Product category:
Ground Engineering
News Release from: Aarsleff Piling | Subject: Piling contractor
Edited by the Buildingtalk Editorial
Team on 02 November 2006
Foundation piles support wind turbines
Ecotricity and its specialist piling contractor Aarsleff Piling, has been the key to overcoming unexpectedly stiff ground to successfully install foundation piles to support wind turbines
Close cooperation between Green energy provider Ecotricity and its specialist piling contractor Aarsleff Piling, has been the key to overcoming unexpectedly stiff ground to successfully install foundation piles to support wind turbines for the extension to the Bambers Farm Wind Park at Mablethorpe, Lincolnshire Based on ground conditions from the site investigation Aarsleff had intended to install the precast concrete piles with one of its own Banut fixed leader rigs with a 5 t hammer
This article was originally published on Buildingtalk on 5 Jul 2006 at 8.00am (UK)
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But early refusal of the piles led Aarsleff, working in close agreement with Ecotricity, to change to using two rigs in unison with larger hammers.
Ecotricity is erecting six German Enercon 800 MW turbines with a hub height of 65 m and 48 m diameter three blade rotors on circular piled foundations installed by Aarsleff.
When commissioned the additional turbines, alongside the 10 existing Bambers Farm turbines, will provide a further 14MkWh/year of green electricity to an extra 4,250 local homes.
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For the GBP3.5M Bambers Farm extension Ecotricity is adopting a similar foundation specification and construction technique that turbine supplier Enercon has used on many other wind farms in Germany.
Aarsleff's Danish parent company, Per Aarsleff, has installed thousands of precast concrete foundation piles, made by its sister company Centrum Pandaelig;le A/S, to a German Enercon geotechnical and structural design.
"Enercon design foundations solutions in Germany based on piles from Centrum and now Aarsleff has extended that to the UK," says Ecotricity project manager Simon Vince.
"Bambers is a follow on from Aarsleff's successful work for us at Reading, driving the same section piles, but judging from the soil survey we didn't anticipate problems installing them with the single rig".
"We're still learning as these are big piles which drive differently".
"But we have a good working relationship with Aarsleff and worked closely together to come up with some viable options and agreed a format to move forward using two different rigs with bigger hammers and different driving capabilities".
"I'm very impressed with Aarsleff's professional manner in dealing with the unexpected and we will now work together on our next wind farm project in Bristol".
The foundations for each of the Bambers Farm turbines require 16 equally spaced piles, which are installed in a circle and driven at a 1 in 4 rake.
The completed 400 mm square section piles, which are 20m long and made by Aarsleff's UK subsidiary Centrum Pile, will be capped with a reinforced concrete slab with cast in holding down bolts to take the turbine towers.
"Judging from the pile installation history on the initial adjacent wind farm and the site investigation information, we expected ground conditions on the Bamber extension to be similar," says Aarsleff piling manager Philip Chippindale".
"We took a 5 t hammer to site and although piles started refusing early it wasn't initially considered a problem because the site investigation suggested we may be able to achieve the required pile capacity".
"However, we tested the piles which failed to reach capacity." The ground conditions proved to be different with soft clay overlaying stiff clay over sand and gravel with piles just toeing into to gravel".
""We tried a 6 t hammer with an 800 mm drop and that again didn't get piles to level".
"So we tried a 1 m drop which got them down, but it was a very hard, slow drive, taking 2-3 hours to install a pile".
"However, this proved the 20 m long piles would perform," adds Philip Chippindale".
""Our final solution involved pitching and driving piles down to about 15 m penetration with a 6 t Banut and then completing the drive with a Junttan rig with a 7 t accelerated hammer".
"This operation was refined by pitching and pinning approximately one third of the piles on each base at a time whilst the other rig back drove the piles on another base".
"The rigs were swapped from base to base until all the piles were completed".
"This ensured that the rigs worked safely and efficiently.".
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