Gravity Sewer PVC Pipe Systems

Transcription

1 DESIGN MANUAL 2017 Gravity Sewer PVC Pipe Systems

2 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

3 An introduction to PVC PVC is the preferred material for aboveground soil, waste and vent, and underground gravity sewer systems worldwide. PVC sewer pipes and fittings are practical and economical. Recent market 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 pipe systems installed during 2015 in this size range being PVC. PVC also has a great track record to its benefit, as it has been around for more than 40 years in South Africa and longer in certain other parts of the world. Its continued use and acceptance around the world is a testament to PVC s suitability for sewer and drainage applications. Furthermore, current consciousness of energy savings, low carbon footprint and cradle-to-cradle approach, highlights the greatest benefits of PVC as a sewer pipe material. The longevity and low maintenance nature of PVC sewer installations, along with its recyclability, make PVC very economical during it s service life and beyond. DPI Plastics has been developing and manufacturing PVC sewerage pipes and fittings for more than 30 years and the company has a wealth of knowledge and experience. Our PVC formulations have been honed over the years to aid process ability, and produce high quality products that last. DPI Plastics has pioneered a number of innovations in South Africa, including structured wall (ribbed) underground fittings, increasing stiffness, whilst saving on mass and cost. This manual aims to provide the necessary basic information needed to work with PVC sewer pipes and fittings. More information is available on the DPI Plastics website, or via our technical department. Advantages of PVC in Sewer Pipe Systems PVC is the perfect material for pipes and fittings in gravity sewerage systems. This is evident through its worldwide use in this application. Some of the advantages of PVC versus other materials used in sewer systems are as follows: PVC pipes and fittings have smooth inner surfaces, resulting in low frictional resistance Structured wall PVC pipes and fittings offer high hoop stiffness and low weight PVC is semi-flexible, allowing greater resistance to damage due to ground movement, when compared to traditional sewer pipe materials PVC can be easily painted to match colour schemes or for additional protection PVC has a harder surface than other plastic sewer systems, resulting in increased resistance to damage during rodding of sewer lines PVC is non-corrosive, resists buildup of algae and scale Due to its high tensile strength and modulus, PVC pipes and fittings need thin wall thickness for similar performance as other sewer plastic systems PVC soil, waste and vent pipes are highly resistant to ultraviolet light and can be used in direct sunlight PVC has excellent fire properties; it does not support combustion without a heat source PVC pipes and fittings are supplied with integral rubber ring joints, or with plain sockets for solvent weld joining PVC performs well at low temperatures and remains rigid at 60 Celsius. It has a low coefficient of thermal expansion, compared to many other materials. This results in stable sewer stacks that resist sagging Suspended PVC plumbing pipes, due to their rigidity, need less supports than polyolefin pipes (PP and PE), saving costs and installation time PVC has much lower linear thermal expansion than Polypropylene and Polyethylene DPI Plastics PVC pipes and fittings are manufactured in accordance with latest requirements in terms of exclusion of heavy metals and are safe to use. GRAVITY SEWER PIPE SYSTEMS / 2

4 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 The quality of the output of a factory depends upon the management and control exercised by the organization and functioning of the production unit, over those activities which affect quality. In this respect the ISO 9001 Quality Management System is adhered to by DPI Plastics (Pty) Ltd, in which a set of guidelines and disciplines to ensure optimum product quality based on inputs from the various activities in the production cycle. The disciplines and guidelines specified by ISO 9001 encompass all the processes of planning, organization, directing, risk management and control made up of specific elements. The ISO 9001 Quality System is driven by top management. DPI Plastics quality management system is one of the oldest systems in the local plastic pipe industry, being first awarded more than 20 years ago. This means that the quality system is well entrenched in all areas of the organization and it is lived daily by personnel in all departments. We are immensely proud of our quality and it shows in our products. Apart from ISO 9001, DPI Plastics is also a proud founding member of SAPPMA (Southern African Plastic Pipe Manufacturers Association). SAPPMA is an industry organization with approximately 80% of the plastic pipe manufacturers in South Africa contained in its membership. SAPPMA promotes quality within the plastic pipe industry by conducting ad-hoc audits and specifying additional quality requirements for its members. SAPPMA also shares knowledge about plastic pipes and their benefits through conferences, media publications and their website. Quality Control Quality control procedures are specific to the production operation where product is monitored on a predetermined frequency for compliance with a number of specific product requirements, including: Dimensions Resistance to leakage and deformation Resistance to methylene chloride Pipe stiffness Workmanship Colour Printing Tensile strength Resistance to solar radiation Thermal reversion Hot and cold water cycling test The quality control checks provide a guide to the production process to ensure continued compliance to the product requirements. All quality control data is 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) or the South African Bureau of Standards (SABS). 3 / GRAVITY SEWER PIPE SYSTEMS

