A CASE STUDY OF WESTERMOST ROUGH OFFSHORE WIND FARM

Alastair Muir WoodLead Geotechnical Engineer, DONG Energy

Presentation to Danish Geotechnical Society 24 September 2015

DESIGNING MONOPILES IN CHALK

Reference / Acknowledgement

From DONG Energy:• Michael Mygind• Kris Wessel Andersen• Christian LeBlanc Thilsted • Morten Albjerg Liingaard

From Fugro Geoconsulting:• Brian Mackenzie• Darren Burbury• Mike Rattley

From University of Southampton• Chris Clayton

Muir Wood A., Mackenzie B., Burbury D., Rattley M., Clayton C.R.I., Mygind M., Wessel Andersen K., LeBlanc Thilsted C. and Alberg Liingaard M. (2015) Design of large diameter monopiles in chalk at Westermost Rough offshore wind farm in Meyer eds. Frontiers in Offshore Geotechnics III Taylor & Francis Group, London, vol 1 pp 723-728.

Location and Key Information Turbine Array Detail

Westermost Rough (WMR) offshore wind farm

3

Prevailing wind direction

p

p

H

M

S

Conceptual geological model

From: Lord et al., 2002

Load

PileIntact

Chalk

Remoulded Chalk

Chalk pile interface model

Behaviour dominated by Remoulded Chalk

10

P P P

yr ys y

Cyclicdegradation

Chalk remoulded due to pile driving

Structured chalk(fractured or assumed intact)

Combined behaviour(yr + ys)

Total pile displacementWeak rock modelReese (1997)

Model based on plateloading tests of

Remoulded Chalk

Load response of remoulded chalk

11

P

yr

𝑦𝑟 𝑚𝑎𝑥= ??

𝑃

𝑦𝑟= ??

762mm pile

Load

100x100x12mm

angular channel

welded to pile

Remoulded chalk

13

Load response of remoulded chalk

14

P

yr

𝑦𝑟 𝑚𝑎𝑥 = tr ≈𝑡

2𝑃

𝑦𝑟= ??

pile

Load

Remoulded chalk

PD

tr

𝑃

𝑦𝑟=𝐷

𝑡𝑟×𝑀

Constrained modulus

Load response of remoulded chalk

16

P

yr

𝑦𝑟 𝑚𝑎𝑥 = tr ≈𝑡

2

𝑃

𝑦𝑟=𝐷

𝑡𝑟×𝑀

Final design at Westermost Rough

A CASE STUDY OF WESTERMOST ROUGH OFFSHORE WIND FARM

Alastair Muir WoodLead Geotechnical Engineer, DONG Energy

Presentation to Danish Geotechnical Society 24 September 2015

DESIGNING MONOPILES IN CHALK