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Fast Fastening

Steel shortages led to Bullivant developing an alternative and cost-saving foundation solution for a Bovis Homes development in Staffordshire.

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Uplands Mill in Biddulph was once the home of the UK’s only Velcro factory but redevelopment of the site as a residential area led to the need for fastenings of a different kind when it came to the foundations.

Jointed precast concrete piles became key to progressing the construction work when supply shortages meant that waiting for the availability of the planned steel tubular foundations would impact on the programme.

Without finding an alternative design solution, work on the £30M project to develop 197 new homes - with 65 affordable units - on the former factory site faced the risk of delays and higher costs. With no quick solution to the steel shortage in sight, piling contractor Bullivant suggested using its precast concrete driven piles with a mix of joints to ensure the scheme remained on budget.

“Bovis had originally asked us to install steel tube piled foundations for the latest phase of redevelopment at Uplands, but we were experiencing difficulties in getting the right steel at that time,” explains Roger Bullivant operations manager Alan Oakton.

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“By using a mix of our tension and full moment pile joint systems we were able to meet the demands placed on the design by the ground conditions and deliver a lower cost solution in the process.”

At the site, superficial deposits of glacial till, which overlays the carboniferous Pennine Lower Coal Measures, meant that there was a high risk of heave in the clay. “There was also a risk of running sand at the site and we had to ensure that the toe of the pile was below this layer,” says Oakton.

The solution that Bullivant offered involved using its 250mm by 250mm square section precast concrete piles with a capacity of 500kN driven to a depth of 13.5m.

The piles are formed of three sections - two 4m sections for the base joined by a basic tension joint. The top 4m section is connected to a 6m pile with Bullivant’s full moment Emeca joint.

The new joint was developed with Finland-based Emeca specifically for use with Bullivant’s precast piles. Bullivant primarily looked at developing the joint in a bid to move the company into foundations for civils work and larger contracts.

“By using a mix of tension and full moment pile joint systems we were able to meet the demands placed on the design by the ground conditions”

This has widened the company’s market share and kept its precasting facility in Burton-on-Trent busy. “Widening the markets we can serve has meant that we have not had to reduce staff numbers at the casting yard during the recent recession,” says Bullivant chief structural engineer John Hull.

While the aim of the Emeca joint development was the larger civils market, at Biddulph it is helping Bovis to save money and meet the geotechnical challenges of the site.

“Using the Emeca joints for both connections would have made the solution too expensive,” explains Oakton. “Only the top 5m of ground is at risk of heave so the bottom joint does not need to be a full moment joint.”

Hull explains that only the top section will be exposed to lateral loads, while the rest will only take compressive loading.

The tension joints used for the lower section of the piles at Biddulph have also undergone redevelopment in recent years and these now feature a locking mechanism.

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According to Oakton, work on site has progressed well. “Once the first few piles were installed at the site, they were left over the weekend to allow full skin friction to develop before they were tested to ensure the piles met with the expected capacity predicted by the design,” he says.

In total, Bullivant installed 88 piles for the latest three blocks of development at the site in less than five days.

With the cost of the solution proving cheaper than the steel tube option, Oakton believes that the precast concrete pile using a combination of joints to make them cost effective could eventually replace steel tube piling for this type of application.

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