Centrifuge Modeling of Temperature Effects on the Pullout Capacity of Energy Piles in Clay-Paper

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This study used centrifuge experiments to examine how heating and cooling affect the pullout capacity of energy piles embedded in normally consolidated kaolinite clay. Three model piles were tested: two underwent drained heating to approximately 44°C or 63°C, followed by cooling to ambient temperature, while a third remained unheated as a baseline. At 50 g, the experiments represented prototype piles about 1.25 m in diameter and 12.75 m long. T-bar penetration tests measured the clay’s undrained shear strength before and after thermal treatment.<br /><br />Heating and cooling increased the undrained shear strength of the surrounding clay, with larger gains at higher temperatures and at greater depths. Post-test measurements also showed lower void ratios in the more strongly heated soil, consistent with thermal contraction and the strength increase.<br /><br />The heated piles had substantially greater pullout capacities than the unheated pile. Net capacity rose from 370 kN for the baseline to 520 kN after heating to about 44°C—an increase of roughly 40%—and to 723 kN after heating to 63°C, an increase of about 95%. The capacity improvement appeared approximately proportional to the temperature change. Despite these differences in capacity, the pullout load–displacement curves had similar slopes, possibly because thermal expansion of the pile affected its loading state before pullout.<br /><br />The results indicate that drained thermal cycles can strengthen soft clay around energy piles and improve pile–soil interaction and pullout resistance. The findings are based on scale-model tests and warrant consideration when assessing energy piles in soft clay.

Keywords

energy piles

pullout capacity

centrifuge experiments

kaolinite clay

drained heating

thermal cycling

undrained shear strength

thermal contraction

pile-soil interaction

soft clay