Cyclic thermally-induced axial load for energy piles embedded in a saturated soft clay

Energy piles are subjected to cyclic thermal loads during the entire lifespan which act in conjunction with the mechanical solicitations by the overlying structure, complying with the double role of heat exchanger and load transferring elements. When installed in soft soil they show accumulation of cyclic displacements which are larger in magnitude in case of clay subjected to thermal collapse. Possible effects of the latter phenomenon on the thermally-induced axial load are investigated in this study through fully coupled thermo-hydro-mechanical numerical analyses of a single energy pile embedded in a normally consolidated saturated clay. The simulations are carried out also employing some advanced constitutive models for the soil to capture peculiar behavioral aspects. The results are presented in terms of thermally-induced axial force along the energy pile and its evolution cycle after cycle. The comparison between the models allowed to isolate the role of the thermal collapse on the pile performance and investigate the suitability of simpler models to describe the pile-soil interaction. A strong dependence of axial force on the cyclic thermal load was found, highlighting the importance of considering such aspect in the energy pile design.