Incorporation of heat exchangers into drilled shaft foundations can be used to improve the energy efficiency of building heat pump systems and provide necessary structural support using the same construction materials. If not accounted for in design, changes in foundation behavior due to thermal soil-structure interaction may lead to differential movements of building foundation, or in the worst-case, changes in axial capacity of the drilled shaft. Although proof tests are typically used to evaluate the load capacity of foundations, they are not appropriate for evaluation of changes in load capacity during cycles of heating and cooling. In this study, a non-destructive evaluation technique is evaluated to qualitatively characterize changes in the capacity of energy foundations that can be expected after cycles of heating and cooling. Specifically, a series of centrifuge-scale tests on energy foundations were performed to measure the frequency response of energy foundations with different end boundary conditions using the impulse response method. Specifically, this method was used to evaluate the resonant frequency and phase velocity of the foundation having known dimensions and materials properties. Results indicate that the phase velocity of the piles increases up to 15% as the temperature increases from 19 to 40 °C. During cooling, a decrease in the phase velocity of pile was observed but with a rebound in the phase velocity as temperature nears room temperature. This was found to be due primarily to an increase in the confinement induced by radial expansion of the foundation, with some impact resulting from changes in the end bearing of the foundation during axial thermal expansion.
|Advisor:||McCartney, John S.|
|Commitee:||Ko, Hon-Yim, McCartney, John S., Znidarcic, Dobroslav|
|School:||University of Colorado at Boulder|
|School Location:||United States -- Colorado|
|Source:||MAI 50/02M, Masters Abstracts International|
|Keywords:||Deep foundation, Thermal soil interactions, Wave velocity|
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