottom of the trench, or the bottom of the trench exhibits a quick tendency. In thesecases remove the water by means such as well points or underdrains until the pipe has been installedand the trench backfilled to a height sufficient to prevent flotation of the pipeline or collapse of thetrench. The gradation of the pipe zone backfill, bedding and foundation material shall be such that,under saturated conditions, fines from these areas will not migrate into the adjacent soil of the trenchbottom or walls, and material from the trench bottom or walls will not migrate into those areas. Anymigration or movement of soil particles from one area to another can result in the loss of the

necessary foundation or side support for the pipe, or both. The migration of fine materials can beprevented by use of a suitable filter fabric, as shown in Figure 5.

Key

1 Pipe zone

2 Bedding

3 Filter fabric

Figure 5 — Protection against material migration

If filter fabrics are welded together, the fabrics shall be laid with at least 0,3 m overlapping. Unweldedfabrics shall be laid with an overlap of at least 0,5 m.

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When the soil is weak or soft such that it is not possible for persons to work safely in the trench thenreinforcement of the trench may be necessary before laying the bedding. Reinforcement of the trenchbottom can be made using a wooden mattress (see Figure 6), reinforced concrete or geotextiles. If theground water table could be adjacent to the mattress, boards impregnated with appropriate

preservatives are recommended (see the referring standard).

Key

1 Bedding

2 Wooden boards

3 Connecting boards

4 Minimum width

Figure 6 — Trench bottom reinforced by a wooden mattress

Typical uses of geotextiles are shown in figures 7 to 10.

Key

1 Geotextile

Figure 7 — Geotextile reduces uneven settlement in soil transition zones

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Key

1 Geotextile

Figure 8 — Geotextile forms a partial groundbeam containment and support

Key

1 Geotextile

Figure 9 — Geotextile forms a total groundbeam, containment and support

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Key

1 Geotextile

Figure 10 — Geotextile acts as an anchor to prevent flotation

If pipes conveying water or sewage are installed at depths shallower than the expected frostpenetration depth, thermal insulation shall be provided.

Thermal insulation should be made of extruded polystyrene foam panels, or of other insulating materialsuitably protected from the ingress of moisture, located in accordance with Figure 11.

The choice of insulation arrangement according to Figure 11 shall be made with regard to the frostsusceptibility of the native soil and the backfill material.

a) Thermal insulation in clayey and sil ty soils b) Thermal insulation at deeper frostpenetration depths in granular soils

c) Thermal insulation on shallow trenches d) Thermal insulation using preformedextruded polystyrene shells

Figure 11 — Examples of thermal insulation of buried pipes

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5.1.4.4.4 Bedding

A pipe requires uniform support for the whole of its length and this is provided by the bedding layer. Toprovide this uniform support the bedding layer should generally have a thickness of 100 mm to150 mm and be not less than 50 mm.

The material used shall be granular, such as gravel, sand or crushed rock, and shall conformto 5.1.6.3.

The bedding material should be spread evenly across the full width of the trench and levelled to thegradient of the pipeline but not compacted.

In uniform, relatively soft, fine-grained soils free from large stones and other hard objects, and wherethe bottom can readily be brought to an even finish providing a uniform support for the pipes over theirwhole length it may be satisfactory to lay pipes with nominal sizes up to and including DN 700 directlyon the trimmed bottom of the trench.

5.1.4.4.5 Jointing preparation

Where appropriate to allow for proper assembly of the joint or to prevent the weight of the pipe frombeing carried on the joint, provide a jointing hole beneath the joint. The jointing hole shall not be largerthan is necessary to accomplish proper joint assembly. When the joint has been made, carefully filland compact the jointing hole with bedding material to provide continuous support of the pipethroughout its entire length.

5.1.5 Pipe installation, procedures and control

5.1.5.1 Handling

Store and handle the pipe so as to prevent pipe damage. Carefully inspect each pipe, especially at jointing surfaces, for damage prior to installation. It is also advisable to check for blockage andpossible contamination.

5.1.5.2 Laying

Lay the pipe in the trench so that it bears evenly on the bedding throughout its length. Makeallowances for thermal movement, particularly if laying takes place in extreme weather conditions.Make the joint in accordance with the manufacturer's recommendations.

5.1.5.3 Angular deflection

During installation the direction of the pipe may be changed at the joint by up to the maximum angle ofdeflection declared by the manufacturer.

NOTE When changes in direction are made in this way it is essential to appreciate that the capabilityof the joint to tolerate ground movement has been reduced.

Alternatively, make changes in direction by using fittings or, if the pipe material's properties aresuitable, by cold bending in accordance with 7.1.

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5.1.5.4 Connection to rigid structures

Where a pipeline enters or exits a structure, such as a building, manhole or anchor block, means oftolerating differential settlement shall be provided. Typical connections to rigid structures are shown infigures 12 to 15. However, their applicability shall be checked against national and/or local regulations.Where the piping system uses flexible joints, they should be located as shown in Figure 12 or 13.Some materials such as polyethylene are sufficiently flexible to tolerate such movements and may beconnected as shown in Figure 14.

Key

1 Flexible joint 4 Pipe bed

2 Short pipe section: max. 2 m; min. 1 m 5 Native soil

3 Flexible joint in the structure 6 Well compacted material

Figure 12 — Connection type 1

When casting a coupling or bell in concrete, as shown in Figure 12, maintain its roundness such thatlater joint assembly may be accomplished easily.

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Key

1 Flexible joint 4 Pipe bed

2 Short pipe section: max. 2 m; min. 1 m 5 Native soil

3 Rubber or bitumen 6 Well compacted material


For connections in accordance with Figure 13, place the first flexible joint within a distance L of400 mm or 0,5 X d e, whichever is the greater.

NOTE 1 A rubber or bitumen wrap at the concrete interface can provide stress relief from expansion,shear, and/or bending loads. This is particularly important for limiting radial shear and discontinuity

stresses in a pressure pipe.

NOTE 2 To minimize shear and bending stresses, effective support is particularly necessary for thepipe protruding from the structure.

Key

1 Pipe bed

2 Native soil

3 Well compacted material


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For low flexibility piping systems using rigid joints, a means of reducing the bending and shear loadson the pipe resulting from differences in settlement of the pipe and structure is use of a shield pipe(see Figure 15).

Key

1 Shield pipe

2 Rigid joint

3 Pipe bed

4 Native soil

5 Well compacted material


5.1.6 Backfilling

5.1.6.1 General

For installations in accordance with Figure 2 or Figure 3, Table 1 or Table 2, as applicable, backfillingshall be completed in accordance with 5.1.6.2 to 5.1.6.4 inclusive.

5.1.6.2 Basic procedure

Place the pipe zone backfill in layers on each side of the pipe and compact in accordance with 5.1.6.4to the degree and height specified in 5.1.6.3, unless otherwise specified in the project specification.

Take care to compact the material under the haunches of the pipe.

Backfill free fall to the pipe crown should be kept to a minimum.

The backfill above the pipe zone should be placed by spreading in approximately uniform layers, ifapplicable, compacted in accordance with 5.1.6.3.

Where it is expected that ground water may flow through the granular embedment the provision ofbarriers such as clay stanks should be considered.

5.1.6.3 Pipe zone embedment

The embedment is primarily dependent upon the pipe stiffness, the depth of cover and the nature ofthe native soil.

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Where imported material is used for the primary zone it is recommended that a well-graded granularmaterial with a maximum particle size in conformance with Table 4 is used. Where single-sizedmaterials are used it is recommended that the maximum particle size should be one size smaller thanthat given in Table 4.

