Manhole Technical Guide
Manhole Technical Guide
Manhole Technical Guide
UDC
628.24
1: SYSTEM DESIGN 04
1.1 Pipeline Hydraulic Design 04
2: INSTALLATION- PIPES 37
2.1 Planning 37
2.4 Jointing 42
2.5 Reinstatement 44
2.6 Testing 44
3.3 Advantages 47
3.4 Products 48
4: INSTALLATION - MANHOLES 49
4.1 Planning 49
4.3 Construction 49
4.4 Jointing 50
4.5 Reinstatement 51
4.6 Testing 51
1: SYSTEM DESIGN
CONTENTS
1.1 PIPELINE HYDRAULIC DESIGN
1.1.1 Pipeline Design
Background
1. Surface (or Storm) water systems which generally discharge untreated into rivers or water
courses. Surface water includes agricultural, roof or paved areas and highway drainage.
2. Foul water systems that feed into sewage treatment plants. Foul water can be from either
domestic or industrial sources.
Up to the early 20th century, the majority of drainage systems were ‘combined’, that is, the foul
and surface water fed into the same main sewer. More recent installations opted for separate
systems. To further complicate the situation there are partially separate systems where in times
of surface water flooding, provision is made for cross-linking of the two systems. Combined
systems are still sometimes used, although the government is insisting that they are phased
out and replaced by separate systems.
Even today, for some new installations, mis-connections between surface water and foul water
systems are a problem. A clear need exists for improved training and site supervision.
Design considerations
In the design of a surface water or foul water sewer, similar criteria must be considered:-
The volume of water can be estimated by applying one of the traditional methods such as the
Lloyd-Davies or ‘Rational’ method which was modified by TRL and widely used in the UK for many
years. More recently the Wallingford Procedure was introduced by the Hydraulics Research
Station, now HR Wallingford.
This incorporates sophisticated computer programs that take into account the catchment
geography, predicted rainfall intensity, return period and duration of storms, nature of the soil,
percentage of impermeable area (i.e. roads, flags and roofs) and the ranking of the area. The
procedure includes a simplified method that can be applied without the need to refer to the suite
of computer programs.
Foul sewers
Traditionally the volume of flow (generally expressed in litres per second) has been calculated
using the general rule of thumb equations of 4 x dry weather flow for a new sewer with joints
inherently sound or 6 x dry weather flow in the case of a sewer where infiltration might be expected.
1: SYSTEM DESIGN 5
More recently, domestic flow according to “Sewers for Adoption” (Water UK) has been based on
4000 litres/unit dwelling/day. Foul sewage from industrial sources should be assessed taking
account of the type of use of the property; this should be discussed with the local authority’s
planning department to ascertain projected usage and capacity.
There has been extensive research on the comparative roughness - Ks factor - of pipes of
different materials. The findings of HR Wallingford suggest that regardless of material a Ks
value of 1.5mm should be used for all foul sewers and 0.6mm for surface water sewers. These
recommendations have been incorporated within “Sewers for Adoption” as a robust and
practical approach for hydraulic design.
Concrete pipes manufactured to BS EN 1916 and BS 5911-1 readily satisfy these requirements
whether for surface water or foul sewage. For self-cleansing properties, the foul sewer must
flow at a minimum of 0.75 m/sec at one third of the design flow, the main governing factors being
the pipe diameter, the gradient and the volume of effluent. (The larger the pipe and the flatter
the gradient, the greater amount of effluent will be required to achieve self-cleansing velocity).
If there is only a small flow, it is unwise to select too large a pipe “to allow for possible
development” as this may lead to settling out of solids, long retention periods, blockages and
build-up of septicity. A limited period of surcharge and backing up of a sewer is generally
preferable to a consistently low velocity and its attendant problems.
6 1: SYSTEM DESIGN
Design methods
The various design methods used in the UK have been Crimp and Bruges, Manning, Hazen-
Williams, Colebrook-White, Kutter, Chezy, Bazin and Darcy. In recent years the Colebook-White
equation for transitional flow has been adopted by TRL as the basis for their design tables and
has gradually become accepted nationally.
1 = - 2log10 Ks + 2.51
√λ 3.71 Re√λ
Where:
λ = Darcy friction coefficient, 64/Re
Ks = a linear measure of effective roughness (m)
Re = Reynolds number, V D where V = mean fluid velocity (m/s)
ℵ
D = hydraulic diameter of pipe (m)
ℵ = Kinematic viscosity (1.31 x 10-6m2/sec) = μ/ρ (m/s) where
μ = dynamic viscosity (Ns/m2 or kg/ms)
ρ = density of the fluid (kg/m3)
In engineering terms, the expression for transitional pipe flow may be written:
• Tables for the Hydraulic Design of Pipes, Sewers and Channels (8th Edition).
HR Wallingford, DIH Barr, 2006, Thomas Telford.
• Charts for the hydraulic design of channels and pipes. Hydraulics Research Station Sixth
Edition 1990.
It should be noted that the following hydraulic design charts are for reference only to
help demonstrate a basic hydraulic design process. Users should acquire the full
HR Wallingford publication if they wish to carry out their own design projects. Pipe
networks, with interconnecting branches, manholes and changes in pipe size, direction
and gradients are far more complex design challenges and would normally require
computer modelling software.
1: SYSTEM DESIGN 7
Chart A1. Relative Velocity and Discharge in a Circular Pipe for any Depth of Flow.
1.0
0.9
0.8
0.7
Proportional Depth of Flow
0.6 E
A RG
S CH
L DI
0.5 NA
RTU
O PO
PR
0.4
0.3
Y
OCIT
EL
0.2 A LV
UN
O RT
OP
PR
0.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
For design purposes Water UK, via ‘Sewers for Adoption’, recommends Ks values of 0.6mm
for surface (storm) water and 1.5mm for foul sewers irrespective of pipe material. The charts
(A2 and A3) relate to those values. Research has shown that whilst for mature foul sewers the
Ks value may well exceed 1.5mm over short periods of their service this figure is acceptable
as the build-up of slime will reach a maximum and then be reduced by normal flow patterns of
the sewer.
For further detailed information on system design see also ‘BS EN 752 Drain and sewer systems
outside buildings’ and ‘Sewers for Adoption’.
Note: At the time of writing this guide, a European standard, EN 16933-2 should supersede
EN 752 on aspects of hydraulic design for drains and sewer systems
8 1: SYSTEM DESIGN
Chart A3
Example
1(b):
2.14m3/s
Example
1(a):
0.3m3/s
1:153
1: SYSTEM DESIGN 11
1.0
0.9
0.8
Example 2
0.75
0.7
Proportional Depth of Flow
0.6 E
A RG
S CH
L DI
0.5
U NA
O RT
OP
PR
0.4
0.3
Y
Example 1(b)
OCIT
0.25
VEL
0.2 N AL
TU
P OR
PRO
0.1
0
0.14 0.92 1.13
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Step 1: read off 0.25 (a quarter) on the proportional depth of flow y-axis and project a
line horizontally to intersect with the proportional discharge curve
Step 2: at the intersection of Step 1, project a line vertically down to the x-axis
Step 3: read off proportional discharge = 0.14
Step 4: equivalent full pipe flow is 0.3m3/sec /0.14 = 2.14m3/sec
Step 5: from the chart on page 10, project a line horizontally from discharge =
2.14m3/sec on y-axis
Step 6: project a line vertically from hydraulic gradient = 1:153 to intersect with Step 5
Step 7: project line parallel to sloping line for pipe (internal/nominal) diameter lines.
The required pipe size is between DN975 and DN1050. DN975 is insufficient capacity so
select DN1050
12 1: SYSTEM DESIGN
On this chart
Step 5: project horizontal line from y-axis at discharge = 0.11m3/sec
Step 6: project parallel sloping line at velocity = 0.66m/sec
Step 7: Intersection of Step 5 and 6 is between DN450 and DN525. DN450 is
insufficient capacity so select DN525
0.66m/s
Example 2:
0.11m3/s
1: SYSTEM DESIGN 13
The use of sustainable drainage systems, known as SuDS, and best management practices
should be an integral part of any development’s surface water management strategy. This should
provide a basis for replicating the response of a catchment and its surfaces by mimicking,
to some extent, the behaviour of surface water on the developed site as if it had remained
undeveloped. Modern sustainable drainage systems should aim to offer improvements to
existing surface water runoff, negating any increased risk of flooding by using methods for
managing surface water by focusing on three key elements:
It is essential that planners, designers, installers and operators of SuDS systems take into account
the importance of whole life maintenance and the use of suitable components that deliver
authentic sustainable drainage performance and longevity.
Management Train
- Regional Control; e.g. SuDS features within amenity space before final outfall
CPSA members offer a wide variety of proprietary SuDS components and systems suitable for
use within a sustainable drainage system.
These are listed in the following table indicating their functions within the Management Train.
For specific product information, please consult our members.
14 1: SYSTEM DESIGN
Attenuatte
Infiltrate
Convey
Re-Use
SuDS Component
Collect
Treat
Rigid pipeline system with flexible joints for
conveyance of stormwater and storage /
attenuation, available with optional dry weather
Circular pipe • • • flow channel and side entry manhole access.
Perforated version enables stormwater to
percolate into the ground.
Attenuate
Infiltrate
Convey
SuDS Component
Re-Use
Collect
Treat
Hydro-
dynamic Chamber for silt capture, litter and
Vortex • some oils.
Separator
Cascade
Unit • To protect embankments from erosion.
Perforated
For shallow and deep channel
Drainage • • applications.
Trough
Attenuate
Infiltrate
Convey
SuDS Component
Re-Use
Collect
Treat
Rainwater
Domestic and commercial rainwater
Harvesting • • harvesting systems
Tank
Rainwater
Rainwater harvesting pre-tank for leaf and
Filter • grit removal.
Chamber
Grey Water
Domestic and commercial grey water
Recycling • • • recycling systems
Tank
SuDS References
3. Local Authority SuDS Officers Organisation (LASOO). How-to guidance on SuDS standards.
www.lasoo.org.uk/non-statutory-technical-standards-for-sustainable-drainage
5. BS 8582:2013 Code of practice for surface water management for development sites.
6. CIRIA. Designing for Exceedance in Urban Drainage Good Practice C635. www.ciria.org
7. CIRIA. Sustainable Drainage Systems. Hydraulic, Structural and Water Quality Advice C609. www.ciria.org
12. Local Government Association. Flownet Knowledge Hub. A group for all those interested or involved in
flood risk and water management. https://knowledgehub.local.gov.uk/group/flownet
13. National Standards for sustainable drainage systems. Designing, constructing, operating and maintaining
drainage for surface runoff. www.defra.gov.uk
14. For information on SuDS legislation, questions on government policy and to register to receive updates.
email suds@defra.gsi.gov.uk
1: SYSTEM DESIGN 17
B) Soil pressures transmitted to the pipe from surface loads, i.e. traffic and other transient loads.
