Wind Power

The Government’s drive to increase the nation’s renewable energy capacity has led to an increased national demand for wind power and to a number of investigation projects by Geotechnics Limited from Scotland to the South West.

Fullabrook Down

Devon Wind Power proposes to construct a major new onshore wind farm at Fullabrook Down, North Devon.  Twenty two new Wind Turbine Generators (WTGs), each 110 metres high, with 45m long blades and 65m from ground to hub will be constructed.  The new wind farm is understood to have an installed capacity of 66 megawatts and is expected to produce the equivalent of over 80% of domestic electricity consumption in North Devon and will serve the needs of nearly 30,000 domestic customers.

Geotechnics Ltd was approached by Magna Project Services Ltd on behalf of Devon Wind Power to undertake a site investigation and provide geotechnical advice for the design of the foundations for the new WTGs.

Tim Thornburn and Gareth Lewis from the Exeter regional office carried out a Preliminary Geotechnical Appraisal comprising a desk study of the site together with trial pitting to assess geotechnical risks at each turbine location.  A Multi-Channel Analysis of Surface Waves (MASW) geophysical survey was undertaken at ten of the locations to obtain dynamic stiffness moduli to assist in foundation design for dynamic loadings.  The Preliminary Appraisal included an assessment of risks from natural and man made cavities, seismic and landslide hazards, liquefaction and soft ground.  Outline foundation options were provided for each WTG, in addition to excavatability and information on re-use of site won material as haul road aggregate. 

A rotary core borehole investigation together with the preliminary assessment and trial pit investigation will provide detailed foundation design parameters for the WTGs once the final specification for the turbines is formulated.

Mostyn Docks

In the North West, Geotechnics Chester office has undertaken an investigation at Mostyn Docks on the Dee Estuary where the main structural columns for the enormous off shore North Hoyle wind farm development are stored prior to shipping to site.  The project comprised cable percussion boreholes and plate load testing and was managed by Ray Macklin, with Keith Nicholls assisting in developing a foundation scheme for the temporary racks which will carry the columns.  The work was done for Port Dredging Ltd, and their Engineer MT Hojaard (of Denmark).

Workington

The Dunblane team has been involved with wind farm developments in Workington in Cumbria over some time but more recently has completed their engineer-intensive investigation for a proposed 20 turbine (900ha) wind farm and associated 30 kilometre haulage road in a beautiful, but remote location above the western bank of Loch Awe in Argyll and Bute.  Under the supervision of Engineer, Mott Macdonald, for Client, Greenpower (Carriag Ghael) Limited, more than 400 Trial Pits with CBR determinations have been excavated and over 650 peat probes sampled, by up to five Geotechnics Engineers.

The wealth and diversity of natural habitats, particularly nesting birds, even rare ospreys and golden eagles, meant that the changing ecological considerations have taken priority, necessitating continual review and revision of fieldwork planning to optimise productivity and protection to the environment.

Although generally fortunate with the weather and midge swarms, there have been days where the natural elements have powerfully demonstrated the suitability of this site for its proposed development as a source of wind energy!  Further logistical challenges relating to limited vehicular access and the large scale of the site have also been conquered; all terrain vehicles were used where practicable to help transport engineers, operators, soil and rock samples; but walks of several hours through the undulating terrain, which includes dense managed forests, peat moorland, rock outcrops, lochans and burns were not uncommon before ‘starting work’!  Remarkably, where access was available, the team led by Site Agent, Greg Anton, still managed to achieve their tendered target of 8 trial pits or more per machine day.

In addition Keith Nicholls and Len Threadgold have contributed some design ideas to the Carbon Trust for innovative foundation solutions for the next wave of development of offshore wind farms.  The new generation of turbines will be sited in water in excess of 30m deep and the marine foundations will require innovative foundation design strategies.