Abstract
A comparative modelling exercise involving several independent teams from the DECOVALEX-2015 project is presented in this paper. The exercise is based on various laboratory experiments that have been carried out in the framework of a French research programme called SEALEX and conducted by the IRSN. The programme focuses on the long-term performance of swelling clay-based sealing systems that provide an important contribution to the safety of underground nuclear waste disposal facilities. A number of materials are being considered in the sealing systems; the current work focuses on a 70/30 MX80 bentonite–sand mixture compacted at dry densities between 1.67 and 1.97 Mg/m3. The improved understanding of the full set of hydro-mechanical processes affecting the behaviour of an in situ sealing system requires both experiments ranging from small-scale laboratory tests to full-scale field emplacement studies and coupled hydro-mechanical models that are able to explain the observations in the experiments. The approach was to build models of increasing complexity starting for the simplest laboratory experiments and building towards the full-scale in situ experiments. Following this approach, two sets of small-scale laboratory experiments have been performed and modelled. The first set of experiments involves characterizing the hydro-mechanical behaviour of the bentonite–sand mixture by means of (1) water retention tests under both constant volume and free swell conditions, (2) infiltration test under constant volume condition, and (3) swelling and compression tests under suction control conditions. The second, more complex, experiment is a 1/10th scale mock-up of a larger-scale in situ experiment. Modelling of the full-scale experiment is described in a companion paper. A number of independent teams have worked towards modelling these experiments using different conceptual models, codes, and input parameters. Their results are compared and discussed. This exercise has enabled an improved modelling of the bentonite–sand mixture behaviour, in particular accounting for the dependence of its retention curve on the dry density. Moreover, it has shown the importance of the technological voids on the short-term behaviour of the sealing system.
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Acknowledgments
The work described in this paper was conducted within the context of the international DECOVALEX project. The authors are grateful to the funding organizations who supported the work. The views expressed in the paper are, however, those of the authors and are not necessarily those of the funding organizations. Nor do the views expressed herein necessarily reflect the views or regulatory positions of the US Nuclear Regulatory Commission (USNRC) and do not constitute a final judgment or determination of the matters addressed or of the acceptability of any licensing action that may be under consideration at the USNRC.
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This article is part of a Topical Collection in Environmental Earth Sciences on “DECOVALEX 2015”, guest edited by Jens T Birkholzer, Alexander E Bond, John A Hudson, Lanru Jing, Hua Shao and Olaf Kolditz.
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Millard, A., Mokni, N., Barnichon, J.D. et al. Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture. Environ Earth Sci 75, 1311 (2016). https://doi.org/10.1007/s12665-016-6118-z
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DOI: https://doi.org/10.1007/s12665-016-6118-z