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Aarsleff Piling has landed the piling that will provide the foundation support for a £38M wind farm on a former Second World War aerodrome at Lissett, a few miles south of the eastern coastal town of Bridlington, East Yorkshire. The precast concrete piles will support 12 turbines at the old airfield, which was the onetime base for the RAF’s 158 squadron flying Handley Page Halifax bombers. Shortly after the war Lissett airfield was returned to agricultural use and later included a small industrial park.
  
The Junttan PM26 LC with the HHK 9A accelerated hammer installing up 30m long inward and outward raking piles at Lissett, is the largest rig in the Aarsleff fleet and was bought specifically for driving the large section Centrum precast concrete piles required to take cyclical loadings for wind turbine foundation bases. Click images to enlarge.
Renewable energy provider Norvera Energy UK is now further expanding the site’s use into a 30MW wind farm that will generate electricity for about 13,400 homes, equivalent to 10% of the households in the East Riding of Yorkshire. Norvera has appointed the privately owned contractor McNicholas, who then appointed the German consulting engineer HCE Ingenieurgesellschaft, as its main design and build contractor for the approximate £4M civil works part of the project. In turn McNicholas awarded Aarsleff Piling a £512,000 supply, handle, pitch and drive contract for the turbine base piling, which the specialist driven piling contractor is performing in two visits.
At Lissett Aarsleff has to install 30 piles in each of the 12 bases equally spaced on a ground level pitch circle diameter of 16m and driven alternately on a 1:5 inward and 1:6 outward rake. The 360 piles are driven to a design length through clay with bands of sands and gravels for toeing into the underlying chalk. HCE’s design calls for 400mm square section precast concrete piles ranging from 20m to 30m long. These are made up of a standard under pile jointed to a special 15m long over pile, which is strengthened with additional reinforcement to achieve a compressive working load of 1,200kN and tension of 170kN. Aarsleff will also supply and install an additional six piles of smaller 350mm square section to support an 80m tall Metmast that will monitor weather conditions at the exposed site.
HCE, based in Hamburg, has considerable experience designing wind turbine foundations in Europe and is matched with Aarsleff’s knowledge in engineered piling solutions, which has included working together designing and installing the piled foundations for many other wind turbine bases in the UK.
As the over piles are 15m long and very heavy, Aarsleff believes the only rig in the UK that can handle, pitch and drive these at a backward and forward rake is the Finnish Junttan PM26LC. Aarsleff also believes that its subsidiary, Centrum Pile, is the only precast pile manufacturer in the UK that can make 18m long, 400mm square section piles in a single length and well within the 15m required for Lissett.
The Junttan PM26 LC, with its HHK 9A accelerated hammer, is the largest rig in Aarsleff’s fleet and was bought in direct response to the company’s sustained increase in demand for its services and especially in the renewable energy sector. There is a growing requirement for much larger precast concrete piles up to 400mm square section needed to accommodate the high cyclical loadings generated by wind turbines.
The HHK 9A hammer is one of a new generation of Junttan hydraulic impact hammers with an adjustable segmental drop weight of 9t, 7t, and 5t and variable stroke of up to 1.2 m. It is operated from the rig’s hydraulic system and hydraulically accelerates the drop weight during the fall, boosting the impact energy and increasing by up to 20% the efficiency at full stroke over a conventional free fall drop hammer of the same weight. The hammer produces maximum impact energy of 106kNm at full 1.2 m stroke when equipped with the largest 9t drop weight, but at Lissett the hammer is in the mid size 7t mode. Impact energy, drop height and blow rate can be infinitely adjusted by the rig operator to suit ground conditions and pile type as the hammer is suitable for driving all types of precast concrete, steel tube and sheet and timber piles. All relevant pile driving data is displayed on the rig’s computer screen in the operator’s cab.
As Aarsleff finishes the piling in each base, McNicholas follows on cutting piles to level to expose the reinforcing and complete the 17m diameter heavily reinforced concrete foundation bases and other ancillary works and access roads. The 2.5MW Nordex N90 wind turbines, which each have a hub height of 80m and 90m diameter blades, will then be erected, tested and commissioned by Nordex with the first two expected to be operational by the end of 2008. As a reminder of Lissett Airfield’s wartime role, Norvera will erect a memorial and name the 12 individual turbines after the names of some of the Halifax bombers that flew from the base.
For further information please contact:
Jeremy Pilch, Junttan UK, London House,
266 Fulham Road, London SW10 9EL
Tel: +44 (0) 207 351 3130
Email: junttanuk@aol.com
Web: www.junttan.com
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