5 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): The Southern African Vinyls Association (SAVA): The Water Institute of SA (WISA): The Institute of Municipal Engineers SA (IMESA): 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

6 Pipe Dimensions Outside diameter (mm) Soil, Vent and Waste Pipes Nominal Wall Thickness (mm) 2,0 2,2 2,2 3,2 3,3 Mass (kg/meter) 0,40 0,53 0,79 1,67 2,54 FREEFLO soil, waste and vent pipes and fittings are manufactured to SANS 967 and are designed specifically for use above ground and outdoor in non-pressure drains and venting applications. Class 51 Normal Duty Sewer & Drain Pipes Class 34 Heavy Duty Outside diameter (mm) Nominal Wall Thickness (mm) Mass (kg/meter) Outside diameter (mm) Nominal Wall Thickness (mm) Mass (kg/meter) 110 2,2 1, ,0 1, ,2 2, ,7 3, ,9 3, ,9 5, ,0 6, ,3 8, ,2 9, ,2 14, ,0 12, ,2 18, ,9 15, ,7 22, ,8 19, ,2 29, ,8 24, ,6 35, ,0 28, ,3 42, ,4 36, ,4 53,90 DURODRAIN normal duty sewer and drainage pipes are manufactured to SANS 791 and are used in underground drains. DPI Plastics offer a range of DURODRAIN fittings to complete the range. DURODRAIN heavy duty sewer and drainage pipes are manufactured to SANS 791 and are used in underground sewers. The DPI Plastics DURODRAIN range of fittings is used with these pipes. Outside Diameter (mm) Structured Wall PVC Pipes Class 100 Normal Duty E4 / ID (mm) 0,4 / 105 0,5 / Mass (kg/m) 1,0 2,0 - - Class 200 Medium Duty E4 / ID (mm) 0,4 / 103 0,5 / Mass (kg/m) 1,1 2,5 - - Class 400 Heavy Duty E4 / ID (mm) 0,4 / 100 0,5 / 150 0,6 / 186 0,7 / 232 Mass (kg/m) 1,4 2,8 4,4 6,9 ULTRACOR and ULTRAPIPE structured wall sewer and drainage pipes are manufactured to SANS 1601 and are used in underground drains and sewers. DPI Plastics multi-layer, foamed center technology offers high stiffness and low weight, compared to solid wall PVC sewer and drainage pipes. ULTRAPIPE also uses 100% recycled material in the centre layer, thereby re-using PVC material for a greener product. 5 / GRAVITY SEWER PIPE SYSTEMS

7 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 Fittingstings Type 110mm Seal Type Junction, Square, Plain Gulley P-Trap ABC Rodding Eye Stop End, Male and Female Stop End Access, Female PVC/EW Adaptor, Female Bend Long Radius Double Socket, Kimberley or Repair Single Socket Inspection Pipe, Access Plain Bend, 22½, 45, 90 Access Bend, 45, 90 Rubber Ring or Spigot/Socket Rubber Ring and Spigot Rubber Ring Solvent Weld (f); Spigot End (m) Solvent Weld Rubber Ring Spigot/Socket. 22½, 45, 90 Rubber Ring Rubber Ring/Solvent Weld Rubber Ring Rubber Ring Rubber Ring NOTE: 160mm and larger fabricated fittings also available. GRAVITY SEWER PIPE SYSTEMS / 6

8 Installation Joining of Pipes Rubber Ring Joints Cutting Cut the pipe square with a cross cut saw or angle grinder depending on pipe size. Observe all safety requirements for the equipment being used. Clean away swarf and chamfer the pipe end to 15 and at least 50% through the pipe wall to ensure easy insertion when making a joint. Cleaning the seal It is important to ensure that the seal is free of grit and mud before making the joint. Pipe ends are often accidentally dipped into the sand. Lubrication DPI Plastics can supply liquid lubricant or jelly-like lubricant, known as gel or soft soap. Both products are designed for lubricating pipe seals. In order to make a leak-free joint effortlessly, use liberal amounts of lubricant, but avoid getting it into the seal housing. Lumps 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 When making a joint, push the pipe fully home into the socket to avoid hang-up and possible blockages. For large, heavy pipes, take care not to damage the socket by pushing with excessive force when the pipe nears the end of insertion, when using mechanical means to join pipes. Jointing It is important that the pipe ends and socket are aligned and free of burrs, otherwise insertion into the seal ring will be difficult, or damage to the seal may occur. For protection of the pipe ends use a lever against a wooden block. Joints Flexible rubber ring joints are available for all types of pipe and should be used in preference to rigid joints, allowing the pipeline to flex in the event of soil movements and also allowing for thermal change. 7 / GRAVITY SEWER PIPE SYSTEMS

