A proprietary foundation system allowed follow-on trades to get in alongside the piling contractor on a Thames Gateway site. Damon Schünmann reports.
What attracted [main contractor and developer] Ward Homes to this foundation system is it does not need a piling carpet which makes it cheaper on this job, ' says Abbey Pynford chairman and owner, Paul Kiss. 'But that's not the main selling point of Housedeck, which is that it's always quicker than a traditional system.'
The housing development in question is a Thames Gateway development near Chattenden, about 50km south east of central London.
'It's normally a similar price to a traditional foundation but the advantages are it takes between one half to two thirds the time to build and also reduces risk. This is because if you have a traditional pile and beam system and have an obstruction under a pile you're knackered, ' he says. 'But with Housedeck we can move a pile, using So stik software, which may just then need a bit more load on it or a bit more steel in the slab. With a traditional pile the original designer may take a day to do a redesign. But as well as reducing risk when dealing with obstructions, we take on the risk when setting out.'
The other benefit Kiss is keen to point out is that subsequent building trades can immediately follow on while the foundations for an adjacent plot are being built, because of the small piling rig used.
The subcontractor's area manager, Mike Dorman says: 'On a normal job the ground beams would have to be completed before the bricklayers could start because of the heavy machinery needed for putting them in but this site is more progressive as the other trades can follow on right behind us.'
Housedeck replaces a traditional pile and beam foundation with a piled slab. While the inner leaf is supported by the slab, the outer is built up from a stainless steel angle cast into the edge of the slab.
The result means substructure brickwork is not needed. Where ground conditions might have dictated a conventional anti-heave material around a reinforced concrete beam, this can be replaced by an under-slab void.
At the Thames Gateway site, the Housedeck system going in is catering for a clay stratum prone to heaving, with the void version.
The piles are going in at 10m to 13m depth, which is the norm for this system, ' says Kiss. Although the rig crew had been putting in 200mm diameter piles for the Ward Homes job, they may go in at up to 300mm for other projects.
The developer first brought Abbey Pynford on site in May to install foundations on two plots that had been released for development after site workers had installed traditional pile and beam foundations in surrounding plots. The small piling rig was able to nip in and install the piling contractor's proprietary system in the tightly confined area available. The developer was sufficiently impressed with the work to award Abbey a £1M contract for the remaining plots.
'We are using Kitten rigs which are about 750kg in weight with an operating height of 2.5m to 2.8m and a tracking height of 1.7m. But a normal pile and beam machine would weigh around 35t, ' says Kiss.
Abbey Pynford aims to complete work by the end of this year.
Simple but not stupid 'My name is Kiss and the Housedeck system is 'keep it simple, stupid', ' says Abbey Pynford chairman and owner, Paul Kiss. He is referring to the well-known acronym and principle often used during the design process as a reminder to avoid unnecessary complexity.
'I've no idea why somebody else had not come up with this. There are more piles but less effort with everything else. We put the piles in for one plot in two days, the deck in a week and there is no way you could do that with a pile and beam system.
'I was looking for was a void system for underpinning when I was working on the M3 motorway and I made a deck support, which is a key to the system, and that's how it started.' First used commercially in 2000, the method now annually nets about £9M for Abbey Pynford.
Kiss hopes that constant modication of the technique will mean it can replace traditional strip footings - once the company has managed to bring the price of Housedeck down to a competitive level - perhaps within two to three years.