To ensure offshore wind turbines are still upright 20 years down the track, more research is needed into the behaviour of the soil structures underlying them, says the latest report from Wind Energy Update.
A distinguishing feature of offshore wind turbine structures is that the turbines impose a large horizontal load, at a great height, above the turbine’s foundation. The over-turning forces at foundation level resulting from this high ratio of lateral-to-vertical loading implies a loading regime that is very different from that of existing offshore oil and gas installations.
“The behaviour of the soil / foundation system at these high ratios, particularly over the long-term under dynamic loading, is not as well researched and understood as for lower ratios of horizontal to vertical stressing,” says Alan Tricklebank, author of the Offshore Wind Installations and Construction Report.
“There is a case for further basic research on this aspect of foundation design given the importance of achieving a long and reliable life for turbine support structures,” he adds.
Water depth, exposure, and soil properties
The UK’s Round 3 sites are situated predominantly in depths beyond 20m, with 54% in the 20-40m range; 17% in 40-50m; and 25% beyond 50m depths. For the transitional depths (20-50m), the major lateral load of the turbine on an otherwise relatively modestly loaded structure is further compounded by additional loadings from waves and currents, which increase significantly as water depth and exposure increases.
