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Speed is of the essence

PILING

Abbey Pynford has teamed up with Keller to speed up the construction of house foundations. Andrew Barker watches the prototype under construction in Kent

ABBEY Pynford is on to something. In a collaboration with Keller Ground Engineering the piling firm has developed a package that it says offers clients a platform for constructing houses wh ich can be installed in as lit tle as half the t ime of its competitors.

The formula , being trialled on a site in Buck inghamshire, is to combine Keller's ground improvement expertise with Abbey's Housedeck system, a successful and patented arm of its business that has been going strong for six years.

'We can't emphasise enough how quickly we can get this into the ground. Sometimes we do the work in two-thirds of the time, sometimes half, of the traditional methods of pile and beam, ' says Paul Kiss, managing director of Abbey Pynford.

The Fuller's Yard site in Chesham, Buckinghamshire, is a small residential plot. The total value of work for Abbey is a mere £60,000. But Mr Kiss is erring on the side of caution with this first job of the partnership.

'I'd rather start with a small one because the next will be about half a million, when we get it, ' he says.

The two teams have so far found working side by side so benef icial that Mr K iss's opt im ism is understandable. He didn't divulge the exact location of the next 'big' project but hints that it is somewhere in Gloucestershire.

The 140 compaction points where the ground has been treated are dotted all over the small site. A standard crawler crane with a 12 m-long vibrating poker was used to bore into the ground. The holes were filled with an inert aggregate then the poker was reinserted to firm up the columns.

'The longer you keep the poker in the ground the tighter the aggregate will interlock together, ' says Nick Hodder, commercial director for Abbey Pynford. The columns of tightly packed aggregate provide the support for Abbey's slab, a cheap and quick alternative to conventional piling.

Vibro is not exactly new on the scene, having been launched in the 1970s. Nor is it a viable solution for all ground types.

'It's horses for courses. If you had a soft, peaty, organic soil you'd struggle with that stone column. It would bulge, disperse outwards and the integrity would be put in question, ' says Mr Hodder.

The advantage of using Housedeck on a contaminated site is that the airf low under the slab can be controlled by putting a void in under the house. Martyn Singleton, marketing manager for Keller, describes how it can contain the residual contamination.

'We will be building a capillary break in the ground , ' he says.

'The vibro treatment will be through that to the ground below untreated. And to avoid strip foundations or ground beams that could break into that ground, we will use the Housedeck style, which can then sit on top of the capillary break. It avoids soil removal and it's also cost-effective.'

With clay soils the system offers the advantage that the piles can be moved around as they go along, which is also far easier when the designers are working alongside the ground engineers.

Abbey had to trim the platform to a decent level and then construct a standard 225 mm-thick reinforced concrete slab on top. But this was only after the ground had been treated. Three metres of treated ground now sits on top of a chalk bed, which negates the need for driven piles.

'It was good for the client because he got a relatively cheap and quick solution, ' says Mr Kiss.

Housedeck grew out of a piling technique but it can now cover all the different ground types. The first ever job took four weeks; now the same sized slab, for a typical four-bed detached house, would take half that.

The new package covers design, drainage, piling and concrete, and can save valuable time for a commercial developer, says Abbey, although that was not the market the company went for originally. Now with more than 100 plots completed the company has launched a spinoff, Comdeck, which can cater for larger commercial projects of up to six stories, such as hotels.

'It's a theme on a theme, ' says Mr Kiss. 'In these cases a thicker slab and bigger piles are used to take the heavier loads.

What they like about it is it's a one-stop shop.

'More and more clients are looking for a package with just one subcontractor with one warranty and one guarantee.'

And that's exactly what's on offer.