Gravity Sewer PVC Pipe Systems - DESIGN MANUAL 2017 - www.dpiplastics.co.za - DPI Plastics
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DESIGN MANUAL 2017 Gravity Sewer PVC Pipe Systems www.dpiplastics.co.za
Index Introduction 2 Advantages Of PVC in Sewer Pipe Systems 2 Quality Assurance & Control 3 Membership 4 Pipe Dimensions • Freeflo Soil & Vent Pipe 5 • Durodrain Sewer & Drain Pipe 5 • Ultrapipe Structured Wall PVC Pipe 5 PVC Fittings • Freeflo Soil & Vent Fittings 6 • Durodrain Sewer & Drain Fittings 6 Installation • Joining Rubber Ring Joints 7 • Joining Solvent Weld Joints 8 • Trenching, Bedding & Backfilling 8 • Recommended Fall 10 • Repairs 10 • Rodding 10 • Water Jetting 10 • Testing 11 Support Spacing for Suspended Pipes 12 Bending 12 Storage, Loading & Transport 13 PVC Properties • Pipe Stiffness 14 Design • Soil/Pipe Interaction 15 • Deflection 17 • Live Loads from Soil Surface 19 • Wall Stress 19 • Deflection Comparison 20 • Effects of Soil Modulus 20 • Velocity and Flow 21 UV Resistance 22 Chemical Resistance 22 Disclaimer 25 Bibliography 25
An introduction Advantages of PVC in
Sewer Pipe Systems
to PVC
PVC is the perfect material for pipes and fittings in
PVC is the preferred material for aboveground soil,
gravity sewerage systems. This is evident through its
waste and vent, and underground gravity sewer
worldwide use in this application. Some of the
systems worldwide. PVC sewer pipes and fittings
advantages of PVC versus other materials used in
are practical and economical. Recent market
sewer systems are as follows:
studies in South Africa have shown that PVC
dominates the gravity sewer market for pipe sizes
up to 500mm diameter, with more than 95% of the • PVC pipes and fittings have smooth inner surfaces,
resulting in low frictional resistance
pipe systems installed during 2015 in this size
range being PVC. • Structured wall PVC pipes and fittings offer high hoop
stiffness and low weight
PVC also has a great track record to its benefit, as
• PVC is semi-flexible, allowing greater resistance to
it has been around for more than 40 years in
damage due to ground movement, when compared to
South Africa and longer in certain other parts of traditional sewer pipe materials
the world. Its continued use and acceptance
• PVC can be easily painted to match colour schemes or
around the world is a testament to PVC’s suitability
for additional protection
for sewer and drainage applications.
• PVC has a harder surface than other plastic sewer
Furthermore, current consciousness of energy systems, resulting in increased resistance to damage
savings, low carbon footprint and cradle-to-cradle during rodding of sewer lines
approach, highlights the greatest benefits of PVC • PVC is non-corrosive, resists buildup of algae and scale
as a sewer pipe material. The longevity and low
• Due to its high tensile strength and modulus, PVC pipes
maintenance nature of PVC sewer installations, and fittings need thin wall thickness for similar
along with its recyclability, make PVC very performance as other sewer plastic systems
economical during it’s service life and beyond. • PVC soil, waste and vent pipes are highly resistant to
DPI Plastics has been developing and ultraviolet light and can be used in direct sunlight
manufacturing PVC sewerage pipes and fittings for • PVC has excellent fire properties; it does not support
more than 30 years and the company has a combustion without a heat source
wealth of knowledge and experience. Our PVC • PVC pipes and fittings are supplied with integral rubber
formulations have been honed over the years to ring joints, or with plain sockets for solvent weld joining
aid process ability, and produce high quality • PVC performs well at low temperatures and remains
products that last. DPI Plastics has pioneered a rigid at 60° Celsius. It has a low coefficient of thermal
number of innovations in South Africa, including expansion, compared to many other materials. This
structured wall (ribbed) underground fittings, results in stable sewer stacks that resist sagging
increasing stiffness, whilst saving on mass and • Suspended PVC plumbing pipes, due to their rigidity,
cost. need less supports than polyolefin pipes (PP and PE),
saving costs and installation time
This manual aims to provide the necessary
• PVC has much lower linear thermal expansion than
basic information needed to work with PVC
Polypropylene and Polyethylene
sewer pipes and fittings. More information is
• DPI Plastics PVC pipes and fittings are manufactured in
available on the DPI Plastics website,
accordance with latest requirements in terms of
www.dpiplastics.co.za, or via our technical
exclusion of heavy metals and are safe to use.
department.
GRAVITY SEWER PIPE SYSTEMS / 2
Quality Assurance & Control
PVC pipes and fittings for aboveground soil, waste and vent systems, and for underground sewer and drainage
systems are manufactured by custom designed extrusion and injection moulding processes, and to exacting
specifications, to ensure the long term performance of pipes and fittings. PVC pipes and fittings are designed as
complete systems, which work together perfectly to ensure reliability and durability during everyday use.
Quality Assurance Quality Control
The quality of the output of a factory depends upon the Quality control procedures are specific to the
management and control exercised by the organization production operation where product is monitored on a
and functioning of the production unit, over those predetermined frequency for compliance with a number
activities which affect quality. In this respect the ISO of specific product requirements, including:
9001 Quality Management System is adhered to by
• Dimensions
DPI Plastics (Pty) Ltd, in which a set of guidelines and
• Resistance to leakage and deformation
disciplines to ensure optimum product quality based on
• Resistance to methylene chloride
inputs from the various activities in the production
• Pipe stiffness
cycle. The disciplines and guidelines specified by ISO
• Workmanship
9001 encompass all the processes of planning,
• Colour
organization, directing, risk management and control
• Printing
made up of specific elements. The ISO 9001 Quality
• Tensile strength
System is driven by top management.
• Resistance to solar radiation
DPI Plastics quality management system is one of the • Thermal reversion
oldest systems in the local plastic pipe industry, being • Hot and cold water cycling test
first awarded more than 20 years ago. This means that
the quality system is well entrenched in all areas of the
The quality control checks provide a guide to the
organization and it is lived daily by personnel in all
production process to ensure continued compliance to
departments. We are immensely proud of our quality
the product requirements. All quality control data is
and it shows in our products.
recorded, collated and stored in such a way that the
records are readily retrievable to demonstrate
compliance to specific requirements.
