Cyclic t-z model for the long-term thermomechanical analysis of energy piles

Many elastoplastic and nonlinear models have simulated the long-term behavior of energy piles under cyclic thermomechanical loads. Although they consider the strain–stress hysteretic relationship at the pile–soil interface, the interface strength is assumed independent of the number of thermomechanical cycles. This simplification may cause errors in predicting the long-term responses of energy piles. Therefore, we propose a cyclic t-z model for the long-term thermomechanical analysis of an energy pile. Here, the interface strength of the model changes with the cycle number of thermomechanical loads. In addition, the accumulation of irreversible deformation at the pile–soil interface can be modeled. Moreover, the cyclic performance of interface shear tests and the long-term behavior of an in situ energy pile were simulated. Comparisons between the measured and simulated results indicate several vital aspects of the energy pile–soil interaction, including strength degradation, strain ratcheting phenomenon of the interface, and long-term pile responses under cyclic thermomechanical loading. Furthermore, numerical simulations were used to evaluate the effects of model parameters on the long-term behavior of energy piles under thermomechanical loads.