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Acta Geotechnica

, Volume 10, Issue 2, pp 179–195 | Cite as

Evaluation of thermo-mechanical and thermal behavior of full-scale energy foundations

  • Kyle D. Murphy
  • John S. McCartney
  • Karen S. Henry
Research Paper

Abstract

Eight full-scale energy foundations were constructed for a new building at the US Air Force Academy. The foundations are being used to demonstrate this technology to the United States Department of Defense and have several experimental features in order to study their thermal–mechanical behavior. Three of the foundations are instrumented with strain gages and thermistors, and their thermo-mechanical response during a heating and cooling test was evaluated. For a temperature increase of 18 °C, the maximum thermal axial stress ranged from 4.0 to 5.1 MPa, which is approximately 25 % of the compressive strength of concrete (estimated at 21 MPa), and the maximum upward displacement ranged from 1.4 to 1.7 mm, which should not cause angular distortions sufficient enough to cause structural or aesthetic damage of the building. The end restraint provided by the building was observed to change depending on the location of the foundation. The heat flux per meter was measured by evaluating the temperatures and flow rates of a heat exchanger fluid entering and exiting the foundations. The heat flux values were consistent with those in the literature, and the foundation with the three continuous heat exchanger loops was found to have the greatest heat flux per meter. The transient thermal conductivity of the subsurface measured using the temperatures of the subsurface surrounding the foundation ranged from 2.0 to 2.3 W/mK, which is consistent with results from thermal response tests on energy foundations reported in the literature.

Keywords

Deep foundations Geothermal heat exchange Thermal response test Thermo-mechanical behavior 

Notes

Acknowledgments

Support from DoD ESTCP project EW-201153 is gratefully acknowledged, as are the contributions of the 819th Air Force RED HORSE Squadron, who provided support for the heating test. The views in the paper are those of the authors alone.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Kyle D. Murphy
    • 1
  • John S. McCartney
    • 1
  • Karen S. Henry
    • 2
  1. 1.Department of Civil, Environmental, and Architectural EngineeringUniversity of Colorado Boulder, 428BoulderUSA
  2. 2.Department of Civil EngineeringUnited States Air Force AcademyColorado SpringsUSA

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