The weight of water within the pipe is only significant for larger diameter pipes.
a) “Narrow” trench.
b) “Wide” trench, or on the surface of ground over which an embankment is then built (positive
projection condition).
c) Narrow trench over which an embankment is then built (negative projection condition).
The load Wc imposed by the backfill on a pipe in a “narrow” trench can be found from Marston’s
formula from which the Tables have been compiled in Section 1.2.5.
These Tables are only applicable to rigid pipes laid in “Narrow” trench conditions.
Measurements have shown that on large civil engineering works pipes may well be subjected
to their highest loads during construction. Here, three categories of traffic loading are considered
and rigid pipes should normally be designed to withstand the most onerous likely to occur.
If during construction it is clear that excessive site traffic loading will occur, the design should
be checked accordingly or special crossing places must be designated.
a) Main road loading is intended to apply to all main traffic routes and to roads liable to
be used for the temporary diversion of heavy traffic.
As a guide it may be assumed that such roads carry at least 200 commercial vehicles
per day in each direction. HA and HB loading are assumed to use such roads
b) Light road loading applies to all other roads where heavy traffic is unlikely to pass.
c) Field loading applies to fields, gardens and lightly trafficked access tracks. This loading
is also considered to be adequate to cater for occasional heaps or stacks of materials
on the ground surface. Massive heaps or stacks likely to produce a more severe loading
should be treated as a special design.
In assessing the loading category, regard should be paid to the possible future upgrading of a
road. Pipes under verges should normally be treated as though under the road, with the
possible exception of motorways and trunk roads and should take account of any planned road
improvement. For non-public roads such as industrial estate roads or roads within works, an
assessment should be made of the heaviest vehicle likely to use the road, and one of the above
three loading conditions selected as appropriate.
18 1: SYSTEM DESIGN
British Standards for concrete pipes give maximum crushing loads for each diameter and
strength class of pipe. Loads are applied in a 3 edged loading test described in BS EN 1916 and
BS 5911-1. The pipe must not collapse under the maximum load specified.
Proof test loads are also specified. Reinforced pipes must not crack by more than a specified
amount under the proof load. The only proof load test for unreinforced pipes is the maximum load.
Pipes of a small diameter (up to DN 300) may fail as a beam. BS EN 1916 and BS 5911-1
include suitable values of bending moment resistance.
Pipe bedding
This term is used to describe the complete arc of material within the trench, or in the case of
Class “C” or Class “D” beddings, a special preparation of the trench bottom. For further information,
see Section 1.2.4 “Pipe Bedding”.
Bedding factor
In the standard test on pipes the vertical loading and supporting reactions are line loads and
any trench situation in the field is unlikely to produce such an onerous loading condition. The
strength of the pipe determined in the crushing test can therefore be multiplied by a bedding
factor which represents the amount by which the stresses in the pipe are reduced because of
the spreading properties of the bedding for load and reaction.
The value of a bedding factor for a particular method of construction is not a precise figure
but is affected by the quality of workmanship. The values given whilst being conservative
assume a reasonable standard of workmanship and supervision. If the designer needs a
somewhat higher bedding factor than stated a high standard of workmanship and supervision
must be specified and guaranteed; alternatively a higher strength pipe may be considered
where available. If a higher strength pipe is available adequate time must be allowed for the
manufacturer to supply.
Factor of safety
For structural design to BS EN 1295 unreinforced pipes should be designed with a factor of safety
(Fse) of 1.25 (generally DN225–DN600 units are unreinforced but some manufacturers may
have a different range of such pipes). The factor of safety increases to 1.5 for reinforced pipes.
Confirmation should be obtained from the manufacturer or a conservative approach would be
to use a 1.5 factor of safety.
The Tables in Section 1.2.7 are applicable only to a single pipeline laid in its own trench, and
have been set out to give the loads on pipes under three surface conditions, Main Roads, Light
Roads and Fields.
Backfill loads
The Tables are calculated using an equivalent soil density of 19.6 kN/m3 (approximately
2.0 tonnes/m3).
Traffic loads
a) Main roads
Static wheel load of 86.5kN and an impact factor of 1.3, giving a Total Static wheel load of
112.5kN; contact pressure 1100kN/m2.
a) Light roads
Static wheel load of 70kN and an impact factor of 1.5, giving a Total Static wheel load of 105kN;
contact pressure 700 kN/m2.
b) Fields
Static wheel load of 30kN and an impact factor of 2.0, giving a Total Static wheel load of 60 kN;
contact pressure 400kN/m2.
Superimposed loads
These are not included in the Tables. If however such loads are encountered and are of sufficient
magnitude, an allowance should be made.
Water Loads
These are included in the Tables. If the pipe is laid below the ground water table, an allowance
for this load is not needed. However, as these loads are small by comparison with other loads
on the pipe, it has been considered appropriate to include them only for pipes of DN 600 and over.
Frictional factor K
a) lt is advisable that pipes laid under roads should have cover over the pipe of not less than
1.2m. This cover should be maintained for main roads, light roads (which may on occasion
carry main road traffic) and for pipes laid under grass verges adjacent to a road (Tables A3 and
A4). Where pipes have to be laid with less than 1.2m cover special consideration is needed to
reduce the risk of damage. Loads in columns headed 0.9 and 1.0 in Tables A3 and A4 should
be used only as a guide.
b) For pipes laid in fields a minimum cover of 0.6m should be provided. At shallower depths
there is a risk of damage from agricultural operations.
Key 3
1 Backfill 5 Compressible material 5
2 Concrete slab 6 Pipe 4
It is important that the slab extends sufficient distance beyond the trench and would depend on
soil conditions (minimum bearing of 300mm each side advised). A layer of compressible material
directly over the pipeline aids in the prevention of the slab loading directly onto the pipeline
should settlement occur.
Another method of protection at shallow cover depth is via the use of a concrete surround. It is
important in such installations to install compressible material at least every other pipe joint to
ensure that the pipeline retains its flexibility.
Special consideration should be given where construction plant has to cross pipelines with
shallow cover depth. Where possible, traffic should be routed over dedicated crossing points. Crossing
points may consist of heavy steel plates to transfer vehicle loads or temporary additional cover
emplaced over the pipeline.
Where a pipeline is laid under an embankment, or where the pipeline is installed in a deep
trench, it can be critical for the trench width to be kept minimal for a distance above the crown
of the pipe. Any slight increase over the designed trench width can greatly increase the
pipeline’s loading.
For convenience, two or more pipelines may be installed in the same trench and at different levels.
Trenches can be excavated to the maximum depth to accept all pipelines, or they may be stepped
in construction where levels of the pipelines are different.
Careful consideration should be undertaken to assess the loading and possible implications of
installing multiple pipelines in the same trench.
The horizontal distance between adjacent pipelines will largely be dependent on the type of
bedding/backfill material used to surround the pipelines. With rounded gravels it’s possible to
achieve minimal spacing between the pipelines (just room to provide access for the gravel to
be working in and around the pipes), whereas an angular/cohesive material may require
upwards of 400mm or greater (depending on pipe sizes) to enable suitable access for placement
and compaction of the materials.
In general pipelines are laid in trenches and the pipes used are designed to carry the backfill,
traffic loads and, when the diameter is 600mm or more, some part of the water load under
working conditions.
In order to improve the load carrying capacity of the pipe it is laid on one of several classes of
bedding (see Table A2). Each type of bedding is allocated a “bedding factor” (Fm) which may
be regarded as a multiplier applied to the test load of the pipe.
The trench is excavated in the natural soil, the pipe is laid on the selected bedding and the
trench backfilled. Load on the pipe due to the backfill develops as the fill material settles. The
load on the pipe due to the backfill is therefore the weight of the backfill taken over the full
trench width but reduced by the shear force from the trench walls acting upwards (see Fig.A1).
1: SYSTEM DESIGN 21
This state is called the narrow trench condition. The backfill load is calculated by
using the Marston formula:
Wc = Cd w Bd2
Where:
Wc = Backfill load (kN/m)
Cd = Load coefficient, dependent on soil type and ratio of cover depth to trench width
w = Soil density (kN/m3)
Bd = Width of trench (m)
Provided that the trench width does not exceed the values given in the tables, the loads given
are conservative and may be used with confidence.
The trench widths given will provide adequate working space around the pipe for laying and
jointing and also sufficient room to place and consolidate the bedding specified.
As indicated, the friction acting against the backfill is provided by the trench walls and is roughly
constant at a particular depth. If however the trench width is increased radically, Bd2 in the
Marston formula is also increased and a reappraisal of the load on the pipe must be considered.
H
Bd Bd
Downward Downward
pull pull
Bc
=
D
O
Upward Upward Upward Upward
friction Bedding friction friction Bedding friction
For any depth there is a trench width where friction planes from the trench walls become remote
from the pipe and no longer contribute to the reduction of the fill load. In fact the settlement of
the side prisms of backfill tend to increase the load (see Fig.A2). This state is called the wide
trench condition. It is a positive projection condition. The backfill loading on the pipe does not
take any relief from undisturbed ground.
In preparing the tables, due consideration has been given as to whether at any trench width
and depth, the narrow or wide trench condition and load is applicable, and the standard practice
of using the lesser of these values has been adopted. The tables give the total loads for pipes
of all diameters specified in BS 5911-1. This load includes loading from backfill and traffic for
depths of cover over the top of the pipe as follows:
Table A1. Minimum crushing loads (Fn) for strength class 120 units with a circular bore
for use in a trench – BS 5911-1:2002+A2:2010.
2000 240
2100 252
2200* 264
2400* 288
NOTE 1 Classic sizes, denoted by an asterisk, will be phased out if called for by further European harmonisation.
NOTE 2 Sizes DN 225 to DN 600 inclusive are normally only manufactured unreinforced in the United Kingdom.
NOTE 3 Sizes DN 1000 and above are normally only manufactured reinforced in the United Kingdom.
NOTE 4 Table NA.5 of BS EN 1295-1: recommends that the minimum value of safety factor for the structural design of reinforced
pipelines should be increased from the normal 1.25 to 1.5 if, as is the case of BS EN 1916: 2002, the proof load is 67% of the
minimum crushing load.
* Sizes marked with asterisk are not readily available in the UK
Pipe settlement will be kept to a minimum by the proper selection and compaction of the bedding
material. The bedding should be compacted to a density not less than that of the natural soil in
the sides and bottom of the trench. The bedding directly beneath or above the pipeline must not
be over compacted otherwise line loading of the pipes will result.
