Long-term thermo-mechanical behaviour of an energy pile installed in clay: Field experiments and numerical simulations

This study investigates the long-term thermo-mechanical behaviour of an energy pile installed in clay using field experiments and numerical simulations, aiming both to understand its response under sustained mechanical loads and cyclic thermal loading, and to develop a novel numerical model that can provide practical guidance for the design of energy piles. Firstly, full-scale experiments were performed on energy piles (0.42 m in diameter and 12 m in length) subjected to constant axial loads combined with three or five cyclic thermal loads. One pile was loaded to 30 % of its bearing capacity, and another to 50 %. Under these constant axial loads, the piles were subjected to several thermal loading cycles. Mechanical loading was finally applied to these piles after thermal cycles. A third pile was only mechanically loaded until the pile’s bearing capacity was reached. Results for the pile temperature and axial strain, pile head displacement, and axial load are shown. Secondly, a numerical model was developed based on a one-dimensional nonlinear finite element approach to investigate the long-term thermomechanical behaviour. This model was validated against the experimental results. It was then used to simulate 30 thermal cycles, revealing that the irreversible settlement of the pile head increases with higher axial loads, and that the first thermal cycle induces the largest irreversible settlement.