SIST-TP CEN/TR 1046:2014

SLOVENSKI STANDARD
01-februar-2014
1DGRPHãþD
SIST ENV 1046:2002
SIST ENV 1401-3:2002
SIST-TS CEN/TS 14758-3:2006
SIST-TS CEN/TS 1852-3:2003
SIST-TS CEN/TS 1852-3:2003/A1:2005
Cevni in kanalski sistemi iz plastomernih materialov - Sistemi zunaj stavb za
transport vode ali kanalizacije - Postopki za vgradnjo pod zemljo
Thermoplastics piping and ducting systems - Systems outside building structures for the
conveyance of water or sewage - Practices for underground installation
Thermoplastische Rohrleitungs- und Schutzrohr-Systeme - Systeme außerhalb der
Gebäudestruktur zum Transport von Wasser oder Abwasser - Verfahren zur
unterirdischen Verlegung
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 la pose en
aérien et en enterré
Ta slovenski standard je istoveten z: CEN/TR 1046:2013
ICS:
23.040.20 Cevi iz polimernih materialov Plastics pipes
93.025 Zunanji sistemi za prevajanje External water conveyance
vode systems
93.030 Zunanji sistemi za odpadno External sewage systems
vodo
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 1046
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
December 2013
ICS 23.040.01 Supersedes CEN/TS 14758-3:2006, CEN/TS 1852-
3:2003, ENV 1046:2001, ENV 1401-3:2001
English Version
Thermoplastics piping and ducting systems - Systems outside
building structures for the conveyance of water or sewage -
Practices for underground installation
Systèmes de canalisations et de gaines en matières Thermoplastische Rohrleitungs- und Schutzrohr-Systeme -
thermoplastiques - Systèmes d'adduction d'eau ou Systeme außerhalb der Gebäudestruktur zum Transport
d'assainissement à l'extérieur de la structure des bâtiments von Wasser oder Abwasser - Verfahren zur unterirdischen
- Pratiques pour la pose en enterré Verlegung

This Technical Report was approved by CEN on 9 March 2013. It has been drawn up by the Technical Committee CEN/TC 155.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 1046:2013 E
worldwide for CEN national Members.

Contents Page
Foreword .3
Introduction .4
1 Scope .5
2 Normative references .5
3 Terms and definitions .6
4 Symbols and abbreviations .7
5 Transport, handling and storage at depots and sites .7
5.1 General .7
5.2 Transportation of pipes .8
5.3 Handling .9
5.4 Storage . 10
6 Installation . 10
6.1 Pipes in trenches . 10
6.2 Special installation techniques . 30
7 Methods of assembly (jointing) . 30
7.1 General . 30
7.2 Joints using an elastomeric seal . 31
7.3 Mechanical compression joints . 32
7.4 Other joints and jointing methods . 33
8 Bends . 33
8.1 Cold bending . 33
8.2 Hot bending . 33
9 Inspection and testing . 33
9.1 Inspection . 33
9.2 Testing . 34
Annex A (normative) Classification of soils . 35
Annex B (informative) Behaviour of buried flexible pipes . 37
Annex C (normative) Joint and jointing examples . 39
C.1 General . 39
C.2 Joints capable of resisting end thrust . 39
C.3 Mechanical threaded joints . 45
Bibliography . 47

