Project Summary: Tubular towers supporting large, onshore multi-megawatt wind turbine generators (WTGs) require massive reinforced concrete mat foundations (Figures 1 and 2a). Several construction problems are associated with such foundations, especially in remote construction sites: they require extensive excavation work with heavy machinery and frequent need for excavation dewatering, very labor-intensive steel reinforcement work, and large amounts of concrete. Another problem associated with the large mat foundation is the need for a very large crane to position the tubular tower at the center of the foundation.
A viable alternative is the pile foundation system (Figure 2b) that has been sporadically used for small and medium size onshore WTGs. Such a foundation system could be applied for large WTGs (>100 m high) as this foundation system is easier to construct and more economical than the conventional reinforced concrete mat foundation system. The alternative pile foundation system (Figure 2b) can substantially reduce the quantity of required construction materials (concrete and steel), thus reducing cost and alleviating negative environmental effects.
The use of pile foundations for large onshore and offshore WTGs presents unprecedented challenges related to the fundamental aspects of soil behavior and soil-pile interaction. The stress state around each pile in a pile group changes repeatedly as a result of wind loads. There is compelling evidence that suggests repeated loading has a profound influence on soil behavior, particularly manifested as excess pore pressures, softening and subsequent deformations. Wind loads exert a combination of large cyclic axial and lateral loads on each pile. There is not a well-established understanding on how the cyclic nature of this coupled cyclic axial-lateral loading affects soil behavior and soil-pile interface response. The major goal of the proposed study is to better understand the behavior of piles under wind induced load cycles, as the combined cyclic axial and lateral loads potentially change the soil properties around the pile, and the soil-pile interface properties, and thus affect its load-deformation behavior. The project, therefore, potentially supports enhancement of existing energy technologies for a clean and renewable energy source while promoting concepts of environmental sustainability through drastic reduction in cement usage for a large built infrastructure.
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Figure 1. Reinforced concrete WTG mat foundation |
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Figure 2. Vestas V82 (1.65 kW): (1) mat foundation, and (2) proposed pile foundation |
