Electronic Thesis and Dissertation Repository


Master of Engineering Science


Civil and Environmental Engineering


Dr. Timothy A. Newson


This thesis describes full-scale field monitoring and analysis of an onshore shallow wind turbine foundation and an associated laboratory testing program. The aim of the study was to investigate the soil-structure interaction under coupled cyclic vertical-horizontal-moment loading. This involved simulating the soil element behavior in controlled laboratory tests, evaluating the accumulated cyclic soil damage and correlating this with the observed wind and turbine responses. The results form an important part of the ‘wind-chain’, providing information for optimizing the performance of wind turbines, extending their operational lifespans and potentially for development of structural health monitoring systems. The field monitoring systems for the foundation, tower and wind fields are described, and the responses for high/low probability wind events are discussed. The identified spectral peaks from the field measurements corresponded with the literature. The measured foundation response was compared to numerical elastic models and a finite element model of the turbine foundation of study with some success. The laboratory testing program is described and the implications for assessing the soil strength and stiffness degradation due to the associated small loading cycles during the operation of the wind turbine are quantified and examined. A threshold strain value of cyclic degradation is identified and the degradation parameter for a compilation of strain levels for different stress states is developed. An example degradation calculation from the field measurements for a time history is carried out with some success.