Product performance and requirements are set by the
South African National Standards (SANS) and ensure
that conforming products are easily identifiable by
consumers. Conforming products may carry the SANS
mark once audited and verified by independent
technical auditing firms such as the South African
Technical Advisory Service (SATAS).
3 / GRAVITY SEWER PIPE SYSTEMS
Membership
In addition to the aforementioned memberships, DPI Plastics
is also a member of various industry associations and
institutes including, inter alia:
• The Institute of Plumbing SA (IOPSA): www.iopsa.org.za
• The Southern African Vinyls Association (SAVA):
www.savinyls.co.za
• The Water Institute of SA (WISA): www.wisa.org.za
• The Institute of Municipal Engineers SA (IMESA):
www.imesa.org.za
Memberships enable DPI Plastics to participate in technical
committees and working groups and contribute to strategic
industry discussions, as well as promote the plastics industry.
GRAVITY SEWER PIPE SYSTEMS / 4
Pipe Dimensions
Soil, Vent and Waste Pipes
FREEFLO soil, waste and vent pipes
Outside diameter Nominal Wall Thickness Mass
(mm) (mm) (kg/meter) and fittings are manufactured to
SANS 967 and are designed
40 2,0 0,40 specifically for use above ground and
50 2,2 0,53 outdoor in non-pressure drains and
venting applications.
75 2,2 0,79
110 3,2 1,67
160 3,3 2,54
Sewer & Drain Pipes
Class 51 – Normal Duty Class 34 – Heavy Duty
Outside Nominal Wall Mass Outside Nominal Wall Mass
diameter Thickness (kg/meter) diameter Thickness (kg/meter)
(mm) (mm) (mm) (mm)
110 2,2 1,14 110 3,0 1,55
160 3,2 2,51 160 4,7 3,67
200 3,9 3,80 200 5,9 5,63
250 5,0 6,18 250 7,3 8,97
315 6,2 9,69 315 9,2 14,15
355 7,0 12,30 355 10,2 18,45
400 7,9 15,68 400 11,7 22,83
450 8,8 19,79 450 13,2 29,15
500 9,8 24,23 500 14,6 35,91
560 11,0 28,92 560 16,3 42,43
630 12,4 36,68 630 18,4 53,90
DURODRAIN normal duty sewer and drainage pipes are DURODRAIN heavy duty sewer and drainage pipes are
manufactured to SANS 791 and are used in underground manufactured to SANS 791 and are used in underground
drains. DPI Plastics offer a range of DURODRAIN fittings sewers. The DPI Plastics DURODRAIN range of fittings is
to complete the range. used with these pipes.
Structured Wall PVC Pipes
ULTRACOR and ULTRAPIPE
structured wall sewer and drainage
Class 100 Class 200 Class 400 pipes are manufactured to SANS 1601
Outside Normal Duty Medium Duty Heavy Duty
Diameter and are used in underground drains
(mm) E4 / ID Mass E4 / ID Mass and sewers. DPI Plastics multi-layer,
E4 / ID Mass
(mm) (kg/m) (mm) (kg/m) (mm) (kg/m) foamed center technology offers high
stiffness and low weight, compared to
110 0,4 / 105 1,0 0,4 / 103 1,1 0,4 / 100 1,4
solid wall PVC sewer and drainage
160 0,5 / 154 2,0 0,5 / 152 2,5 0,5 / 150 2,8 pipes. ULTRAPIPE also uses 100%
200 - - - - 0,6 / 186 4,4 recycled material in the centre layer,
thereby re-using PVC material for a
250 - - - - 0,7 / 232 6,9
greener product.
5 / GRAVITY SEWER PIPE SYSTEMS
PVC Fittings
DPI Plastics manufactures a complete range of fittings for aboveground and below ground sewer applications.
Fittings have been designed to meet the relevant SANS criteria and for ease of use, longevity and cost
effectiveness. DPI Plastics pioneered underground ribbed fittings, with ribs specifically designed to optimize
stiffness, whilst reducing fitting mass and cost. The following fittings are manufactured by DPI Plastics:
Soil & Vent Fittings
Type 40mm 50mm 75mm 110mm
Bend 87.5°, Plain or Access
Bend 45°, Plain or Access
Adaptor, 1 ½ - 2” BSP, Male and Female
Single Socket
Double Socket (Repair)
Junction 45° Single
Junction 45° Double
Junction 87.5° Single
Junction 87.5° Double
Junction 45° Reducing Single
Junction 45° Reducing Double
Junction 87.5° Reducing Single
Junction 87.5° Reducing Double
Pan Connector, Straight, Bent, Offset
Reducer, Eccentric, Concentric
Holder Bat, PVC or Aluminum
Vent Valve, One way or Two way
Stop End, Male or Female
Gulley Head and Grate, Round or Square
110mm Underground Sewer & Drain Fittings
Type 110mm Seal Type
Junction, Square, Plain Rubber Ring or Spigot/Socket
Gulley P-Trap Rubber Ring and Spigot
ABC Rodding Eye Rubber Ring
Stop End, Male and Female Solvent Weld (f); Spigot End (m)
Stop End Access, Female Solvent Weld
PVC/EW Adaptor, Female Rubber Ring
Bend Long Radius Spigot/Socket. 22½°, 45°, 90°
Double Socket, Kimberley or Repair Rubber Ring
Single Socket Rubber Ring/Solvent Weld
Inspection Pipe, Access Rubber Ring
Plain Bend, 22½°, 45°, 90° Rubber Ring
Access Bend, 45°, 90° Rubber Ring
NOTE: 160mm and larger fabricated fittings also available.