On steep gradients, or where dewatering has taken place, it is important to restrict ground water
movement within the completed trench. Selection of bedding or clay dams across the full width
of the trench will assist in this.
Under no circumstances should blocks or bricks be placed beneath pipes. Any pegs used for
setting out or levelling must be removed.
1: SYSTEM DESIGN 23
Bedding materials
Any stable soil will act adequately as a bedding material provided that it is placed and compacted
around the pipeline. From a practical point of view granular material is compacted more readily
and has become widely accepted.
The bedding material should be of similar particle size to that in the trench sides. Where the
ground is clay or silt, bedding material must consist of all-in gravels to prevent the trench from
becoming a drainage channel and carrying away fines from the trench walls and bedding and
causing settlement of the pipes.
The ideal is crushed rock or gravel but similar locally available material having an angular or an
irregular shape may be used. Rounded single sized material is not recommended as it may not
provide a stable bed especially for heavy larger diameter pipes.
Water Research Centre (WRc) Information and Guidance Note (IGN) 4-08-01 provides guidance
on the particle size of material relating to pipe diameter.
Sands containing an excess of fine particles are more difficult to place and compact and will
require a greater degree of supervision on site to achieve a stable embedment for the pipeline.
This should consist of uniform readily compactable material, free from tree roots, vegetable
matter, building rubbish and frozen soil. When used as fill, the material should not contain large
clay lumps or cobbles. When used as bedding, all clay lumps should be excluded.
“As dug” material may be used provided that it is readily compatible and provides stable embedment.
The strength of an installed pipeline depends on a combination of the strength of the pipe and
the class of bedding.
The selection of the bedding class is influenced by many factors, which include the nature of
the ground, the loads acting on the pipeline in the trench, strength class of pipe, and the local cost
and availability of the bedding material.
Taking into account the cost of labour, it is generally more economical to lay the pipes on a
bedding of non-cohesive materials, or alternatively scarify the trench bottom rather than hand
trim the formation.
Normally loading calculations are made considering the pipeline in complete lengths, between
manholes. The calculated installation condition to satisfy the most severe loading condition
between each pair of manholes is then used throughout the length.
24 1: SYSTEM DESIGN
The normally accepted classes of pipe bedding are shown in Table A2 and in Fig A3.
Class D Class N
Hand trimmed flat bottom. Bedding factor = 1.1 Flat granular layer. Bedding factor = 1.1
Bc
300mm
300mm
Well compacted,
especially under
haunches of pipe
Well compacted,
especially under
haunches of pipe Y
Class C Class F
Hand shaped bottom. Bedding factor = 1.5 Granular bedding. Bedding factor = 1.5
Bc 300mm
300mm
Well compacted,
especially under
haunches of pipe
Well compacted,
especially under
haunches of pipe
Y
Suitable in uniform soils and relatively dry conditions. Lay pipes on a flat layer of granular bedding material on the
Bottom of the trench, or formation, profiled to fit barrels formation, (see Note1). Scoop out socket holes with 50mm
over a width of not more than 1/2 Bc with socket holes minimum clearance; lay joint pipes which will settle slightly in
to give at least 50mm clearance under the sockets of to the bedding. Sidefill, placed and well compacted in layers.
sufficient length to permit jointing*
* Scarifying formation is generally adequate in practice
Class B Class S
180º Granular bedding. Bedding factor = 1.9 360º Granular bedding & surround. Bedding factor = 2.2
300mm 300mm
Well compacted,
Well compacted,
especially under
especially under
haunches of pipe
haunches of pipe
Y Y
Lay pipes on a layer of granular bedding material on the Lay, joint and bed pipes as for Class B then place and
formation, (see Note1). Scoop out socket holes, lay and well compact layers of the same bedding material at each
joint pipes, place and well compact layers in the same side, up to crown level, taking care not to displace the
bedding material at each side of pipes, up to springing pipes. This is followed by 300mm of granular bedding
level, taking care not to displace them. material but lightly compacted directly over the pipe, after
which ordinary backfilling is commenced.
Selected Grade
Normal Granular
backfill C20
backfill material
material concrete
26 1: SYSTEM DESIGN
Class A
Plain concrete cradle. Bedding factor = 2.6 Reinforced concrete cradle. Bedding factor = 3.4
Bc Bc
300mm 300mm
Reinforcement 40
1/4 Bc
1/4 Bc
Screed
Class A concrete bedding, either plain or reinforced each 120º cradle. Screed the formation, place blocks on the screed to support
pipes behind each socket. Lay pipes, using packers on blocks to achieve correct line and level. At pipe joints, form construction joints
through concrete bed ensure flexibility of pipeline. Minimum width of cradle 11/4 Bc or Bc plus 200mm. Minimum thickness 1/4 Bc.
Pour concrete carefully from one side to prevent voids. Backfill when concrete has attained required strength.
NOTES:
1. Generally thickness of bedding (Y), minimum of 100mm under barrels and 50mm under sockets. In rock 200mm under barrels and 150mm
under sockets subject to maximum of 400mm. Minimal compaction directly beneath pipe.
2. Sidefills, whether of bedding material or of selected material, must be well compacted.
3. Backfill or bedding material to be highly compacted above sidefills to 300mm above the crown but lightly compacted directly over the pipe.
4. Normal backfill to be compacted as appropriate.
5. With reasonable workmanship and supervision these bedding factors are conservative.
Fn = We x Fse
Fm
where Fn = required BS 5911-1 test strength (kN/m)
We = load from Tables A3 or A4 (kN)
Fse = factor of safety
Fm = bedding factor chosen
In the UK, standard circular pipes to BS EN 1916 and BS 5911-1 are usually to Class 120. To
calculate the test strength apply 120 x pipe nominal diameter in metres e.g. for DN450 pipe,
Fn=120 x 0.45=54kN/m (see Table A1).
For a reinforced concrete pipe Fc is the load which the pipe will sustain without developing a
crack exceeding 0.30mm in width over a length of 300mm and Wt is the load which the pipe will
sustain without collapse, irrespective of crack width. However, to further simplify the procedure it
is more straightforward to use the maximum test load Fn and applying the factor of safety of Fse.
Nominal Outside Recommended Waterload Total design load “We” in kN/m for cover depths “H” in metres Nominal
Diameter Diameter Trench Included Diameter
in mm in mm width in m in kN/m in mm
0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
225 280 0.70 31.9 31.4 28.5 28.3 27.7 27.9 28.5 28.6 29.9 30.7 31.4 32.0 32.2 32.4 32.6 23.9 33.2 33.2 33.3 33.5 33.7 33.9 34.1 34.2 34.3 34.5 34.7 34.9 35.0 35.0 35.1 35.1 35.2 35.2 35.3 35.3 35.4 225
300 380 0.75 43.4 38.9 37.8 38.3 37.8 37.9 38.0 38.1 38.2 38.3 38.5 38.7 38.9 39.0 39.2 39.5 39.8 40.1 40.4 40.6 40.8 41.1 41.3 41.5 41.7 41.9 42.1 42.3 42.4 42.5 42.7 42.8 42.9 43.0 43.2 43.2 43.3 300
375 500 1.06 55.7 53.9 50.1 49.1 48.1 49.4 50.5 51.6 52.6 54.3 56.1 57.8 58.8 59.9 60.9 61.9 62.9 63.7 64.3 65.4 66.3 67.3 67.9 68.7 69.4 70.2 70.9 71.5 72.2 72.8 73.5 74.0 74.6 75.1 75.7 76.3 76.9 375
450 560 1.15 64.3 62.8 55.7 58.4 57.3 58.0 59.3 60.7 62.1 63.2 64.2 65.4 66.1 66.8 67.8 68.8 69.7 70.8 71.9 73.0 74.0 74.8 75.7 76.7 77.5 78.4 79.2 80.0 80.9 81.7 82.5 83.2 83.9 84.4 85.0 85.6 86.2 450
525 670 1.20 73.2 71.6 66.7 65.7 66.2 66.8 67.6 68.4 69.0 70.0 71.0 72.0 72.8 73.7 74.7 75.6 76.9 78.0 79.1 80.3 81.4 82.5 83.7 84.5 85.3 86.2 87.3 88.4 89.4 90.4 91.3 92.3 93.0 93.7 94.5 95.2 95.8 525
