Precast Concrete (PCC) chamber rings from 900mm Ø – 2400mm Ø, PCC Perfect Manhole System from 1200mm Ø – 1800mm Ø, PCC pipes (including Sulphate Resistant) with internal dimaters from 150mm – 200mm, PCC road gullies and PCC headwalls are all available, generally on full load, direct to site deliveries.
PCC chamber rings
Recommended to be installed at 100 metre intervals, whenever there is a significant change in the direction of a sewer, where another sewer is connecting with the main run of another sewer, or where there is a change is size or gradient of the pipeline, PCC chamber rings hold a number of advantages over in-situ concrete construction systems, such as:
• Wide selection of sizes and depths are available.
• Simple to assemble, requiring relatively unskilled labour on site.
• Units are capable of being constructed as flexible watertight structures. Elastomeric joint seals are in compliance to EN681. Butyl sealant strips also available as a seal option.
• The structure is durable with its own inherent strength.
Built on to a run of sewer with or without connections. Where conditions are permitting, the soffit level of sewers connecting on to a manhole should be the same.
Where one sewer connects with another at a substantially different level, the manhole is built on the lower sewer and incorporates a vertical or nearly vertical drop pipe from the higher sewer. The drop pipe, which may be inside or outside the manhole chamber, has its lower end discharging in to the main sewer, and at its upper end rodding eye for cleaning through the higher sewer.
Dual & Crossing Manholes
Where surface water and foul sewers are laid in the same trench, with the surface water normally being located above the foul, a normal manhole chamber is built for the foul sewer and the surface water is carried across the chamber in a separate pipe which may have a sealed inspection cover.
Pipes Adjacent to Manholes
There may possibly be differential settlement between a structure and the pipeline resulting in angular deflection of the joint. This creates no problem for the joint itself however, when this movement is “excessive” there is a shear force that can cause structural failure of the pipe, either shear behind the collar or from beam fracture of the pipe barrel.
To prevent this, the first pipe in the line can be restricted in length. This is known as a “rocker” pipe. The contractor should access the likelihood of differential settlement and make use of rocker pipes as appropriate
The minimum clear opening through a cover slab should be 600mm x 600mm.
Slabs with other sized accesses/multiple accesses or rebated accesses are quite often required
in cases of split wall chambers, pumping stations, where flow control devices are fitted within
the chamber etc. (these would be made to order products).
The access is normally located in an eccentric position i.e. usually 150mm – measured from
edge of access (mid-point of side) to face of chamber wall below. This allows for safe and clear
access to steps or ladder system below (where fitted).
Cover slabs are generally suitable for installation below highways (some small units are available
for use in non-trafficked areas and hence should not be installed in a highway).
Landing slabs are generally required on manholes greater than 6m depth (landing slabs should
be installed at minimum of 2 metres and maximum of 6 metres spacing for the depth of the manhole).
It is usual for the access in the landing slab to be 900mm circular and is usually positioned
offset on site so that there is a break in the steps/ladders vertically (alternatively a hinged
safety grill may be fitted over the access).
On large, deep chambers (usually DN1800 or greater), it is common practice to reduce the
upper access shaft to a smaller, more economic solution of typically DN1200 size.
Where double steps are fitted in the main chamber, the steps alignment is maintained through
the reduced shaft section.
Corbel units and adjusting units
The access in the concrete cover slab may be reduced in size (typically from 750 mm x 600
mm to 600 mm x 600 mm) via the use of corbel units.
Adjusting units can be installed between the concrete cover slab and the access cover and
frame (can be used in replacement of engineering brickwork in most situations).
Perfect Manhole System
The Perfect Manhole System is available in 1200mm, 1350mm, 1500mm and 1800mm diameters. The system comprises of:
• a monolithic precast concrete bases (available pre-benched in any configuration within just days of requisition).
• a sealed chamber ring.
• a rubber joint or butyl sealant strip.
• a sealed cover slab which is supplied with your required access.
• a sealed pipe connection for various pipe types.
Designed and manufactured to last a minimum of 120 years. This is a sealed manhole system that gives up to 40% savings on greenhouse gases compared to traditional manhole construction and eliminates the need of ready mixed concrete to form the traditional base and chamber benching.
The Perfect Manhole can be installed in as little as 25 minutes, reducing the need to work in confined spaces, helping safe site practice, and eliminates the need for wet trades resulting in rapid construction compared to traditional methods as well as a reduction in the time the excavation is open.
Within the concrete pipe range, there are two different systems available; Ogee pipes, mainly for surface water and land drainage and Concrete Sewer Pipes for the conveyance of sewage.
Ogee pipes are manufactured a metre long. Spigot & socket vary from 1.25 metres for 150mm and 225mm diameter, to 2 metres for 300mm diameter, and 2.5 metres for all other sizes.
I.S.6 Concrete Sewer Pipe specification deals with the manufacture and properties of flexible jointed concrete pipes and fittings, either reinforced with steel or unreinforced, intended to be used for the conveyance of sewage, or sewage and surface water at atmospheric pressure. These test requirements may be found in I.S. 6: 2004 and are to be used in conjunction with ISEN 1916: 2004. These new Standards are also be available from NSAI.
Sulphate resistant pipes for applications where sulphuric acid is present in the groundwater, or where an internal acid attack is thought to be likely. These are made to order and to comply with sulphate class 4b of I.S. 6: 2004 Table 2 and give a high-class resistance to attack. High Sulphate Resistant Hydraulic Cement is used in concrete exposed to severe sulphate action, principally where soils or groundwaters have high sulphate content. It gains strength more slowly than General Use hydraulic cement. Use of a low water-to-cementing-materials ratio and low permeability are critical to the performance of any concrete exposed to severe sulphate attacks. Like other Portland cements, it is not resistant to acids and other highly corrosive substances.
Headwalls are generally for pipeline outfalls to discharge in to open watercourses, so are situated at the outlet of stormwater pipes or box culverts.
These precast outfalls & spilways can be fitted with a range of accessories such as flap valves, penstocks, Kee Klamp® handrails and a selection of gratings depending on the application.
PCC Road Gullies
Used as part of a healthy and effective Sustainable Urban Drainage System (SUDS)