This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The U.S. is currently pursuing technologies to improve the energy efficiency of buildings. One approach, which is the focus of this research, involves embedding geothermal heat exchange systems within deep foundations to gain improved energy efficiency of building heat pumps. Despite the potential cost savings gained through the combined use of equipment and construction materials for both the foundation support and heating/cooling systems, this approach is not without risk. The thermal interaction between the inhabited part of a building and its subsurface structural components may lead to both geotechnical and building system concerns. For example, drawing excessive amounts of heat from geothermal foundations may lead to ground freezing and potential surface heave, cyclic expansion and contraction of foundation materials due to rapid fluctuations in heat pump temperatures may lead to changes in side friction, and non-sustainable heat exchange patterns can lead to a reduction in heat exchange efficiency between the building and ground over time. A research approach involving numerical simulations of the thermal, hydraulic, and mechanical interaction between geothermal foundations and surrounding soils is being used to better characterize these risks. The parameters for these simulations are being determined using novel true-triaxial tests with temperature and hydraulic control, and the results from the simulations are being validated against a series of centrifuge modeling experiments on geothermal foundations under different temperature and loading conditions. The validated simulation tool will be used to provide practical design guidance to engineers to aid in defining the appropriate heat exchanger geometric configuration, foundation size and spacing, and building heat pump control conditions to gain both optimal heat exchange and foundation performance for a given soil profile. Interaction with industry partners (ADSC) will aid in the transfer of research findings to practicing engineers and foundation contractors. This study is being used to augment education at the CU Boulder through integration of topics from soil mechanics, building heating systems, physical modeling and constitutive modeling; which will provide new opportunities for broad-based training to students entering this new field. Under-represented students will be recruited through cooperation with established diversity initiatives at CU Boulder, as these populations are particularly missing from the foundation engineering community.
