Numerical analysis of energy piles using a coupled thermo-hydro-mechanical hypoplastic constitutive model for fine-grained soils

The use of energy piles has grown significantly due to their environmental and economic benefits. These structures serve both as building foundations and as integrated geothermal systems, where pipes embedded within the piles circulate a heat-carrying fluid. This system extracts heat from the ground in winter and injects it back during summer, providing heating and cooling for the building. During operation, cyclic thermo-hydro-mechanical (THM) loads are induced in the surrounding soil, which can affect pile performance. Predicting these effects is challenging because of the coupled nature of THM interactions; for instance, changes in temperature will produce a mechanical response. Therefore, robust constitutive models and their proper validation are indispensable for understanding this behavior from a numerical perspective. In this study, a coupled thermo-hydro-mechanical hypoplastic constitutive model (THM-hypo-ISI) was employed for the finite element simulation of energy piles. The constitutive model was incorporated in the open-source finite element software OpenGeoSys for coupled thermo-hydro-mechanical processes. Subsequently, centrifuge experiments of energy piles subjected to cyclic thermal loading in fine-grained soils were simulated in the program. The simulation results indicate that the constitutive model effectively captures the cyclic thermo-hydro-mechanical behavior of fine-grained soils at different over-consolidation ratios. However, some limitations remain and are further discussed. • The proposed coupled thermo-hydro-mechanical hypoplastic constitutive model is able to capture the behaviour of energy piles. • The proposed coupled thermo-hydro-mechanical hypoplastic constitutive model describes the dependency of temperature on the response of fine-grained soils. • The proposed coupled thermo-hydro-mechanical hypoplastic constitutive model reproduced the soil response behaviour when subjected to cyclic thermo mechanical loading.