Foreword
This document (CEN/TR 1046:2013) has been prepared by Technical Committee CEN/TC 155 “Plastics
Piping Systems and Ducting Systems”, the secretariat of which is held by NEN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes ENV 1046:2001, ENV 1401-3:2001, CEN/TS 1852-3:2003 and
CEN/TS 14758-3:2006.
This Technical Report 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 International Organization
for Standardization (ISO) (see Bibliography), modified as necessary to be applicable to piping systems of any
thermoplastics materials and any relevant application.
Introduction
This Technical Report contains guidance for installation procedures for thermoplastics piping systems and
their components intended to be used below ground for pressure and non-pressure applications outside
building structures. It is intended to be used in conjunction with general standards for installation
recommendations, for example those issued by CEN/TC 164 “Water supply” and CEN/TC 165 “Waste water
engineering” as stated in EN 805 and EN 1610 respectively.
NOTE Guidelines for installation of pipelines made out of thermosetting materials can be found in the ISO 10465
series [11, 12, 13].
This Technical Report is based on the results from research with full-scale trials undertaken by the
thermoplastics pipes industry and expressed in CEN/TS 15223.
This Technical Report is a guidance document only. It provides a set of general guidelines which gives best
practices for installation of thermoplastics piping and ducting systems outside building structures underground.
This Technical Report includes recommendations for the pipe surround and backfilling procedures but not
road base and road sub-base details. Attention is drawn to any national regulations which may cover these or
other aspects of installation.
This Technical Report does not cover matters relating to renovation of existing pipeline systems using lining
techniques, or replacement of existing pipeline systems using trenchless techniques.
This Technical Report is intended to be used by authorities, design engineers, installation contractors and
manufacturers.
In this Technical Report, much of the guidance is expressed as requirements, e.g. by use of “shall” or by
instructions 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”.
1 Scope
This Technical Report is applicable to the installation of thermoplastics piping systems to be used for the
conveyance of water or sewage under gravity and pressure conditions underground. It is intended to be used
for pipes of nominal size up to and including DN 1600.
Wherever the term “pipe” is used in this Technical Report, it also serves to cover any “fittings”, “ancillary”
products and “components” if not otherwise specified.
NOTE 1 This document does not apply to pipelines for gas supply (see EN 12007–2, Gas infrastructure - Pipelines for
maximum operating pressure up to and including 16 bar - Part 2: Specific functional requirements for polyethylene (MOP
up to and including 10 bar).
NOTE 2 It is assumed that additional recommendations and/or requirements are detailed in the individual materials
voluntary product standards. Instances where this is expected to apply include those indicated in this Technical Report as
follows:
a) any special transportation requirements (see 5.2);
b) maximum storage height (see 5.2 and 5.4);
c) maximum storage period in direct sunlight (see 5.4);
d) any climatic conditions requiring special storage (see 5.4);
e) limiting initial and/or long-term deflections (see 6.1.1 and 6.1.2);
f) information on mole ploughing and boring (see and 6.2), if applicable;
g) selection of appropriate jointing system (see Clause 7);
h) recommended radii of curvature for cold bending (see 8.1);
i) permitted rates of loss of water under test (see 9.2.1);
j) if applicable the relationship between SDR and stiffness.
Requirements and instructions concerning commissioning of systems can be found in EN 805 and EN 1610
and the relevant national and/or local regulations.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 476, General requirements for components used in drains and sewers
EN 681 (all parts), Elastomeric seals - Materials requirements for pipe joint seals used in water and drainage
applications
EN 805, Water supply - Requirements for systems and components outside buildings
EN 1610, Construction and testing of drains and sewers
CEN/TS 15223, Plastics piping systems - Validated design parameters of buried thermoplastics piping
systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
deflection
deviation of the circle cross section of the pipe (in percent)
3.2
average deflection
measured average deflection over the inspected length of the pipeline (in percent)
3.3
trench
excavation of the soil for the underground embedment of the pipeline
Note 1 to entry: See Figure 1 for an illustration of the meaning and limits of the terms used in this Technical Report.

