Full-Scale Field Testing of Energy Piles

Abstract

Energy piles are deep foundation elements designed to utilize near- surface geothermal energy, while at the same time serve as foundations for buildings. The use of energy piles for geothermal heat exchange has been steadily increasing during the last decade, yet there are still pending questions on their behavior during temperature changes. A series of field tests on three different energy piles was carried out in Richmond, TX, with the aim of quantifying the thermal influences on the performance and capacity of energy piles. The field test program included conventional pile load tests and application of temperature cycles with maximum temperature of 45°C (113°F) and minimum of 8°C (47°F) over a total duration of six weeks. The test piles with and without maintained structural loads were exposed to heating-cooling cycles to investigate the effect of thermo-mechanical and thermal loads on the energy piles, respectively. With the use of fiber optic cables, vibrating wire strain gauges, thermistors and thermal integrity profile wires, the temperature and strain profiles were monitored on the test piles throughout the field tests. This paper presents the findings inferred from the recorded data along with the details of the in-situ tests on energy piles.