9 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 In order to make a solvent cement joint you need: A fine tooth hack saw or angle grinder A sealed container with fresh solvent cement. Nonpressure solvent cement is designed for use with sewer pipes A clean brush for applying solvent cement. A 50mm paint brush works well on larger joints, while a 25mm brush is fine for smaller SV joints A clean rag or paper towel for cleaning the pipe and fitting surfaces to be joined A pipe cleaning solution. These are normally available with the solvent cement and used to degrease the surfaces to be joined. Alternatively one can sand the surfaces using a 200 grit sandpaper. Procedure Use the rag or towel paper and pipe cleaning solution to clean the pipe and socket surfaces to be joined. Do not touch the surfaces after cleaning as oils from your skin prevent bonding where you touch the joining surface. Let the solvent evaporate before continuing. When using sanding paper, sand the surfaces in the circumferential direction. Only dull the surface, do not sand too much Apply the solvent cement evenly to the pipe and socket using the brush. Rather apply too much than too little Immediately after applying the solvent cement, push the pipe into the socket, turning the pipe a quarter turn as it is pushed home. Wipe any excess solvent cement from the joint 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 series. Trench Width Fill in with excavated trench material tamping at each 300mm layer 300mm 300mm Pipe diameter Recommended minimum depth (see:minimum cover over sewers and drains) 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

10 Excavation Pipe trenches shall be excavated to a depth suitable for the provision of adequate cover over the crown of the pipe, and to a specified or allowable width. The sides of the trenches shall be as near vertical as possible for a height of at least a full diameter of the pipe, plus the specified depth of selected fill blanket over the pipe. Trench bottom: material unsuitable for the bottom of the trench shall be excavated. The trench must be refilled with selected material and compacted. Bedding must be smooth and level. It is important that the trench is not opened too far in advance of the pipe laying operation. Pipes must be backfilled immediately after laying, with joints left open for testing. It is recommended that the depth of cover, from the top of the pipe to the ground surface, be not less than 0.9m for sewers and 0.3m for drains. Bedding Bedding and fill shall be selected granular material. The trench bed must be free of stone or hard projections which are likely to cause damage to the pipe. Backfill Material Selected fill material shall be used and shall be free of vegetation, lumps or stones or any other foreign particles of diameter exceeding 30mm. Bedding Cradle PVC-U pipe must be supported on a continuous bed of selected granular material of compacted depth of at least 100mm, and covering the full width of the trench. Selected granular material must be of a granular, non-cohesive nature, graded between 0.6mm and 19mm, free draining and the specified compactability Compaction density for the bedding cradle must be 90% modified AASHTO Additional selected granular material must be placed around the pipe in layers of approximately 100mm and compacted to the specified density up to a height of 100mm above the crown of the pipe. Fill Blanket The fill blanket must be compacted to 90% modified AASHTO up to a depth of at least 300mm above the pipe crown. Take particular care not to damage, deflect or displace the pipeline during laying. Minimum Cover over Sewers and Drains Design the sewer invert level to provide a minimum crown depth cover over the top of the pipeline of 900mm for sewers and 300mm for drains. Calculate the expected traffic loads on sewers and drains where they run under roads or sidewalks, and, if necessary, increase the minimum cover in such areas. Backfilling Backfilling of pipe trenches must commence after the pipe has been laid and firmly bedded in the bedding cradle, and the selected fill blanket placed and compacted, as specified above. The pipe must be backfilled immediately after laying, leaving the joints exposed for testing. The pipeline must be laid directly on the prepared bedding in the trench, and any temporary supports, bricks or other foreign hard bodies must be removed. Compaction Backfilling must be done in 300mm layers and each layer compacted to 90% modified AASHTO density. In areas of road traffic loads, trenches must be backfilled in layers not exceeding 150mm (after compaction) and the material compacted to 93% modified AASHTO density for cohesive soils and to 98% in the case of non-cohesive soils. 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 SYSTEMS

