SPECIFICATION FOR
BELOW GROUND DRAINAGE SYSTEMS
SECTION R12
Revision / Date / Issue Authorised ByApproved for Issue
Date
To be read in conjunction with Preliminaries/ General conditions.
GENERAL
110BELOW GROUND DRAINAGE SYSTEMS for FOUL SEWAGE, SURFACE WATER and ROOFWATER.
Surface water and rainwater drainage sources: road and yard gullies in internal roads, car parks and paved areas – roof-water downpipes discharging into gullies.
Foul drainage sources: school toilets, wash hand basins, showers, kitchen equipment and other appliances.
Pipes, bends and junctions: PVCu with flexible joints
-Accessories: rodding eyes, grease traps, gullies
Manholes and inspection chambers: precast concrete and polypropylene.
Disposal: foul sewage to public sewer, surface water to watercourse via attenuation.
PRODUCTS
315ONE PIECE ROAD GULLIES AND COVERS
Standards:
-Cast iron: To BS 437 and Kitemark certified, or Agrément certified.
-Clay: To BS EN 295-1 and Kitemark certified, or Agrément certified.
-Concrete: To BS 5911-6 and Kitemark certified, or Agrément certified.
-Plastics: To BS 4660 and Kitemark certified, or Agrément certified
-Polypropylene: To BS EN 1852-1
Material: precast concrete
Manufacturer: Contractor’s choice
-Product reference: n/a
-Sizes: 375mm dia x 750mm depth
Outlet sizes: 150mm dia.
Covers: Contractor’s choice
-Product reference: n/a
-Type: one piece – non rocking
-Material: ductile iron
-Sizes: 360mm x 310mm
-Loading grades to BS EN 124: D400
316ONE PIECE YARD GULLIES AND COVERS
Standards: as Clause 315
Material: precast concrete / clay
Manufacturer: Contractor’s choice
Size: 225mm dia.
Outlet size: 150mm dia.
Covers: Contractor’s choice
Type: non rocking
Material: ductile iron
Size: 225mm x 225mm
Loading grade: C250
329PIPES, BENDS AND JUNCTIONS – SUPPLY
Pipes and fittings: From same manufacturer for each pipeline.
344PIPES, BENDS AND JUNCTIONS – PVCu – STRUCTURED WALL PIPES for surface water.
Standard: To WIS 04-35-01, Kitemark or Agrément certified.
Manufacturer: Contractor’s choice
-Product reference: n/a
Sizes: 150mm, 225mm, 300mm
Jointing type: flexible sleeve
346PIPES, BENDS AND JUNCTIONS – PVC-U – PLAIN WALL PIPES for foul drainage
Standard: To BS EN 1401-1, class SN4, with flexible joints, Kitemark certified.
Manufacturer: Contractor’s choice
-Product reference: n/a
Sizes: 100mm, 150mm, 225mm
Application area code: UD.
359FLEXIBLE COUPLINGS
Standard: To BS EN 295-1 or WIS 04-41-01 and Kitemark certified, or Agrément certified.
Manufacturer: Contractor’s choice
-Product reference: n/a
371RODDING POINTS FOR FOUL AND SURFACE WATER
Standards:
-Cast iron: To BS 437 and Kitemark certified, or Agrément certified.
-Clay: To BS EN 295-1 and Kitemark certified, or Agrément certified.
-Concrete: To BS 5911-6 and Kitemark certified, or Agrément certified.
-Plastics: To BS 4660 and Kitemark certified, or Agrément certified
Material: PVCu
Manufacturer: Contractor’s choice
-Product reference: [n/a
Sizes: 100mm, 150mm.
373ROOT BARRIERS
Manufacturer: Contractor’s choice
-Product reference: n/a
401INSPECTION CHAMBERS – PLASTICS - polypropylene
Standards: To BS 7158 or BS EN 13598-1, or Agrément certified.
Diameter: 475mm dia.
Manufacturer: Contractor’s choice
Bases:
-Product reference: n/a
Shaft units:
-Product reference: n/a
Access covers and frames:
-Product reference: n/a
-Loading grades to BS EN 124: C250
405 BMANHOLES AND INSPECTION CHAMBERS – BRICKWORK
Dimensions: 900mm x 675mm
Brickwork: Engineering
Base slab: Class C20 concrete.
Access covers and frames:
-Product reference: Contractor’s choice
-Loading grades to BS EN 124: C250
407MANHOLES AND INSPECTION CHAMBERS – CONCRETE RINGS
Standards:
To BS 5911-3 and BS EN 1917 and Kitemark certified; or.