GRAVITY SEWER PIPE SYSTEMS / 6
Installation
Joining of Pipes – Rubber Ring Joints
Cutting Cleaning the seal Lubrication
Cut the pipe square with a cross cut It is important to ensure that the seal is DPI Plastics can supply liquid lubricant
saw or angle grinder depending on free of grit and mud before making the or jelly-like lubricant, known as gel or
pipe size. Observe all safety joint. Pipe ends are often accidentally soft soap. Both products are designed
requirements for the equipment being dipped into the sand. for lubricating pipe seals. In order to
used. Clean away swarf and chamfer make a leak-free joint effortlessly, use
the pipe end to 15° and at least 50% liberal amounts of lubricant, but avoid
through the pipe wall to ensure easy getting it into the seal housing. Lumps
insertion when making a joint. of gel lubricant on pipe seals or spigots
can be smoothed with a wet rag. Take
care not to leave lumps of gel lubricant
on the seal or pipe spigot. Take care to
keep pipe ends free of dirt.
Depth of Entry Jointing Joints
When making a joint, push the pipe It is important that the pipe ends and Flexible rubber ring joints are available
fully home into the socket to avoid socket are aligned and free of burrs, for all types of pipe and should be
hang-up and possible blockages. For otherwise insertion into the seal ring will used in preference to rigid joints,
large, heavy pipes, take care not to be difficult, or damage to the seal may allowing the pipeline to flex in the event
damage the socket by pushing with occur. For protection of the pipe ends of soil movements and also allowing
excessive force when the pipe nears use a lever against a wooden block. for thermal change.
the end of insertion, when using
mechanical means to join pipes.
7 / GRAVITY SEWER PIPE SYSTEMS
Joining of Pipes – Solvent Cement Joints
Solvent cement joining of small bore (up to 160mm) PVC pipes is an effective joining method, provided that care
is taken when joining the pipes. When done properly, solvent cement joints are just as strong as the pipe and
fittings being used. The guidelines below will assist in ensuring that a proper joint is made every time.
Equipment Procedure
In order to make a solvent cement joint you need: • Use the rag or towel paper and pipe cleaning solution to
clean the pipe and socket surfaces to be joined. Do not
• A fine tooth hack saw or angle grinder
touch the surfaces after cleaning as oils from your skin
• A sealed container with fresh solvent cement. Non-
prevent bonding where you touch the joining surface.
pressure solvent cement is designed for use with sewer
Let the solvent evaporate before continuing. When
pipes
using sanding paper, sand the surfaces in the
• A clean brush for applying solvent cement. A 50mm
circumferential direction. Only dull the surface, do not
paint brush works well on larger joints, while a 25mm
sand too much
brush is fine for smaller SV joints
• Apply the solvent cement evenly to the pipe and socket
• A clean rag or paper towel for cleaning the pipe and
using the brush. Rather apply too much than too little
fitting surfaces to be joined
• Immediately after applying the solvent cement, push the
• A pipe cleaning solution. These are normally available
pipe into the socket, turning the pipe a quarter turn as it
with the solvent cement and used to degrease the
is pushed home. Wipe any excess solvent cement from
surfaces to be joined. Alternatively one can sand the
the joint
surfaces using a 200 grit sandpaper.
• Leave the joint to cure before use. Instructions on the
solvent cement container will indicate the curing time.
Rule of thumb: curing period of not less than 4 hours is
recommended.
Trenching, Bedding and Backfilling
The procedures for trenching is based on the standard specification for civil engineering construction, SANS
2001 DB1 and DB4. Additional standards and recommendations are based on the code of practice SANS 0120
and the application of the national building regulations SANS 10400 series.
Trench Width
Pipe Recommended
diameter minimum depth
(see:Minimum cover
over sewers and drains)
300mm
Fill in with excavated trench material tamping at each
300mm layer 300mm
Selected fill blanket compacted uniformly 300mm
Bedding cradle and sidefill of compacted, selected granular
material. Allow 150mm sidefill (minimum) on both sides of
the pipe and 100mm above the pipe.
Bedding (not less than 100mm, not more than 200mm)
Level required to obtain specified minimum bedding cradle
thickness
GRAVITY SEWER PIPE SYSTEMS / 8
Excavation • Additional selected granular material must be placed
Pipe trenches shall be excavated to a depth suitable for around the pipe in layers of approximately 100mm and
the provision of adequate cover over the crown of the compacted to the specified density up to a height of
pipe, and to a specified or allowable width. 100mm above the crown of the pipe.
The sides of the trenches shall be as near vertical as
Fill Blanket
possible for a height of at least a full diameter of the pipe,
The fill blanket must be compacted to 90% modified
plus the specified depth of selected fill blanket over the
AASHTO up to a depth of at least 300mm above the pipe
pipe.
crown. Take particular care not to damage, deflect or
Trench bottom: material unsuitable for the bottom of the displace the pipeline during laying.
trench shall be excavated. The trench must be refilled with
selected material and compacted. Bedding must be Minimum Cover over Sewers and Drains
smooth and level. Design the sewer invert level to provide a minimum crown
depth cover over the top of the pipeline of 900mm for
It is important that the trench is not opened too far in
sewers and 300mm for drains. Calculate the expected
advance of the pipe laying operation. Pipes must be
traffic loads on sewers and drains where they run under
backfilled immediately after laying, with joints left open for
roads or sidewalks, and, if necessary, increase the
testing. It is recommended that the depth of cover, from
minimum cover in such areas.
the top of the pipe to the ground surface, be not less than
0.9m for sewers and 0.3m for drains. Backfilling
Backfilling of pipe trenches must commence after the pipe
Bedding has been laid and firmly bedded in the bedding cradle,
Bedding and fill shall be selected granular material. The
and the selected fill blanket placed and compacted, as
trench bed must be free of stone or hard projections
specified above. The pipe must be backfilled immediately
which are likely to cause damage to the pipe.
after laying, leaving the joints exposed for testing. The
pipeline must be laid directly on the prepared bedding in
Backfill Material
the trench, and any temporary supports, bricks or other
Selected fill material shall be used and shall be free of
foreign hard bodies must be removed.
vegetation, lumps or stones or any other foreign particles
of diameter exceeding 30mm.
