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Many elastoplastic and nonlinear models have simulated the long-term behavior of energy piles under cyclic thermomechanical 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 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 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. Furthermore, numerical simulations were used to evaluate the effects of model parameters on the long-term behavior of energy piles under thermomechanical loads. Key words: cyclic behavior, energy pile, thermoactive structure, shallow geothermal energy, 1. Introduction Energy piles are green energy-saving structures that use shallow geothermal energy by coupling a building pile foundation with a heat exchanger (Sani et al. 2019; Rotta Loria and [...]

The presence of bound water in clay has a significant impact on the physical and chemical properties of clay, particularly its strength, permeability, and creep behavior. In this paper, the bound water in clay has been studied from the perspective of water potential. Initially, the adsorption isotherms of powders and consolidated samples for Na- and Ca-bentonite and illite were measured, and the bound water content was determined by subtracting the capillary water in the isotherms, with the capillary water being calculated by mercury intrusion porosimetry tests. The results indicated that bound water is independent of the void ratio and pore structure of clay, which is consistent with previous studies. Then, metadynamics was conducted to determine the adsorption free energy landscapes of the three clays, and the lowest suctions of the three clay minerals were determined to be −1.7 , −5.4 , and −2.1 GPa , respectively. Finally, through a comparison of the simulations and experiments in this study and in the literature, three important conclusions were drawn. Firstly, the lowest water potential for montmorillonite exhibits a linear relationship with the hydration free energy of exchangeable cations. Secondly, the critical water potential for tightly bound water is determined as the first inflection point in the relationship between water potential and water content, and the critical value of montmorillonite is found to be correlated to the valence of exchangeable cations. Lastly, the boundary between loosely bound water and capillary water is determined as the starting point of capillary water formation. Overall, this research highlights the importance of considering water potential as a key factor in understanding the behavior of bound water in clay. [ABSTRACT FROM AUTHOR]