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April restart set for wind farm foundation work

Heavy snowfall has stalled work on the piled foundations on the UK mainland’s highest onshore windfarm but contractor Aarsleff is hoping to restart piling in April.

Aarsleff started work on the Dunmagalss wind farm scheme, that is up to 825m above sea level,  for main contractor R J McLeod in November last year.

Work started in winter despite the risk the weather presented to the piling operations in a bid to keep the contract for the 94MW wind farm on schedule for its 2016 opening date.

The new 33 turbine wind farm is being built for SSE Renewables with piled foundations, designed by Donaldson Associates, supporting five of the turbines and gravity foundations, designed by Grontmij, for the remaining structures.

Each of the piled foundations is supported by 40 driven steel piles that are being driven through peat and soft clays and underlying dense granular deposits and to refusal into the bedrock which is a mix of granite, schsists and psammite. According to Aarsleff, this means that the piles penetrate any weathered rock.

Piles completed on the project before the weather halted work have been driven to depths of between 14 and 23m, which is in line with where the ground investigation suggested rockhead would be encountered.

The 339mm diameter piles are recycled North Sea drill casings with a 12mm wall thickness and have called for some careful planning. The casings available in 11m and 13m lengths, so care is needed to ensure the piles provide sufficient length to reach bedrock with the joint located at least 5m below ground level to avoid bending moment stresses being applied to the joint.

Aarsleff’s piling rig left the Dunmagalss site in January but the company is hopeful that the snow will be cleared enough to restart the work in April. It has said that it will take four weeks to complete the piling work.

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