The mechanical properties of soil could be affected by its temperature change and these effects may lead to additional issues in the thermo-mechanical behaviour of energy piles. Laboratory experiments were conducted to assess the thermo-mechanical behaviour of a small-scale instrumented energy pile installed in a saturated clay at different stress histories. The energy pile was subjected to five heating/cooling cycles. The experimental programme involved monitoring the changes in the surrounding soil temperature, pile-head displacement, pile axial load and pile-tip resistance as the temperature of the pile changed. The results show that the thermo-mechanical behaviour of the energy pile depended on the stress history of the surrounding saturated clay. The normally consolidated clay showed a higher irreversible pile-head settlement and pile-tip resistance compared with the overconsolidated clay. This behaviour could be explained in light of the expected contraction thermally induced volume change of the normally consolidated clay that could induce an additional negative skin friction on the pile. Moreover, the observed mechanical engineering behaviour of the energy pile under thermal heating/cooling cycles could be explained in terms of the expected degradation of shaft friction due to the cyclic thermally induced interface shear stress.

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