Geotechnical Assessment of Founding Conditions for Large Wind Turbines
Author: Steven Price
Presented/Published: Young Geotechnical Engineers Conference, Adelaide 2006.
Keywords: Tararua, Geotechnical, Geology, Wind, Turbine, Founding Conditions.
Abstract:
The Tararua Windfarm is one of the world’s top three wind farm sites. Its owner has committed to a stage 3 extension involving construction of 35 large wind turbines standing 65m, producing 3MW each.
The Tararua Ranges are located immediately adjacent to an active fault zone and have recently been up-thrusted. The ranges consist of shattered greywacke sandstone with a complex capping of Tertiary and Quaternary marine deposits, along with re-worked loess.
Proposed sites for the turbines are generally challenging as ‘easier’ sites are already occupied by in excess of 100 smaller turbines.
Though theoretically relatively low strength material is required to support the turbine weight resting on 15m diameter octagonal pads, cyclical rocking under wind and possibly seismic load, requires strong material of high stiffness. Thus, greywacke rock is the preferred founding material.
In January 2006 construction of the stage 3 extension commenced. Large earthworks are required to form foundations and adjacent crane platforms. Excavations to date have generally been consistent with conditions inferred from the geotechnical investigation, however, some sites have revealed geology more complex than envisaged, such as localised low strength gully fills on ridge crests. Thus, foundation designs have been adapted to the subsurface conditions encountered.