Key
b width of the cross section
b horizontal clearance between the pipe or fitting and the trench sidewall or an
S
adjacent pipe or fitting
de external diameter of a pipe
1 depth of cover above the pipe
2 height of embedment above the pipe 100 mm to 300 mm
3 ground surface
4 native soil
5 embedment
6 main backfil
7 pipe zone
8 upper bedding (according EN 1610, also known as haunch zone, of which the
height is 1/3 of the pipe diameter)
9 trench bottom
10 lower bedding (according EN 1610)
Figure 1 — Trench cross-section showing terminology
Key
1 slope (0/00, m/km, mm/m)
Figure 2 — Trench axial-section showing slope of the pipeline
4 Symbols and abbreviations
For the purposes of this Technical Report, the following symbols apply:
b width of a trench cross-section (see Figure 1);
b horizontal clearance between the pipe or fitting and the trench sidewall or an
S
adjacent pipe or fitting (see Figure 1, Figure 7 and Table 4);
d (mean) external diameter of a pipe (see Figure 1 and Figure 8);
e
DN/OD nominal outside diameter of a pipe and associated fittings (see Table 4);
e
pipe wall thickness;
M compaction classification: Moderate (see Figure 9 and Table 7);
N compaction classification: Not (see Figure 9 and Table 7);
S initial specific stiffness (see Table 3);
SN stiffness number or classification (see Table 3);
SDR standard dimension ratio (see Table 3)
W compaction classification: Well (see Figure 9 and Table 7);
5 Transport, handling and storage at depots and sites
5.1 General
Thermoplastics pipes may be supplied in straight lengths or coiled forms (either free standing or on drums).
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 exercised when decoiling coiled pipes
as considerable forces can be released.
Additional information should be given in the System Standards, if applicable.
For additional explanations, see Figure 3 to Figure 5 which deal with transport, handling and storage.
5.2 Transportation of pipes
When transporting pipes or pipe package, vehicles should be used. The bed shall be free from nails and other
projections. When practicable, pipes should rest uniformly on the vehicle.
Secure the pipes or pipe package effectively before transporting. When pipes are transported in bundles, the
bundles should be secured effectively and off loaded as described hereunder.
When loading socketed pipes, the pipes should be stacked on the vehicle so that the sockets do not take
loads.
The largest diameter pipes should be placed on the bed of the vehicle.
Care should be taken to avoid positioning the pipes near to any exhaust systems or any other potential
hazards such as diesel oil.
Pipes should be inspected by the purchaser or his representative for damage and compliance with the order
during unloading at the destination.
When pipes and/or fittings require special transportation practices, the manufacturer shall notify the customer
of the procedures to be used.
Figure 3 — Transport
Figure 4 — Handling and storage

Figure 5 — Preferred pipe packaging
NOTE Attention is drawn to the need to conform to national and/or local transport regulations.
5.3 Handling
When handling the pipes, care shall be taken to prevent damage.
When pipes are to be handled individually, they should be lifted, lowered and carried in a controlled fashion
and should never be thrown, dropped or dragged (see Figure 4).
It is preferable to use fabric slings or rope to lift the pipe or pipe bundle. Metal bars, slings, hooks or chains will
damage the pipe if they are used incorrectly. When loading or unloading pipes, pipe bundles with forklift
equipment, only forklift trucks with smooth or suitably protected forks should be used. Care should be taken to
ensure that forks do not strike the pipe when lifting.
The impact resistance of thermoplastics pipes is reduced at low temperatures; under these conditions, take
more care during handling. Where cold conditions are expected, the advice of the manufacturer should be
sought.
When loosening a coil, personnel should be aware of potential danger in the operation.
5.4 Storage
Although thermoplastics pipes are light, durable and resilient, take reasonable precautions during storage.
When it is intended to store pipes or coils on site in stacks, the manufacturer's advice regarding correct
practice should be sought.
Stack the pipes or coils on reasonably flat surfaces free from sharp objects, stones or projections in order to
avoid localized deformation or damage to the pipes. For the maximum stacking height, see the manufacturer's
technical documentation.
Where pipes are supplied with end caps, plugs or wrappings, these should be removed prior to jointing.
Do not place pipes or rubber seals in close proximity to fuels, solvents, oils, greases, paints or heat sources.
Storage in direct sunlight for long periods and/or high temperatures could cause deformations affecting the
jointing.
To avoid this risk, the following precautions are recommended:
a) limit the height of the stacks of pipes;
b) shield the stacks of pipes from continuous and direct sunlight and arrange to allow the free passage of air
around the pipes;
c) store the fittings in boxes or sacks manufactured so as to permit the free passage of air.
The fading of the colour caused by outside storage does not affect the mechanical properties of pipes and
fittings.
If pipes are supplied in a bundle or in other packaging, the restraints and/or packaging should be removed as
late as possible prior to installation.
6 Installation
6.1 Pipes in trenches
6.1.1 Behaviour of flexible pipes under load
The behaviour of a pipe, when subject to a load, depends upon whether it is flexible, semi-rigid or rigid (see
EN 476). Thermoplastics pipes are flexible. When loaded, a flexible pipe deflects and presses into the
surrounding material without fracture. This generates a reaction in the surrounding material which controls
deflection of the pipe. The amount of deflection which occurs is limited by the care exercised in the selection
and laying of the bedding and side-fill materials. Hence, flexible pipes rely on the bedding and side-fill
materials for their load-bearing properties.
The level of deflection reached by a buried pipe depends on the properties of the surrounding material and to
a much lesser extent on the stiffness of the pipe but not on its strength properties. Therefore, for flexible pipes,
the crushing strength test and design procedures applied to rigid pipes are not appropriate.
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 a reasonable period of
time. The use of the installation procedures detailed in this Technical Report will minimize the levels of both
the initial and final deflections. If the pipeline is pressurized then a reduction in the amount of deflection will
occur. A more detailed description of this behaviour is given in Annex B.
6.1.2 Limiting deflection
There are several methods of structural design (see EN 1295-1:1997 [1]) that are used to estimate the
deflection 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 the expected average
deflections.
Pipes made from different materials have different limiting deflection levels. For the applicable maximum
permissible initial and, if appropriate, long-term deflection see Table 1, Figure 6, Annex B and the relevant
System Standard. If this document is followed, it is expected that the deflections will be less than the limiting
values given in Table 1 or the relevant System Standards.
Table 1 — Recommended allowable average deflection for thermoplastic pipes for gravity applications
Way of installation Recommended allowable Remark
average deflection
a
Installation according to this ≤ 8 % Based on measured
Technical Report deflection values short after
installation, at commissioning

