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 thermomechan-ical loads. Although they considered the strain-stress hysteretic relationship at the pile-soil interface, the interface strength was assumed independent of the number of thermomechanical cycles. This simplification may cause errors in predicting the long-term responses of energy piles. Therefore, we proposed 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 addi-tion, 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 mea-sured and simulated results indicated 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. Further-more, numerical simulations were used to evaluate the effects of model parameters on the long-term behavior of energy piles under thermomechanical loads.