Cyclic Load-Transfer Approach for the Analysis of Energy Piles

Energy piles, due to their unique roles of coupling the structural support and heat exchange with the surrounding ground, are subject to temperature cycles during their lifetime. Although their behaviour during individual temperature increase or decrease has been evaluated thoroughly in various experimental and numerical studies, there are still pending questions on their response to cyclic thermal load applications. To investigate this problem, a full-scale field test with the application of multiple heating-cooling cycles on three energy piles has been implemented. Moreover, a two-dimensional finite-element model has been developed by incorporating unloading-reloading responses into the monotonic load-transfer curves to define the soil-energy pile interaction during heat exchange operations. In this paper, the development of the finite-element model and information on the full-scale field test are presented along with the validation of the model with the observational data for the application of pure temperature cycles. This study reveals that the proposed model yields satisfactory results in terms of cyclic thermal behavior of energy piles, where the development of appropriate load-transfer curves representing the soil-pile interaction is of paramount importance. (C) 2018 American Society of Civil Engineers.