The native soil may be used for the pipe zone backfill providing it conforms to all of the followingcriteria:

a) no particles greater than the applicable limit given in Table 4;

b) no soil lumps greater than twice the applicable maximum particle size given in Table 4;

c) no frozen material;

d) no debris (e.g. asphalt, bottles, cans, trees);

e) where compaction is specified, the material shall be compactible.

Table 4 — Maximum particle size

Nominal size

DNMaximum size

mm

DN < 100100 DN < 300300 DN < 600600 DN

15203040

NOTE The values are the ones used in the descriptors of a grading, e.g.6/14, 8/12 etc. It is acknowledged that in such gradings individual particleslarger than the descriptors can occur.

Fine-grained soils with medium to high plasticity and organic soils (with group 5 or group 6classification; see Annex A) are generally considered unsuitable for primary pipe zone backfillmaterial, unless the pipe and installation have been designed for this condition.

The structural properties of the pipe zone backfill material are primarily dependent upon the type ofmaterial and the degree of compaction achieved. The degree of compaction can be varied by usingdifferent types of equipment and by varying the numbers of layers. Table 5 gives for groups of materialclassified in conformance with Annex A the degree of compaction expressed in Standard ProctorDensity (SPD) for the three classes of compaction used in this prestandard, i.e. "W", "M" or "N".

NOTE Proctor Density determined in accordance with DIN 18127.

Table 5 — Standard Proctor densities for compaction classes

Compac-- Backfill material group

tion Description *) (see Annex A)class

English French German

4SPD

%

3SPD

%

2SPD

%

1SPD

%

NMW

NotModerateWell

NonModéréSoigné

NichtMäßigGut

75 à 8081 à 8990 à 95

79 à 8586 à 9293 à 96

84 à 8990 à 9596 à 100

90 à 9495 à 9798 à 100

*) For information.

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5.1.6.4 Recommended compaction methods

Table 6 gives the recommended maximum layer thicknesses and the number of passes required toachieve the compaction classes for the various types of equipment and pipe zone backfill materials.Also included are recommended minimum cover thicknesses required above the pipe before therelevant piece of equipment can be used over the pipe.

The details given in Table 6 are a guide and where the installation is of a sufficient size it isrecommended that trials using a variety of the above combinations are carried out so that the optimumpractice is selected for the purpose.

Table 6 — Recommended layer thicknesses and number of passes for compaction

Equipment Number of passesfor compaction

class

Maximum layerthickness, in metres,

after compaction for soil group

Minimum thicknessover pipe crown

before compaction

(see Annex A)Well Moderate 1 2 3 4 m

Foot or handtampermin. 15 kg 3 1 0,15 0,10 0,10 0,10 0,20

Vibrating tampermin. 70 kg 3 1 0,30 0,25 0,20 0,15 0,30

Plate vibratormin. 50 kgmin. 100 kgmin. 200 kgmin. 400 kgmin. 600 kg

44444

11111

0,100,150,200,300,40

0,100,150,250,30

0,100,150,20

0,100,15

0,150,150,200,300,50

Vibrating rollermin. 15 kN/mmin. 30 kN/mmin. 45 kN/mmin. 65 kN/m

6666

2222

0,350,601,001,50

0,250,500,751,10

0,200,300,400,60

0,601,201,802,40

Twin vibratingrollermin. 5 kN/mmin. 10 kN/m

min. 20 kN/mmin. 30 kN/m

66

66

22

22

0,150,25

0,350,50

0,100,20

0,300,40

0,15

0,200,30

0,200,45

0,600,85

Triple heavy roller(no vibration)min. 50 kN/m 6 2 0,25 0,20 0,20 1,00

5.1.6.5 Remaining backfill

The remaining part of the backfill can be made with excavated material with a maximum particle sizeof up to 300 mm providing there is at least 300 mm cover to the pipe. If compaction is required the

material shall be suitable for compaction and shall have a maximum particle size not greater than 2/3of the compaction layer thickness.

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NOTE Attention is drawn to any relevant local and/or national regulations.

Under non-trafficked areas compaction class N (see Table 5) is felt to be sufficient. Under traffickedareas compaction class W (see Table 5) shall be used.

5.1.7 Compaction quality control

Conformance with the design assumptions should be confirmed by one or more of the followingmethods:

- close monitoring of the backfill procedures;

- verification of the initial deflection of the installed pipe;

- on-site verification of the degree of compaction.

After repair and additional connection procedures, care should be taken that when replacing sidefilland backfill the new density values are approximately equal to those immediately adjacent to thereplaced zones.

5.1.8 Special precautions

During the installation procedures take precautions to avoid flotation of the pipe. Avoid displacement ofthe pipe while placing material under the haunches.

Take precautions when removing sheeting, safety shields or other trench protection to avoid disruptionof the compacted material. When moving the protection, perform this in stages, as the side fillingproceeds, with as little disruption of the compacted sidefill as possible. Take care to fill voids andrecompact. If the possibility of disruption cannot be excluded with a sufficient degree of certainty, usea pipe designed to tolerate those installation uncertainties.

In some cases it therefore may be necessary when designing the pipeline either to reduce, e.g. theassumed nominal Proctor density and/or to choose a higher pipe stiffness class.

In the process of backfilling the trench, protect the pipe from falling objects and direct impact fromcompaction equipment or other sources of potential damage. When the backfill is to be compacted upto the ground surface, do not use the compaction equipment directly above the pipe until sufficientbackfill has been placed. Do not use rolling equipment or heavy tampers to consolidate the finalbackfill unless their use is recommended by the pipe and equipment manufacturers. Provide at leastthe minimum thickness over the pipe crown given in Table 6, or a greater amount if recommended bythe pipe and equipment manufacturers, before using such consolidation equipment.

Parallel piping systems laid within a common trench shall be spaced sufficiently far apart to allowcompaction equipment to compact the pipe zone backfill material between the pipes.

A clearance of not less than 150 mm greater than the width of the widest piece of compactingequipment used may be considered as a practical clearance between the pipes.

Compact the pipe zone backfill material between the pipes to the same density as the materialbetween the pipe and the trench wall.

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5.2 Special installation techniques

The particular properties of plastics pipes have resulted in a wide range of proprietary equipmentbeing developed for their installation which exploits the properties of the materials. Typical techniquesthat are frequently used are generally termed mole ploughing or boring. For outline details of thesetechniques see the relevant System Standards, if applicable.

5.3 Laying of pipes above ground

5.3.1 Provision of supports

General stress and deflection analysis for pipes supported at intervals on saddles or pedestals, filledor partly filled with liquid, is complicated and time consuming.

For many pipe installations, the axial stresses and deflections can however be evaluated separatelywith sufficient accuracy by applying the normal beam theory.

The beam theory assumes that the cross-section of the pipe will not change, and that the ratio ofsupport spacing to pipe diameter is such that shear deformations can be neglected. For limitations onthe use of the theory, relevant literature should be consulted.

The designer shall also consider the important difference between a pipe and an ordinary beam, i.e.the influence of the axial load component acting in the liquid column inside the pipe.

The designer of an above-ground pipe system shall consider the following implications of this loadcomponent:

- when a component in a pressurized pipeline has a change in cross-sectional area or direction itinduces a resultant load. Hence components such as bends, reducers or branches shall either be

anchored or the pipeline be designed to withstand such loads;

- every pipeline, however carefully manufactured and installed, has some minor variations incross-sectional area and unintended deviations from straight alignment. Those deviations will alsoinduce loads as explained in the previous paragraph.

Whilst for a buried pipeline, adequate resistance is provided for by the pipe embedment, suchresistance may not be provided at the supports of an above ground pipeline.

Extra care shall be exercised to minimize such deviations and all components shall be provided withall the necessary support to ensure the stability of the pipeline;

- all above-ground pipes supported at intervals will deflect due to the various loads acting on the

pipe. When the liquid in the pipe is pressurized the curvature, caused by deflection, will result in areaction load. This is identical to what happens in pipe bends.

