Numerical investigation on thermomechanical behavior of driven energy piles subjected to cyclic thermal loading in sand

Abstract

A sound understanding of the thermomechanical behavior of energy piles under cyclic thermal loading is crucial to achieve long-term reliable and efficient design. Although there has been extensive research on bored energy piles, the understanding about the thermomechanical performance of driven energy piles remains limited. In this study, a unified numerical modeling campaign is proposed to investigate the thermomechanical behaviors of driven energy piles in sand under cyclic thermal loading conditions. The pile-driving process is simulated using the Coupled Eulerian-Lagrangian (CEL) technique, and the obtained post-installation results are mapped to an axisymmetric finite element model to analyze the thermomechanical behavior of driven energy piles. The state-dependent behavior of sand is modelled by an advanced hypoplastic model. The proposed numerical framework is validated against centrifuge model tests. Results indicate that the pile-driving process induces significant axial force and negative skin friction, which decreases monotonically during subsequent heating-cooling cycles. The reduction is primarily due to soil volumetric contraction at the interface. Meanwhile, minor unloading occurs at the pile toe, resulting in minimal heave after thermal cycles. In comparison, thermally induced cumulative settlement is observed for bored piles due to the continuous reduction of upward shaft resistance and the mobilization of base resistance.