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A double-structure model, based on the general framework for expansive materials proposed by [4]
has been developed to explain the hydro-mechanical behaviour of the bentonite and extended to
consider the effect of temperature on swelling [3]. The existence of two pore structures (macro and
micropores) has been explicitly included in the formulation, what provides the opportunity to take
into account the dominant phenomena that affect the behaviour of each structure in a consistent
way: the swelling features of clay minerals are explicitly considered through a microstructural law,
the relevant effects of the granular-like skeleton are contemplated through the macrostructural law,
and the model also considers the interaction between both structural levels. To account for the temperature
effects, a dependence of the microstructural law on temperature has been suggested (Fig.
2.4), since the clay particles cause the expansive behaviour. In this way, the model is able to capture
the main trends observed in the tests (Fig. 2.3).
(p+s) (MPa)
100.0
10.0
1.0
0.1
Δ T (ºC)
0 20 40 60
1000 1500 2000 2500 3000 3500
K 1 (MPa)
469
τ : 0.12
Figure 2.4. Changes in micro-structural stiffness with temperature
3. Conclusions
The laboratory tests performed, in which the expansive clay and the THM conditions are close to
the ones expected in a DGR, have been very useful to understand the behaviour of the FEBEX clay
and validate the mathematical formulations and computer codes. Most of the constitutive model and
parameters assumed in the analyses are the same ones adopted for the main analysis of large-scale
tests (i.e. FEBEX mock-up and in situ tests). The fact that the model can reproduce the global
trends observed in the tests at different scales with a unique set of parameters points to an appropriate
selection of the processes and parameters.
4. Acknowledgements
Work co-funded by ENRESA and the European Commission (Contract FI6W-CT-2003-02389).
References
[1] Villar, M.V. & Gómez-Espina, R. 2007. NF-PRO. Deliverable 3.2.13. Final report on laboratory
tests performed by CIEMAT for WP3.2. 57 pp.
[2] Olivella, S., Carrera J., Gens, A. & Alonso, E.E. 1994. Non-isothermal multiphase flow of
brine and gas through saline media. Transport in porous media 15: 271-293.
[3] Sánchez, M. & Gens, A. 2007. NF-PRO Project. Deliverable 3.2.14. 93 pp.