53 REVUE FRANÇAISE DE GÉOTECHI NQUE N° 81 4e trim es tre 1997 contraintes thermiques et par des contraintes capillaires : σext = σc + σcap + σT (OCR = 1) et σext =σ R + σcap + σT (OCR > 1)Laboratory experiments on the thermo-hydro-mechanical behaviours of swelling and unswelling clayey rocks Abstract Some tests allowed to analyse at macroscopic and microscopic levels, the thermo-hydro-mechanical behaviour of swelling and unswelling clayey rocks. The mechanical behaviour was studied by oedometric cyclic tests with and without measurement of the radial stress, as well as undrained compression triaxial tests at different confining pressures. The influence of the consolidation pressure on the textures was analysed from results of porosimeter and BET tests. These tests allowed to point out an elasto-plastic behaviour during the loading for different swelling and unswelling clayey rocks. In the case of the swelling rocks, the unloading and the reloading curves showed hysteresis loops, which proved the existence of irreversible strains and an elasto-plastic behaviour. The ko coefficient for the different rocks could be valued by linear relation with the stresses ratio q/p'. Thus for the normally consolidated states, the variations of the external stress are level-headed by the evolution of the stress of contact : δ σ ex l = δσc. In return for the overconsolidated states and in the case of the swelling clayey rocks, the variations of the external stress are compensated by the physico-chemical repulsion stress : δσext = δσR-A . To study the thermo-mechanical behaviour, we performed on one hand isothermal tests on some oedometric and undrained triaxial paths, and on the other hand thermal cycles under mechanical constant loading at normally and over consolidated states on some oedometric paths. The anisotropy of the strain under thermal solicitations and the irreversible strain of clayey rock textures were studied. Thus they allow to associate a tensorial operator, the thermal stress σi to thermo-mechanical solicitations. The main phenomena due to the hydro-mechanical behaviour of highly compacted clayey rocks were pointed out by oedometric and trixial tests at constant suction and by sorption desorption cycles. So sorption desorption tests show two domains : a quasi saturated domain for which the strains are isotropic and a no saturated one characterised by reversible anisotropic strain. A tensor of capillary stress σcap is suggested in order to translate these strains. So in the general case of thermo-hydro-mechanical solicitations, the variations of external stress are equilibrated by the contact stress (OCR = 1) or repulsion stress (OCR >1), and by the thermal stress and the capillary stress : σext=σc+σcap+σT (OCR =1) and σext = σr +σcap + σT (OCR > 1) 54 REVUE FRANÇAISE DE GÉOTC HNIQUE N° 81 4e trimestre 1997

After remembering the physico-chemical mechanism of saturated clay in isothermal conditions, we propose an elastoplastic model for expansive clays. The formulation considers in normally consolidated states, an irreversible strain of micro structure due to macro-pores compaction. The irreversible macroscopic strains result from the deformation of micro structures are described with associative plastic law. In the overconsolidated states, the repulsive stresses provoke an irreversible dilatancy of macro-pores. The macroscopic swelling of the last phenomenon is formulated by the second plastic mechanism with the combined isotropic and kinematics hardening. The rheological model schematises the normally consolidated states by mechanical hardening and the over consolidated states by « physico-chemical » hardening. The model is able to describe the fundamental characteristic of saturated expansive clays, especially the hysteresis loop in odometer tests and the existence of the volume change in triaxial tests at over-consolidated states. The model needs eight parameters that must be identified by means of the odometer and triaxial tests. Finally, this paper shows the predictions of model for the different tests with the experiments performed on Boom clay. The comparison between experimental results and model confirm the behaviour of the expensive clays.

RésuméAprès avoir rappelé les mécanismes de base du transfert de l'eau dans les milieux poreux indéformables en conditions isothermiques, nous proposons un modèle de transfert de masse dans les argiles à faible porosité. La formulation présentée considère que les flux sont de type convectif pour l'eau libre, l'eau capillaire et le gaz et de type diffusif pour l'eau adsorbée. Le modèle est formulé avec deux variables intensives : les pressions de l'eau et de l'air. Un coefficient de transfert global de l'eau est déterminé dans le cas où le gaz est à la pression atmosphérique. La résolution numérique est établie en associant la méthode des éléments finis pour discrétiser l'espace et le schéma des différences finies pour discrétiser le temps. La validation du modèle est effectuée sur des profils hydriques obtenus à partir des essais d'imbibition d'une colonne d'argile fortement compactée. Enfin le modèle est appliqué à l'étude de la désaturation, par ventilation d'air, d'un ouvrage souterrain installé dans un massif argileux. AbstractFollowing a description of different mechanisms of water transfer in porous non deformable media under isothermal conditions, a mass transfer model for low porosity clays is proposed. The model considers that in these clays the flow is convective for free and capillary water as well as for gas, while it is diffusive for adsorbed water. The model is formulated with two variables : water pressure and gas pressure. When gas pressure is equal to atmospheric pressure we determine a total transport coefficient of water. Numerical calculations are made using the finite element method for space dis cretization and the finite differences method for time discretization. Model vali dation is performed on hydraulic profiles from soaking tests on a highly com pacted Boom clay. Finally, the model is applied to study the effect of ventilation with relative humi dity below saturation on the development of an unsaturated zone in tunnels.BP 6747. 45067 Orléans. Route du Panorama Robert-Schuman, BP 38, 92266 Fontenay-aux-Roses. N° 61 REVUE FRANÇAISE DE GÉOTECHNIQUE