Effect of Heating and Cooling Cycles on the Skin Friction of Energy Piles in Soft Clays

The use of energy piles is gaining acceptance as a sustainable method of resource management and conservation. Energy piles are structural foundations that act as thermal exchangers designed and executed to reduce the energy required for heating and cooling demands. Published work on energy piles shows that in granular and very stiff, moderately to highly overconsolidated clayey soils, thermal effects on the mechanical properties of the soils may be neglected. However, heating may induce flow of water around the pile and could affect the skin friction and the adhesion between the pile and the surrounding soil. This issue has not been fully investigated in the literature. The main objective of this paper is to investigate the impact of utilizing energy piles in slightly overconsolidated clay by conducting laboratory-scale pile load tests on identical “ordinary” and “energy” model piles. The energy model piles are fitted with small diameter copper pipe loops that function as the transport medium through which temperature-regulated water is circulated. Results indicate that the adhesion between the pile and the clay was reduced by about 15 to 20% in energy piles that were subjected to three cycles of heating and cooling when compared to the adhesion of an identical control pile.