Energy piles are deep foundation elements designed to access and exploit the relatively constant temperature of the ground and its heat storage capacity for efficient heating and cooling of buildings. Energy piles present an innovative way to harvest near-surface geothermal energy, while at the same time serve as foundations for buildings and other structures such as bridges. This research project answers two fundamental questions related to the behavior of energy piles under thermally induced load cycles: (1) Do the thermal load cycles change the properties of the soil around the energy pile on an elemental level, thereby affecting the pile's load-deformation behavior? (2) Do the thermal load cycles alter the soil-pile interface properties on an elemental level, thereby reducing the axial load capacity of the pile? The research project focuses both on the effect of cyclic straining and deformations at the pile-soil interface as well as the effect of temperature cycles on soil behavior. This research will quantify the effect of temperature cycles on serviceability (i.e. temperature induced settlement) and ultimate state (i.e. capacity) of energy piles, and will investigate heat exchange behavior and temperature-induced effects around the energy pile through a carefully designed laboratory testing program, a full-scale field test, and advanced numerical modeling. This research will help us better understand energy pile behavior with particular emphasis on the fundamental aspects of soil-pile interface behavior. Findings from this research will help us develop refined design guidelines for energy piles.

Energy piles provide the means to use the ground as a renewable heating and cooling resource, thereby reducing the demand on conventional energy sources, reducing seasonal energy demand fluctuations on the electric power system, and reducing harmful CO2 emissions. A better understanding of the fundamental aspects of energy pile behavior will have broad impact on the use of pile foundations as heat exchangers. The study has the potential to increase the use of energy pile systems on a commercial scale in the U.S. and worldwide. The project will also integrate research and education to support the emerging workforce needed to grow the nation's green energy industry, an area that is growing and in need of educated professionals.

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University of Wisconsin Milwaukee
United States
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