The Kingsnorth Commercial Park, a 115 acre greenfield site on the Isle of Grain, is being developed by property firm Goodman to provide up to 2 million sq ft of industrial and commercial space. But its location on the marshy island means that surface water drainage is a significant challenge which requires an extensive network of ditches and ponds.
As part of its contract, Volker Fitzpatrick is installing culverts and approximately 150 headwalls – small retaining walls placed at the outlet of a stormwater pipe or culvert – as a vital element of the drainage system.
Instead of adopting the traditional approach of building headwalls by hand out of brick or in-situ concrete, Volker Fitzpatrick chose Kijlstra’s precast units which could be delivered to site just-in-time and quickly lifted into position.
“On a project of this scale it makes sense to use pre-cast components rather than hand-build each one” says Volker Fitzpatrick sub-agent Eleni Gkolfinou. “In terms of labour, time and materials, it is far more efficient”. The contract for the pre-cast products was worth approximately £300,000.
Kijlstra produces a range of standard and fully customised headwalls which can be made to specific client requirements – as here at Kingsnorth. The company’s three standard designs can all be modified in terms of height, pipe connection size and the size and slope of the wing walls in order to suit customer requirements.
Most types of pipework, including concrete, clay and plastic, can be connected to the headwalls and a variety of flow control devices such as flap valves, penstocks, tilting weirs, static weirs and hydrobrakes can be fitted at the factory to make on-site installation quicker, safer and easier.
“We believe in doing as much off-site as we possibly can” comments Kijlstra technical manager Weiger Faber. “We fit everything in the factory so that the site simply becomes an assembly line where you lift the finished product into place and move quickly on to the next one”.
Replacing on-site activity such as bricklaying and formwork erection with factory production reduces construction times, minimises labour costs and optimises product quality. “The up-front cost is marginally higher, but those costs are fixed” explains Mr Faber. “The contractor can budget accurately and – with all the other advantages of speed and quality, there are significant overall cost savings”.
Volker Fitzpatrick started work on site in May 2010 and is due to complete this phase of the works by November 2011. Using pre-cast headwalls and culverts has helped ensure the drainage works has remained on time and within budget, says Ms Gkolfinou:
“This type of product is fairly new to us but I have been impressed by the quality of the product. We have had a very good relationship with Kijlstra, who have helped with ongoing advice throughout the contract”, she says.