Compaction
Backfilling must be done in 300mm layers and each layer
Bedding Cradle
compacted to 90% modified AASHTO density. In areas of
PVC-U pipe must be supported on a continuous bed of
road traffic loads, trenches must be backfilled in layers not
selected granular material of compacted depth of at least
exceeding 150mm (after compaction) and the material
100mm, and covering the full width of the trench.
compacted to 93% modified AASHTO density for
• Selected granular material must be of a granular, cohesive soils and to 98% in the case of non-cohesive
non-cohesive nature, graded between 0.6mm and soils.
19mm, free draining and the specified compactability
• Compaction density for the bedding cradle must be
90% modified AASHTO
Encasing Pipe in Concrete
Concrete encasing of horizontal PVC pipelines is not recommended, as it converts a flexible pipeline into a long,
unreinforced concrete beam of negligible strength, likely to fracture with minor ground movement.
Under concrete slabs of raft foundations, a minimum compacted cushion of 75mm fill between the pipe crown and
soffit of the slab should be provided. Where the pipe passes through a ground beam or footing, a lintel, reveling arch,
or similar device, should be used to provide a minimum of 50mm clearance.
When casting concrete around a vertical pipe, note that concrete has a high density and it is recommended that
casting be done slowly, taking care not to collapse the pipe. The critical buckling strength of the pipe has to be taken
into consideration.
9 / GRAVITY SEWER PIPE SYSTEMSRecommended Fall
Maximum Gradients and Anchoring
Grade the sewer to follow the slope of the ground as far as practical. Where slopes greater than 1 in 10 are required, provide
20MPa concrete anchor blocks that are at least 300mm wide and that are embedded into the sides and bottom of the
trench to a depth of 150mm. Avoid sharp transitions at the bottom of steep slopes.
Minimum Gradients
The minimum permissible full bore velocity, normally 0.9m/s, determines the minimum gradient. In exceptional circumstances
only, a minimum velocity of 0.6m/s may be used. The minimum gradient is required to ensure movement of solids and liquids
in the sewer pipeline, to prevent blockage. The flow in a gravity sewer can be calculated using Manning’s equation. See
section Design for details.
Repairs
The Kimberley socket is used to make repairs to pipework or to insert new fittings into the pipeline.
To insert a socketed fitting, proceed as below, but first fit a length of pipe into each socket of the fitting and position it
between two Kimberley sockets as before.
Cut and remove the portion of Lubricate both seal rings of Fit the replacement unit Slide the Kimberley
the pipe to be replaced the Kimberley socket and into position socket over the joint
a. Chamfer and remove burrs locate the fitting on the between the new and
b. Prepare the replacement existing pipe existing pipe
pipe and fittings
Rodding Water Jetting
If the drainage system is designed and laid correctly, Water jetting is becoming increasingly popular as a
rodding is seldom needed. Note that incorrect rodding method for cleaning and maintaining sewers and drains.
procedures can lead to damage to the drain, regardless of This method is suitable for use on PVC-U systems.
what material it is constructed from. It is strongly
DPI Plastics successfully conducted a series of tests
recommended that a drain cleaning expert is consulted for
under the auspices of the Structured Wall Pipe Association
advice on the correct type of equipment to use.
of South Africa. The United Kingdom based Water
It is imperative that one ensures that the rubber seal ring Research Council’s acceptance testing methods were
and pipe are well cleaned before making a connection. adopted as a pipe material selection criteria suited for
The major reason for rodding is caused by root ingress installation where water jetting is to be carried out.
which can be avoided if rubber seal rings are not DURODRAIN solid wall, ULTRACOR and ULTRAPIPE
dislodged or damaged during installation. structured wall pipe systems meet the test criteria which is
far more onerous than operating conditions.
• Ensure rubber seal ring and pipe are well cleaned before
making a joint Equipment manufacturers provide instructions for correct
• Correct amount of lubrication must be used. cleaning methods that will prevent unnecessary accidents
Correct system design is also very important to ensure to the operations and the sewer system.
rodding friendly pipelines. The use of ABC rodding eyes at
the end of every straight pipe section and long radius or
45 degree bends where rods can pass are recommended.
GRAVITY SEWER PIPE SYSTEMS / 10Testing
Air testing (manometer test) in sewers and drains is the accepted method that has been adopted by the industry
as the most effective means of establishing acceptance by the respective authorities. Water testing is an easier
method of finding leaks, but water is not always available and generally is too costly an exercise. SANS 2001: DP
4 describes the test and acceptance / rejection criteria.
Equipment required Procedure
• An approved Manometer in a leak free condition • Check all the equipment for leaks
• Testing plugs in a leak free condition (ensure the rubber • Ensure that the section of pipeline to be tested has
seals are not perished and that end caps are sealed been sealed off at all branches and that all access
and not cracked) openings are secure
• Stopwatch for recording the time • Insert testing plugs and secure properly
• Bottle of soapy water to check for air leaks • Adjust the water level in the Manometer to zero on the
• Large bucket scale (by adding water slowly)
• Small funnel for filling the Manometer tube. • Open the valve on the Manometer and pump until a
reading of 400mm is reached (this reading equals a
pressure of 4.00kPa). 400mm has been selected as it is
Scale on Manometer in mm easier to read than 375mm (3.75kPa) referred to in the
specification
• Close the valve and allow the water column to settle for
two minutes. There might be a marginal drop in
pressure. Should it not stabilise, check the connections
on the Manometer and plugs for leaks by pouring soapy
water on them. Should there be any leaks, these must
be repaired before proceeding with the test
• Open the valve and adjust the pressure to a reading of
250mm (2.50kPa) and start recording time. The
pressure is permitted to drop to a reading of 125mm
(1.25kPa) and the time taken to drop to this level should
be no less than the time stated in the table below.
Minimum Time for Pressure to
Pipe Size
Drop from 250mm (2.50kPa)
(mm)
to 125mm (1.25kPa) in min.
110 2
160 3
200 4
250 4.5
315 6
355 7.5
400 8
450 9
500 10
560 11
630 12
Useful tip
Test the line at short intervals to simplify the locating of possible leaks. Allocate responsibility of testing to a crew.
Their familiarity with the equipment will save time and effort.