NOTE 1 Thermoplastics pipes allow high deflection because of the huge strain-ability of these
materials. Strain-ability and pipe wall stability are checked in the ring flexibility test during which the
pipes are deformed up to 30 % deflection.
NOTE 2 For pressure applications after pressurization a re-rounding effect takes place.
NOTE 3 For long-term deflection see Annex B.
a
At commissioning, local initial maximum deflection in pipelines may be allowed for PVC-U ≤ 10 %

and for PE and PP ≤ 12 %.
Where it can be expected that a product covered by the System Standard may be delivered with some
distortion, e.g. pipes delivered in coils, then this should be stated. The average deflection is to be assumed to
be in addition to this distortion.
6.1.3 Design considerations
6.1.3.1 General
If it is essential to determine the soil conditions that relate to trench construction and pipe installation prior to
construction; the native soil and the backfill material shall be classified in accordance with Annex A. The
classification shall be used to choose a suitable pipe stiffness in accordance with 6.1.3.2.
NOTE The classification will also indicate the areas of suitable materials for pipe zone backfill, so that importation of
material may be minimized. Native materials conforming to Table A.1 are all suitable as backfill in the pipe zone. If backfill
materials have to be imported, it is suggested that group 1 or 2 materials are used.
6.1.3.2 Choice of pipe stiffness
The choice of pipe stiffness shall be made either using the tables or Figure 6 in this Technical Report or on the
basis of calculations in accordance with CEN/TS 15223 or on the basis of previous experience.
Where calculations show that a pipe stiffness lower than that given in Table 2 or Table 3 is appropriate, then
pipes with this lower stiffness may be used. Where pipes are intended to be used in conditions where they
have by previous experience proved to be satisfactory it is not necessary to verify this by detailed calculation
even though their stiffness may be lower than the appropriate value given in Table 2 or Table 3.
If such experience is not available then the minimum stiffness required shall be selected from Table 2 or
Table 3. 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 2);
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 0,6 m or more
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 give the
equivalent stiffness values in its relevant part.
Generally, the choice of pipe stiffness depends upon the native soil, the pipe zone backfill material and its
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 been classified
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 selected from
Table 2 or Table 3. Using a pipe of this stiffness installed in an embedment formed from the appropriate
backfill material compacted to the specified degree of compaction should result in deflections of not more than
the limiting values given in the relevant System Standard.
Designers first need to establish permitted deflections, average and maximum. (National requirements product
standards, this Technical Report, etc. offer guidance.)
For the deflection mentioned in the design graph, the strain will be far below the design limit.
Key
A nominal ring stiffness I well compacted
B initial deflection, as a percentage II moderate
III non-compacted
Figure 6 — Design graph for determining the pipe deflections depending on Installation type
Table 2 — Validity of the design graph
Pipe system Fulfilling requirements in EN 1401-1 [2], EN 1852-1 [3], EN 12666-1 [4],
EN 13476-2 [5], EN 13476-3 [6] or EN 14758-1 [10] as applicable.
Installation depth 0,8 m – 6,0 m
Traffic loading Included
Installation quality “Well” compaction
Embedment granular soil is carefully placed in the haunching zone and
Installation categories
compacted followed by placing the soil in shift of a maximum of 30 cm after which
“well”, “moderate” (and
each layer is compacted carefully. The pipe should be covered at least by a layer
“none”) should reflect the
of 15 cm. The trench is further filled with soil of any type and compacted. Typical
workmanship on which
values for the standard proctor density are above 94 %.
the designer can rely.
“Moderate” compaction
Embedment granular soil is placed in shifts of a maximum of 50 cm, after which
each layer is compacted carefully. The pipe should at least be covered by a layer
of 15 cm. The trench is further filled with soil of any type and compacted. Typical