To BS 5911-4 and BS EN 1917.
Manufacturer: Contractor’s choice
Shape: circular
Sizes: 1200mm dia.
Cement type: OPC
Chamber sections:
-Product reference: Contractor’s choice
-Jointing type: Contractor’s choice
Cover slabs:
-Product reference: Contractor’s choice
-Loading grades to BS EN 124: D400
-Openings to suit access covers.
419GREASE TRAPS AND CONVERTERS
Standards: In accordance with BS EN 1825-1 and to BS EN 1825-2, and Kitemark or Agrément certified.
Manufacturer: Contractor’s choice
-Product reference: n/a
Material: PVCu
Inlet pipe size: 100mm dia.
Outlet pipe size: 100mm dia.
421OIL AND PETROL INTERCEPTORS – PLASTICS
Standards: To Environment Agency PPG 3 and BS EN 858-1, with oil level alarm.
Manufacturer: Contractor’s choice
-Product reference: N/A
Size: NSB4
Inlet pipe size: 225mm dia.
Outlet pipe size: 225mm dia.
Accessories: oil level alarm system
460TANKS for attenuationstorage
Material: corrugated steel
Manufacturer: Tubosider or similar approved
Capacity (minimum): 530 cum
Internal arrangements: open tube
Access shaft extension: n/a
Access arrangements: preformed shafts
Inlet pipes: structured wall PVCu
-Sizes: 300 mm
-Invert depth below ground level: not exceeding 3 metres
Outlet pipes: structured wall PVCu
-Sizes: 300mm
-Invert depth below ground level: not exceeding 3 metres.
-Connected to: headwall
Vent pipes: PVCu
-Sizes: 100 mm dia.
Accessories: flow regulator
464STORMWATER HONEYCOMB UNITS (Alternative to Clause 460)
Manufacturer: Contractor’s choice
-Product reference: n/a
Size: 530 cum
471ACCESS COVERS AND FRAMES for Inspection Chambers and Manholes
Standard: To BS EN 124.
Types: non-rocking
Manufacturer: Contractor’s choice
-Product reference: n/a
Materials: ductile iron
Sizes: 675mm clear opening
Loading grades to BS EN 124: D400 for vehicle loading, C250 for pedestrian loading.
483CONCRETE (GENERAL)
Standards: To BS 8500-2.
Concrete: GEN3 to BRE Special Digest 1, Concrete in Aggressive Ground.
485CONCRETE (STRUCTURAL)
Standards: To BS 8500-2.
Concrete: Class C20
487 ACONCRETE (ADOPTABLE MANHOLE BENCHINGS AND SURROUNDS)
Standard (Edition current at award of contract):
-England and Wales, Northern Ireland: To WRc “Sewers for Adoption 6th Edition”.
-Scotland: To WRc ‘Sewers for Scotland’.
Concrete: Class C20
489 ACONCRETE (ADOPTABLE MANHOLE BENCHING TOPPING)
Standard (Edition current at award of contract):
-England and Wales, Northern Ireland: To WRc ‘Sewers for Adoption’.
-Scotland: To WRc ‘Sewers for Scotland’.
Concrete: High strength.
492GEOTEXTILE MEMBRANES – FILTER IN FORMPAVE
Manufacturer: Contractor’s choice
-Product reference: n/a
-
494GEOTEXTILE MEMBRANES – IMPERVIOUS
Manufacturer: Contractor’s choice
-Product reference: n/a
496GRANULAR MATERIAL
Standard: To BS EN 12620.
-Size: Dependent on location – see Execution clauses in this section, and in sections R16, R17 and R18, if used.
498GRANULAR SUB-BASE MATERIAL
Standard: To Highways Agency Volume 1 ‘Specification for Highway Works’, Type 1 Unbound mixtures for sub-base.
FABRICATION
501 BOUTLET HEADWALLS AT WATERCOURSE
Concrete base: Plain in-situ concrete, thickness 200mm
Splash plate: Contractor’s choice
Vermin grating: As clause 510.
510VERMIN GRATINGS FOR OUTFALLS AND OUTLET HEADWALLS
Construction: Mild steel frame extending 75mm beyond pipe opening all round, with 25mm maximum opening steel mesh grille. Top hinged on built-in fish-tail straps and with bottom pin lock.
Finish: Galvanised to BS EN ISO 1461 after fabrication.
Submit: Shop drawings.
-Timing: Before manufacture.
