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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

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SUMMARYThis paper presents an elastoplastic model for saturated expansive and non-expansive clays. The original feature of this model is that a plastic mechanism is introduced during unloading to take into account the irreversible swelling of the macroporosities. These strains are induced by the repulsive stresses which are unbalanced at the scale of the microporosities. Thus two yield surfaces are activated: a classical contact yield surface (F ! ) similar to an associated modi"ed Cam-clay approach and a swelling yield surface (F 0\) based on the non-associated plasticity. The formulation considers that for the normally consolidated stress states, the strains are mainly produced by an increase of the contact stresses. For the overconsolidated stress states, the repulsive stresses balance the external stresses. The rheological parameters are easily determined from the results of either triaxial or oedometer tests. The model is then used in a "nite element program, using the classical concepts of plasticity, especially for the loading}unloading criterion based on the sign of the plasticity multiplier. Simulations of the convergence of a gallery (under an earth retaining structure) sunk at great depth in Boom clay are presented. The results are compared with those obtained with the Cam-clay model.