The reaction load usually adds on to the other loads acting on the pipe, increasing axial stresses anddeflections. This implies that the axial load acting in the liquid column shall be treated in the same wayand added to a load acting in the pipe itself when combinations of axial and lateral loads are analysed,i.e. beam-column theory shall be used.

The significance of this phenomenon is depending on the ratio between the sum of axial loads, carriedby the pipe and the liquid column, and the critical axial load for the pipe as a column. The boundaryconditions are also of importance.

Generally the axial load is most significant for small diameter pipes operating under high pressure.The limiting pipe diameter and pressure for buckling to be critical is material dependent.

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It is important to be aware of the fact that plastics materials have time-dependent properties, e.g.creep. For long-term axial loads, causing creep, the critical axial load will obviously be reduced.

The analysis of large above-ground pipe systems often gets complicated. Several software packageshave been developed for such analysis, but it is doubtful that all of them incorporate the beam-columntheory. Procedures applicable to analyse simple above-ground pipeline installations are presented inAnnex E to this prestandard. Annex E can be used as a guide to determine whether or not thebeam-column theory has to be applied.

5.3.1.1 Support spacing

Assuming that the longitudinal E-modulus and the dimensions required to calculate the linear momentof inertia are available in the individual System Standards or provided by the manufacturer, thespacing of supports shall be such that the midspan deflection, , does not exceed 1/200th of the span.The maximum deflection shall be calculated in accordance with Annex E.

The pipe manufacturer shall ensure that the joints' maximum angular movement exceeds the angularmovement calculated using the procedures described in Annex E.

The pipe stiffness shall be such as to ensure that a minimum factor of safety of 2,5 exists againstbuckling due to internal negative pressure.

5.3.1.2 Types of support

5.3.1.2.1 Continuous support

Continuous supports may be made of various materials, such as concrete, steel or wood, providedthat they are sufficiently robust and comprise a saddle or V-shapes for holding the pipe. An example of

a continuous support is given in Figure 16.

The pipe shall be fixed on to the support by means of clips or clamps which shall allow the pipe to slidefreely. The support shall have a smooth surface to prevent wear of the pipe and, if applicable,additional strength shall be provided at changes of direction to resist thrust.

Key

1 Indicated spacing

2 Anchorage

3 Drain

Figure 16 — Typical continuous support

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5.3.1.2.2 Isolated supports

Isolated supports, examples of which are given in Figure 17, may be used. Provisions for movementshall be provided.

Key

1 Rounded angle

2 Smooth surface

Sleeve is preferred

For small expansion For large expansion

Figure 17 — Typical isolated supports (continued)

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Individualsupports

Pairedsupports

Key

1 Span 3 Strap

2 Joint 4 Pipe

Individual orpaired supports

Singlesupport

Individual orpaired supports

Key

1 Pipe 4 Support 7 Pipe wall

2 Joint 5 Concrete cradle 8 Strap anchor

3 Galvanized straps 6 Bolt 9 Compressible material

Figure 17 — (concluded)

5.3.1.2.3 Provisions of support for control devices

All control devices (such as valves) shall be individually supported so that the pipe is not subjected to

any additional load.

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5.3.2 Thermal considerations

5.3.2.1 It is recommended that plastics piping systems and ducting systems installed above groundare designed in such a way that the thermal expansion or contraction is accommodated or otherwisecheck that the thermal stresses are within the design limits of the respective material.

5.3.2.2 The coefficient of linear thermal expansion, L, of plastics materials varies betweenapproximately 20 10-6 per degree Celsius and 200 10-6 per degree Celsius.

The coefficient of linear thermal expansion, L,is a material property. For the applicable values see therelevant System Standards.

Detailed information for the consideration of thermal expansion/contraction is given in Annex B of thisprestandard.

5.3.2.3 Some plastics pipes cannot withstand the freezing of the fluids which they contain; in suchcases measures shall be taken to drain and/or insulate sections which are likely to freeze.

5.3.2.4 Plastics pipes shall be laid at a sufficient distance from hot objects to prevent the materialbeing damaged by heat.

Guidance should be sought from the pipe manufacturer.

5.3.3 Direct sunlight

If so specified in the System Standard, the pipes shall not be installed in areas exposed to directsunlight.

6 Methods of assembly (jointing)

6.1 General

6.1.1 A range of jointing techniques is available for plastics pipes which can provide rigid or flexible joints.

The methods used to assemble the joint shall follow the joint manufacturer's recommendedprocedures.

All jointing techniques require skilled personnel to achieve satisfactory joints.

For the applicability of any particular jointing system see the relevant System Standard.

6.1.2 Joints are divided into two categories as follows: category A: Joints which are capable of withstanding end thrust. Examples: fusion joints,mechanical joints, e.g. with flanges;

category B: Joints which are not capable of withstanding end thrust. Examples: socket and spigot joints with elastomeric seals, some types of mechanical joints with sealing gaskets.

6.1.3 Either category of joint may form an integral part of sockets already provided on the pipe itself;in this case they are termed "preformed joints". As an alternative, two joints may be combined as adouble socket for joining pipes with smooth ends; in this case they are termed "couplers".

6.1.4 Pipe joints of category B (see 6.1.2) are not intended to resist end thrust which occurs at

changes in direction and at valves. Consequently the pipe or fitting shall be adequately anchored ifsuch joints are used.

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6.1.5 If it may be necessary at some time to dismantle the piping system, the selection of joint shouldtake this into account.

6.2 Joints using an elastomeric seal

6.2.1 The seal may be located in the socket or the spigot as indicated in Figure 18. The details of theseal and of the joint depend on the manufacturer's design. The seals to be used shall be thosesupplied by the manufacturer for his own assembly system. If the seal is not in place at the time ofdelivery, clean the groove and then locate the seal correctly.

6.2.2 Seals shall conform to the relevant European Standard.

6.2.3 Joints covered by category B are not intended to withstand end thrust. Particular attention shallbe paid to the correct anchorage of the elements.

6.2.4 Assembly of some joints requires them to be lubricated in accordance with the manufacturer'sinstructions prior to jointing. Use a lubricant which does not have any harmful effect on the pipe, fittingor seal. If the pipe is to carry water intended to be used for human consumption, the lubricant shallconform to the requirements given in the relevant System Standard.

Following lubrication the spigot shall be aligned with and introduced into the socket taking care toavoid any risk of contamination. The spigot shall be inserted into the socket up to the reference mark ifpresent.

NOTE Seals which have slipped out of place and dirt under the seals are the most frequent causes ofleaks. Both problems can be avoided by correct jointing procedure.

The pipes may be cut on site but, if so, the cut shall be square and the end shall be chamfered asappropriate for the joint.

Continuous profile Rubber ring in socket

Figure 18 — Typical flexible joints

6.3 Mechanical compression joints

These are similar to automatic joints, the main difference being that the elastomeric ring iscompressed by means of an external tightening system. Examples of these are shown in figures 19and 20. Mechanical compression joints are useful for joining pipes of different materials, usingadapters where necessary.

Care should be taken not to overcompress the seal which is in contact with the plastics pipe, otherwisethere is a risk of the pipe deforming and the tightness of the joint can be impaired. For some pipes, a

stiff internal sleeve may be used to increase their rigidity.

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Key

1 Pipe 4 Bolt

2 Rubber profile 5 Joint

3 Steel casing 6 Seal

Figure 19 — Typical compression joints for large diameters

Key

1 Compression fitting

2 Compression ring

3 Plastics pipe

Figure 20 — Typical compression joints

6.4 Other joints and jointing methods

Other joints and examples for jointing methods are given in Annex D. These are not generally used forall plastics piping systems; for their applicability see the relevant System Standards.

