- Microstructure and anisotropic swelling behaviour of compacted bentonite/sand mixture
- S. Saba ; J.D. Barnichon ; Y.J. Cui ; A.M. Tang ; P. Delage
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2014 , Volume: 6
- Rock Mechanics
- Keywords: microstructure ; bentonite ; swelling pressure
- Description
- Pre-compacted elements (disks, torus) of bentonite/sand mixture are candidate materials for sealing plugs of radioactive waste disposal. Choice of this material is mainly based on its swelling capacity allowing all gaps in the system to be sealed, and on its low permeability. When emplaced in the gallery, these elements will start to absorb water from the host rock and swell. Thereby, a swelling pressure will develop in the radial direction against the host rock and in the axial direction against the support structure. In this work, the swelling pressure of a small scale compacted disk of bentonite and sand was experimentally studied in both radial and axial directions. Different swelling kinetics were identified for different dry densities and along different directions. As a rule, the swelling pressure starts increasing quickly, reaches a peak value, decreases a little and finally stabilises. For some dry densities, higher peaks were observed in the radial direction than in the axial direction. The presence of peaks is related to the microstructure change and to the collapse of macro-pores. In parallel to the mechanical tests, microstructure investigation at the sample scale was conducted using microfocus X-ray computed tomography (μCT). Image observation showed a denser structure in the centre and a looser one in the border, which was also confirmed by image analysis. This structure heterogeneity in the radial direction and the occurrence of macro-pores close to the radial boundary of the sample can explain the large peaks observed in the radial swelling pressure evolution. Another interesting result is the higher anisotropy found at lower bentonite dry densities, which was also analysed by means of μCT observation of a sample at low bentonite dry density after the end of test. It was found that the macro-pores, especially those between sand grains, were not filled by swelled bentonite, which preserved the anisotropic microstructure caused by uniaxial compression due to the absence of microstructure collapse.
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- Thermal pressurization in Boom clay
- A.M. Tang ; M. Mohajerani ; J. Sulem ; P. Delage ; M. Monfared
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
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- On the thermal impact on the excavation damaged zone around deep radioactive waste disposal
- P. Delage
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2013 , Volume: 5
- Rock Mechanics
- Keywords: radioactive waste ; Thermal impact ; Hollow cylinder triaxial ; Thermal behaviour ; Thermal pressurization ; Clay ; Claystone
- Abstract
Clays and claystones are considered in some countries (including Belgium, France and Switzerland) as a potential host rock for high activity long lived radioactive waste disposal at great depth. One of the aspects to deal with when assessing the performance of the disposal is related to the effects of the temperature elevation due to the placement of exothermic wastes on the host rock. The potential effects of the thermal impact on the excavation damaged zone (EDZ) in the near field are another important issue that was the goal of the TIMODAZ European research project. In this paper, some principles of waste disposal in clayey host rocks at great depth are first presented and a series of experimental investigations carried out on specific equipment specially developed to face the problem are presented. Both drained and undrained tests have been carried out to investigate the drained thermal volume changes of clays and claystone and the thermal pressurization occurring around the galleries. The importance of proper initial saturation (under in situ stresses) and of satisfactory drainage conditions (in spite of the significantly low permeability of claystones) is emphasized, leading to the development of a new hollow cylinder apparatus. It is observed that claystones cannot be considered as overconsolidated clays given that they can exhibit, as the Callovo-Oxfordian claystone does, a thermoplastic contraction. Mechanical and thermal hardenings are however observed, extending the knowledge already gained on clays to claystones. A new method of determining the thermal pressurization coefficient in the laboratory is described and the data obtained allow completing existing data in the field. Finally, the hollow cylinder apparatus makes it possible to demonstrate that the good self-sealing properties of clays and claystones can be extended to temperature effects, an important conclusion in terms of performance assessment. PDF |