11 Recommended 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 the pipe to be replaced a. Chamfer and remove burrs b. Prepare the replacement pipe and fittings Lubricate both seal rings of the Kimberley socket and locate the fitting on the existing pipe Fit the replacement unit into position Slide the Kimberley socket over the joint between the new and existing pipe Rodding Water Jetting If the drainage system is designed and laid correctly, rodding is seldom needed. Note that incorrect rodding procedures can lead to damage to the drain, regardless of what material it is constructed from. It is strongly recommended that a drain cleaning expert is consulted for advice on the correct type of equipment to use. It is imperative that one ensures that the rubber seal ring and pipe are well cleaned before making a connection. The major reason for rodding is caused by root ingress which can be avoided if rubber seal rings are not dislodged or damaged during installation. Ensure rubber seal ring and pipe are well cleaned before making a joint Correct amount of lubrication must be used. Correct system design is also very important to ensure 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. Water jetting is becoming increasingly popular as a method for cleaning and maintaining sewers and drains. This method is suitable for use on PVC-U systems. DPI Plastics successfully conducted a series of tests under the auspices of the Structured Wall Pipe Association of South Africa. The United Kingdom based Water Research Council s acceptance testing methods were adopted as a pipe material selection criteria suited for installation where water jetting is to be carried out. DURODRAIN solid wall, ULTRACOR and ULTRAPIPE structured wall pipe systems meet the test criteria which is far more onerous than operating conditions. Equipment manufacturers provide instructions for correct cleaning methods that will prevent unnecessary accidents to the operations and the sewer system. GRAVITY SEWER PIPE SYSTEMS / 10

12 Testing 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 An approved Manometer in a leak free condition Testing plugs in a leak free condition (ensure the rubber seals are not perished and that end caps are sealed and not cracked) Stopwatch for recording the time Bottle of soapy water to check for air leaks Large bucket Small funnel for filling the Manometer tube. Scale on Manometer in mm Procedure Check all the equipment for leaks Ensure that the section of pipeline to be tested has been sealed off at all branches and that all access openings are secure Insert testing plugs and secure properly Adjust the water level in the Manometer to zero on the scale (by adding water slowly) 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 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. Pipe Size (mm) Minimum Time for Pressure to Drop from 250mm (2.50kPa) to 125mm (1.25kPa) in min. 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 / GRAVITY SEWER PIPE SYSTEMS

13 Support 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 DPI Plastics recommends that FREEFLO pipe clips or holder bats be used with FREEFLO SVW piping systems, as they are specifically designed to work with the pipes and offer good grip and support. Piping, fixtures, tanks and equipment are to be supported independent of each other. (e.g. You can't hang a pipe from another pipe.) Pipe hanger spacing Vertical pipe is supported at its base and at alternating floors to a maximum spacing of 5 meters. Horizontal pipe and tubing is supported at intervals along its length depending on the material and pipe size. PVC plumbing pipes require the following maximum spacing between hangers and supports: When supporting plastic pipes, care must be taken not to compress or damage the pipe. Expansion type inserts or built in hanger supports are to 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. Type of Pipe PVC PP Maximum Hanger Spacing 1.2 m 0.8 m 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 / 12

14 Storage, 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 with sockets and spigots alternating and sockets protruding from spigots to avoid damage. A flat-bodied vehicle is ideal for transporting pipes. When a mixed load of pipes (i.e. pipes of varying diameters) is to be transported, the larger pipes should be placed at the bottom. Pipes should not overhang the vehicle by more than 1m. Ensure that the load is securely tightened so that pipes do not move during transport. Protection should be used on corners when using straps to tighten pipes, so that corner pipes are not flattened / damaged. 13 / GRAVITY SEWER PIPE SYSTEMS

15 PVC Properties Polyvinyl Chloride (PVC) is a thermoplastic resin with specific properties. PVC raw material is derived from salt (57%) and ethylene, derived from oil (43%). Because of the low dependence of PVC feedstock on oil, it is considered to be one of the least energy intensive thermoplastics. It is also not as taxing on valuable oil or coal reserves as many other thermoplastics. PVC resins are blended with a variety of additives to obtain dry blends of raw material which are tailored to make products with specific properties. Types of additives which are added to give specific properties are, among others, UV stabilisers, impact modifiers, colourants and plasticisers. The adjacent table lists the properties of PVC-U material, used in the production of aboveground and below ground sewer pipes. Physical Property Co-efficient of linear expansion Density Flammability (oxygen index) Shore Hardness (D) Softening point (Vicat minimum) Specific heat Thermal conductivity (at 0-50 C) Mechanical Property Elastic modulus Tensile strength Elongation at break Poisons ratio Friction Factor Manning K -1 Units Kg/m 3 % C J/kg/K W/m/K MPa MPa % PVC-U Values 6 x x x 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 pipe Applicable Pipe Stiffness Stiffness standard class (kpa) (SN) Solid Wall PVC-U SANS PVC-U SANS Structured Wall PVC-U SANS PVC-U SANS PVC-U SANS GRAVITY SEWER PIPE SYSTEMS / 14

