Thermomechanical Behavior of Soil: Energy Extraction through Pile Foundation

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Increasing energy demands, dwindling fossil fuel reserves and a heightened concern for the detrimental effects of carbon emissions have made it necessary to search for alternate, renewable and clean energy sources. Geothermal energy is a form of clean and renewable energy that can be extracted economically through pile foundations (energy piles). It is estimated that the use of geothermal energy in residential and commercial buildings may lead to 45-80% reduction in CO2 emissions and to 18-56% cost savings. The extraction of geothermal energy through energy piles is very viable in Canada, particularly during the winter months, because the temperature at a few feet below the earth's surface remains stable within a narrow range of 20°-35°C. The main concern in using energy piles is the lack of a precise design method because mechanics-based rational design equations are not available for energy piles. There is no definitive information available regarding the load transfer mechanism of energy piles and regarding how the thermo-mechanical behavior of soil affects the energy pile-soil interaction. Thus, the reliability of energy piles is not well established in the piling industry resulting in their restricted use. The proposed research will address this issue by (1) investigating the thermo-mechanical behavior of soil and soil-concrete interface using laboratory tests, (2) developing a thermoplastic, non-isothermal soil constitutive model based on the laboratory experiments, (3) relating the thermo-mechanical properties of soil and soil-pile interface to energy pile response by analyzing energy piles using an analytical and numerical framework, and (4) proposing rational design equations based on the analysis. The proposed research program will establish a pioneering, rational framework for the analysis and design of energy piles. As the profession will recognize the value of the research, the framework will be adopted in practice, which will contribute to the sustainable development of civil infrastructure in Canada with a clean energy technology.