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7 Bends

7.1 Cold bending

Thermoplastics pipes have a degree of flexibility and can follow the undulations of the ground. Theallowed radius of curvature varies with the pipe diameter and the type of material. When a material issuitable for being cold bent on site to make a change in direction, see the applicable System Standardfor the recommended radii of curvature for the various sizes of pipes.

7.2 Hot bending

With most thermoplastics pipes bends can be made utilising the thermoplastic properties of thematerial. However, this is a specialised operation and it shall only be carried out within themanufacturer's works.

8 Inspection and testing

8.1 Inspection

8.1.1 Inspection upon receipt

8.1.1.1 The pipes should be inspected by the purchaser or their representative at the time of delivery.

8.1.1.2 The markings on the pipes shall be checked to ensure that they correspond to the detailsspecified for the project.

8.1.1.3 Damaged pipes shall be isolated either for rectification or for return to the supplier, asapplicable.

8.1.2 Inspection in situ

The marking on components shall be checked during and/or after installation as practicable to ensurethat they correspond with the details specified for the installation.

8.2 Testing

8.2.1 Pressure testing

Prior to a pressure test being carried out, make a check to ensure that the pipeline, and in particular

the bends, thrust blocks, and other fittings have been designed to resist the forces to be exerted bythe test pressure.

Perform the pressure test in accordance with the relevant European Standard(s).

For the permitted rate of loss of water and/or pressure, which shall take into account the behaviour ofplastics pipe(s) under internal pressure, see the relevant System Standards.

8.2.2 Permissible deflection

Pipe-laying work can be checked, particularly in respect to compaction and the use of the correctbedding material, by measuring vertical deflection.

The maximum permissible deflections are material-dependent and the limiting values are specified inthe relevant System Standard(s).

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The pipe's deflection shall not exceed the permissible level given in the relevant System Standard(s).

In the event of one or more pipes exceeding the limit then due consideration should be given to theactions required.

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Annex A(normative)

Classification of soils

In this prestandard three types of soil are considered, namely granular, cohesive and organic. Each ofthese has subgroups, which for granular material are based on particle size and granulation and forcohesive material are based on levels of plasticity. Table A.1 shows the criteria and the suitability foruse as a backfill material.

Table A.1 — Soil groups

Soil group To be

Soil type # Typical nameSym-bol* Distinguishing mark Example(s)

used as

backfill

granular 1 Single-sized gravel (GE)[GU]

Steep granulation line,predominance ofone-grain-size zone

Crushed rock, riverand beach gravel,morainic gravel,

YES

Well-graded gravels,gravel-sand mixtures

[GW] Continuous granulation line,several grain-size zones

scoria, volcanic ash

Poorly graded gravel-sand mixtures

(GI)[GP]

Steplike granulation line, oneor more absent grain zones

2 Single-sized sands (SE)[SU]

Steep granulation line,predominance of one grainsize zone

Dune and drift sand,valley sand, basinsand

YES

Well-graded sands,sand-gravel mixtures [SW] Continuous granulation line,several grain size zones Morainic sand,terrace sand, beachsand

Poorly graded sand-gravel mixtures zones

(SI)[SP]

Steplike granulation line, oneor more absent grain zones

granular 3 Silty gravels, poorlygraded gravel-sand-siltmixtures

[GM](GU)

Broad/intermittent granulationline with fine grained silt

Weathered gravel,slope debris, clayeygravel

YES

Clayey gravels, poorlygraded gravel-sand-clay mixtures

[GC](GT)

Broad/intermittent granulationline with fine grained clay

Silty sands, poorly

graded sand-siltmixtures

[SM]

(SU)

Broad/intermittent granulation

line with fine grained silt

Liquid sand, loam,

sand loess

Clayey sands, poorlygraded sand-claymixtures

[SC](ST)

Broad/intermittent granulationline with fine grained clay

Loamy sand, alluvialclay, alluvial marl

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Table A.1 — (concluded)

Soil group To be

Soil type # Typical name Sym-bol*

Distinguishing mark Example(s)used asbackfill

cohesive 4 Inorganic silts, veryfine sands, rock flour,silty or clayey finesands

[ML](UL)

Low stability, rapid reaction,nil to slight plasticity

Loess, loam YES

Inorganic clay,distinctly plastic clay

[CL](TA)(TL)(TM)

Medium to very high stability,no to slow reaction, low tomedium plasticity

Alluvial marl, clay

organic 5 Mixed grained soilswith admixtures ofhumus or chalk

[OK] Admixtures of plant or non-plant type, decay smell, lightweight, large porosity

Top soils, chalkysand, tuff sand

NO

Organic silt and

organic silt clay

[OL]

(OU)

Medium stability, slow to very

quick reaction, low to mediumplasticity

Sea chalk, top soil

Organic clay, clay withorganic admixtures

[OH](OT)

High stability, nil reaction,medium to high plasticity

Mud, loam

6 Peat, other highlyorganic soil

[Pt](HN)(HZ)

Decomposed peats, fibrous,brown to black coloured

Peat NO

Muds [F] Sludges deposited underwater, often interspersed withsand/clay/chalk, very soft

Muds

* The symbols used are taken from two sources. Symbols in square brackets [..] are taken from British StandardBS 5930. Symbols in round brackets (..) are taken from German Standard DIN 18196.

Where a soil is a mixture of types then whichever is the predominant one present can be used for theclassification.

Frequently the density or degree of consolidation is indicated for a soil. This can be in the form ofwords or numbers. Table A.2 gives the approximate relationship for the various descriptions used.

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Table A.2 — Consolidation class terminology

Description Degree of consolidation

% Standard Proctor 1) 80 81 to 90 91 to 94 95 to 100

Blow count 0 to 10 11 to 30 31 to 50 50

NOT (N)Expected degreesof consolidationachieved by the MODERATE (M)

compaction classesin this prestandard

WELL (W)

Granular soil loose medium dense dense very dense

Cohesive and organicsoil

soft firm stiff hard

1) Determined in accordance with DIN 18127.

NOTE Table A.2 is meant to be an aid for interpretation of descriptions used in various sources into theterms used for the degrees of consolidation in this prestandard

Where detailed information of the undisturbed native soil is not available then it is usually assumedthat it has a consolidation equivalent to between 91 % and 97 % Standard Proctor Density (SPD).

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Annex B(normative)

Thermal considerations on laying of pipes above ground

B.1 General

Variations in length, l , shall be calculated (in millimetres) using the following equation:

∆ ∆l = x xL

α L T ... (B.1)

where:

L is the coefficient of linear thermal expansion (X 10-6 per degree Celsius);

L is the initial length, in millimetres;

T is the difference in temperature, in degree Celsius.

In cases where the length variation because of thermal expansion/contraction is prevented by theconstruction, the reaction force, F T, in newtons, on to the fixed support is calculated as follows:

F d e E T T e x L

= x x x x xπ α ∆ ... (B.2)

where:

d e is the external diameter of the pipe, in millimetres;

e is the pipe wall thickness, in millimetres;

E x is the elastic modulus of the pipe material in the longitudinal direction, in newtons per squaremillimetre.

Figure B.1 illustrates the possible reactions of plastics pipes because of thermal expansion (+l 2) orcontraction (l 1).

is a fixed point

|| is an axial guide

Figure B.1 — Thermal expansion or contraction

Figure B.2 illustrates the length, LBC, i.e. the compensation portion of the stem of a branch pipe.

