Thermo-poro-mechanics under adsorption applied to the anomalous thermal pressurization of water in undrained clays

Pore fluid pressurization, one of the main causes of soil instability, is known to be anomalously high for interstitial water in clay submitted to undrained heating. This anomaly is attributed to the confinement of water in nanometric micropores. In this work, we use molecular simulation to investigate how confinement affects the thermo-mechanical properties of water and we use a new poromechanical formulation (Laurent and Túlio in Int J Eng Sci 152:103296, 2020) to relate these confined properties to the macroscopic pressurization of water during undrained heating. This new formulation considers the effects of confinement on the thermo-mechanical moduli of water in micropores, and, in particular, it accounts for the break of extensivity with respect to the volume (Gibbs–Duhem equation not valid). The predictions regarding water thermal pressurization are consistent with the available experimental data when considering a double porosity medium (micro- and macro-pores) with osmotic equilibrium between the porosities. It suggests that the excess fluid pressurization arises from the drainage of water from the micro-porosity to the macro-porosity. The proposed poromechanics offers the first quantitative thermo-hydro-mechanical description of clay based on the physics of adsorption with wide perspectives for applications and transposition to other adsorption-sensitive materials (cement-based materials, wood, bones, microporous carbons etc.).