11 / GRAVITY SEWER PIPE SYSTEMSSupport Spacing for
Suspended Pipes
Using Pipe Hangers and Supports
All piping in a plumbing system must be supported using various pipe hangers, clamps, brackets or other
supports that are capable of keeping the pipe and its contents, from unwanted movement. Without proper
support for pipes, some or all of the following adverse effects may cause problems with your plumbing systems:
• Pipe sag - Plastic pipes are especially susceptible to sagging from heat and even under it's own weight if improperly
supported. Sagging can cause blockages and improper venting within the system
• Mechanical failure - Improperly supported pipe causes extra strain on joints that can lead to breakages or joint
separation
• Thrust - A properly supported pipe will limit the effects of thrust; this will extend the piping's longevity and limit noise
from vibration
• Expansion - Every type of pipe will expand and contract with temperature fluctuations. Using the right hangers and
supports to accommodate these changes, will protect the piping from damage.
Rules for pipe supports Pipe hanger spacing
DPI Plastics recommends that FREEFLO pipe clips or Vertical pipe is supported at its base and at alternating
holder bats be used with FREEFLO SVW piping systems, floors to a maximum spacing of 5 meters.
as they are specifically designed to work with the pipes
Horizontal pipe and tubing is supported at intervals along
and offer good grip and support.
its length depending on the material and pipe size. PVC
Piping, fixtures, tanks and equipment are to be supported plumbing pipes require the following maximum spacing
independent of each other. (e.g. You can't hang a pipe between hangers and supports:
from another pipe.)
When supporting plastic pipes, care must be taken not to Type of Pipe Maximum Hanger Spacing
compress or damage the pipe.
PVC 1.2 m
Expansion type inserts or built in hanger supports are to
PP 0.8 m
be used when supporting pipe from concrete. Always
keep thermal expansion of PVC pipe in mind when
installing a pipeline. PVC pipe will expand / contract
linearly by 0.06mm per 1 meter of pipe for every degree
Celsius (°C) rise/fall.
Bending and Angular Deflection
DPI Plastics pipes and rubber ring joint fittings can be
deflected up to 2 degrees through each socket to
accommodate small changes in direction. Small bore
pipes (up to 110mm) can also accommodate up to 2
degrees of bowing through a 6 meter length. Larger
changes in direction are accommodated by using
DURODRAIN bends.
Take care to keep the pipes aligned during installation /
jointing. The required deflection should be done after
jointing. This minimizes the risk of damage to the rubber
ring during jointing. Also note that solvent weld joints offer
no deflection through the joint.
GRAVITY SEWER PIPE SYSTEMS / 12Storage, Loading and Transport Handling Pipes and fittings manufactured in PVC-U are strong, durable and light weight and easy to handle. In common with most construction materials, they should nevertheless not be handled carelessly, as this may cause damage. Pipe should not be dropped or dragged along the ground. Storage Pipe should be stored on level, flat ground, free of stones or sharp protrusions. Alternatively, they may be stored on timber supports of at least 75mm width placed 1.5m apart with side supports. The height of pipe stacks should not exceed 1.5 metres. All pipe stacks and stored fittings should be covered to avoid prolonged exposure to direct sunlight. Where the pipes are fitted with an integral socket, they should be stacked with sockets protruding at alternate ends. Fitting boxes should not be stacked higher than 1/3 of the shortest base length. All products must be stacked on a hard, even surface. Keep fitting boxes dry when stacked to preserve the rigidity of the box material and prevent movement. Loading & Transport Pipes containing integral sockets should always be loaded bottom. Pipes should not overhang the vehicle by more with sockets and spigots alternating and sockets than 1m. protruding from spigots to avoid damage. A flat-bodied Ensure that the load is securely tightened so that pipes do vehicle is ideal for transporting pipes. When a mixed load not move during transport. Protection should be used on of pipes (i.e. pipes of varying diameters) is to be corners when using straps to tighten pipes, so that corner transported, the larger pipes should be placed at the pipes are not flattened / damaged. 13 / GRAVITY SEWER PIPE SYSTEMS
PVC Properties
Polyvinyl Chloride (PVC) is a thermoplastic Physical Property Units PVC-U Values
resin with specific properties. PVC raw
Co-efficient of linear expansion K-1 6 x 10-5
material is derived from salt (57%) and
ethylene, derived from oil (43%). Because Density Kg/m3 1.45 x 103
of the low dependence of PVC feedstock Flammability (oxygen index) % 45
on oil, it is considered to be one of the
Shore Hardness (D) 70 - 80
least energy intensive thermoplastics. It is
also not as taxing on valuable oil or coal Softening point (Vicat – minimum) °C 78 - 81
reserves as many other thermoplastics. Specific heat J/kg/K 1.0 x 103
PVC resins are blended with a variety of
Thermal conductivity (at 0° - 50°C) W/m/K 0.14
additives to obtain dry blends of raw
material which are tailored to make Mechanical Property
products with specific properties. Types of
Elastic modulus MPa 3 300
additives which are added to give specific
properties are, among others, UV Tensile strength MPa 45
stabilisers, impact modifiers, colourants Elongation at break % 45
and plasticisers. The adjacent table lists
Poisons ratio 0.4
the properties of PVC-U material, used in
the production of aboveground and below Friction Factor
ground sewer pipes. Manning 0.008 – 0.009
Pipe Stiffness
The introduction of structured wall pipes to the South African market led to the preparation of the SANS 1601 specification.
This introduced the concept of pipe stiffness ratings as a pipe classification. The use of kPa rating (100, 200 and 400kPa) is
often confused with a pressure class rating, but in fact relates to the amount of external pressure needed to deform the pipe
by 5% of its diameter.
The Durodrain solid wall PVC-U sewer pipes manufactured to SANS 791 contains two stiffness classes – Class 51 (normal
duty), being 100kPa minimum and class 34 (heavy duty), being 300kPa minimum.
