A hole in one

Lateral thinking
Pennine Vibropiling has spent the last two years developing Penpile, which it says brings together the best of different types of piling. Driven piles produce no spoil but they do generate a lot of noise and vibration, whereas bored piles may be quieter but create large amounts of spoil.

Penpile is a specially adapted auger that displaces soil laterally. Because it pushes soil to the sides of the pile, there is only a small amount of spoil and vibration. It can be bored to 13m and can manage up to 25 piles a day.

The base of the pile can also be rammed to increase the load capacity. The pile can hold up to 400 kilonewtons, and is best suited to such projects as shops, business parks and housing, where the load capacity required is at the lighter end of the scale.

According to Pennine's southern sales manager, Derek Taylor, the system is ideal on polluted sites. "Penpile is most cost-effective on contaminated land because, unlike conventional piling, there's no need to carry soil away. It's also useful on sites with restricted access, where the contractor doesn't want hundreds of lorryloads of spoil to take away."

Taylor says that Penpile has proved popular with housebuilders. Richard Wild, technical co-ordinator at Bellway Homes, is one convert to the system. Penpile was one of three piling methods from Pennine used by Bellway to convert Lower Addiscombe station in Croydon into houses. The piling took six weeks, which is comparable with other methods.

"We had different types of ground conditions throughout the site, and we used Penpile at the front of the site, which was in close proximity to existing properties," says Wild. "Other forms of driven pile cause ground disruption, which we had to avoid, so as not to disturb the basements of the existing buildings. Using this system we could achieve that."

Wild adds that no problems have cropped up with the piling as yet, although Bellway has yet to test the load-bearing capacity of the piles. However, he doesn't expect any problems. "We anticipate using this system on another site that also has poor ground conditions, as Penpile is beneficial on contaminated land."

One barrowload of spoil
May Gurney Technical Services brought over the Omega pile under licence from Belgium in 1994 and was the first UK firm to use displacement auger piling (DAP). It decided to create its own DAP three years ago and has been developing it ever since.

The piles are formed by an auger, which compacts soil into the sides of the earth, so there is very little spoil.

Like Pennine's Penpile, DAP was developed with contaminated land in mind. "It's ideal for poor ground conditions, because the contaminants in the ground stay there," says Mark Annetts, marketing manager at May Gurney. "This is better than bringing them to the surface and having to dispose of the polluted land."

instead of the standard two dumper loads of spoil, each pile was producing one wheelbarrow’s worth of waste material

The Omega pile can be inserted up to 30m in the soil and hold a force of up to 1,200 kilonewtons. It is best suited to sand and gravel because the softer material lets the auger work more effectively in compacting the soil into the sides of the earth.

"You don't have to worry about clearing away the soil," says Annetts, "which makes this a very quick method in appropriate conditions."

Between 40 and 50 piles a day can be laid in the right ground conditions. Annetts adds that higher loads can go on smaller piles because the auger makes the ground more dense as it bores down.

Guy Shepherd, a project manager at Galliford Midlands, used May Gurney's DAP system on a £21.6m factory/shopping centre at Chatham in Kent.

The site was heavily contaminated with phytotoxic waste including copper and heavy metals. Using DAPs has meant a significant saving for Galliford, according to Shepherd.

"To take away the contaminated ground would have cost £450 per lorry load. And when you consider that instead of generating two dumper loads of material per pile, as we would have using a continuous flight auger pile, one wheelbarrow of waste per pile was produced, which we remediated and used on site." Some 1,200 piles were put in over a 10-week period, between 15m and 18m deep.

There were also structural benefits. "Because the soil was consolidated in the ground, the load-bearing capacity of the pile was increased. And as we were working within a 155-year-old Grade II listed building, the fact that there was no vibration was also important, so as not to disturb the existing timber piles."

Shepherd says he was very pleased with the performance of the system. "We have worked with May Gurney before and worked well with them, though we would have used our sister company Rock & Alluvium if it had been available. I would happily use this system again. I'd use DAP wherever possible."