Strain Distributions in Full-Scale Energy Foundations-Article

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The study evaluates the thermal and structural response of two full-scale energy foundations at a senior living facility in Denver, Colorado. Energy foundations are drilled shafts fitted with heat-exchanger tubing, allowing them to exchange heat with the surrounding ground while also supporting a building.<br /><br />The two 0.91 m-diameter shafts, founded in claystone bedrock, were connected to the building’s ground-source heat-pump system. Temperature sensors and strain gauges monitored the foundations during construction and building operation. The system began operating in March 2012.<br /><br />During heating and cooling, temperatures within both foundations remained relatively uniform. The largest measured difference between incoming and outgoing heat-transfer fluid was about 10°C, indicating effective heat exchange. Seasonal ground-temperature variations were greater near the surface and diminished with depth.<br /><br />Thermal strain profiles showed behavior consistent with end-bearing foundations: movement was most evident near the top, while the bedrock and soil’s side resistance constrained movement elsewhere. The measured thermal strains were small compared with typical reinforced-concrete limits, and estimated foundation movement was negligible. Thermal stresses were also well below levels expected to cause structural damage. The study notes that the absolute strain estimates depend on an assumed instrument correction factor, which should be better established in future work.<br /><br />Overall, the findings suggest that energy foundations can provide useful heat exchange with little additional installation cost and without significant effects on foundation performance. Longer-term monitoring is needed to confirm the influence of design details, such as the number of tubing loops, and to assess performance over repeated thermal cycles.

Keywords

energy foundations

ground-source heat pump

thermal response

structural response

drilled shafts

claystone bedrock

heat-exchanger tubing

thermal strain

thermal stress

Denver Colorado