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|| is an axial guide

Figure B.2 — Compensation length variations

The pipe should be laid to minimise stresses in the system. A solution is to locate expansion jointsbetween fixed points. Examples of correct arrangements are shown in Figure B.3.

is a fixed point

|| an axial guide

Figure B.3 — Examples of ways of accommodating expansion

Some arrangements that allow for thermal movement are shown in figures B.4 to B.7 together with therelevant equations to calculate the amount of movement and the resulting forces for the four patternsof expansion joint thus illustrated.

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Material properties which are time-, temperature- or environment-dependent together with the pipedimensions are needed for solving the associated equations and shall be obtained from the relevantSystem Standards.

B.2 L-shaped expansion joint

is a fixed point

— — is an axial guide

Figure B.4 — L-shaped expansion joint

For an L-shaped expansion joint, as shown in Figure B.4, subject to the following conditions forvalidity:

L L1C S, max

0,8 x≤

L LLC S, max

0,8 x≤

To determine the position of fixed points on the basis of P1 and P2 on the basis of given values for L1Cand LLC, the following conditions shall be satisfied:

LL

c d L

11C

2

1C

0,296 x

e+ (0,777 x )≤

x

LL

c d L

LLC

2

eLC

0,296 x

+ (0,777 x )≤

x

where:

cT

= x xL

x, r

α σ

x E ∆

where:

x,r is the remaining longitudinal design stress capability in the pipe wall, i.e.σ σ σ σ

x, r

x, d x, p x, q= - - ... (B.3)

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where:

x,p is the stress in the longitudinal direction induced by the internal workingpressure, if present;

x,q

is the stress in the longitudinal direction induced by distributed vertical loads (see5.3.1);

σ

σ

x, d

x,u,L

S

=F

... (B.4)

where:

x,u,L is the long-term failure strength in the longitudinal direction (see referringSystem Standard);

F S is the safety factor.

Conversely, to determine the compensation section lengths L1C and LLC on the basis of given fixedpoints P 1 and P 2 located at distances L1 and LL from the expansion joint, the following conditions shallbe satisfied:

( ) ( )[ ] ( )L c d L c d c d 1C e 1

2e

20,5

e3,376 x x x + 1,722 x x - 1,313 x x≥

( ) ( )[ ] ( )L c d L c d c d LC e L

2e

20,5

e3,376 x x x + 1,722 x x - 1,313 x x≥

The thermal expansion of the pipes L1 and LL are given by the following equations:

∆ ∆L L T 1, h L 1= x xα ... (B.5a)∆ ∆L L T

L, v L L= x xα ... (B.5b)

The horizontal, F H, and vertical, F V, fixed point forces resulting from thermal expansion are determinedusing the following equations:

( )[ ]F

E R L

L R

E R L

LH

x 03

1, h

LC3

0

x 01,5

L, v

LC3

=7,5 x x x x

x 0 ,3 x + 0 ,7-

4,5 x x x x I I ∆ ∆... (B.6)

( )[ ]F

E R L

L R

E R L

LV

x 13

1, v

LC3 1

x 11,5

L, h

LC3

=7,5 x x x x

x 0 ,3 x + 0 ,7

-4,5 x x x x I I ∆ ∆

... (B.7)

where:

I = x-

64e

4i4

πd d

... (B.8)

R L

L0LC

1C

= ... (B.9)

R L

L11C

LC

= ... (B.10)

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B.3 Z-shaped expansion joint

is a fixed point


Figure B.5 — Z-shaped expansion joint

For a Z-shaped expansion joint, as shown in Figure B.5, subject to the following conditions for validity:

L L La 1 2

= + ... (B.11)

L L L0 1C 2C

= 2 x = 2 x ... (B.12)

( ) L

L

La 12,083 x

x- 1,5 x1C

2

e1C

≤c d

( ) ( ) ( )[ ]L c d c d c d L1C e

2e

2e a

0,50,062 x x + 0,00385 x x + 0,083 x x x≥

then

∆ ∆L T L1, h L a

= x xα ... (B.13)

∆ ∆L T LL, v L 0= x xα ... (B.14)and

( ) ( )F

E

H

1, h L, V

1C3

=0,0414 x x x x 4 x + 3 x I L L

L

∆ ∆... (B.15)

( ) ( )F

E

V

1, h L, v

1C3

=0,0414 x x x x 3 x + 4 x I L L

L

∆ ∆... (B.16)

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B.4 U-shaped expansion joints

B.4.1 Type A

is a fixed point


Figure B.6 — U-shaped expansion joint, type A

For a U-shaped expansion joint, type A, as shown in Figure B.6, subject to the following conditions for

validity:

L L L La 1 2 3

= + + ... (B.17)

L L L1C 3C 2

= = 0,5 x ... (B.18)

L L0 2

= 3 x ... (B.19)

LL

c d a

6,667 x

x2

2

e

≤

( )L L L c d 1C 3C a e

0,5

= 0 ,038 x x x≥

then

∆ ∆L T L1, h L a= x xα ... (B.20)

∆ ∆L T LL, v L 2= x xα ... (B.21)

F E H x

1, h

23

= 0,3 x x x I

∆ L

L

.. (B.22)

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B.4.2 Type B

is a fixed point


Figure B.7 — U-shaped expansion joint, type B

For a U-shaped expansion joint, type B, as shown in Figure B.7, subject to the following conditions forvalidity:

L L L L1C 2 3 0

= = = 0 ,5 x ... (B.23)

L L

c d a0

2

e

2,333x

≤ x

( )L L c d 1C a e

0,50,107 x x x≥

then

L T L1, h L a

= x xα ∆ ... (B.24)

∆ ∆L T LL, v L 0

= x xα ... (B.25)

F E H

1, h

03

= 1,29 x x x x I ∆ L

L

.. (B.26)

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Annex C(informative)

Behaviour of buried flexible pipes

A buried pipe will be subjected to soil loads and traffic loads. In the case of a buried flexible pipe theload-bearing capacity of the system depends on the stiffness of the pipe as well as on the stiffness ofthe surrounding soil. Even if the installation is executed to the highest standards it is known fromexperience that the deflection will vary along the pipeline. The varying deflection reflects differences ofsupport and variation of the external load acting on the pipes. (Variation of the external load alsooccurs on rigid pipes but the effects cannot be seen as they can with flexible pipes.) The deflectionarising from the external load on a buried flexible pipeline is in principle as shown in Figure C.1.

key

1 Pipe deflection2 Maximum deflection after installation3 Normal pipe installation4 Average deflection after installation5 High class pipe installation6 Length of pipeline

Figure C.1 — Typical changes in deflection along a pipeline for two levels of installationworkmanship

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This phenomenon has been verified by numerous deflection measurements on flexible pipes in manycountries. The difference between the average initial and maximum deflection varies and will be largerif the pipes are of a low stiffness than if they are of a high stiffness. A good, well supervised pipeinstallation will give smaller differences than a poor installation. For pipes of stiffness class 8000 N/m2

or lower it is not unusual for the maximum initial deflection to be 1 % to 2 % higher than the averageinitial deflection.

Since the average initial deflection of flexible pipes is often in the range of 2 % to 4 % it is evident thatthe variations in the external loading or the installation workmanship are quite considerable.

The deflection of a buried flexible pipe increases in the course of time. Almost all of the increase indeflection takes place during the first 1 year to 2 years after installation and thereafter the deflectionwill stabilize as indicated in Figure C.2.

key

1 Pipe deflection2 With traffic3 Without traffic4 Settlement deflection5 Installation deflection6 Time after installation7 Phase 18 Phase 2

Figure C.2 — Typical deflection of buried pipe as a function of time

The final deflection will be reached quicker if the pipe is subjected to traffic loads. The change indeflection after installation depends mainly on settlement and consolidation of the surrounding soil.