600 790 1.35 2.1 86.5 82.4 78.9 78.9 79.1 79.6 80.4 81.4 82.4 83.5 84.7 86.1 87.0 88.0 89.4 90.9 92.3 93.7 95.1 96.6 98.1 99.5 101 102 104 105 107 108 109 110 111 112 113 114 115 116 118 600
675 880 1.45 2.6 95.8 93.2 87.3 86.7 87.0 87.3 88.1 88.9 89.5 90.8 92.1 93.4 94.4 95.4 97.0 98.6 100 102 103 105 107 108 110 111 113 114 116 117 119 120 121 122 124 125 126 128 129 675
750 950 1.5 3.3 104 100 94.5 93.4 93.6 94.0 94.7 95.5 96.2 97.6 99.0 100 102 103 104 106 108 109 111 113 115 117 119 120 122 123 125 126 128 129 131 132 134 135 137 139 140 750
825 1040 1.60 3.9 113 109 103 102 101 101 102 103 104 105 107 108 109 110 112 114 116 118 119 123 123 125 127 129 131 133 135 136 136 140 142 143 145 147 148 150 151 825
900 1120 1.90 4.7 122 118 111 110 111 112 115 118 121 124 126 128 130 132 135 137 140 143 146 149 152 155 157 160 163 166 169 171 174 177 180 182 184 186 189 192 193 900
1050 1300 2.05 6.4 141 135 128 125 127 128 130 132 136 139 141 144 145 148 151 154 157 160 164 167 170 173 176 179 183 186 189 192 195 198 201 204 207 209 212 215 218 1050
Table A3. Total Design Loads - Main Roads. “H” = 0.9 metres to 8.0 metres
1200 1400 2.30 8.3 158 153 147 142 143 145 148 152 155 158 160 163 166 169 172 176 179 183 187 191 195 199 203 207 211 215 218 221 225 229 233 237 240 244 247 250 253 1200
1350 1650 2.45 10.6 175 169 163 160 160 161 163 166 170 173 176 179 182 185 188 192 196 200 205 209 213 218 222 226 230 234 249 243 247 251 255 259 263 267 271 274 278 1350
1500 1830 2.60 13.0 192 187 180 177 177 187 181 184 187 190 193 196 198 201 205 209 214 218 223 228 232 237 241 246 251 255 260 264 269 273 278 282 287 391 296 300 305 1500
1800 2240 2.95 18.7 234 228 222 218 217 218 220 223 225 228 232 235 238 241 246 251 257 262 268 273 279 284 290 296 301 307 313 319 324 330 335 341 346 352 357 362 368
1800
2100 2560 3.25 25.5 278 267 255 249 247 249 252 254 257 260 263 267 270 273 278 284 289 295 302 309 315 321 328 334 340 346 353 359 366 372 379 385 392 399 404 410 416 2100
2400 2800 3.55 33.3 317 304 292 286 284 284 287 289 292 295 298 301 305 309 315 321 327 334 341 348 355 362 370 377 364 391 399 406 414 421 428 435 443 450 457 464 471 2400
1: SYSTEM DESIGN 27
28
Nominal Outside Recommended Waterload Total design load “We” in kN/m for cover depths “H” in metres Nominal
Diameter Diameter Trench Included Diameter
in mm in mm width in m in kN/m in mm
0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
225 280 0.70 27.1 25.0 23.1 22.0 21.8 21.9 22.5 23.3 24.2 25.3 26.2 27.2 27.6 28.0 28.4 28.9 29.3 29.7 30.1 30.4 31.0 31.1 31.4 31.7 32.0 32.3 32.6 32.8 33.1 33.2 33.4 33.5 33.5 33.6 33.7 33.8 33.9 225
1: SYSTEM DESIGN
300 380 0.75 36.9 34.3 31.5 30.0 29.4 26.8 29.9 30.1 30.5 31.0 31.6 32.2 32.6 33.0 33.5 34.1 34.7 35.2 35.7 36.3 36.8 37.3 37.8 38.1 38.4 38.7 39.0 39.3 39.6 39.9 40.2 40.4 40.7 41.0 41.2 41.4 41.6 300
375 500 1.06 47.3 44.1 40.6 38.6 38.3 38.7 39.7 41.2 42.7 44.8 46.9 48.9 50.5 52.1 53.5 54.8 56.1 57.4 58.6 59.9 61.1 62.2 63.4 64.3 65.3 66.3 67.2 68.0 68.8 69.6 70.4 71.1 71.8 75.2 73.3 74.0 74.5 375
450 560 1.15 55.4 51.0 47.6 45.2 44.8 45.5 46.6 48.4 50.3 52.0 53.5 55.2 56.4 57.5 59.0 60.5 52.0 63.5 64.9 66.4 67.7 68.9 70.3 71.5 72.7 73.8 74.7 75.9 77.0 77.5 78.8 79.6 80.4 81.3 82.1 82.9 83.7 450
525 670 1.20 61.9 58.3 54.5 52.0 51.5 52.2 53.5 54.4 55.5 57.4 58.8 60.3 61.6 62.9 64.5 66.2 58.0 69.6 71.3 72.9 74.3 75.8 77.3 78.1 80.0 81.4 82.6 83.8 84.9 86.0 87.1 88.3 89.2 90.2 91.1 92.0 92.9 525
600 790 1.35 2.1 72.9 68.2 63.8 62.3 62.3 62.9 63.7 64.7 66.3 68.7 70.4 72.2 72.9 75.4 77.6 79.6 81.7 83.7 85.6 87.7 89.6 91.6 93.7 95.4 97.2 100 101 102 104 105 106 108 109 110 111 112 114 600
675 880 1.45 2.6 80.4 75.5 70.1 68.7 68.2 68.4 69.1 70.1 71.4 73.6 75.8 78.1 79.8 81.5 83.8 86.4 88.4 90.7 93.1 95.3 97.4 99.4 102 103 106 107 109 111 113 114 116 117 119 120 122 123 125 675
750 950 1.5 3.3 87.5 81.0 75.7 73.5 72.8 73.5 74.6 75.8 77.0 79.0 81.4 83.8 85.5 87.5 90.0 92.6 95.0 97.4 99.9 102 105 107 110 112 114 116 118 119 121 123 125 127 129 130 132 134 136 750
825 1040 1.60 3.9 94.7 94.1 83.4 80.4 78.9 78.8 79.4 80.9 82.7 84.8 87.3 89.7 91.7 93.7 96.4 99.2 102 104 107 110 112 115 117 120 122 125 127 129 131 133 135 137 139 141 413 145 147 825
900 1120 1.90 4.7 101 95.1 88.1 84.8 85.3 87.4 91.3 95.2 99.1 102 105 109 112 114 118 122 125 129 133 136 140 143 147 150 154 157 160 163 166 169 173 176 178 181 183 185 188 900
1050 1300 2.05 6.4 116 110 101 97.1 97.1 98.9 102 106 110 114 118 121 124 127 131 135 140 144 148 153 156 160 164 168 172 176 179 183 186 189 193 196 199 203 206 209 212 1050
1200 1400 2.30 8.3 130 123 115 110 110 112 117 122 126 130 134 138 142 145 150 155 160 165 170 175 180 184 189 194 198 203 207 211 215 219 224 228 232 235 239 243 246 1200
Table A4. Total Design Loads - Light Roads. “H” = 0.9 metres to 8.0 metres
1350 1650 2.45 10.6 143 135 127 122 122 124 128 132 137 141 146 151 155 159 164 169 175 180 185 191 196 201 207 212 216 221 226 231 236 240 245 249 254 258 262 266 270 1350
1500 1830 2.60 13.0 156 149 140 133 133 136 140 145 150 155 159 164 168 172 179 184 190 196 202 208 213 219 225 230 235 241 246 251 257 262 267 272 277 282 287 292 297 1500
1800 2240 2.95 18.7 185 177 167 161 161 164 169 173 178 184 190 196 201 206 212 220 227 234 242 249 255 262 269 276 283 290 296 303 309 316 322 328 334 340 346 352 359
1800
2100 2560 3.25 25.5 209 201 191 185 184 186 191 197 202 209 215 222 227 232 240 248 246 254 272 279 287 295 303 311 319 327 334 342 349 355 363 371 378 385 391 398 404 2100
2400 2800 3.55 33.3 236 228 217 212 211 213 219 223 229 236 243 250 256 263 272 281 289 298 308 317 326 334 342 352 360 367 377 386 394 402 411 419 427 434 442 450 458 2400
Nominal Outside Recommended Waterload Total design load “We” in kN/m for cover depths “H” in metres Nominal
Diameter Diameter Trench Included Diameter
in mm in mm width in m in kN/m in mm
0.6 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
225 280 0.70 23.5 21.0 20.0 18.2 18.0 18.1 19.0 20.2 21.4 22.8 24.0 25.0 26.0 26.5 27.0 27.5 28.0 28.5 28.9 29.4 30.3 30.7 31.0 31.3 31.6 31.9 32.1 32.5 32.8 32.9 33.1 33.2 33.4 33.5 33.5 33.6 33.7 33.9 225
300 380 0.75 31.2 25.7 24.7 23.9 24.0 24.7 25.8 26.5 27.3 28.0 29.0 29.7 30.5 31.0 31.7 32.3 33.0 33.7 34.3 34.8 35.5 36.0 36.5 37.0 37.5 37.9 38.3 38.5 38.8 39.2 39.5 39.8 40.1 40.4 40.6 40.9 41.2 41.4 300
375 500 1.06 39.1 33.0 32.0 31.0 31.2 32.1 33.7 35.8 37.7 39.6 42.0 44.4 46.9 48.6 50.3 51.8 53.3 54.9 56.2 57.6 58.8 60.0 61.2 62.5 63.6 64.6 65.7 66.6 37.5 68.4 69.1 69.9 70.4 71.4 72.2 72.8 73.4 74.0 375
450 560 1.15 46.1 37.7 36.9 36.4 36.8 37.7 39.3 41.6 43.5 45.4 37.2 49.1 51.0 52.9 54.8 56.6 58.5 60.5 61.9 63.7 65.2 65.6 68.0 69.4 70.6 71.8 73.0 74.0 75.1 76.3 77.3 78.2 79.1 80.0 80.7 81.5 82.3 83.1 450
525 670 1.20 52.2 42.7 41.9 41.4 42.2 43.2 45.4 47.6 49.6 51.3 53.3 55.3 57.4 58.9 60.5 62.4 64.3 66.2 67.9 69.7 71.5 73.1 74.6 76.3 77.7 79.0 80.5 81.8 83.1 84.3 85.4 86.5 87.7 88.7 89.6 90.6 91.6 92.5 525
600 790 1.35 2.1 61.7 50.7 49.5 46.9 50.5 53.0 54.8 57.4 59.3 61.4 53.7 65.2 69.0 70.9 72.7 75.0 77.4 79.5 81.8 83.9 86.2 88.3 90.3 92.5 94.3 96.0 97.9 99.6 101 103 104 106 107 108 109 111 112 113 600
675 880 1.45 2.6 68.0 56.1 53.9 53.5 54.9 56.9 59.3 67.1 64.0 66.4 69.1 61.6 74.0 76.5 78.5 81.0 83.6 86.2 88.7 91.1 93.6 95.8 98.1 100 102 104 106 108 110 112 113 115 116 118 120 121 123 124 675
750 950 1.5 3.3 73.1 60.9 58.8 57.8 59.3 61.3 63.7 65.7 68.7 71.0 74.0 76.9 79.8 82.4 85.0 87.6 90.2 92.7 95.1 97.8 101 103 105 105 110 113 115 117 118 120 122 124 126 128 130 132 134 136 750
825 1040 1.60 3.9 78.2 66.2 54.7 62.8 64.2 66.1 68.4 70.6 73.6 76.1 79.4 82.4 85.4 87.8 90.1 93.2 96.2 99.2 102 105 108 111 113 116 119 121 124 126 128 130 132 134 136 138 140 142 144 146 825
900 1120 1.90 4.7 83.8 71.1 68.7 67.3 68.2 71.1 76.2 82.4 87.8 91.7 96.1 100 104 107 110 114 118 123 126 130 134 138 142 146 149 152 156 159 162 165 168 172 175 177 180 182 185 187 900
1050 1300 2.05 6.4 94.4 81.3 79 77 78.5 81.4 85.9 92.2 98.1 112 107 120 116 119 123 127 132 137 141 146 150 154 158 162 167 171 176 179 182 185 188 192 195 198 202 205 209 213 1050