EXECUTION
601 BWORKMANSHIP
Workmanship is to be in accordance with BS 8000-14 Code of Practice for Below Ground Drainage.
602 BSEQUENCE OF WORK
The works are to be carried out in accordance with the requirements of the contract programme. Prior to the commencement of each section of the drainage works, the Contractor shall consider in detail the elements of work to be put in hand and raise any queries with the engineer in good time to receive instructions as to the intended action to be taken in order to obviate the possibility of disruption to the progress of the Contract Works.
603 BAS-BUILT DRAWINGS
The Contractor is to keep a copy of the drainage drawings on site specifically for recording as built modifications. They are to be continually updated as the work proceeds. At Practical Completion the marked up drawings are to be handed to the CA for use in the preparation of the As Built Drawings.
611 AEXISTING DRAINS
Setting out: Before starting work, check invert levels and positions of existing drains, sewers, inspection chambers and manholes against drawings. Report discrepancies in particular the invert levels of the storm and foul outfall connection points are to be surveyed and the results given to the CA before commencing any work on the drainage installation. Costs for abortive work due to failure to comply with this requirement will be the responsibility of the Contractor.
Protection: Protect existing drains to be retained and maintain normal operation if in use.
612 BABANDONED DRAINS
Where drains are specified as being abandoned they are to be treated in accordance with the requirements of Building Regulations Approved Document H – Appendix H1-B and to the satisfaction of the CA.
613EXCAVATED MATERIAL
Turf, topsoil, hardcore, etc: Set aside for use in reinstatement.
616SELECTED FILL FOR BACKFILLING
Selected fill: As-dug material, free from vegetable matter, rubbish, frozen soil and material retained on a 40mm sieve.
-Compaction: By hand in 100mm layers.
623LOWER PART OF TRENCH (GENERAL)
Trench up to 300mm above crown of pipe: Vertical sides, width as small as practicable.
Width (minimum): External diameter of pipe plus 300mm.
625LOWER PART OF TRENCH – TRANSITION DEPTH
Trench widths up to 300mm above crown of pipe (maximum):
-DN 100 pipelines more than 6.0m deep: 600mm.
-DN 150 pipelines more than 5.4m deep: 700mm.
-DN 225 pipelines more than 4.0m deep: 800mm.
-DN 300 pipelines more than 2.9m deep: 900mm.
631TYPE OF SUBSOIL
General: Where type of subsoil at crown of pipe differs from that stated for the type of bedding, surround or support, give notice.
635FORMATION FOR BEDDING
Timing: Excavate to formation immediately before laying beddings or pipes.
Mud, rock projections, boulders and hard spots: Remove. Replace with consolidated bedding material.
Local soft spots: Harden by tamping in bedding material.
Inspection of excavated formations: Give notice.
641PIPES AT DIFFERENT LEVELS IN COMMON TRENCH
Subtrench: Permissible provided soil of step is stable and unlikely to break away.
-Sub-trench not permissible: Trench depth as required for lower pipe. Increase thickness of bedding to upper pipe as necessary.
Lower pipe: Backfill with compacted granular material to at least half way up higher pipe.
Clear horizontal distance between pipes (minimum):
-Pipes up to DN 700: 350mm.
-Pipes exceeding DN 700: 500mm.
651CLASS A HALF DEPTH CONCRETE SUPPORT FOR PIPEWORK
Type of subsoil: stiff to very stiff clay.
Blinding:
-Material: concrete grade GEN 1
-Thickness (minimum): 25mm.
-Width: Full width of trench.
-Allow to set before proceeding.
Pipes:
-Temporary support: Two-layer pads of bituminous dpc or equivalent, on precast concrete cradles.
-Clearance under pipes (minimum): 100mm.
-Adjust pipes to line and gradient.
Bed:
-Material: concrete grade GEN 1
-Compact thoroughly.
-Thickness: From top of blinding to pipe invert.
-Width (minimum): External diameter of pipe plus 200mm.
Shutter vertical sides of concrete or extend concrete across full width of trench.
Initial testing before placing support: to be agreed.
Support:
-Material: concrete grade GEN 1
-Compact thoroughly.
-Height: Halfway up each side of pipe.
-Width: Full width of concrete bed or full width of trench.
Backfilling:
-Material: Protective cushion of selected fill.
-Depth: To 150mm (250mm for adoptable sewers) above crown of pipe.
-Compaction: By hand in 100mm layers.
653CLASS B HALF DEPTH GRANULAR SUPPORT FOR PIPEWORK
Type of subsoil: stiff to very stiff clays
Granular material:
-Pipe sizes DN 100 and DN 150: Size 4/10.
