Aarsleff Piling landed the piling that will provide the foundation support for a £38 million 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 support 12 turbines at the old airfield, which was the one-time 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 was included.
The renewable energy provider Norvera Energy UK was further expanding the site’s use into a 30-MW wind farm that generates electricity for about 13,400 homes, equivalent to 10% of the households in the East Riding of Yorkshire in 2008. The Norvera-appointed contractor McNicholas awarded Aarsleff Piling a £573,000 supply, handle, pitch, and drive contract for the turbine base piling.
At Lissett Aarsleff had to install 30 piles in each of the 12 bases, equally spaced on a ground-level pitch circle diameter of 16 m 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. As the over piles are 15 m long and very heavy, Aarsleff believed the only rig in the UK able to handle, pitch, and drive these at a backward and forward rake is the Finnish Junttan PM26LC.
The Junttan PM26 LC, with its HHK9A accelerated hammer, was the largest rig in Aarsleff’s fleet in 2008 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 with up to a 400-mm square section needed to accommodate the high cyclical loadings generated by wind turbines.
The HHK9A hammer is one of a new generation of Junttan hydraulic impact hammers with an adjustable segmental drop weight of 9 t, 7 t, and 5 t 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 compared with a conventional free fall drop hammer of the same weight. Most importantly, all relevant pile driving data is displayed on the rig’s computer screen in the operator’s cab.
The work at Lissett was completed in scheduled time in 2008 after a thorough testing and commissioning by Nordex, the wind turbine manufacturer.
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Junttan UK, Jeremy Pilch, junttanuk@aol.com