1200 1400 2.30 8.3 102 91.9 89.2 87.9 89.0 92.2 97.1 104 110 116 122 127 132 136 140 145 150 156 161 167 172 177 182 187 192 196 201 205 209 213 218 222 227 231 235 238 242 246 1200
Table A5. Total Design Loads - Fields, etc.. “H” = 0.6 metres to 8.0 metres
1350 1650 2.45 10.6 115 99.1 98 97.6 99 103 107 115 120 127 132 138 144 150 155 160 166 171 176 182 188 193 199 204 209 214 219 224 229 234 239 243 248 252 257 261 266 271 1350
1500 1830 2.60 13.0 125 112 109 108 110 113 118 126 131 138 144 152 156 151 167 173 179 185 191 198 204 210 215 222 228 233 239 244 249 255 260 265 270 275 280 285 290 295 1500
1800 2240 2.95 18.7 145 133 130 130 132 136 143 152 161 165 172 180 187 194 201 207 214 222 229 237 244 251 259 266 273 280 287 294 300 307 314 320 326 332 338 345 351 357 1800
2100 2560 3.25 25.5 167 153 152 150 152 156 163 172 180 187 196 204 212 218 225 233 241 249 258 266 275 283 291 299 307 215 324 331 339 346 354 361 367 376 383 389 396 403 2100
2400 2800 3.55 33.3 188 175 173 172 175 180 186 195 203 212 222 231 240 246 253 262 272 281 291 301 311 320 330 338 347 356 365 374 383 391 400 408 417 425 432 440 447 454 2400
1: SYSTEM DESIGN 29
30 1: SYSTEM DESIGN
Example 1
Size of pipe: DN900 (reinforced) Cover depth:3.00m Design load: Main road
Nominal Outside Recommended Waterload Total design load “We” in kN/m for cover depths “H” in metres Nominal
Diameter Diameter Trench Included Diameter
in mm in mm width in m in kN/m in mm
0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
225 280 0.70 31.9 31.4 28.5 28.3 27.7 27.9 28.5 28.5 29.9 30.7 31.4 32.0 32.2 32.4 32.6 23.9 33.2 33.2 33.3 33.5 33.7 33.9 34.1 34.2 34.3 34.5 34.7 34.9 35.0 35.0 35.1 35.1 35.2 35.2 35.3 35.3 35.4 225
300 380 0.75 43.4 38.9 37.8 38.3 37.8 37.9 38.0 38.1 38.2 38.3 38.5 38.7 38.9 39.0 39.2 3.5 39.8 40.1 40.4 40.6 40.8 41.1 41.3 41.5 41.7 41.9 42.1 42.3 42.4 42.5 42.7 42.8 42.9 43.0 43.2 43.2 43.3 300
375 500 1.06 55.7 53.9 50.1 49.1 48.1 49.4 50.5 51.6 52.6 54.3 56.1 57.8 58.8 59.9 60.9 61.9 62.9 63.7 64.3 65.4 66.3 67.3 67.9 68.7 69.4 70.2 70.9 71.5 72.2 72.8 73.5 74.0 74.6 75.1 75.7 76.3 76.9 375
450 560 1.15 64.3 62.8 55.7 58.4 57.3 58.0 59.3 60.7 62.1 63.2 64.2 65.4 66.1 66.8 67.8 68.8 69.7 70.8 71.9 73.0 74.0 74.8 75.7 76.7 77.5 78.4 79.2 80.0 80.9 81.7 82.5 83.2 83.9 84.4 85.0 85.6 86.2 450
525 670 1.20 73.2 71.6 66.7 65.7 66.2 66.8 67.6 68.4 69.0 70.0 71.0 72.0 72.8 73.7 74.7 75.6 76.9 78.0 79.1 80.3 81.4 82.5 83.7 84.5 85.3 86.2 87.3 88.4 89.4 90.4 91.3 92.3 93.0 93.7 94.5 95.2 95.8 525
600 790 1.35 2.1 86.5 82.4 78.9 78.9 79.1 79.6 80.4 81.4 82.4 83.5 84.7 86.1 87.0 88.0 89.4 90.9 92.3 93.7 95.1 96.6 98.1 99.5 101 102 104 105 107 108 109 110 111 112 113 114 115 116 118 600
675 880 1.45 2.6 95.8 93.2 87.3 86.7 87.0 87.3 88.1 88.9 89.5 90.8 92.1 93.4 94.4 95.4 97.0 98.6 100 102 103 105 107 108 110 111 113 114 116 117 119 120 121 122 124 125 126 128 129 675
750 950 1.5 3.3 104 100 94.5 93.4 93.6 94.0 94.7 95.5 96.2 97.6 99.0 100 102 103 104 106 108 109 111 113 115 117 119 120 122 123 125 126 128 129 131 132 134 135 137 139 140 750
825 1040 1.60 3.9 113 109 103 102 101 101 102 103 104 105 107 108 109 110 112 114 116 118 119 123 123 125 127 129 131 133 135 136 136 140 142 143 145 147 148 150 151 825
900 1120 1.90 4.7 122 118 111 110 111 112 115 118 121 124 126 128 130 132 135 137 140 143 146 149 152 155 157 160 163 166 169 171 174 177 180 182 184 186 189 192 193 900
1050 1300 2.05 6.4 141 135 128 125 127 128 130 132 136 139 141 144 145 148 151 154 157 160 164 167 170 173 176 179 183 186 189 192 195 198 201 204 207 209 212 215 218 1050
1200 1400 2.30 8.3 158 153 147 142 143 145 148 152 155 158 160 163 166 169 172 176 179 183 187 191 195 199 203 207 211 215 218 221 225 229 233 237 240 244 247 250 253 1200
Example 2
A 900mm diameter pipeline with Class B bedding is to be laid across fields.
What is the greatest cover depth that these pipes may be laid?
Nominal Outside Recommended Waterload Total design load “We” in kN/m for cover depths “H” in metres Nominal
Diameter Diameter Trench Included Diameter
in mm in mm width in m in kN/m in mm
0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
225 280 0.70 21.0 20.0 18.2 18.0 18.1 19.0 20.2 21.4 22.8 24.0 25.0 26.0 26.5 27.0 27.5 28.0 28.5 28.9 29.4 30.3 30.7 31.0 31.3 31.6 31.9 32.1 32.5 32.8 32.9 33.1 33.2 33.4 33.5 33.5 33.6 33.7 33.9 225
300 380 0.75 25.7 24.7 23.9 24.0 24.7 25.8 26.5 27.3 28.0 29.0 29.7 30.5 31.0 31.7 32.3 33.0 33.7 34.3 34.8 35.5 36.0 36.5 37.0 37.5 37.9 38.3 38.5 38.8 39.2 39.5 39.8 40.1 40.4 40.6 40.9 41.2 41.4 300
375 500 1.06 33.0 32.0 31.0 31.2 32.1 33.7 35.8 37.7 39.6 42.0 44.4 46.9 48.6 50.3 51.8 53.3 54.9 56.2 57.6 58.8 60.0 61.2 62.5 63.6 64.6 65.7 66.6 37.5 68.4 69.1 69.9 70.4 71.4 72.2 72.8 73.4 74.0 375
450 560 1.15 37.7 36.9 36.4 36.8 37.7 39.3 41.6 43.5 45.4 37.2 49.1 51.0 52.9 54.8 56.6 58.5 60.5 61.9 63.7 65.2 65.6 68.0 69.4 70.6 71.8 73.0 74.0 75.1 76.3 77.3 78.2 79.1 80.0 80.7 81.5 82.3 83.1 450
525 670 1.20 42.7 41.9 41.4 42.2 43.2 45.4 47.6 49.6 51.3 53.3 55.3 57.4 58.9 60.5 62.4 64.3 66.2 67.9 69.7 71.5 73.1 74.6 76.3 77.7 79.0 80.5 81.8 83.1 84.3 85.4 86.5 87.7 88.7 89.6 90.6 91.6 92.5 525
600 790 1.35 2.1 50.7 49.5 46.9 50.5 53.0 54.8 57.4 59.3 61.4 53.7 65.2 69.0 70.9 72.7 75.0 77.4 79.5 81.8 83.9 86.2 88.3 90.3 92.5 94.3 96.0 97.9 99.6 101 103 104 106 107 108 109 111 112 113 600
675 880 1.45 2.6 56.1 53.9 53.5 54.9 56.9 59.3 67.1 64.0 66.4 69.1 61.6 74.0 76.5 78.5 81.0 83.6 86.2 88.7 91.1 93.6 95.8 98.1 100 102 104 106 108 110 112 113 115 116 118 120 121 123 124 675
750 950 1.5 3.3 60.9 58.8 57.8 59.3 61.3 63.7 65.7 68.7 71.0 74.0 76.9 79.8 82.4 85.0 87.6 90.2 92.7 95.1 97.8 101 103 105 105 110 113 115 117 118 120 122 124 126 128 130 132 134 136 750
825 1040 1.60 3.9 66.2 54.7 62.8 64.2 66.1 68.4 70.6 73.6 76.1 79.4 82.4 85.4 87.8 90.1 93.2 96.2 99.2 102 105 108 111 113 116 119 121 124 126 128 130 132 134 136 138 140 142 144 146 825
900 1120 1.90 4.7 71.1 58.7 67.3 68.2 71.1 76.2 82.4 87.8 91.7 96.1 100 104 107 110 114 118 123 126 130 134 138 142 146 149 152 156 159 162 165 168 172 175 177 180 182 185 187 900
1050 1300 2.05 6.4 81.3 79 77 78.5 81.4 85.9 92.2 98.1 112 107 120 116 119 123 127 132 137 141 146 150 154 158 162 167 171 176 179 182 185 188 192 195 198 202 205 209 213 1050
CPSA has developed online Structural and Material Cost calculators and a web App to help with the calculation and optimisation of the
structural design and material cost of underground sewer pipeline systems.
The App offers a two-stage process:
Stage 1 Structural Design Calculator enables users to quickly establish acceptable structural bedding Classes for buried pipes based on
the recommendations in BS EN 1295-1 “Structural design of buried pipelines”.
Stage 2 Material Cost Calculator where users can compare the cost of materials required for each bedding Class option. The calculator
takes into account the pipe cost (including connectors, gaskets, etc), imported granular bedding material and the disposal of surplus
excavated material removed from the trench.
The App not only helps to improve pipeline construction cost efficiency by enabling users to minimise the amount of expensive imported
granular bedding used during construction, it can also reduce the embodied carbon of the installation.
1: SYSTEM DESIGN 31
Fig. A4a. Typical Cast In-situ Manhole Base with Fig. A4b. Typical Precast Manhole Base with
Tongue and Groove Jointed Rings Elastomeric Seal Jointed Rings
Manhole Cover
Manhole Cover
Adjusting Units
Seal
Cover Slab
Shaft section
Shaft section
Seal
Reducing Slab
150mm Reducing Slab
Cast In Situ
Surround Seal
Chamber Section
Landing Slab
Seal
Landing Slab
Chamber Section
Chamber Section
Spigot Spigot Seal
Butt Pipe Butt Pipe
Socket Butt Pipe Socket Butt Pipe
Cut Away Detail Cut away assembly detail Cut Away Detail Cut away assembly detail
32 1: SYSTEM DESIGN
Base units can be supplied with circular or semicircular holes (cut-outs or dog kennels) cut in
the chamber walls or with factory made flexible joints to incorporate a sealing ring to connect
pipes to the chamber.