values for the standard proctor density are in the range of 87 % to 94 %.
“None” compaction
Sheet piles should be removed before compaction, in accordance with the
recommendations in EN 1610. If, however, the sheet piles are removed after
compaction, one should realize that the “well” or “moderate” compaction level will
be reduced to the “none” compaction level.
Additional National rules may apply.
Deflections were verified for pipe diameters up to and including 1 600 mm. However, when applying the
volume approach technique, it was found that the graph is also valid for bigger diameters.
6.1.3.3 Selection of fitting stiffness or class
Because of their geometry, solid-wall fittings have a stiffness greater than the stiffness of the pipe with
corresponding wall-thickness series. Therefore, the recommended stiffness classes/wall-thickness series of
fittings for use with structured-wall pipes given in Table 3 applies:
Table 3 — Minimum fitting classes recommended for use with structured wall pipes
Pipe stiffness Minimum stiffness of fittings according Minimum wall-thickness series of fittings
class to: according to
EN 13476-2 [5]
and EN 13476-3 EN 14758-1 [10] EN 1852-1 [3] EN 1401-1 [2] EN 12666-1 [4]
[6]
SN 2 SN 2 SN 4 S 20 SDR 51 SDR 33
SN 4 SN 4 SN 4 S 20 SDR 51 SDR 33
SN 8 SN 8 SN 8 S 16 SDR 41 SDR 26
SN 16 SN 16 — S 13,3 SDR 34 SDR 21
6.1.3.4 Types of installation
The two most commonly used practices for the installation of thermoplastics pipes are either to surround the
pipe with the same material (see Figure 7) or splitting the surround into two materials or degrees of
consolidation (see Figure 8). The use of such a split embedment is normally only found to be practical with
pipes of nominal sizes greater than DN 600.
Key
1 embedments surrounding the pipe
2 lower- bedding
b trench width for compaction
s
Figure 7 — Trench with full surround pipe zone

Key
1 split level
2 secondary pipe zone backfill
first backfill (upper bedding): 0,5 d ≤ height ≤ 0,7 d
e e
4 lower bedding
5 invert
Figure 8 — Trench with split surround pipe zone
If a split embedment is used it is important that the split level between the lower and upper material should
occur at between 50 % and 70 % of the pipe diameter above the bedding (see Figure 9). This is 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 surround, the
following rules shall be applied:
a) The material in the lower-bedding zone (see Figure 8) of a split surround should be at least one grade
stiffer than that required in the pipe zone of a full surround, where a grade is a particular combination of
material group and a compaction class, a change by one step in either of which comprises a one-step-
change of grade. Thus, the one grade change may be achieved by either increasing the compaction class
or using a higher group of material (see Table 5). For instance, if an application using a full surround
requires backfill material group 2 moderately compacted, then a split surround would require either a well
compacted group 2 material or a group 1 material with moderate compaction.
b) The material in the secondary pipe zone (see Figure 8) of a split surround may be up to two grades less
stiff than that in the pipe zone of a full surround. Care shall be taken that the maximum total difference
between primary and secondary pipe zone is not more than two grades. 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 an uncompacted material of group 4. For instance, for the case
described in item a), the requirements would be fulfilled in the secondary pipe zone by using
uncompacted group 2 (one grade lower) or moderately compacted group 3 (also one grade lower) or
uncompacted group 3 (three grades lower) material. The last option is not allowed because in this case
the maximum two grades difference would be exceeded.
6.1.3.5 Parallel piping systems
Parallel piping systems laid within a common trench shall be spaced sufficiently far apart to allow compaction
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 used is considered as a practical
clearance between the pipes.
The pipe zone backfill material between the pipes shall be compacted to the same compaction class as the
material between the pipe and the trench wall.
In cases of parallel piping systems laid within a stepped trench (see Figure 9), the pipe zone backfill material
for both pipes shall be granular and shall be compacted to compaction class W.