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Annex D(normative)

Joint and jointing examples

D.1 Joints capable of resisting end thrust

D.1.1 Joints using adhesives

D.1.1.1 The dimensions of the sockets and spigots shall conform to the relevant System Standard. Atypical joint is shown in Figure D.1.

Figure D.1 — Example of a cemented joint

D.1.1.2 The adhesives shall be suitable for use with the materials to be joined and the performancerequirements of the relevant System Standard.

D.1.1.3 When used in pipe lines for conveying drinking water, the adhesives shall not contain anysubstance which is likely to affect the taste or odour of the water, or to have a toxic effect, or toencourage the growth of bacteria.

Newly laid pipes shall be rinsed out.

D.1.1.4 Depending upon the nature of the adhesive and the clearance tolerances between the spigotend and the socket, there are different methods of cementing. Follow the manufacturers' instructionsaccordingly and pay attention to all the following points, which are common to all joints usingadhesives:

a) adhesives are inflammable and toxic. Do not smoke in the area in which they are being used.Apply the adhesive in a well ventilated space;

NOTE Attention is drawn to relevant local and/or national regulations.

b) use an adhesive having the necessary viscosity, and do not dilute it;

c) ensure that the pipe is cut square to its axis;

d) when the manufacturer's instructions so require, chamfer the ends of the pipe with a suitabletool.

The chamfer on the spigot and socket should be approximately the same. The angle should bebetween 15° and 45°, in accordance with the manufacturer's instructions. The minimum remaining wallthickness should be at least one third of the wall thickness, as shown in Figure D.2;

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key

1 15° to 45°

Figure D.2 — Chamfer of pipes

e) ensure that the surfaces to be joined are clean, dry and free from grease;

f) take special precautions when jointing is performed at temperatures close to freezing;

g) apply the adhesive in an even layer in a longitudinal direction, but with a thicker coating on thespigot end;

h) unless otherwise specified by the manufacturer, perform the jointing quickly.

Two persons may be required to apply the adhesive to the spigot and to the socket simultaneously;

i) remove smudges of adhesive as soon as the joint has been made. Once the joint is made,leave to dry without disturbing for at least 5 min;

j) because joints using adhesives become resistant to pressure only after an additional period,which depends upon:

- the type of adhesive (see the manufacturer's instructions);

- the gap between the socket and spigot;

- the ambient temperature;

- the test pressure,take care not to subject the joint to pressure too soon;

k) for diameters of 200 mm and above, check whether special bonding techniques need to beused and proceed accordingly.

D.1.2 Butt and strap jointing

The materials used for this type of joint (see Figure D.3) are normally glass fabrics and thermosettingresin. The design and fabrication of this joint should be carried out in accordance with ISO/DTR 7512.

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Key

1 Pipe wall

2 GRP wrapping

Figure D.3 — Butt and strap joint

D.1.3 Flanged joints

Flanges can be used for joining together plastics pipes and for joining them to metal flanges, valvesand flanged fittings. The seal is obtained by compression of a gasket or ring placed against the flange.The flanges may be assembled using a variety of techniques. Typical examples are shown infigures D.4 and D.5.

Key

1 Loose flange

2 Collar for flat gasket

3 Collar for O-ring

4 Flange with compression joint

Figure D.4 — Examples of flange and collar

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Key

1 Flange shaped or butt fused onto pipe

2 Flange fastened to ring joint

Figure D.5 — Examples of a compression joint

D.1.4 Restrained joints

On many piping systems special joints are available to resist movement or end thrust. Such joints areshown in Figure D.6. The procedures detailed by the manufacturer shall be followed to ensure therequired performance of the joint.

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Key

1 Sleeve

2 Rubber gasket

3 Locking key

4 Pipe

5 Joint

Figure D.6 — Socket/spigot with anchorage withstanding end thrust

D.1.5 Fusion assembling

D.1.5.1 General

This method uses heating to melt both surfaces to be joined at the same time and is applied tospecially designed moulded socket fittings and to fittings for butt fusion. The socket fusion, butt fusionand electrofusion methods differ from each other.

A brief description of these methods is given in D.1.5.2 to D.1.5.4, but in all cases the manufacturer'sinstructions shall be followed.

D.1.5.2 Socket fusion

This method involves the use of moulded fittings with joints of the spigot and socket type.

A special metal tool is used (see Figure D.7).

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Key

1 Joint

2 Heating male end

3 Heating element

4 Heated socket

5 Pipe

Figure D.7 — Socket fusion tool

When the tool is hot, one of its ends fits tightly over the pipe, while the other end fits tightly into thesocket of the fitting.

The tool is heated to the temperature required in accordance with the manufacturer's instructions, thenthe end of the pipe and the socket of the fitting are brought into contact with the tool until their surfacesare in the molten state. The tool is then withdrawn and the end of the pipe is inserted into the socket of

the fitting, pressing one against the other in accordance with the manufacturer's instructions until theyhave cooled sufficiently to remain connected.

With pipes of large diameter, it is recommended that a circumferential force be applied around thesocket during cooling, e.g. by means of a spring.

Care shall be taken that the heating tools are clean prior to use, to ensure that oxidized particles arenot included in the weld as this may make it brittle. Care shall also be taken not to overheat the partsfor assembly, nor to press on them too hard because either treatment may constrict the inside of thepipe.

D.1.5.3 Butt fusionThis technique also can be used only with fusible materials but does not necessarily require the use offittings. These are however available and can be used.

The joint is made by heating the surfaces for assembly on a flat hot plate, usually coated withpolytetrafluorethylene (PTFE), and then bringing these surfaces into contact under a controlledpressure in accordance with the manufacturer's instructions. This method can be used for pipes of anydiameter but ancillary equipment is necessary for correctly aligning the larger pipes and pressing themtogether.

This method comprises three separate stages, as follows:

a) Surface preparation: Check that the matching surfaces for assembly are cut square and arefree from physical or material defects;

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b) Heating of surfaces: Ensure that the surface of the hot plate is clean and is kept at therequired temperature throughout the heating period in accordance with the manufacturer'sinstructions. Keep the surfaces to be heated pressed against the hot plate until a thin bead ofmolten material is formed. Then reduce the pressure so that the bead does not grow any

larger while heating continues;c) Fusion assembling: Remove the hot plate and press the heated surfaces together in

accordance with the manufacturer's instructions. Maintain the pressure until the fused zonehas cooled.

NOTE This method produces a bead inside and outside the pipe.

D.1.5.4 Electrofusion

In this method the process comprises three stages, as follows:

a) Preparation of the pipe surface: Measure the fusion zone, mark the insertion depth, remove

the oxidized layer by using a scraper or a scraping tool. Clean the fusion surface;b) Assembling of the electrofusion fitting: Insert the pipe ends into the electrofusion fitting (see

Figure D.8). Use rounding clamps to correct ovalized pipes. During assembly the operatinginstructions of the manufacturers shall be followed. Connect the fusion control box with thecontact pins of the fitting;

c) Electrofusion: Switch on the fusion control box, start the fusion process. After fusion, cool theassembly for at least the cooling time recommended by the manufacturer before pressurizingthe piping.

Figure D.8 — Typical socket for electrofusion

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D.2 Mechanical threaded joints

Some plastics materials can be threaded, e.g. as indicated in Figure D.9. There is a range of such joints for assembly to other threaded pipes. These frequently require the use of adaptor fittings.

Figure D.9 — Threaded joint

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Annex E(normative)

Beam-column theory

E.1 Scope of the design procedure

The procedures covered by this annex deal with the most commonly encountered conditions forabove-ground pipeline installations. Formulas are given for the determination of deflections, stressesand buckling resistance for single and multiple span installations. The effects of water column aredealt with in detail, as this has been identified as a significant loading condition for above-ground pipeinstallations. The formulations can be applied to the design of both pressure and non-pressure

pipelines.The formulations in this document are not valid for very large diameter pipes with short spans(short/deep beams). For such pipes shear deflections can be significant and will influence the stressdistribution and a short beam theory may need to be applied.