1.3.3 Advantages
6. All CPSA member factories are licensed to manufacture ‘Kitemarked’ standard units
under BS EN ISO 9001 quality management systems.
9. Units are watertight structures without the need for a concrete surround. Soil backfill is
normally sufficient.
10.They can be supplied ready fitted with double steps complying with BS EN 13101.
Manholes are built on a run of sewer with or without side connections. Where conditions permit,
the soffit level of sewers connecting to a manhole should be the same.
Manholes may be constructed with or without a shaft. It is recommended that reducing slabs
and shafts are only used for DN1800 manholes and larger. Landing slabs are generally required
for manholes 6 metres deep or greater.
Smaller diameter chambers should be constructed up to full height and use a cover slab. There
are also inspection chambers which are constructed over a subsidiary drain or sewer of not
more than DN 225 to permit inspection and access for rodding. Most manholes are sited
symmetrically over the main sewer pipeline. Side-entry manholes which are formed integral to
the crown of the pipe are also manufactured. These can be advantageous in terms of installation
time and cost savings.
1) Conventional manholes
Concrete base, channel/s and benching installed in-situ. With the bottom section of the first manhole ring being built
in to the base concrete by a minimum of 75mm. Distance between top of pipe and underside of first manhole ring to
be minimum of 50mm to a maximum of 300mm. Generally and in accordance with ‘Sewers For Adoption’ a concrete
surround is required with this type of manhole construction.
Inlet(s) and outlet positions are configured to site requirements and delivered with all channels and benching complete.
Watertight joints and thicker walls means units do not require a concrete surround, unless specified. A faster, safer,
higher quality, lower installed cost and reduced carbon footprint alternative to conventional manholes. (The product’s
finish is not subject to the skills of site operatives)
For more information on precast manhole base systems, refer to CPSA and member product information:
3) Side-entry manholes
4) Backdrop manholes
Where one sewer connects with another at a substantially different level, the manhole is built
on the lower sewer and incorporates a vertical or ramped drop pipe from the higher sewer. The
drop pipe, which may be inside or outside the manhole chamber, has its lower end discharging
into the main sewer, and at its upper end has a rodding eye for cleaning through the higher sewer.
Wherever possible, steeper gradients are preferred over the use of backdrops in ‘Sewers For
Adoption’.
Where surface water and foul sewers are laid in the same trench, the surface water being normally
above the foul, a normal manhole chamber is built for the foul sewer and the surface water is
carried across the chamber in a separate pipe which may have a sealed inspection cover.
The chamber should be a minimum of DN 1050 and is the smallest size that may be fitted
with steps, but are only permitted to be used to a depth of 1.5m. DN 1200 is the smallest size
that can be used deeper than 1.5m and to which ladders may be fitted. It should have ample
benching at least 225mm wide on one side of the channels. On the other side, the benching
should be wide enough to stand on, at least 450mm.
For deep manholes, the chamber should be large enough to provide benching or a landing
adequate for two persons to stand upon.
A guide for the minimum chamber diameters required for various sizes of sewer pipes entering
the manhole is given in Table A6. When a manhole is sited on a curve, or where additional pipes
enter at the sides a larger size may be required.
Maximum size of pipe (DN) through chamber Minimum Chamber diameter (DN)
To prevent this, the first pipe in the line can be restricted in length. This is known as a “rocker
pipe”. The likelihood of differential settlement should be assessed and rocker pipes used as
appropriate.
Guidance on rocker pipes may be found in “Civil Engineering Specification for the Water
Industry” and “Sewers for Adoption”.
In certain conditions where excessive differential movement is possible, for pipes ≥ DN750,
it may be advisable to use multiple rocker pipes to avoid unacceptable angular deflection or
shear force at the joint.
The minimum clear opening through a cover slab should be 600mm x 600mm.
Slabs with other sized accesses/multiple accesses or rebated accesses are quite often required
in cases of split wall chambers, pumping stations, where flow control devices are fitted within
the chamber etc. (these would be made to order products).
The access is normally located in an eccentric position i.e. usually 150mm - measured from
edge of access (mid-point of side) to face of chamber wall below. This allows for safe and clear
access to steps or ladder system below (where fitted).
Cover slabs are generally suitable for installation below highways (some small units are available
for use in non-trafficked areas and hence should not be installed in a highway).
2) Landing slabs
Landing slabs are generally required on manholes greater than 6m depth (landing slabs should
be installed at minimum of 2 metres and maximum of 6 metres spacing for the depth of the manhole).
36 1: SYSTEM DESIGN
It is usual for the access in the landing slab to be 900mm circular and is usually positioned
offset on site so that there is a break in the steps/ladders vertically (alternatively a hinged
safety grill may be fitted over the access).
3) Reducing slabs
On large, deep chambers (usually DN1800 or greater), it is common practice to reduce the
upper access shaft to a smaller, more economic solution of typically DN1200 size.
Where double steps are fitted in the main chamber, the steps alignment is maintained through
the reduced shaft section.
The access in the concrete cover slab may be reduced in size (typically from 750 mm x 600
mm to 600 mm x 600 mm) via the use of corbel units.
Adjusting units can be installed between the concrete cover slab and the access cover and
frame (can be used in replacement of engineering brickwork in most situations).
Manhole rings can be pre-fitted with double steps or supplied plain for post fitting of ladder
system or where winch access only is permitted.
1.3.9 Soakaways
Manhole rings can also be supplied with perforations for the use in the construction of
soakaway chambers.
Special chambers are widely being precast that can include flow control and treatment devices,
weir walls and manifold units (multiple pipelines entering parallel into connecting chamber) etc.
Where manholes are required to be constructed and normal construction methods would not
be suitable (e.g. large depth, poor ground or high water table), suppliers are also available to
offer units for sinking top down via a caisson sinking system.
Where a pipeline discharges into a watercourse such as rivers, ditches, ponds or swales, spillway
headwalls are commonly installed.
The spillway headwall not only anchors the end of the pipeline, but also helps to control erosion
and scour and the units can be fitted with grills to help prevent materials (or animals/people)
entering the pipeline.
2: INSTALLATION - PIPES 37
2 - INSTALLATION: PIPES
This section describes the recommended procedure for the installation of concrete pipelines
in trenches for non-pressure (gravity) applications or when occasional periods of hydraulic
surcharge may occur. It covers the types of laying conditions most commonly encountered
in practice. In situations beyond these general conditions, the pipeline designer and the site
engineer should give suitable instructions to supplement this guidance.
Pipelines laid under embankments require special consideration whilst those installed by pipe
jacking require the use of specialised techniques.
2.1 Planning
General
Prior to constructing the pipeline, the contractor will need to organise the work from the contract
documents, specification, drawings and bill of quantities.
The line and level of the sewer, any side connections and the positions of the manholes will have
been determined at the design stage but some flexibility in construction should be permitted to
cater for circumstances such as foundations or buried services not shown on the drawings. An
agreed re-siting of a manhole may save time and additional expense.
Sequence of operations
e) Check for damage, lay and joint pipes, air testing every third or fourth pipe as laying
proceeds. Check line and level.
Time and place of off-loading should be agreed before units arrive on site. The contractor should
have suitable equipment for off-loading, stacking and stringing out pipes and other units on site.
All lifting tackle must be of good sound construction and should be regularly tested and certificated.
Off-loading
Whenever possible, pipes and other units should be off-loaded in the reverse order that they
were loaded. The vehicle must not be moved if any part of the load is unsecured. Off-loading
38 2: INSTALLATION - PIPES
should take place at the nearest hard standing to the point of installation; all units must be left in
a stable position well clear of the edge of the trench.
For further information, refer to the CPSA Health & Safety Off-loading Guide
http://www.concretepipes.co.uk/page/pipe-laying-lifting
CPSA member companies are also available to advise on general handling of products and
appropriate lifting equipment. Member companies contact details can be found here:
http://www.concretepipes.co.uk/suppliers
Use of tackle
Where provided, lifting holes, anchors etc. must be used with the correct equipment to lift the
units (note - installed lifting points may not necessarily be suitable for the transportation of a
product across a site).
Pipes
Pipes should be handled individually using a properly designed “C” hook, beam sling or other
purpose-designed system. Small diameter pipes may be slung through the bore providing the
sling is sleeved and protected around the joint. This is important in order to avoid damage to
jointing surfaces and consequent leakage of the laid pipe. ‘Pipe hooks’ must not be used. Slings
may be made of cordage, canvas, or man-made fibres, but not unprotected chains.
Many manufacturers offer a combined lifting and jointing system using a three-legged chain and
cast-in facilities (larger pipe sizes only). A special concrete pipe lifter is also available providing
improved site safety, reduced installation time, labour and cost savings. Further details relating
to the concrete pipe lifter and other proprietary lifting devices can be found in the CPSA Site
Guide, available at www.concretepipes.co.uk and directly from CPSA members.
How to Use
• Perform appropriate pre-work checks to ensure all equipment is working properly and has valid
operating certificates, where required.
• Connect Pipe Lifter to excavator via quick hitch coupling, ensuring correctly attached and locked
in position.
• Fully insert the long lifting arm horizontally into the barrel of the pipe and carefully raise to make
contact with the internal crown. When installing pipes, ensure it is lifted from the socket end.
• The clamp arm will slowly press down onto the top of the pipe and hold it in position.
• The pipe may now be lifted and transferred to a suitable storage location or placed into the
prepared trench and jointed following the application of an approved joint lubricant to the pipe
2: INSTALLATION - PIPES 39
spigot. Care should be taken to avoid lubricant coming into contact with the lifting area as this
can cause the pipe to slip.
• Depending on the weight of pipe, depth of installation and lifting capacity of site plant, the
pipe may be tilted up to 30 degrees from horizontal and maneuvered between struts on trench
support systems. It can also be used to push the pipe home to ensure formation of the correct
joint gap.
• Check limits of use before operation including lifting capacity and the compatibility of trench
support system with the Pipe Lifter to ensure that struts do not interfere with the removal of
the lifter from the pipe.
• When installing a pipe, no personnel should be in the working area or come into contact with
the Pipe Lifter, excavator or any pipe in transit.
Other units
Where lifting eyes or lifting holes are provided they should be used. Extra care should be taken
when lifting bends and junctions (pipes with inlet).
Chocks
When pipes are loaded, transported or stacked, sufficient timber chocks should be provided.
Chocks or packing between individual units should not be removed until lifting tackle is secured.