Type of Applicable Pipe Stiffness Stiffness
pipe standard class (kPa) (SN)
Solid Wall
PVC-U SANS 791 51 100 2
PVC-U SANS 791 34 300 6
Structured Wall
PVC-U SANS 1601 100 100 2
PVC-U SANS 1601 200 200 4
PVC-U SANS 1601 400 400 8
GRAVITY SEWER PIPE SYSTEMS / 14Design
Plastic pipe systems, in particular PVC-U, are economical and a practical material for sewer applications. Flexible
pipes are recognized as having benefits over rigid pipes with regard to load shedding. The flexibility, although
resulting in higher deformation, has the following advantages over rigid pipe:
• Yield under soil load reduces the total soil load as more friction is transferred to the sides of the trench
• Pipe carries relatively less load than the sidefill as it yields, i.e. it sheds load to the sidefill
• The pipe deflects out laterally, thereby activating soil support and creating an arching action
• Yielding of plastics results in stress redistribution across a section, thereby utilizing the entire section in load resistance.
Soil / Pipe Interaction
The mode of failure of a pipe can be due to circumferential Rigidity of the pipe
or longitudinal overloading. This section addresses The more rigid a pipe is relative to the trench sidefill, the
concerns regarding external loads which cause more load it will take. The sidefill tends to settle, thus
circumferential stress. causing a large part of the backfill to rest on the pipe. This
occurs with flexible pipe to some extent, as a pipe is
Flexible PVC pipes deflect under the influence of vertical
supported laterally by the fill and will not yield as much as
external loads and the reactive support of the surrounding
a free standing pipe.
soil. Failures can occur due to high bending, aching
stresses in the wall (more common for rigid pipes) or Type of trench
buckling. In the case of flexible pipes, the stiffness of the The load transmitted to the pipe varies with the width and
surrounding material can be more important in limiting the depth of the trench since friction on the sides of the
deflection than the stiffness of the pipe itself, so controlled trench effects the resultant load. Various trench conditions
backfill is particularly important. The load transmitted to a are illustrated below.
pipe from the external surrounding soil depends on a
number of factors:
Settlement line Settlement Settlement line
line
Alternative
side form
Wide trench - deep embankment: Wide shallow trench: Narrow trench:
Least friction - greater load on the pipe Less friction - more susceptible to Maximum friction - least load on the pipe
superimposed loads such as vehicles
The vertical load due to soil is generally the most severe from the point of view of deflection and circumferential bending
stress. Under embankments of cohesionless and frictionless soil, the vertical pressure at the level of the top of the pipe
could be evaluated using column theory to be:
W = GHD
Where W is the download on pipe (kN/m)
H is the depth (m)
G is the unit weight of soil (kN/m3)
D is the external pipe diameter (m)
15 / GRAVITY SEWER PIPE SYSTEMSThe load must be corrected because the soil is cohesive and the sidefill reacts with the fill over the pipe. In addition, flexible
pipes yield and shed load to the sidefill, thus the net load in KN per unit length of pipe is often less than what the column
theory indicates.
Most pipes are laid in trenches and friction in the side of the trench supports some of the fill. The load in KN/m, i.e. per unit
length of width B is thus:
F = C1GHB
C1 is evaluated in figure 1 as a function of H/B and k tan Ø
(1 – sin Ø)
Where k is the ratio of lateral to vertical soil stress =
(1 + sin Ø)
And Ø is the soil angle of friction
Figure 1: Load co-efficients for trench conditions
k tan ø
10
9
Satura
Silt
Clay
Coa
8
rse
ted C
Gra
7
nu
lay (
Column Loading
lar
6
long
(sh
or
term
t
H/B 5
ter
m
)
)
4
3
2
1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
C1 (in F = C1GHB)
Flexible pipes yield more than the sidefill and therefore the load is shed to the soil. The net soil load in kN/m of pipe is thus:
Ws = Cf F
8EI/ND 3 + E s / 2K
And Cf =
8EI/ND 3 + (1/2K + B/D – 1) Es
Where E is the pipe elastic modulus (Pa)
Es is the soil modulus (Pa)
I is the moment of inertia of the pipe wall (mm4/mm) = t3/12
t is the pipe wall thickness (m)
D is the outside diameter (m)
N is the deflection co-efficient which is a function of the bending angle
K is the sidefill lag factor
B is the trench width (m)
GRAVITY SEWER PIPE SYSTEMS / 16Typical values for the soil modulus, Es (MPa) are shown in the table below:
Soil modulus as a function of density
Soil Type Compaction
Loose 85% 90% 95%
Gravel Stone 7 20 30 50
Sand - 12% fines 3 7 15 20
Silt LL < 50% 1 3 5 10
Clay LL > 50% 0,1 1 3 7
Deflection
Vertical deflection is limited by lateral soil resistance as the pipe tends to deflect outwards laterally. The load is thereby taken
in arch action rather than circumferential bending, so wall stresses are considerably less than for rigid pipe. The deflection in
meter allowing for load shedding is:
Ws Ws
d =
8EI/ND 3 + E s / 2K Ps + Ss
Ws
=
8Et 3 / D 3 + 0.4E s
Where Ws is the load on the pipe (kN/m)
Ps is the pipe stiffness (Pa)
Ss is the soil stiffness (Pa)
The E values for PVC-U sewer pipes, which decrease with age, to be used for soil load and deflection calculations are:
• Instantaneous, E = 2500 x 106 N/m2
• Minimum 50 year, E = 1500 x 106 N/m2
For live loading, one should perform a separate calculation using the short term E value and add up the two deflections
caused by soil and live loads.
% Deflection = d / D x 100
Figure 2: Deflection of PVC-U sewer pipe under load
8
DURODRAIN
7 normal duty (class 51 / 100kPA)
6
ULTRACOR
Deflection %
Maximum available deflection medium duty (200kPA)
5
4 DURODRAIN
heavy duty (class 34 / 300kPA)
3
ULTRACOR
2 heavy duty (400kPA)
1
0
0 50 100 150
Pipe Loading kN/m 2
17 / GRAVITY SEWER PIPE SYSTEMSExample: Deflection
Calculate the deflection and maximum wall stress of a 315mm DURODRAIN heavy duty sewer pipe (wall thickness 9.20mm)
under 3m of average soil in a 900mm wide trench. Take the soil modulus as 3MPa, soil mass 2000kg/m3 or 20kN/m3 and
long term modulus 1500MPa. Take bottom support over 90°, N = 0.095, Nm = 0.13 and sidefill lag factor 1.5, soil friction
angle = 12°.