-Pipe sizes DN 225 and DN 300: Size 4/10, 10/20 or 4/20.
-Pipe sizes DN 375-500: Size 10/20, 4/20.
-Pipe sizes DN 600 and above: Size 10/20, 20/40, 4/20 or 4/40.
Bedding:
-Material: Granular, compacted over full width of trench.
-Thickness (minimum): 50mm for sleeve jointed pipes, 100mm for socket jointed pipes. If trench bottom is uneven, increase thickness by 100mm.
Pipes: Dig slightly into bedding, rest uniformly on barrels and adjust to line and gradient.
Support:
-Material: Granular.
-Depth: Halfway up each side of pipe.
-Compaction: By hand.
Backfilling:
-Material: Protective cushion of selected fill.
-Depth: To 150mm (250mm for adoptable sewers) above crown of pipe.
-Compaction: By hand in 100mm layers.
657CLASS F GRANULAR BEDDING FOR PIPEWORK
Type of subsoil: stiff to very stiff clays.
Granular material:
-Pipe sizes DN 100 and DN 150: Size 4/10.
-Pipe sizes DN 225 and DN 300: Size 4/10 or 10/20.
-Pipe sizes DN 375-500: Size 10/20.
-Pipe sizes DN 600 and above: Size 10/20 or 20/40.
Bedding:
-Material: Granular, compacted over full width of trench.
-Thickness (minimum): 50mm for sleeve jointed pipes, 100mm for socket jointed pipes. Where trench bottom is uneven, increase thickness by 100mm.
Pipes: Dig slightly into bedding, rest uniformly on barrels and adjust to line and gradient.
Backfilling:
-Material: Protective cushion of selected fill.
-Depth: 150mm (250mm for adoptable sewers) above crown of pipe.
-Compaction: By hand in 100mm layers.
667CLASS S GRANULAR SURROUND FOR PIPEWORK
Type of subsoil: stiff to very stiff clays
Trench width up to 300mm above crown of pipe (maximum):
-DN 100 nominal pipe size: 600mm.
-DN 150 nominal pipe size: 700mm.
-DN 225 nominal pipe size: 800mm.
-DN 300 nominal pipe size: 900mm.
Granular material:
-Pipe sizes DN 100 and DN 150: Size 4/10.
-Pipe sizes DN 225 and DN 300: Size 4/10, 10/20 or 4/20.
-Pipe sizes DN 375-500: Size 10/20 or 4/20.
-Pipe sizes DN 600 and above: Size 10/20, 20/40, 4/20 or 4/40.
Bedding:
-Material: Granular, compacted over full width of trench.
-Thickness (minimum): 50mm for sleeve jointed pipes, 100mm for socket jointed pipes. Where trench bottom is uneven, increase depth by 100mm.
Pipes: Dig slightly into bedding, rest uniformly on barrels and adjust to line and gradient.
Surround:
-Material: Granular.
-Depth: To 50mm above crown of pipe.
-Compaction: By hand in 100mm layers.
Backfilling:
-Material: Protective cushion of selected fill.
-Depth: To 150mm (250mm for adoptable sewers) above crown of pipe.
-Compaction: By hand in 100mm layers.
678CLASS Z CONCRETE SURROUND FOR PIPELINES
Type of subsoil: stiff to very stiff clays
Blinding:
-Material: Concrete (general).
-Thickness (minimum): 25mm.
-Width: Full width of trench.
-Allow to set before proceeding.
Pipes:
-Temporary support: Folding wedges of compressible board. Prevent flotation.
-Clearance under pipes (minimum): 100mm.
-Adjust pipes to line and gradient.
Surround:
-Material: granular
-Depth: To 150mm above crown of pipe.
-Width: Full width of trench.
Vertical construction joints:
Location: At face of flexible pipe joints.
Material: 18mm thick compressible board precut to profile of pipe.
Socketed pipes: Fill gaps between spigots and sockets with resilient material to prevent entry of concrete.
680CONCRETE SURROUND FOR PIPE RUNS NEAR FOUNDATIONS
Class Z surround: Provide in locations where bottom of trench is lower than bottom of foundation and as follows (horizontal clear distance between nearest edges of foundations and pipe trenches):
-Trenches less than 1m from foundations: Top of concrete surround not lower than bottom of foundation.
-Trenches more than 1m from foundations: Top of concrete surround not lower than D mm below bottom of foundation, where D mm is the horizontal distance of trench from foundation, less 150mm.