For large diameter pipes at no or very low pressures the cross-section can be ovalized and this resultsin a decreased axial bending stiffness and induces tangential bending stresses. These conditions arenot dealt with in the document.

The critical axial load, Q crit, for a pipe as a column can be calculated using the following equationprovided that the foundations do not restrain rotation of the pipe.

Q crit =x x x2

b

π E

l

I

... (E.1)

where:

Q crit is the critical buckling load for the pipe as a column;

E x is the elasticity modulus of the pipe material in the longitudinal direction;

is the moment of inertia;

l b is the buckling length.

For pipes simply supported at the ends the influence of axial force on moments and deflections can beapproximated by the magnification factor in the following equation.

1

1 -crit

Q / Q

where:

Q is the net sum of all axial loads acting on the pipe and in the liquid column.

For pipes where the influence of the axial force is significant both buckling, stress/strain and deflectionshall be checked. In Figure E.1 typical limitations depending on pipe diameter and pressure for

single-span and multiple-span installations are shown.

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key

1 Pressure2 Buckling3 Stress4 Angular movement5 Diameter

Figure E.1 — Typical limitations

It is important to be aware of the fact that plastics materials have time-dependent material properties,

i.e. creep. It is obvious that this affects the phenomenon mentioned above, and that materialproperties corresponding to the load duration are used. These properties should be verified by themanufacturer.

E.2 Loads

The loading conditions have been split into two classes:

a) those acting in the axial direction, i.e. thermal, Poisson, pressure;

b) those acting normal to the pipe axis, i.e. pipe weight, content, snow, wind etc.

The applicable axial loads will vary with type of installation and type of jointing system used.

Thermal and Poisson loads are generated when rigid joints, such as flanged, cemented or locked joints, are used in a restrained system. These forces can also be generated when clamping typefixtures are used, which develop significant frictional constraints in the system.

E.2.1 Thermal load

For a straight and constrained pipe subject to a change in temperature:

F T E d e e e ϑ

π= x x x x x - xL

α ∆ ... (E.3)

where:

F is the thermal load; L is the coefficient of thermal expansion;

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T is the temperature difference creating temperature load;

e is the pipe wall thickness.

For other arrangements, or more detailed consideration of thermal expansion/contraction, see

Annex B.The load can be either tensile or compressive depending upon whether the temperature change ispositive or negative.

E.2.2 Poisson load

For a straight piece of pipe which is constrained and subject to an internal pressure:

( )F p d e v p E

E v e

2 x

H

= 0,5 x x - x x x ... (E.4)

where: F

is the Poisson load;

is the Poisson ratio;

p is the internal pressure in the pipe;

E H is the hoop tensile modulus of elasticity.

The load is tensile.

E.2.3 Load due to pressure

In pipe systems where the reaction force from the water pressure is resisted by the pipe itself, i.e.

biaxial pressure, the force can be calculated using the following equation:

F d p p i

2= 0 ,25 x x xπ ... (E.5)

where:

F p is the load due to pressure;

d i is the internal pipe diameter.

The load is tensile.

In pipe systems where also the pipe ends are exposed to the water pressure, i.e. flexible joints, theforce acting in the pipe can be calculated using the following equation:

F d e e p p e

= x - x xπ ... (E.6)

The load is compressive.

E.2.4 Self weight of pipe

The uniformly distributed load, q 0, arising from the mass of the empty pipe can be calculated using thefollowing equation:

q d e e 0 0 e

= x x - xπ γ ... (E.7)

where:

q 0 is the self weight of pipe per unit length;

0 is the apparent specific weight of the pipe.

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E.2.5 Weight of liquid

The uniformly distributed load, q l, arising from the mass of liquid contained when the pipe is full can becalculated using the following equation:

q d l l i2= 0 ,25 x x xπ γ ... (E.8)where:

q l is the weight of fluid per unit length;

l is the specific weight of the fluid.

E.2.6 Environmental loads

The most commonly encountered environmental loads are snow and wind, but in some areas otherloads such as icing, seismic, tidal etc. may need to be considered.

E.2.6.1 Snow

In conditions where a liquid, at a temperature above zero, is flowing in the pipe snow load is usuallynot applicable.

In most areas where snow is a significant load guidance on how to deal with it can be found in nationalcodes.

The loading conditions resulting from snow can vary from a simple uniformly distributed load acrossthe top of the pipe to more complex total burial producing embankment type of conditions.

For the case where a uniformly distributed load can be taken as the loading condition then:

q d h s s e s= x xγ ... (E.9)where:

q s is the weight of snow per unit length of the pipe;

s is the specific weight of snow;

h s is the depth of snow.

E.2.6.2 Wind

Usually wind loads are not of importance for the design of the pipe, but can be significant for thedesign of the supports. However, such loading can be very complex and consideration of it is beyond

the scope of this annex. Specialized reports and design guides are however available for mostcommonly encountered conditions.

E.3 Water column compression

In every pressurized pipe system the water column has to be constrained by the pipe. As a conclusionfrom this it has to be accounted for the axial compressive force in the system.

For a pipe supported as a beam the midspan deflection resulting from lateral loads, i.e. self weight ofpipe and liquid content, produces a moment from the axial load in the system, which further increasesthe moment and deflection as a function of the pressure, the cross-sectional area of liquid column and

the radius of curvature of the deflected pipe.

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Because of the relatively low E-modulus of most plastic pipes, this phenomenon has a significantinfluence on deflections in many cases. This applies for pipe systems where the axial pressure thrustis not, or is only partially carried by the pipe itself.

This same phenomenon also needs to be considered when pipes are jointed with double bellcouplings or "sleeves". A slight tilting of the coupling results in angular deviation between the couplingand the pipes. The axial pressure force and the angular deviation between coupling and pipes resultsin a pair of reaction forces acting on the pipe ends. If pipes are installed with long cantilevered endsthese reaction forces cause deflection of the pipe ends that in turn cause additional tilting of thecoupling. If the joint is far from the pipe support this situation can be unstable unless the coupling isrestrained from tilting.

E.4 Deflection

E.4.1 Midspan deflection

The deflection of the midspan depends not only on the loads applied to the pipe but also whether it is asimply supported condition or multiple span condition. Table E.1 gives the necessary equations andmultiplication factors to take into account the added load from the internal pressure for various ratios ofQ / Q crit for various support conditions.

Table E.1 — Deflection

Single span Double span Single span Multiple span Single/multiplespan

Simplysupported

Simplysupported

Simply & fixedsupport

Simplysupported

Fixed supports

Q crit π2

2

E I

l

π2

2

E I

l

π2

2

E I

l

Maximumdeflection

5 x

384 x1

4f q

E

l

I

f q

E

14x

384 x

l

I

f q

E

14x

384 x

l

I

Q /Q critDeflection multiplication factor, f 1

0,1

0,20,30,40,5

1,11

1,251,431,672,00

1,03

1,051,081,111,14

1,11

1,251,421,661,99

E.4.2 Angular movement at joint due to bending

NOTE This clause is only applicable to flexibly jointed pipes.

The angular movement at the joint depends not only on the loads applied to the pipe but also whetherit is a simply supported condition or multiple span condition, like for the midspan deflection. Table E.2

gives the necessary equations and multiplication factors to take into account the added load from theinternal pressure for various ratios of Q / Q crit for various support conditions.

