ABSTRACT : This paper presents a theoretical approach to establish a suitable law to describe the hydromechanical behavior of shales. Because of microscopic chemo-hydro-mechanical interactions, the poroelastic theory cannot be simply applied to these rocks.

The proposed approach uses chemical potentials as variables for non-solid phases. Moreover, local microscopic thermodynamical equilibrium is assumed so that liquid water and vapor can be gathered into a unique "water" phase. Thus, hydro-mechanical behavior of both saturated and unsaturated shales can be modelized with the same partially linearized elastic law.

Then, drying effects on a tunnel structure are studied. Analytical and three-dimensional numerical calculations are performed : they show that high tensile stresses appear and that convergence is significantly increased. It seems to explain the apparition of a regular spaced network on the Tournemire gallery front faces after their excavation.

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