Trench load F at 3m = C1GHB
When H/B = 3/0.9 = 3.3
And k tan Ø = (1 – sin12)/(1 + sin12) x tan12 ° = 0.13
Then C1 = 0.65
F = 0.65 x 20 x 3 x 0.9
= 35.1KN/m
Load on pipe Ws = Cf F
8 E I /ND 3 + E s / 2K
Where Cf =
8 E I /ND 3 + (1/2K + B/D – 1) E s
[8(1.5 x 10 9 )(0.0092 3 /12)/(0.095)(0.315 3 )] + [(3 x 10 6 )/(2 x 1.5)]
=
[8(1.5 x 10 9 )(0.0092 3 /12)/(0.095)(0.315 3 )] + [((1/2 x 1.5) + (0.9/0.315))-1] (3 x 10 6 )
262 245.60 + 1 000 000.00
=
262 245.60 + 6 571 428.57
= 0.1847
Therefore Ws = 0.1847 x 35.1
= 6.483KN/m2
Ws
d=
8Et3 / D3 + 0.4Es
6.483 x 103
=
[8 x ((1500 x 10 6 )(0.0092 3 ))/0.315 3 + 0.4 (3 x 10 6 )]
6 483
=
1 498 959.99
= 0.0043m
Deflection % = d / D x 100
= 0.0043 / 0.315 x 100
= 1.37%
GRAVITY SEWER PIPE SYSTEMS / 18Live loads from soil surface
Pressure on the pipe in KN/m2 due to a live load of P (kN) on the surface of the soil is:
3PH3
w1 =
2 (H 2 + X 2) 5/2
X
Where P is the live load (kN)
X is the lateral distance to live load P (m) Truck
Wheel
H is the depth to the pipe crown (m)
The live load per meter of pipe, W1 = w1D, should strictly P
be corrected for load shedding, but it activates a higher Soil
pipe modulus, E, than the soil load does, as it is only a
H Column
Load
temporary load. The deflection in meters allowing for load
shedding and external live loads is:
Live
Load
D
d Ws
=
D 8EI/ND3 + Es N / 2K
Ws
=
8EI/ND 3 + E s / 2K B
Ws
=
8Et 3 / D3 + 0.4Es
Wall stress
The maximum wall stress around the circumference of a pipe is due to a combination of ring bending under vertical load and
arching. At the haunch it is:
Ws (20Et 2 /D 2 + E s)
f = x
2t (24Et 3 /D 3 + E s)
DURODRAIN and ULTRACOR sewer pipes can withstand stresses up to 10MPa (10 x 106 N/m2) since the short term
minimum tensile strength is 42MPa and the 50 year nominal strength is 25MPa. Actual strength may be considerably more
and depends on stress history.
Example: Wall stress
Ws (20Et2/D2 + Es)
f = x
2t (24Et3/D3 + Es)
(6.483 x 10 3) [20((1500 x 10 6 )(0.0092 2 ))/((0.315) 2 (3 x 10 6 ))]
= x
(2 x 0.0092) [24((1500 x 10 6 )(0.0092 3 ))/((0.315) 3 (3 x 10 6 ))]
28 950 325.02
= 352 336.9 x
3 896 879.96
= 2 584 997.89
= 2.584 x 106 N/m2
= 2.584 MPa
19 / GRAVITY SEWER PIPE SYSTEMSDeflection comparison: Heavy duty (HD) vs. Normal duty (ND)
Percentage Deflection
Diameter (mm)
Depth of Cover
(m) 160mm Pipe 315mm Pipe 500mm Pipe
ND (Cl 100/51) HD (Cl 34) HD (Cl 400) ND (Cl 51) HD (Cl 34) ND (Cl 51) HD (Cl 34)
1 0,586 0,576 0,682 0,669 0,658 0,733 0,714
3 1,095 1,076 1,057 1,541 1,515 1,738 1,693
6 1,285 1,263 1,197 2,181 2,144 2,543 2,477
8 1,313 1,290 1,218 2,383 2,342 2,821 2,748
10 1,322 1,299 1,224 2,495 2,453 2,988 2,911
The table above compares the percentage deflection between DURODRAIN / ULTRACOR normal duty (Class 51 / 100),
DURODRAIN heavy duty (Class 34) and ULTRACOR heavy duty (Class 400) of different diameters and depths of cover. A
low Es value of 3MPa (clay) was used in the above calculations of pipe deflection.
Note: The deflection of the 160mm normal duty pipe under a 3m soil load is 1.095% compared with 1.076% for heavy duty
DURODRAIN and 1.057% for heavy duty ULTRACOR, a difference of no more than 1.5% in the load bearing capacity
between normal and heavy duty, showing that wall thickness has relatively little effect on the soil load bearing capacity.
Effects of soil modulus
The graph below indicates the effect of soil modulus over deflection for DPI Plastics PVC-U pipes.
5
t/d = 0.02
4
w = 50kN/m2
D
d
3
Vertical Deflection
2
1
0
1 2 5 10 20 50
Soil Modulus Es (N/mm2)
GRAVITY SEWER PIPE SYSTEMS / 20Velocity and Flow
The flow in pipelines, flowing full or partially full but not under pressure, is defined as gravity flow because it is maintained by
the slope component of the pipeline, resulting in a hydraulic gradient which is parallel to the pipeline invert. The flow
characteristics can be determined by Mannings’ formula, shown below.
Mannings’ formula:
k
V = R0.667 S0.5
N
Where V = velocity (m/s)
k = 1.0 for full bore flow, 0.5 for 50% of pipe, etc.