Care in handling
Pipes and other units must never be dropped. Pipes which have to be moved should be lifted
and never dragged. When pipes have to be rolled, beware of rocks or boulders. Care should be
taken to avoid damage especially to jointing profiles.
Stacking on site
Ideally, pipes should be strung out and secured beside the trench where they are to be used.
Where stacking is necessary this should be on level ground and the bottom layer of pipes securely
chocked to prevent the stack from collapsing. Pipes should be supported under the barrel so that
the socket is free of load and so that the jointing faces are not damaged. They should be stacked
barrel to barrel with sockets overhanging, or with spigots protruding as preferred.
For safety reasons and to prevent damage to the lower layers of pipes in the stack, pipes should
not be loaded or stacked in a greater number of layers than shown in Table B1 overleaf.
40 2: INSTALLATION - PIPES
150-225 6
300-375 4
450-600 3
675-975 2
above 975 1
Precast concrete pipes are normally supplied with an elastomeric sealing gasket integrally-cast
into the socket of the pipe. For other forms of joint seal, the quantity, type and diameter of
jointing rings or other jointing materials should be checked with the delivery note at the time
of off-loading. Elastomeric rings should be carefully stored and protected from sunlight, oils,
greases and heat. If the rings have been tied they should be separated a few days before use
in order to eliminate minor impressions which the ties may have caused. Rings should not be
stored hanging from a hook.
The trench should be dug to the line, gradient and width indicated on the drawings or in the
specification or as agreed with the Engineer. The safety of the public and site personnel is of
paramount importance.
Trench width
Any increase in trench width above that specified could increase the load on the pipe and
increase the quantity of the excavation and of bedding material.
A trench narrower than that specified may impede the proper placing and compaction of the
bedding material and restrict working conditions in the trench during pipe laying.
A trench adjacent to a manhole may need to be wider but this should be taken into account at
the design stage.
The trench width should allow for safe working alongside the pipeline. For recommended trench
widths see load tables in section 1.2.5, pages 26-29.
Formation
Rock outcrops and soft zones such as peat or boggy material which can cause differential
settlement should be dug out and replaced with well tamped selected material.
Ground water should be kept below the bottom of the trench during pipe laying operations by the
use of temporary drains, sumps or a designed well-point system. The water level should not be
allowed to rise before backfilling is completed.
If the trench bottom is likely to be disturbed by trampling during pipe laying, selected material
should be placed to protect it.
Where the trench bottom is unstable, for example in marshy ground or running sands, special
measures are necessary to ensure proper embedment.
2: INSTALLATION - PIPES 41
A trench excavated in clay should not be kept open any longer than necessary to avoid instability
due to change in moisture content.
Pipe laying
Before lowering into the trench, each unit should be inspected carefully for any damage which
may have occurred in transit or during handling and storage on site. Pay special attention to
jointing surfaces. Units should be lowered carefully into the trench with tackle suitable for their
weight and for the depth of the trench.
The contractor should have available, at the required time, all material and equipment necessary
for carrying out the work in accordance with the specification and statutory safety requirements.
The contractor must ensure that the size and strength class of pipes or other units conform to the
contract specifications and manufacturer’s recommendations. In the case of integrated gaskets,
the joint must be prepared i.e. the application of the correct lubricant and the removal of the
gasket positioning strip (where present).
Normal gradients
Pipes should be supported by the bedding over the length of their barrels and their weight must
never be carried by the sockets or by bricks and rocks in the trench bottom. Bedding under the
pipe should be scooped out to accommodate pipe sockets at each joint. The pipes should be laid
and assembled in correct alignment.
If, in order to curve the pipeline it is necessary to deflect the pipes at the joints, the deflection
should be applied only after the joint has been made in the normal manner and should be limited
to 75% of the manufacturer’s recommended limits to allow for any subsequent movement.
Mechanical plant must not be used to press pipes down to their correct level.
Changing direction
For a pipeline connection to a manhole or passing through a wall it is essential that the pipeline
joint retains its flexibility. This may be achieved by casting a short length of pipe into the wall of
the structure and providing a flexible joint adjacent to the wall. Depending on ground conditions,
short length pipes (rockers) should be used (see Section 1.3.6).
Unstable ground
2.4 Jointing
A number of different joint designs are manufactured, all of which comply with the performance
requirements of BS EN 1916 and BS 5911-1.
The pipe manufacturer’s jointing instructions should be complied with but the basic requirements
for jointing concrete pipes are:
• Pipes should always be handled in a way to avoid damage, especially the spigot and socket
ends and joint surfaces.
• Prior to jointing, the socket and spigot should be cleaned and inspected to ensure they are in
good condition.
• Most standard concrete pipes are supplied with an elastomeric seal integrally cast into the
socket of the pipe
• Remove the protective polystyrene strip (where present) by using the tape provided. Grip the
tab of the tape and pull firmly towards the centre of the pipe.
• Lubricant should be applied to the spigot end of the pipe, ensuring the radius area and entire
length of the spigot is covered. Additional lubrication may be also applied to the seal face to
assist jointing.
• Enter the spigot carefully into the socket, ensuring that the pipes are correctly aligned.
• Stretch and position the seal onto the spigot of the pipe ensuring it is not twisted. Even out
the stretch by lifting and releasing at several points around the spigot.
• The seal should be located on the spigot in accordance with the manufacturer’s instructions.
• Rolling seal joints do not require lubrication. Most sliding seal are internally pre-lubricated
and do not require additional lubrication. If the joint design does require lubrication then
follow the manufacturer’s instructions.
• With rolling ring joints, offer up the pipe spigot to the socket, but keep clear of engagement
by 25mm so that the joint ring is not disturbed. With sliding ring joints, the joint ring should be
just in contact with the socket.
• Enter the spigot carefully into the socket, ensuring that the gasket is correctly positioned and
that the pipes are correctly aligned.
• Jointing tackle or chain systems should be used in accordance with the pipe manufacturer’s
instructions.
• Fully support the pipe so that it does not exert undue weight on the seal whilst closing the
joint to the recommended joint gap.
• Joint the pipes in accordance with the manufacturer’s recommendations, making sure that
the pipe moves without excessive slew or misalignment, that extraneous matter does not
enter the joint and that the joint is not damaged and correctly positioned. For jointing bends,
special procedures may be appropriate.
2: INSTALLATION - PIPES 43
• After adjusting for line and level, release the tackle. Care should be taken not to disturb the
pipe or bedding material when removing slings.
• The finished internal pipe joint gaps should be within the tolerances as specified by the manufacturer.
• It is advisable to carry out an air test on the installed pipeline after the laying of at least every
3-4 pipes to ensure satisfactory installation has been achieved.
Back laying
When this is done, additional care is necessary to ensure that the joint is properly made with
the joint ring correctly positioned and that bedding material is not scooped into the joint.
Fig. B2. Integral sealing ring - standard for most UK concrete pipes
NOTES:
1. Each joint type is diagrammatic and typical.
2. Rolling and fixed rings may be one of a variety of different profiles / cross sections / designs.
3. Tolerances of joint profiles shall be determined by the pipe manufacturer and described in factory documents.
4. Joint assembly shall be watertight / airtight when constructed in strict accordance with the manufacturer’s recommendations.
5. Pipes with integral seals offer some protection to the seal, however the same precautions should still apply to protect the seal.
44 2: INSTALLATION - PIPES
2.5 Reinstatement
Trench reinstatement
After inspection and testing, backfilling should proceed whilst withdrawing trench sheeting in
stages where practicable.
The sidefill is of great importance and close attention to its selection, placing and compaction
will protect a new pipeline.
Good trenching practice including controlled removal of temporary supports and compaction
of backfilling as described above not only protects the pipeline but will also reduce settlement
and the risk of damage to adjacent underground services or structures.
The trench should be backfilled as soon as possible after the pipes are laid bearing in mind any
specified test and inspection requirements. Compaction of the envelope of material immediately
around the pipe is extremely important. In trench installations, as space is limited, mechanical
compactors are commonly used but caution should be exercised so as not to damage or
displace the pipe. The material should be compacted at near optimum moisture content and
should be brought up evenly in layers on both sides of the pipe, withdrawing trench sheeting as
backfill proceeds. Backfill material should not be pushed into the trench from the surface nor
dropped in bulk directly onto the pipe.
Heavy mechanical equipment should not be allowed to traverse pipelines with limited cover
except at prepared crossing places.
Fill material
Material for sidefill, initial and final backfill should be similar in character to the surrounding soil;
for example, the use of single size granular material in clay soil will create a natural drainage
channel that could cause subsequent settlement.
Sidefill and initial backfill should be free from large stones, heavy lumps of clay, frozen soil, tree
roots and other rubbish, and should be readily compactable.
Sidefill
The sidefill should be placed and compacted as soon as possible after laying, or as soon as it
is safe to do so without damaging concrete beddings. Compaction should be carried out evenly
on each side of the pipe to prevent lateral or vertical displacement.
Initial backfill
This should also be placed as soon as possible in order to provide protective cover of not less
than 300mm compacted depth. This should consist of bedding or selected material placed
carefully and evenly over the top of the pipe and lightly compacted by hand.
Remaining backfill
2.6 Testing
Acceptance tests on the completed pipeline give an indication of the level of control of
workmanship and materials during construction.
2: INSTALLATION - PIPES 45
Visual inspection
Check for: -
Man entry sized pipelines can be physically inspected whilst smaller diameters can be visually
inspected from manholes or by means of CCTV cameras.
All lengths of drain and sewer up to DN 750 should be tested for leakage by means of air or
water tests.
These tests should be carried out after laying and before backfilling. Some backfill may be placed
at the centre of each pipe to prevent movement during testing. Short branch drains connected
to a main sewer between manholes should be tested as one system with the main sewer. Long
branches should be separately tested.
Air Test
The air test is more convenient than the water test, but the leakage rate cannot be measured
accurately. An excessive drop in pressure in the air test may indicate a fault in the line such
as a displaced sealing ring or it may be due to faults in the testing apparatus. Therefore, the first
check must be on the apparatus, especially the seals of the stop ends and all connections.
The point of a leakage may be difficult to detect but spraying with soap solution could indicate
such leakage by the presence of bubbles.
Failure to pass this test is not conclusive. When marginal failure does occur, a water test should
be performed and the leakage rate determined before a decision on rejection is made.
Air test requirements are specified in ‘Civil Engineering Specification for the Water Industry’.
It is strongly recommended that inflatable stoppers are used for air testing.
A successful test is achieved if the equipment shows a fall in pressure of no more than 25mm
after 5 minutes, having allowed a suitable period for stabilisation.