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Table E.2 — End rotation


Simplysupported

Simplysupported


Simplysupported

Fixed supports

Q crit π2

2

E I

l

π2

2

E I

l

2,05 2

2π

E I

l

Endrotation

f q

E

24x

24 x

l

I

f q

E

24x

48 x

l

I

f q

E

24x

48 x

l

I


0,10,20,30,40,5

1,111,251,421,661,99

1,051,111,171,251,33

1,111,251,431,682,02

E.5 Stresses

When comparing the stresses calculated using the following equations with the allowable stresses forthe pipe, it is important to be aware of the time dependency in material properties, i.e. creep, aging etc.

E.5.1 Local stresses at supports

For a pipe supported at intervals on saddles or pedestals and filled or partly filled with liquid, the stressanalysis is difficult and the results are rendered uncertain by doubtful boundary conditions. For thesereasons such localized stress analysis is not included in this annex.

E.5.2 Axial stresses

For the net sum of the axial loads, determined from clause E.2, the axial normal stresses can bedetermined using the total pipe cross-sectional area:

σ n

p

=F

A... (E.10)

where:

n is the axial normal stress;

F is the net sum of axial loads;

Ap is the area of a pipe cross-section, π x - xe

d e e .

The bending stresses can be determined using the following equation:

σ b

b e= x2 x

M d

I

... (E.11)

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where:

b is the axial bending stress;

M b is the bending moment.

The relevant moment equations are given in Tables E.3 and E.4.

Table E.3 — Maximum moment


Simplysupported

Simplysupported


Simplysupported

Fixed supports

Q crit π22

E

l

I

π22

E

l

I

2,05 22

πE

l

I

π22

E

l

I

4 22

πE

l

I

Maximummoment

f ql

E

34x

8 x I

9 x

128 x3

4f ql

E I

9 x

128 x3

4f ql

E I

f ql

E

34x

24 x I

f ql

E

34x

24 x I


0,10,20,30,40,5

1,111,261,441,692,03

1,031,071,111,161,21

1,071,171,281,441,65

1,021,031,051,071,09

1,071,161,281,431,64

Table E.4 — Minimum moment


Simplysupported

Simplysupported


Simplysupported

Fixed supports

Q crit π22

E

l

I

2 05, π22

E

l

I

π22

E

l

I

4π22

E

l

I

Minimummoment

- f ql

E

34x

8 x I

- f ql

E

34x

8 x I

- f ql

E

34x

12 x I

- f ql

E

34x

12 x I


0,10,20,30,40,5

1,031,071,111,161,21

1,071,171,281,441,65

1,021,031,051,071,09

1,071,161,281,431,64

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E.6 Buckling

Buckling of a pipe wall will occur if the pipe wall becomes unstable due to high external loadsgenerated by one or more of the following:

soil load; water table;

traffic load;

superimposed load,

or it may become critical where negative pressures occur.

Buckling can occur in two different ways, namely:

long-term or creep buckling as a result of external pressure or internal negative pressure over aperiod of time;

short-term or elastic buckling as a result of rapid transient external pressure or an internalnegative pressure.

Pipes subjected to prolonged external loads such as soil load, water table and/or superimposed loadcan experience creep buckling.

Pipes subjected to rapid intermittent external loads such as traffic load or internal negative pressure inconjunction with prolonged external loads can experience elastic buckling.

E.6.1 Global buckling

E.6.1.1 Due to negative pressure

A pipe installed above-ground can have a global buckling failure due to two different loadingconditions. The pipe can fail due to high negative pressure and it can fail as a column due to too highaxial compressive forces.

Global buckling due to high negative pressure can be calculated using the following equation:

( ) ( )p

E e

L d e v

e

d e

critH

2

s e2

3 2

e

2

0,25

x

x -x

1

1 -x

-= 2,283 x

... (E.12)

where:

p crit is the critical negative pressure creating global buckling;

LS is the length of pipe span between support centres.

E.6.1.2 Due to compressive axial force

Global buckling due to high compressive axial forces can be determined using the following equation:

Q crit

2x

b2=

x xπ E

l

I

... (E.13)

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The buckling lengths, l b, for various boundary conditions are given in the following figures.

E.6.1.2.1 Single span installation simply supported

Figure E.2 — Simply supported single span pipe installation

The buckling length for a simply supported single span installation is equal to the total pipe length (see

Figure E.2).

It is assumed that the joint does not resist rotation, i.e. the joint acts as a hinge.

E.6.1.2.2 Double span installation simply supported

Figure E.3 — Simply supported double span pipe installation

The buckling length for a simply supported double span installation is equal to the total pipe length(see Figure E.3).

It is assumed that the joint does not resist rotation, i.e. the joint acts as a hinge.

E.6.1.2.3 Multiple span installation simply supported (equal spans assumed)

Figure E.4 — Simply supported multiple span pipe installation

The buckling length for a simply supported multiple span installation can be taken to be equal to the

distance from the pipe end to the second support (see Figure E.4).It is assumed that the joint does not resist rotation, i.e. the joint acts as a hinge.

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E.6.1.2.4 Single/multiple span installation with fixed supports

Figure E.5 — Fixed supported single/multiple span pipe installation

The buckling length for a fixed supported single/multiple span installation is equal to the span betweensupports (see Figure E.5).

E.6.2 Local buckling

High compressive stresses can create a locally unstable situation and buckling will occur. Localbuckling can be checked using the following equations:

Maximum compressive stress:

σ σ σ c, max c, n c, b

= + ... (E.14)

where:

c,max is the maximum axial compressive stress;

c,n is the axial compressive normal stress;

c,b is the axial compressive bending stress.

Critical compressive stress:

( ) ( )[ ]σ

γ

c, critH

e2

0,5=

2 x x x

- x 3 x 1 -

E e

d e v

... (E.15)

where:

c,crit is the critical axial compressive stress;

is the correction factor according to Figure E.6.

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key

1 Correction factor

Figure E.6 — Correction factor,

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Bibliography

The following documents have served as references in the preparation of this prestandard:ISO/TR 4191:1989, Unplasticized polyvinyl chloride (PVC-U) pipes for water supply —

Recommended practice for laying (published version)

ISO DTR ISO/TC138/SC2 N 563, 1985-07-01, Polyethylene (PE) pipes for the conveyance of water

under pressure — Recommended practice for laying

ISO Draft 11 (October 1988) of Technical Report, ISO/TC138/SC6/WG4 N 117, Underground

installation of flexible glass fibre reinforced thermosetting resin (GRP) pipes

ISO/TR 7073:1988, Recommended techniques for the installation of unplasticized poly(vinyl chloride)

(PVC-U) buried drains and sewers

BS 5930:1981, Code of practice for site investigations

DIN 18127:1993 E, Soil; testing procedures and testing equipment ; Proctor test (Baugrund; Versuche

und Versuchsgeräte; Proctorversuch )

DIN 18196:1988 E, Soil classification for civil engineering purposes (Erd- und Grundbau —

Bodenklassifikation für bautechnische Zwecke )

ATV Arbeitsblatt A 127, Richtlinie für die statische Berechnung von Entwässerungskanälen und

-leitungen , 2. Auflage 1988 (ATV Work Sheet A 127 Guidelines for Static Calculation of

Drainage Conduits and Pipelines , 2nd edition 1988) (published by: Gesellschaft zur Förderungder Abwassertechnik e. V., St. Augustin, Germany)

KRV Richtlinie, Planungs- und Konstruktionshinweise für GFK-Rohrleitungen ; Ausgabe August 1981(Planning and Design for Piping made of Fibreglass Reinforced Plastics , August 1981 edition)(published by: Kunststoffrohrverband e. V., Bonn, Germany)

Janson, Molin:January 1991, Design and installation of buried plastics pipes (published by:AKA-PRINT ApS, Århus, Denmark)

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