Chapter 1 Poromechanics of saturated isotropic nanoporous materials

1.1 Abstract Poromechanics offers a consistent theoretical framework for describing the mechanical response of porous solids. When dealing with fully saturated nanoporous materials, which exhibit pores of the nanometer size, additional effects due to adsorption and confinement of the fluid molecules in the smallest pores must be accounted for. From the mechanical point of view, these phenomena result into volumetric deformations of the porous solid, the so-called " swelling " phenomenon, and into a change of the apparent permeability. The present work investigates how poromechanics may be refined in order to capture adsorption and molecular packing induced effects in nanoporous solids. The revisited formulation introduces an effective pore pressure, defined as a thermodynamic variable at the representative volume element scale (mesoscale), which is related to the mechanical work of the fluid at the pore scale (nanoscale). Accounting for the thermodynamic equilibrium of the system, this effective pore pressure is obtained as a function of the bulk fluid pressure, the temperature and the total and excess adsorbed masses of fluid. We derive the analytical swelling strains due to sorption and molecular packing. A good agreement in the comparison with experimental data dealing with the swelling of coal due to methane and carbon dioxyde sorption is observed, as a preliminary stage towards modelling partially saturated solids and applications to cement paste. Poromechanics offers a consistent theoretical framework for describing the mechanical response of porous solids saturated, or partially saturated with a fluid phase. The theory is based upon the superposition of the solid and liquid phases. In the case of fully saturated porous solids, it is assumed that the fluid-solid interaction is restricted to the influence of the pressure on the inner surface of