16 Design 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 or longitudinal overloading. This section addresses concerns regarding external loads which cause circumferential stress. Flexible PVC pipes deflect under the influence of vertical external loads and the reactive support of the surrounding soil. Failures can occur due to high bending, aching stresses in the wall (more common for rigid pipes) or buckling. In the case of flexible pipes, the stiffness of the surrounding material can be more important in limiting deflection than the stiffness of the pipe itself, so controlled backfill is particularly important. The load transmitted to a pipe from the external surrounding soil depends on a number of factors: Rigidity of the pipe The more rigid a pipe is relative to the trench sidefill, the more load it will take. The sidefill tends to settle, thus causing a large part of the backfill to rest on the pipe. This occurs with flexible pipe to some extent, as a pipe is supported laterally by the fill and will not yield as much as a free standing pipe. Type of trench The load transmitted to the pipe varies with the width and the depth of the trench since friction on the sides of the trench effects the resultant load. Various trench conditions are illustrated below. Settlement line Alternative side form Settlement line Settlement line Wide trench - deep embankment: Least friction - greater load on the pipe Wide shallow trench: Less friction - more susceptible to superimposed loads such as vehicles Narrow trench: Maximum friction - least load on the pipe 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: Where W = GHD W is the download on pipe (kn/m) H is the depth (m) G is the unit weight of soil (kn/m 3 ) D is the external pipe diameter (m) 15 / GRAVITY SEWER PIPE SYSTEMS

17 The 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 = C 1 GHB C 1 is evaluated in figure 1 as a function of H/B and k tan Ø Where k is the ratio of lateral to vertical soil stress = (1 sin Ø) (1 + sin Ø) And Ø is the soil angle of friction Figure 1: Load co-efficients for trench conditions k tan ø Coarse Granular (short term) Silt Clay Saturated Clay (long term) H/B Column Loading C 1 (in F = C 1 GHB) 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: W s = C f F And C f = 8EI/ND 3 + E s / 2K 8EI/ND 3 + (1/2K + B/D 1) E s Where E is the pipe elastic modulus (Pa) E s is the soil modulus (Pa) I is the moment of inertia of the pipe wall (mm 4 /mm) = t 3 /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 / 16

18 Typical 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 Sand - 12% fines Silt LL < 50% Clay LL > 50% 0, 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: d = W s 8EI/ND 3 + E s / 2K W s P s + S s = Ws 8Et 3 / D Es 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 10 6 N/m 2 Minimum 50 year, E = 1500 x 10 6 N/m 2 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 7 DURODRAIN normal duty (class 51 / 100kPA) Deflection % Maximum available deflection ULTRACOR medium duty (200kPA) DURODRAIN heavy duty (class 34 / 300kPA) 3 2 ULTRACOR heavy duty (400kPA) Pipe Loading kn/m 2 17 / GRAVITY SEWER PIPE SYSTEMS

19 Example: 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/m 3 or 20kN/m 3 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 = C 1 GHB When H/B = 3/0.9 = 3.3 And k tan Ø = (1 sin12)/(1 + sin12) x tan12 = 0.13 Then C 1 = 0.65 F = 0.65 x 20 x 3 x 0.9 = 35.1KN/m Load on pipe Ws = C f F Where C f = 8EI/ND 3 + E s / 2K 8EI/ND 3 + (1/2K + B/D 1) Es = [8(1.5 x 10 9 )( /12)/(0.095)( )] + [(3 x 10 6 )/(2 x 1.5)] [8(1.5 x 10 9 )( /12)/(0.095)( )] + [((1/2 x 1.5) + (0.9/0.315))-1] (3 x 10 6 ) = = Therefore Ws = x 35.1 = 6.483KN/m 2 d = Ws 8Et 3 / D Es = x 10 3 [8 x ((1500 x 10 6 )( ))/ (3 x 10 6 )] = = m Deflection % = d / D x 100 = / x 100 = 1.37% GRAVITY SEWER PIPE SYSTEMS / 18

