Modelling the hydration of bentonites under isothermal and non-isothermal conditions using a double-porosity approach

The constitutive model for expansive materials described here follows the usual double-porosity approach that represents the clay soil as two overlapping pore media (microstructure and macrostructure) coupled through a micro-macro strain mechanism. However, the current formulation also includes a local water mass transfer controlling the saturation of the microstructure, the definition of water retention curves for each structural level, and the occurrence of thermal strains in both pore domains. These additional features enhance the model's ability to simulate the response of bentonites under varying moisture conditions. This double-porosity model satisfactorily simulated some infiltration tests taken from the literature, reproducing the main test observations and validating its use for predicting the behaviour of bentonites in various geotechnical engineering scenarios. The infiltration tests selected were carried out in columns made of FEBEX and MX-80 bentonites under isothermal and non-isothermal conditions to characterize the main hydro-mechanical and thermo-hydro-mechanical processes that occur within a bentonite barrier hydrated under confined conditions. The numerical simulations showed that structural changes in bentonite materials during the transient hydration phase are due to the irreversible response of the macrostructure (changes in macroporosity) but also depend on the mechanisms controlling the saturation of the microstructure.