Numerous geotechnical applications are significantly influenced by changes of moisture conditions, such as energy geostructures, nuclear waste disposal storage, embankments, landslides, and pavements. Additionally, the escalating impacts of climate change have started to amplify the influence of severe seasonal variations on the performance of foundations. These scenarios induce thermo-hydro-mechanical loads in the soil that can also vary in a cyclic manner. Robust constitutive numerical models are essential to analyze such behaviors. This article proposes an extended hypoplastic constitutive model capable of predicting the behavior of partially saturated fine-grained soils under monotonic and cyclic loading. The proposed model was developed through a hierarchical procedure that integrates existing features for accounting large strain behavior, asymptotic states, and small strain stiffness effects, and considers the dependency of strain accumulation rate on the number of cycles. To achieve this, the earlier formulation by Wong and Ma & scaron;& iacute;n (CG 61:355-369, 2014) was enhanced with the Improvement of the intergranular strain (ISI) concept proposed by Duque et al. (AG 15:3593-3604, 2020), extended with a new modification to predict the increase in soil stiffness with suction under cyclic loading. Furthermore, the water retention curve was modified with a new formulation proposed by Svoboda et al. (AG 18:3193-3211, 2023), which reproduces the nonlinear dependency of the degree of saturation on suction. The model's capabilities were examined using experimental results on a completely decomposed tuff subjected to monotonic and cyclic loading under different saturation ranges. The comparison between experimental measurements and numerical predictions suggests that the model reasonably captures the monotonic and cyclic behavior of fine-grained soil under partially saturated conditions. Some limitations of the extended model are as well remarked.

Due to the increasing need to find new alternative energy sources, more attention has been given to the development of energy geostructures, which not only serve as foundations, but also employ the geothermal properties of soils for heating and cooling structures, inducing mechanical and thermal loads. Additionally, the up -growing effects of climate change are influencing the performance of foundations due to the increase in temperature and seasonal variations. The previously mentioned examples correspond to scenarios where soils are subjected to thermo-hydro-mechanical loading, which can vary cyclically. To predict this behavior, in this article a coupled thermo-hydro-mechanical hypoplastic model for partially saturated fine-grained soils that accounts for both monotonic and cyclic loading is presented. The proposed constitutive model is capable of reproducing temperature and suction effects at large strains and asymptotic states. Additionally, coupled effects are predicted by incorporating a Water Retention Curve (WRC) that depends on temperature and void ratio. Small strain stiffness effects are captured based on the Improvement of the Intergranular Strain concept (ISI), modified to include the influence of temperature under cyclic loading, as well as a temperature dependent secant shear modulus formulation at very small strains. The capabilities of the constitutive model were evaluated through element tests simulations of monotonic and cyclic mechanical loading tests under temperature- and suction- controlled conditions, as well as heating/cooling experiments at constant stress. The proposed constitutive model shows accurate predictions when compare to experimental data. Nevertheless, some limitations have been encountered and further discussed.