Foundation Soil Response to Wind Turbine Generator Loading

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

A wind turbine generator (WTG) structure is typically supported on a large octagonal (at the base) mass of concrete and steel rebar reinforcement that supports overturning, rotational stiffness, and bearing capacity stability requirements. The overturning stability and maximum bearing pressure of the system vary as a function of wind speed and direction. The highly eccentric loading conditions (i.e., large ratio of overturning moments to vertical gravity loads) lead to an uneven pressure distribution that is assumed as a uniform soil pressure distribution over an oval-shaped effective area offset from the center of the foundation by the system eccentricity. However, this assumed distribution is mechanically incorrect. Current WTG foundation theory relies on elastic halfspace models that have been developed for other purposes, with little physical evidence to support the model in a WTG foundation system. Because of this, field verification of dynamic shear modulus values and pressure distribution assumptions is very relevant to establishing mechanistically correct WTG foundation responses, along with dynamic stress-strain relationships versus depth correlations (relevant for stiffness and settlement analyses). The University of Wisconsin-Madison is working with Heartland Community College (Illinois) on instrumenting a WTG foundation that will shortly be put into service, with emphasis on evaluating the dynamic forces and the foundation soil response to in-service wind action. The monitoring will measure dynamic force parameters (magnitudes and periods), monitor foundation soil responses, and analyze and develop recommendations for a mechanically validated, dynamic foundation response. The results of the proposed research program will be leveraged across multiple educational environments through outreach and teaching activities. The project will provide an opportunity to engage undergraduate and graduate students with the construction, analysis, and operation of a renewable energy system. Experimental results and analyses will be incorporated into the PI?s nationally recognized and attended continuing engineering education short courses in wind energy including Wind Turbine Foundation and Tower System Design and Wind Energy Civil Balance-of-Plant Design. In addition, results will be directly used in the PI's first of its kind, for-credit design course in the UW-Madison College of Engineering - CEE639, Wind Energy Site Design and Construction.