Key
1 well compacted zone (class W)
Figure 9 — Parallel pipes in a stepped trench
6.1.4 Trench construction
6.1.4.1 Safety
Operations in trenches are carried out in potentially hazardous conditions.
Where appropriate, shore, sheet, brace, and slope or otherwise support the trench walls to protect any person
in the trench. Take precautions to prevent objects from falling into the trench, or its collapse caused by the
position or movements of adjacent machinery or equipment, whilst the trench is occupied.
Excavated material should be deposited at a distance of not less than 0,5 m from the edge of the trench, and
the proximity and height of the spoil bank should not be allowed to endanger the stability of the excavation.
NOTE Attention is drawn to any local and/or national safety regulations.
6.1.4.2 Trench width
The width of the trench at the springline of the pipe need not be greater than necessary to provide adequate
room for jointing the pipe in the trench and compacting the pipe zone backfill at the haunches. Typical values
for b (see Figure 1) are given in Table 4.
S
Wider trenches may be necessary for installations involving, e.g. relatively deep burial or unstable native soils.
Narrower trenches may be used when the system design permits or access by persons is not required.
Table 4 — Typical values for b
S
Nominal size b
S
DN/OD
mm
DN/OD ≤ 225 200
225 < DN/OD ≤ 350 250
350 < DN/OD ≤ 700 350
700 < DN/OD ≤ 1 200 425
1 200 < DN/OD 500
Furthermore, the minimum trench width shall be the greater of the values taken from Table 4 and Table 5.
Table 5 — Minimum trench width in relation to trench depth
Trench depth Minimum trench width
m M
< 1,00 no minimum width required
≥ 1,00 ≤ 1,75 0,80
> 1,75 ≤ 4,00 0,90
> 4,00 1,00
6.1.4.3 Trench depth
Determine the trench depth by the pipeline design, intended service, pipe properties, size of pipe and local
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 passing under
traffic areas should usually be a minimum of 600 mm, although shallower depths may be used when the
installation is designed accordingly.
When determining the trench depth, allowance for a suitable bedding should be incorporated.
Take care to ensure that the burial depth is sufficient to prevent the conveyed fluids from being affected by
frost.
Sufficient cover should be provided to prevent accidental pipe flotation in potentially high ground water areas.
It is generally recommended not to dig the trench too far in advance of pipe laying and to backfill as soon as
possible after pipe laying. In frost conditions, it may be necessary to protect the trench bottom so that frozen
layers are not left under the pipe.
6.1.4.4 Trench bottom
6.1.4.4.1 Under-bedding
The under-bedding at the trench (see Figure 1) shall be continuous, uniform and free of particles greater than
those specified in Table 6 for the applicable pipe size.
6.1.4.4.2 Over-excavation
Where rock, cobbles or hardpan are encountered, over-excavate the trench bottom.
Quick sands or similar soils, organic soils or soils that exhibit a volume change with a change in moisture
content may be encountered in the bottom of the trench. In such cases, the engineer may specify that further
excavation be carried out and a foundation zone be provided. Each such situation shall 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 is
recommended that the material for the foundation zone shall be the same as for the lower-bedding zone and
shall be compacted to class W (see 6.1.6.3).
Compact the foundation material uniformly in accordance with 6.1.6.2 and 6.1.6.3.
6.1.4.4.3 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 10 can provide a solution. However, where large-scale soil movements
are anticipated, this solution may not be effective. In such cases, it is recommended to seek expert advice.
Special conditions which may be encountered during laying include running or standing water occurring in the
bottom of the trench, or the bottom of the trench exhibiting a quick tendency. In these cases, remove the water
by such means as well points or under-drains until the pipe has been installed and the trench backfilled to a
height sufficient to prevent flotation of the pipeline or collapse of the trench. 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 trench bottom or walls, and material from the trench bottom or
walls will not migrate into those areas. Any migration 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 be prevented by use of a suitable filter fabric, as shown in Figure 10.
Key
1 ≥ pipe zone
2 bedding
3 filter geotextile
Figure 10 — Protection against material migration
If filter fabrics are welded together, the fabrics shall be laid with at least 0,3 m overlapping. Un-welded fabrics
shall be laid with an overlap of at least 0,5 m.
When the soil is weak or soft such that it is not possible for persons to work safely in the trench then
reinforcement of the trench may be necessary before laying the bedding. Reinforcement of the trench bottom
can be made using a wooden mattress (see Figure 11), reinforced concrete or geotextiles. If the ground 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 11 — Trench bottom reinforced by a wooden mattress
Typical uses of geotextiles are shown in Figure 12 to Figure 15.

