Comparative modelling approaches of hydro-mechanical processes in sealing experiments at the Tournemire URL

Millard, Alain; Mokni, Nadia; Barnichon, Jean-Dominique; Thatcher, K.; Bond, Alexander E.; Fraser-Harris, Andrew; Dermott, C. Mc; Blaheta, Radim; Michalec, Zdeněk; Hasal, Martin; Nguyen, Thanh Son; Nasir, Othman; Yi, Haiyang; Kolditz, Olaf

doi:10.1007/s12665-016-6324-8

Cited by 14 publications

(5 citation statements)

References 16 publications

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“…The numerical studies of the mock-up and in situ experiments of the SEALEX project, in general, performed well and could often predict the endpoints of the experiment, such as swelling pressure and the amount of injected water. The details of the transient effects, however, were much more difficult to predict [13,20,[22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Properties of Bentonite-Based Sealing Materials during Hydration

Bajestani,

Nasir,

2023

Minerals

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A typical deep geological repository (DGR) design consists of a multi-barrier system, including the natural host rock and the engineered barrier system. Understanding the swelling behavior of bentonite-based sealing materials (BBSM), as a candidate material for the engineered barrier system, is crucial for DGR’s long-term safety. In this study, a hydromechanical (HM) column-type test was designed to model the hydration of BBSM from the underground water and determine the resulting swelling pressure in vertical and radial directions. Five hydration tests were carried out on identical compacted samples of 70% bentonite and 30% sand (70-30 bentonite-sand) mixtures with a dry density of 1.65 g/cm3 for varied durations of hydration, between 1 day and 120 days. The experiments were performed parallel to the compaction direction. Following each HM column-type test, the advancement of the wetting front was determined for each test. After 120 days, 56,339 mm3 of water infiltrated the sample and the wetting front reached over 50% of the sample height. The evolution of axial swelling pressure revealed an initial increase in swelling pressure with time in all tests, followed by a reduction in the rate at later times. After early stages of swelling, radial sensors showed an increase in swelling pressure. After 120 days, the radial pressure sensor closest to the hydration front showed 52% more radial pressure than the axial swelling pressure.

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Section: Introductionmentioning

confidence: 99%

Properties of Bentonite-Based Sealing Materials during Hydration

Bajestani,

Nasir,

2023

Minerals

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“…The core material in the sealing system is a 70/30 mixture of MX80 bentonite-sand compacted at different dry densities ranging from 1.65 to 1.97 Mg/m 3 and chosen so as to target a 4 MPa maximum swelling pressure; the potential swelling pressure is strongly correlated to the initial dry density (other influencing factors such as pore water salinity are out of the scope of this study) of the montmorillonite fraction (80%), which is the main mineralogical component of MX80 bentonite. Before modelling the full-scale in situ tests, which are described in a companion paper (Millard et al, 2016), several laboratory tests were utilized as the first steps in the modelling exercise to characterize the hydro-mechanical properties of the 70/30 mixture of MX80 bentonite-sand.…”

Section: Introductionmentioning

confidence: 99%

“…The results from the first two steps are described in this paper; the two other steps are treated in a companion paper (Millard et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture

et al. 2016

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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 program called SEALEX and conducted by the IRSN. The program 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 Mg/m 3 and 1.97 Mg/m 3. 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 involve characterising the hydro-mechanical behaviour of the bentonite-sand mixture by means of (i) water retention tests under both constant volume and free swell conditions, (ii) infiltration test under constant volume condition, and (iii) 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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“…This work was carried out as part of DECOVALEX-2015 (www.decovalex.org) in which 6 teams developed coupled HM models of the SEALEX experiments. Comparison of the teams' work is discussed in Millard et al (2016a) and Millard et al (2016b). This paper presents the model and modelling results of one of the six teams; Quintessa Ltd on behalf of Radioactive Waste Management Ltd (Bond et al, 2015c).…”

Section: Introductionmentioning

confidence: 99%

A new hydro-mechanical model for bentonite resaturation applied to the SEALEX experiments

et al. 2016

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Bentonite barriers perform safety critical functions in many radioactive waste disposal concepts, but it is challenging to accurately predict bentonite resaturation behaviour in repository settings. Coupled models of the hydro-mechanical (HM) response of bentonite are used to demonstrate understanding of bentonite behaviour in experiments and to predict the response of bentonite in a repository environment. Following trials of a range of numerical approaches, a new model is presented, referred to as the Internal Limit Model, which makes use of key observations on limiting stresses supported in bentonite samples in experimental data. This model is based on the Modified Cam Clay model, and uses the observation that for a given dry density of bentonite, there is a limiting stress that the sample can support, be that stress due to swelling, compaction or suction, to explicitly couple the hydraulic and mechanical models. The model is applied to experimental data from the SEALEX experiments, involving a 70/30 by mass mixture of MX80 bentonite and sand. The model is able to reproduce the experimental data using a single set of parameters for all the experiments considered. This builds confidence that the model will be useful in the future for predictive modelling given appropriate data to characterise the bentonite material being used.

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Comparative modelling approaches of hydro-mechanical processes in sealing experiments at the Tournemire URL

Cited by 14 publications

References 16 publications

Properties of Bentonite-Based Sealing Materials during Hydration

Properties of Bentonite-Based Sealing Materials during Hydration

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture

A new hydro-mechanical model for bentonite resaturation applied to the SEALEX experiments

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