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Waste not want not

Spotlight - Displacement auger piles are becoming increasingly popular, reports John McKenna.

Rising landfill costs and the limited places in the UK to dump hazardous waste are having an impact on piling and foundation work in the UK.

One of the clearest indicators of this, says May Gurney geotechnical and civil engineering director John Chick, is that clients are requesting that the amount of soil removed from site is kept to a minimum, especially when working on brownfield sites. 'We are doing more and more displacement auger piling work, ' says Chick.

Displacement auger piling (DAP) is a method of piling which displaces the ground to form a pile. The displacement tool is screwed into the ground by a powerful, high torque piling rig.

As with a continuous flight auger (CFA), concrete is pumped down the hollow auger stem to form the pile as the auger is withdrawn. But with DAP, the ground is displaced laterally and downwards during boring and concreting, limiting amounts of soil removed.

Chick admits that while DAP is becoming more popular, it has its limitations and is far from replacing CFA as the favoured piling method.

'Displacement is highly dependent on ground conditions, whereas CFA is pretty much a go anywhere tool, ' he says.

Research into improving the efficiency of DAP rigs is ongoing, says Chick, as is the industry's mission to get the most out of all piles.

'There's a real trend in the market to get more capacity out of piles, ' says Chick.

'Rather than invest large amounts of time and money into proving a that a new diameter pile would work, we look at being able to put higher loads on more conventional piles. This is done through a great deal of attention to detail in design and investment in testing.

'Instead of the equation of heavier load means better pile, it's a case of heavier load means better understood pile.' Chick's outlook for the foundations and piling market in 2007 is bright. His prediction is echoed by Westpile general manager Julian Gatward.

'The commercial market in London is picking up and housing is in demand, ' he says.

May Gurney has used soil nails and sprayed concrete in preference to steel sheet piling to reinforce a vertical bank in Hertfordshire. The constricted site for a new supermarket and car park in Rickmansworth is bordered by a railway on its south side and a pedestrian route on an embankment at its north end. Using soil nails instead of sheet piles freed up valuable space, allowing the exit wall of the car park to sit close to the perimeter of the site once the embankment is complete. Main contractor is Kier.

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