INDUSTRY BUZZ concepts of modularisation and prefabrication are being increasingly applied in the house foundations industry. The latest to enter the market is a polystyrene formwork system for ground beams and pile caps which has been used to counteract problems on a backfilled quarry site in Swanscombe, Kent.
Contractor O'Halloran & O'Brien used Rom's latest Beamform formwork system along with prefabricated welded beam cages to form the foundations for 175 houses.
The site was formerly a quarry backfilled with sand to depths of 40m. After removing 500mm of topsoil, the entire site was vibropiled at 2m centres to 4m depth to stabilise the ground before the foundations were built.
Beamform is a sacrificial expanded polystyrene formwork, 1,000mm long, 600mm deep with a 220mm wide base, that tapers towards the top. Normally two lengths of Beamform are used to form both sides of the beam and prefabricated welded steel reinforcement cages are placed before the shuttering.
Rom's Roy Clifton says the system is faster and cheaper to install than traditional timber shuttering, even though Beamform is left in the ground. 'It is lightweight, easy to handle, cut and saw and can be installed rapidly by one site operative.'
As the prefabricated beams are welded they keep their shape and their weight keeps them in position. At the junction of two or three beams, the tie bars are pulled and tied into position. By fitting four spacers to each Beamform unit the exact beam shape is formed.
After the space around the formwork is backfilled, the whole arrangement is stiff enough to withstand the weight of the concrete, which Rom says should 'ensure a straight beam with the correct amount of concrete and very little waste'.