Key
1 geotextile
Figure 12 — Geotextile reduces uneven settlement in soil transition zones
Key
1 geotextile
Figure 13 — Geotextile forms a partial ground-beam containment and support

Key
1 geotextile
Figure 14 — Geotextile forms a total ground-beam, containment and support
Key
1 geotextile
Figure 15 — Geotextile acts as an anchor to prevent flotation
If pipes conveying water or sewage are installed at depths shallower than the expected frost penetration
depth, thermal insulation shall be provided.
Thermal insulation should be made of expanded polystyrene foam panels, or of other insulating material
suitably protected from the ingress of moisture, located in accordance with Figure 16.
The choice of insulation arrangement according to Figure 16 shall be made with regard to the frost
susceptibility of the native soil and the backfill material.
a) Thermal insulation in clayey and b) Thermal insulation at deeper frost
silty clay soils penetration depths in granular soils

c) Thermal insulation on shallow d) Thermal insulation using preformed
trenches extruded polystyrene shells
Figure 16 — Examples of thermal insulation of buried pipes
6.1.4.4.4 Bedding
A pipe requires uniform support for the whole of its length and this is provided by the bedding layer. To
provide this uniform support, the bedding layer should generally have a thickness of 100 mm to 150 mm and
be not less than 50 mm.
The material used shall be granular, such as gravel, sand or crushed rock, and shall conform to 6.1.6.3.
The bedding material should be spread evenly across the full width of the trench and levelled to the gradient
of the pipeline and, if necessary, compacted .
In uniform, relatively soft, fine-grained soils free from large stones and other hard objects, and where the
bottom can readily be brought to an even finish providing a uniform support for the pipes over their whole
length, it may be satisfactory to lay pipes with nominal sizes up to and including DN 700 directly on the
trimmed bottom of the trench.
6.1.4.4.5 Jointing preparation
Where appropriate to allow for proper assembly of the joint or to prevent the weight of the pipe from being
carried on the joint, provide a jointing hole beneath the joint. The jointing hole shall not be larger than is
necessary to accomplish proper joint assembly. When the joint has been made, carefully fill and compact the
jointing hole with bedding material to provide continuous support of the pipe throughout its entire length.
6.1.5 Pipe installation, procedures and control
6.1.5.1 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 and possible
contamination.
6.1.5.2 Laying
Lay the pipe in the trench so that it bears evenly on the bedding throughout its length. Make allowances for
thermal movement, particularly if laying takes place in extreme weather conditions. Make the joint in
accordance with the manufacturer's recommendations.
6.1.5.3 Angular deflection
During installation the direction of the pipe may be changed at the joint by up to the maximum angle of
deflection declared by the manufacturer.
NOTE When changes in direction are made in this way, it is essential to appreciate that the capability of the joint to
tolerate ground movement has been reduced.
Alternatively, make changes in direction by using fittings or, if the pipe material's properties are suitable, by
cold bending in accordance with where a pipeline enters or exits a structure, such as a building, manhole or
anchor block, means of tolerating differential settlement shall be provided. Typical connections to rigid
structures are shown in Figure 17 to Figure 20. 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 17 or Figure 18. Some materials such
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