N = Manning roughness coefficient (0.008 – 0.009)
R = hydraulic radius (m)
S = slope (m/m)
The hydraulic radius is derived from the following equation:
R=A/P
Where A = cross sectional area of flow (m2)
P = wetted perimeter (m)
Using Mannings’ formula, the volume flow can be calculated as follows:
k
Q = AV = A R0.667 S0.5
N
Where Q = volume flow (m3/s)
A = cross sectional area of flow (m2)
21 / GRAVITY SEWER PIPE SYSTEMSEffect of Ultraviolet Light
Most plastics are affected by ultraviolet light. PVC pipes and fittings contain a small amount of UV stabilisers in
their formulations for short term storage. The exceptions are FREEFLO SVW pipes and fittings, which are
extensively UV stabilized for continuous outdoor use.
Pipes and fittings for underground use, like DURODRAIN and ULTRACOR, should be protected against UV attack if they
have to be exposed for prolonged periods (more than 3 months).
DPI Plastics recommends covering pipes with 80% shade cloth, taking care to cover the sides as well to protect spigots and
sockets. Solid sheets, like tarpaulins, are nor recommended, as they do not allow air movement through the pipes, resulting
in excessive heat buildup. This can lead to sagging or deformation of the pipes.
If pipes or fittings intended for underground use are installed where they will be exposed to direct sunlight, they can be
painted with a coat of white alkyd enamel or PVA. Use only water based paint when painting any PVC pipes or fittings. Do
not use thinners or solvents directly on PVC pipes or fittings. It is recommended that FREEFLO pipes and fittings be used
where exposure to direct sunlight is likely, as FREEFLO products are UV stabilised. Where PVC products are painted to
protect them against UV attack, they should be repainted every 2 years.
Chemical Resistance
PVC pipes and fittings are generally inert to a wide range of chemicals and can be used for drainage of a large
number of chemicals and chemical solutions. PVC pipes have been used in the chemical industry for over 60
years.
There are nevertheless a few chemicals that cannot be conveyed by these pipes. They include certain aromatic organic
solvents, ketones and chlorinated hydrocarbons. Take care to ensure that the chemical does not contain impurities which
may reduce the resistance of the pipe.
The following chemical resistance chart rates the resistance of PVC and two commonly used rubber sealing rings to various
chemicals at various concentrations and temperatures. The chart is intended as a guide only and should not be regarded as
applicable to all working conditions. Should there be any doubt about the behaviors of the pipe under specific conditions,
please contact DPI Plastics Technical Department.
GRAVITY SEWER PIPE SYSTEMS / 2223 / GRAVITY SEWER PIPE SYSTEMS
GRAVITY SEWER PIPE SYSTEMS / 24
Disclaimer
Copyright: 2017 DPI Plastics (Pty) Ltd. This work is protected by copyright ownership and any unauthorised copying or use
of any material in this work is considered unlawful.
All information in this work is provided in good faith and based on our company experience and knowledge. DPI Plastics
(Pty) Ltd cannot be held responsible for any losses of any nature, occurring as a result of using information contained within
this work. All pipeline designs should be checked by a qualified wet services engineer before implementation.
DPI Plastics reserves the right to amend or change any information contained in this work at any time, as the company
deems fit.
Drawings contained in this work are not to scale.
All relevant safety precautions have to be followed at all times when working with pipes and fittings, including the wearing of
the necessary PPE (personal protective clothing) and adhering to construction regulations.
Bibliography
DPI Plastics wishes to acknowledge the following sources:
No. Title Author Edition
1 Design guidelines for PVC pressure pipe systems for trenched DPI Plastics 2010
civil applications
2 DURODRAIN Codes of practice DPI Plastics 2004
3 DURODRAIN System design DPI Plastics 2004
4 SANS 2001: DP1 – Construction works, Earthworks for buried SA National Standard 2011, ed. 1.1
pipelines and prefabricated culverts
5 SANS 2001: DP4 – Construction works, Sewers SA National Standard 2008, ed. 1
6 SANS 791 – Unplasticised polyvinyl chloride (PVC-U) sewer and SA National Standard 2014, ed. 5.4
drain pipes and pipe fittings
7 SANS 967 – Unplasticised polyvinyl chloride (PVC-U) soil, waste SA National Standard 2014, ed. 2.6
and vent pipes and pipe fittings
8 SANS 1601 – Structured wall pipes and fittings of unplasticised SA National Standard 2013, ed. 2.02
polyvinyl chloride (PVC-U) for buried drainage and sewerage
systems
9 SANS ISO 4633 – Rubber seals – joint rings for water supply, SA National Standard 2008, ed. 1
drainage and sewerage pipelines – Specification for materials
10 SANS 10252-2 – Water supply and drainage for buildings. Part 2: SA National Standard 1993, ed. 1
Drainage installations for buildings
11 SANS 10400: P – The application of the National Building SA National Standard 2010, ed. 3
Regulations. Part P: Drainage
12 PVC vs. Polypropylene (PP) sewer pipe Uni-Bell, USA 2011
13 Pipe – Soil interaction with flexible pipe, Conference on water Stephenson, D. 1994
pipeline systems, BHRA, Edenburgh
14 Drainage Manual, a water resources technical publication U.S. Department of 1991, ed. 3
the Interior, Bureau of
Reclamation
25 / GRAVITY SEWER PIPE SYSTEMSNotes
GRAVITY SEWER PIPE SYSTEMS / 26PRICE LIST
Products available from DPI Plastics, SA’s leading manufacturer of plastic piping systems
Price List - 2014
for water and sanitation, include:
• Durodrain uPVC solid wall sewer and drain systems to SANS 791
• Ultracor uPVC structured wall sewer and drain systems to SANS 1601
• Ultrapipe (recycled inner) uPVC structured wall sewer and drain systems to SANS 1601
• Freeflo uPVC soil, vent and waste systems to SANS 967
• Rainflo uPVC D-shaped gutter and downpipe systems to SANS 11
• Duroflo uPVC pressure pipes systems to SANS 966-1
• Ultraflo mPVC pressure pipe systems to SANS 966-2
• Mineflo mPVC pressure pipe systems to SANS 1283
• Hi-impact mPVC pressure pipe systems to SANS 1283
• Durothene HDPE pressure pipe systems to SANS 4427
• Durogas HDPE pressure pipe systems to SANS 4437
+27 (0) 11 345 5600 info@dpiplastics.co.za exports@dpiplastics.co.za www.dpiplastics.co.zaYou can also read
