HDDs as part of the Burbo Bank Windfarm Extension

Dong Energy is currently engaged in construction work to expand the Burbo Bank wind farm in Liverpool Bay. The VolkerInfra/VBMS joint venture was commissioned to carry out the work for landfall of the export cable from the wind farm extension. Visser & Smit Hanab was subcontracted to perform the two required horizontal directional drillings, using the 250-tonne drilling rig.

 

 

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The first drilling to be carried out was a HDD landfall, which involved drilling from the land to the beach. The drilling crossed under a railway track, a caravan park, a golf course and a sea defence wall and had a length of 638.5 metres. Because the exit point was on the beach, allowances had to be made for the large difference in tides. For the undersea cable, a PE100 SDR 13.6 cable pipe with a diameter of 800 mm was installed. This drilling was performed between mid-May and mid-June 2015.

The second drilling crossed the A525 and the River Clwyd and has a length of approximately 520 metres. Within it was installed a bundle consisting of 3 PE100 pipes with a diameter of 225 mm and 1 PE100 pipe with a diameter of 125 mm. The subsoil for this drilling consisted of very hard clay alternating with a lot of gravel and stones. This therefore represented a big challenge for the Visser & Smit Hanab drilling crew. Because the exit point was difficult to access, a temporary mud return pipe was also drilled alongside the drilling in order to transport the drilling mud to the entry point. The pull-back operation was successfully performed on 5 July in close cooperation with and to the satisfaction of the client

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