20 Live loads from soil surface Pressure on the pipe in KN/m 2 due to a live load of P (kn) on the surface of the soil is: w1 = 3PH 3 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) H is the depth to the pipe crown (m) Truck Wheel The live load per meter of pipe, W 1 = w 1 D, should strictly be corrected for load shedding, but it activates a higher pipe modulus, E, than the soil load does, as it is only a temporary load. The deflection in meters allowing for load shedding and external live loads is: d D = Ws 8EI/ND 3 + Es N / 2K H D Soil Column Load P Live Load = Ws 8EI/ND 3 + Es / 2K B = Ws 8Et 3 / D Es 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: f = Ws x 2t (20Et 2 /D 2 + Es) (24Et 3 /D 3 + Es) DURODRAIN and ULTRACOR sewer pipes can withstand stresses up to 10MPa (10 x 10 6 N/m 2 ) 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 f = Ws x 2t (20Et 2 /D 2 + Es) (24Et 3 /D 3 + Es) (6.483 x 10 3 ) [20((1500 x 10 6 )( ))/((0.315) 2 (3 x 10 6 ))] = x (2 x ) [24((1500 x 10 6 )( ))/((0.315) 3 (3 x 10 6 ))] = x = = x 10 6 N/m 2 = MPa 19 / GRAVITY SEWER PIPE SYSTEMS

21 Deflection comparison: Heavy duty (HD) vs. Normal duty (ND) Depth of Cover (m) Percentage Deflection Diameter (mm) 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, ,095 1,076 1,057 1,541 1,515 1,738 1, ,285 1,263 1,197 2,181 2,144 2,543 2, ,313 1,290 1,218 2,383 2,342 2,821 2, ,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 4 t/d = 0.02 d D w = 50kN/m2 Vertical Deflection Soil Modulus Es (N/mm 2 ) GRAVITY SEWER PIPE SYSTEMS / 20

22 Velocity 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 = R S 0.5 N Where V = velocity (m/s) k = 1.0 for full bore flow, 0.5 for 50% of pipe, etc. N = Manning roughness coefficient ( ) 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 (m 2 ) P = wetted perimeter (m) Using Mannings formula, the volume flow can be calculated as follows: k Q = AV = A R S 0.5 N Where Q = volume flow (m 3 /s) A = cross sectional area of flow (m 2 ) 21 / GRAVITY SEWER PIPE SYSTEMS

23 Effect 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 / 22

24 23 / GRAVITY SEWER PIPE SYSTEMS

25 GRAVITY SEWER PIPE SYSTEMS / 24

26 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 Design guidelines for PVC pressure pipe systems for trenched DPI Plastics 2010 civil applications DURODRAIN Codes of practice DURODRAIN System design DPI Plastics DPI Plastics SANS 2001: DP1 Construction works, Earthworks for buried pipelines and prefabricated culverts SA National Standard 2011, ed SANS 2001: DP4 Construction works, Sewers SA National Standard 2008, ed. 1 6 SANS 791 Unplasticised polyvinyl chloride (PVC-U) sewer and drain pipes and pipe fittings SA National Standard 2014, ed SANS 967 Unplasticised polyvinyl chloride (PVC-U) soil, waste and vent pipes and pipe fittings SA National Standard 2014, ed SANS 1601 Structured wall pipes and fittings of unplasticised polyvinyl chloride (PVC-U) for buried drainage and sewerage systems SA National Standard 2013, ed SANS ISO 4633 Rubber seals joint rings for water supply, drainage and sewerage pipelines Specification for materials SA National Standard 2008, ed SANS Water supply and drainage for buildings. Part 2: Drainage installations for buildings SA National Standard 1993, ed SANS 10400: P The application of the National Building Regulations. Part P: Drainage SA National Standard 2010, ed PVC vs. Polypropylene (PP) sewer pipe Uni-Bell, USA Pipe Soil interaction with flexible pipe, Conference on water pipeline systems, BHRA, Edenburgh Stephenson, D Drainage Manual, a water resources technical publication U.S. Department of the Interior, Bureau of Reclamation 1991, ed / GRAVITY SEWER PIPE SYSTEMS

27 Notes GRAVITY SEWER PIPE SYSTEMS / 26

28 Products available from DPI Plastics, SA s leading manufacturer of plastic piping systems 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 Ultraflo mpvc pressure pipe systems to SANS 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 (0) info@dpiplastics.co.za exports@dpiplastics.co.za