If the pressure falls sharply and the pipes appear to have failed, check the test equipment is in
good condition, that the stoppers are not leaking (use industrial soap around the edge of the
stopper to provide an effective seal if necessary) and check the joint rings are correctly located
or re-test after allowing temperature to settle.
Water Test
A water test is the more conclusive method of testing a completed pipeline but problems of
availability and disposal of the quantity of water involved may cause difficulty. Before backfilling,
leakage can be clearly located, its amount assessed and where necessary, appropriate
remedies applied.
a) Insert plugs in both ends of the drain or sewer and in connections if necessary. Precautions
should be taken by strutting or otherwise, to prevent any movement of the drain or sewer
during testing.
b) Fill the system with water ensuring all the air has been expelled.
c) Allow at least two hours before test readings are taken to permit conditions to stabilize,
adding water to maintain test head.
It may be necessary to extend this period for large diameter pipes, up to twenty-four hours
or more before a stable condition is reached.
d) Apply required test head at the upper end by means of a flexible pipe leading from a graduated
container or stand pipe.
e) Apply the test pressure of 1.2m head of water above the soffit of the drain or sewer at the
high end with a maximum of 6m head at the low end. If this exceeds 6m test the drain or
sewer in stages.
f) Measure the loss of water over a period of 30 minutes by adding and metering quantities of
water at intervals of 5 minutes to maintain original water level in the standpipe.
Over this 30 minute period, the quantity of water added should not exceed 0.05 litre per 100 linear
metres per millimetre of nominal size of the drain or sewer.
Over this 30 minute period, the quantity of water added should not exceed 0.05 litre per 100
For example:
linear metres per millimetre of nominal size of the drain or sewer.
For a 150m length of DN 800 pipe the allowable leakage would be:
Should the pipeline not comply with these requirements it will probably be attributable
to one of the following:-
b) Trapped air.
The basic pipe jacking method has been used in various forms for centuries but only in the past
decades have we seen significant advances in equipment and technology.
This has raised confidence in the technique and numerous successful pipeline engineering
schemes have used pipe jacking and microtunneling.
Normally, for pipelines constructed in this manner up to DN 900 the technique is referred to as
microtunneling and above this as pipe jacking, but the principle remains the same.
Spoil excavated by the rotating cutting head in the front of the shield is removed by an auger flight
or by mixing with water and pumping to the ground surface for treatment and disposal. Some
progress has been made with the development of machines which can compact soil to the sides
of the shield as it advances. Other equipment types use vacuum systems for the removal of
excavated material to the surface.
Particularly high levels of installation accuracy can be achieved with these systems since they
use sophisticated steering and guidance methods based on laser technology and optional
automatic computer control. Finished bores have frequently been described “like rifle barrels”.
Equipment has been developed which can install pipes in small diameters down to DN150 for
house connections and lateral drains without the need for a trench.
3.3 Advantages
The advantage of using a trenchless method can be substantial. Any attempt to dig up long
trenches within an urban area often results in severe disruption, delays and diversions to traffic,
environmental pollution through noise, dust and dirt, loss of profit for local businesses, damage
to properties or other buried pipes and cables and so on. These items are usually referred to
as social costs and are nearly always absorbed by the community rather than paid as direct
engineering costs.
However, when one considers further, other equally serious problems become apparent. Sometimes,
the as-dug material excavated from the trench is not suitable for re-use as backfill. This waste
spoil must be transported away from the area and disposed at a suitable landfill site. Such sites
are becoming more difficult to find and the cost of using them is increasing. Also, new backfill
material such as crushed stone has to be imported to the site and these operations usually
involve heavy wagons inflicting damage to roads and using fuel which in turn produces more
pollution. These environmental costs are compounded by the damage and visual impact to the
countryside from landfill and quarrying sites.
48 3: INSTALLATION - JACKING PIPES
Pipe jacking and microtunneling can dramatically reduce many of these social and environmental
problems. The technique offers significant benefits in reduced excavation since they only
require relatively small launch and reception shafts for the tunneling equipment. Streets and
roadways can often be kept open to traffic with little hindrance or disruption. The environment in
general benefits from a no-dig approach because far less transportation of trench reinstatement
materials is required, normally limited to only the displaced spoil from the pipes and manholes.
Reduced levels of reinstatement lead to cost savings, as much of the cost of a pipeline scheme
is in the excavation and subsequent reinstatement. Installation depths of up to 35m have
successfully been achieved which would not have been possible with open cut methods.
3.4 Products
The UK concrete pipe manufacturing industry is playing a leading role in the advancement of
trenchless techniques. Several CPSA member companies produce jacking and microtunnelling
pipes in a range of sizes. These pipes are manufactured to produce accurate joint surfaces
with square faces and a strong high density concrete with a smooth surface finish to assist in
reducing jacking forces.
Jacking and microtunneling pipes are available in sizes from DN 450 up to DN 2500 and utilise
elastomeric seals in a steel banded joint. These pipes are manufactured to comply with the
requirements of European Standard EN 1916:2002 and the UK complementary standard BS
5911-1:2002. The external surface of the pipeline is smooth for easy insertion through the ground
during installation. For steel banded joints, both mild and stainless steel are available. Jacking
pipes can be supplied with grout holes and cast-in lifting sockets as required.
Other products for use with this trenchless method include caisson sections in sizes from DN
2000 to DN4000 complete with base sections fitted with cutting shoe. Also produced are lead
pipes which are rebated to accommodate the tunneling shield and interjack pipes (leading and
trailing pipes in pairs) for use with intermediate jacking stations.
The United Kingdom Society for Trenchless Technology (UKSTT) is another useful source of
information on trenchless techniques including pipe jacking.
4: INSTALLATION - MANHOLES 49
4: INSTALLATION - MANHOLES
Manholes may be installed using fresh concrete to construct the base, channels and benching
in-situ or by using a precast base system where units are manufactured and delivered to site with
predetermined positions for connecting pipework using flexible, watertight elastomeric joints.
4.1 Planning
Sequence of operations
a) Place the bottom unit with either integral precast or in-situ concrete base.
b) Erect the required number of standard components and seal the joints as
appropriate in accordance with the design/chosen method of construction.
d) If required, place a corbel slab then add the appropriate number of adjusting units.
2) Cover, landing and reducing slabs are usually cast with anchors allowing the use of hook
and chain/sling sets.
Note: Apparatus used for lifting, may not necessary be suitable for the transporting of products
across a site.
Other lifting methods may be available or available to order – check with manufacture for full details.
Chamber rings should be stored ‘chimney’ fashion i.e. not on their side, or rolled.
Chamber rings and all types of slabs should be stacked on level and stable ground and on
timbers wherever possible.
4.3 Construction
To ensure that the manhole structure is vertical, accurate levelling of the formation for the
precast base unit or the in-situ concrete foundation is essential.
Shaft and chamber sections with tongued and grooved joints should be installed with the
socket / groove facing upwards, whereas units with ogee joints should have the spigot upwards.
Precast cover slabs can be installed onto the shaft or chamber rings (with appropriate mastic,
mortar or seal). Suitable cover and frame can then be bedded on adjusting units to achieve the
finished level required.
Note that the distance from ground level to the first step in the manhole is usually specified as
not to exceed 675mm (where units are fitted with step or ladder system).
Jointing to pipeline
To allow for differential settlement between manhole and pipeline, short “butt” pipes, either
50 4: INSTALLATION - MANHOLES
spigot or socket, should be built into the wall of manholes constructed with an in-situ concrete
base and a flexible joint incorporated as close as possible to the outside of the manhole wall
or concrete surround, if used.
Depending on ground conditions, short length pipes (rockers) then connect the butt pipes to the
incoming pipe runs. Additional care must be taken to ensure that the joints are properly made.
4.4 Jointing
Precast manhole components are provided with joints formed within the wall section. These are
rebated or tongued and grooved and are sealed with proprietary mastic seals, sand / cement
mortar, or with elastomeric joints. Precast concrete manhole units, well jointed, provide an adequate
seal under normal conditions. Any lifting holes will need to be sealed with sand / cement mortar or
a proprietary non-shrink mortar.
Joint strips typically have a thickness of 12mm and are offered in one or two layers as demonstrated
in the table below.
1 or 2 strips
1 or 2 strips
4: INSTALLATION - MANHOLES 51
Joint
4.5 Reinstatement
In-situ concrete surround
In-situ concrete surround to precast concrete manholes, except for side-entry manholes, is
unnecessary other than for exceptional structural reasons such as embankments, in sloping
or unstable ground, where there is a large opening into the manhole, where it is a requirement
due to a permanent head of water or where an individual specification requires it i.e. as in some
types of adoptable manholes specified in Sewers For Adoption.
Note: Sewers For Adoption includes for the use of thicker walled (minimum 125mm thick) manhole
rings without the requirement for a concrete surround.
Side entry manholes should be provided with a suitably designed GEN 3 concrete surround of
at least 150mm thick extending the whole length of the pipe in which the manhole is placed.
Backfilling
As each precast manhole section is placed, backfill should be returned in layers and compacted
as for pipelines. Backfill must be brought up evenly around the manhole to prevent displacement.
Additionally, care should be taken to avoid damaging the connecting pipelines.
Special consideration should be given where construction plant is working in the vicinity of
manholes. Where possible, traffic should be routed away from such structures and may require
temporary protection with heavy steel plates or temporary additional cover material.
4.6 Testing
It is generally unnecessary to apply water tests to manholes. In working conditions manholes
are not normally full of water. This only happens under rare conditions of surcharge. Prevention
of infiltration is of more relevance than exfiltration and where this occurs, it can be remedied by
sealing using an appropriate method.
Where testing of manholes is required, see Sewers For Adoption or Civil Engineering Specification
for the Water Industry for suitable method.
52 5: REFERENCES AND FURTHER READING
1 Sewers for Adoption 6th and 7th Editions March 2006 Water UK / WRc
& August
2012
2 Sewers for Adoption 6th Edition – Combined March 2006 Water UK / WRc
Addendum
3 Civil Engineering Specification for the Water Industry March 2011 WRc
(CESWI) 7th edition
6 Tables for the Hydraulic Design of Pipes, Sewers and 2005 HR Wallingford
Channels 8th edition and D H Barr
9 Guide to Best Practice for the Installation of Pipe Jacks 1995 Pipe Jacking
and Microtunnels Association (PJA)
The information in this guide is to the best of our knowledge true and accurate, but all information provided
is for guidance only and made without guarantee. Since the conditions of use are beyond their control, the
Concrete Pipeline Systems Association disclaims any liability for loss or damage resulting from the use of
this guide. Furthermore, no liability is accepted if use of any products in accordance with this data or these
suggestions infringes any patent. The Concrete Pipeline Systems Association reserves the right to change
product specifications and references without notice.
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