683LAYING PIPELINES
Laying pipes: To true line and regular gradient on even bed for full length of barrel with sockets (if any) facing up the gradient.
Ingress of debris: Seal exposed ends during construction.
Timing: Minimise time between laying and testing.
685JOINTING PIPELINES
Connections: Durable, effective and free from leakage.
Junctions, including to differing pipework systems: With adaptors intended for the purpose.
Cut ends of pipes: Clean and square. Remove burrs and swarf. Chamfer pipe ends before inserting into ring seal sockets.
Jointing or mating surfaces: Clean, and where necessary, lubricate immediately before assembly.
Allowance for movement: Provide and maintain appropriate clearance at ends of spigots as fixing and jointing proceeds.
Jointing material: Do not allow to project into bore of pipes and fittings.
687CONCRETE SURROUND FOR CROSSOVERS
Class Z surround: Provide where two pipelines (other than plastics pipes) cross with less than 300mm separation.
-Extent, on both pipes: 1m centred on the crossing point, and beyond as necessary to come within 150mm of nearest flexible joints.
689PIPELINES PASSING THROUGH STRUCTURES
Pipelines that must be cast in or fixed to structures (including manholes, catchpits and inspection chambers): Provide 600mm long rocker pipes adjacent to the external face of the structure (or both faces where appropriate, e.g. walls to footings), with flexible joints at both ends.
-Distance to rocker pipe from structure (maximum): 150mm.
Provision for movement for pipelines that need not be cast in or fixed to structures (e.g. walls to footings):
-Openings in the structures to give 50mm minimum clearance around the pipeline: Closely fit a rigid sheet to each side of opening to prevent ingress of fill or vermin.
697INSTALLING FLEXIBLE COUPLINGS
Ends of pipes to be joined: Cut cleanly and square.
Outer surfaces of pipes to be joined: Clean and smooth. Where necessary, e.g. on concrete or iron pipes, smooth out mould lines and/or apply a cement grout over the sealing area.
Clamping bands: Tighten carefully to make gas tight and watertight seals.
699 ACONNECTIONS TO SEWERS
General: Connect new pipework to existing adopted sewers to the requirements of the adopting authority or its agent.
Connections are to be made obliquely in the direction of flow using prefabricated proprietary fittings and couplings to ensure a watertight joint. Holes are to be made using a drilling device to avoid damage to the pipes. Connections are to be packed as necessary to avoid differential settlement between the pipes.
705INITIAL TESTING OF PIPELINES
Before testing:
-Cement mortar jointing: Leave 24 hours.
-Solvent welded pipelines: Leave 1 hour.
Method: Block open ends of pipelines to be tested and pressurise. Air test short lengths to BS EN 1610.
711TRENCH SUPPORTS
Removal of trench supports: Sufficient to permit compacted filling of all spaces.
713INSTALLING ROOT BARRIERS
Root barrier installation: Full depth of excavation. Fit closely to trench wall nearest the tree.
715BACKFILLING TO PIPELINES
Backfilling above top of surround or protective cushion: Material excavated from trench, compacted in layers 300mm (maximum) thick.
Heavy compactors: Do not use before there is 600mm (total) of material over pipes.
718BACKFILLING OVER CONCRETE
Minimum times from placing concrete:
-Backfilling generally: 24 hours.
-Heavy compactors and traffic loads: 72 hours.
720 ABACKFILLING UNDER ROADS, PAVINGS AND GROUND BEARING FLOOR SLABS
Backfilling from top of surround or protective cushion up to formation level: Granular subbase material, as clause 498, laid and compacted in 150mm layers.
722PUBLIC ROADS AND PAVINGS
Excavating and backfilling of trenches: To Department of Transport ‘Specification for the reinstatement of openings in highways’.
726 AFOAMED CONCRETE BACKFILL
Preparation: Repair damaged drainage pipelines and ducts. Seal off openings in, and ends of, abandoned pipelines and ducts. Seal off cavities in or next to the excavation which are not to be filled. If in doubt obtain instructions from CA before proceeding.
Backfilling: To British Cement Association 'Foamed concrete - specification for use in the reinstatement of openings in highways'.
732 ATEMPORARY BRIDGES
Trench bridges: As necessary to prevent construction traffic damaging pipes after backfilling. Protection may be provided by suitable barriers to keep traffic away from the line of the sewer.
Heavy materials are not to be stored over drains and sewers.
733 BPROTECTION OF WORKS AGAINST VERMIN
During construction drains and sewers that are left open: Covered when work is not in progress to prevent entry by rats.