Application of Drilled Shaft Foundations for Utility Scale Wind Turbines in a High Seismic Environment

Drilled shaft foundations have been used for several decades for highway and building applications; however they have only seen limited use in foundations for modern utility scale wind turbines. The limited use of drilled shaft foundations for wind turbines is likely due to the perceived difficulty in fatigue analysis, load and resistance factor design, and meeting the dynamic stiffness requirements of the foundation system. The discussion provided in this paper demonstrates how all of these elements can be brought together in a practical manner to create an economical, robust foundation design taking into account all of the potential geotechnical hazards affecting the site. This paper presents a case history of a wind energy project located in Palm Springs, California in an area subject to high seismic loading from the nearby San Andreas Fault Zone, severe scour due to the project location in a flood plain, and constrained by endangered species habitat areas. This paper follows the project through design, including analysis of seismic loading, dynamic stiffness, soilstructure interaction, concrete and steel fatigue and drilled shaft capacity. Construction aspects of the project are also included in the paper.