Wind Turbine Foundation Gapping: How to Avoid Issues During Operational Life
Recorded On: 05/14/2020
Turbine manufacturers typically include a requirement for foundations to be in full contact with the supporting materials during normal power production. The no gapping specification is primarily to ensure that the foundation reliably provides the minimum stiffness and thus operate within the design frequency envelope, and to limit potential for cyclic degradation of the supporting materials.
As turbine sizes and demands on the foundation continue to increase, foundation designers are looking at options to optimize designs. This includes relaxing the no gapping requirement while ensuring that foundation stiffness requirements are met. Such approaches are supported by contemporary industry standards, provided that robust assessing of soil cyclic degradation potential is performed. An advancement in the standard of practice is necessary and will inevitably be required to reliably evaluate the potential risks due to foundation gapping. Cyclic soil testing during geotechnical investigations will be a necessity for on-shore wind farms for reliable evaluation of foundations designed to incorporate gapping.
This paper presents a discussion of no gapping criteria typically employed in wind turbine foundation design standards, potential impact on foundation stiffness and cyclic degradation of the supporting soils, and design considerations for assessing potential risks due to gapping.
Senior Principal Geotechnical Engineer, DNV GL
Eric Ntambakwa is the geotechnical technical lead for DNV GL Energy North America and has 20 years of experience in geotechnical engineering with the last 13 years exclusively in the renewables industry. He has extensive experience in soil mechanics, earthquake engineering and numerical modelling of geotechnical structures.
Matthew Rogers (Moderator)
Team Lead, Civil Engineering at DNV GL Energy - Renewables
Matthew Rogers leads DNV GL’s North America Civil Engineering team, and has 30 years of experience in geotechnical engineering covering a wide breadth of applications to infrastructure and geotechnical engineering areas of expertise, including the last 12 years in the renewables industry.