- The coupled hydro-mechanical behaviours of compacted crushed Callovo-Oxfordian argillite
- Chaosheng Tang ; A.M. Tang ; Y.J. Cui ; P. Delage ; Bin Shi
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2010 , Volume: 2
- Rock Mechanics
- Keywords: compacted argillite ; compressive behaviour ; dry density ; water content ; hydro-mechanical coupling behaviours
- Abstract
Callovo-Oxfordian (COx) argillite obtained from the excavation of high-level radioactive waste geological disposal has been evaluated as an alternative sealing/backfill material in France. This paper presents an experimental investigation into the hydro-mechanical behaviour of compacted crushed COx argillite. A series of oedometer compressive tests including various loading-unloading cycles were conducted on COx argillite powders at different initial water contents. After reaching the desired dry density (2.0Mg/m3), the vertical stress was reduced to different levels (7.0 and 0.5MPa) and the compacted sample was then flooded under constant volume conditions while measuring the changes in the vertical stress. It was found that the initial water content significantly affects the compressive behaviour. The measured saturated hydraulic conductivity is less than 1×10−10m/s. PDF |
- Clays in radioactive waste disposal
- P. Delage ; Y.J. Cui ; A.M. Tang
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2010 , Volume: 2
- Rock Mechanics
- Keywords: high-level radioactive waste HLW) ; engineered barrier ; Temperature ; permeability ; radioactive waste disposal ; swelling cla
- Abstract
Clays and argillites are considered in some countries as possible host rocks for nuclear waste disposal at great depth. The use of compacted swelling clays as engineered barriers is also considered within the framework of the multi-barrier concept. In relation to these concepts, various research programs have been conducted to assess the thermo-hydro-mechanical properties of radioactive waste disposal at great depth. After introducing the concepts of waste isolation developed in Belgium, France and Switzerland, the paper describes the retention and transfer properties of engineered barriers made up of compacted swelling clays in relation to microstructure features. Some features of the thermo-mechanical behaviors of three possible geological barriers, namely Boom clay (Belgium), Callovo-Oxfordian clay (France) and Opalinus clay (Switzerland), are then described, including the retention and transfer properties, volume change behavior, shear strength and thermal aspects. PDF |
- Technical session 1e: Analysis
- R. Nova ; A. Murakami ; M. Rouainia ; P. Delage ; A. Gens ; J. Pestana ; D.V. Griffiths ; R. Uzuoka
- 16th International Conference on Soil Mechanics and Geotechnical Engineering (Osaka)
- Year: 2005
- Other Geotechnical
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- Sur la susceptibilité à l'effondrement des loess du Nord de la France
- Y.J. Cui ; P. Delage ; D. Marcial ; J.-M. Terpereau ; G. Marchadier
- 16th International Conference on Soil Mechanics and Geotechnical Engineering (Osaka)
- Year: 2005
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- Thermal pressurization in Boom clay
- M. Monfared ; P. Delage ; J. Sulem ; M. Mohajerani ; A.M. Tang
- International Conference on Soil Mechanics and Geotechnical Engineering - 18th International Conference on Soil Mechanics and Geotechnical Engineering (Paris)
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- Macroscopic effects of the hydration mechanisms in smectites; applications to engineered and geological barriers for radioactive waste disposal
- P. Delage
- TC106 Conferences in Unsaturated Soils - 7th International Conference on Unsaturated Soils 2018 (Hong Kong)
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- Landfill Engineering ; Laboratory Testing
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- Effondrement d’un matériau de remblai compacté trop sec
- P. Delage
- International Conference on Soil Mechanics and Geotechnical Engineering - 12th International Conference on Soil Mechanics and Foundation Engineering (Rio De Janeiro)
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- Technical session 1e: Analysis
- R. Nova ; A. Murakami ; M. Rouainia ; P. Delage ; A. Gens ; J. Pestana ; D.V. Griffiths ; R. Uzuoka
- International Conference on Soil Mechanics and Geotechnical Engineering - 16th International Conference on Soil Mechanics and Geotechnical Engineering (Osaka)
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- Experimental characterizations of the hydro-mechanical behavior of a pellet/powder bentonite mixture
- A. MolineroGuerra ; N. Mokni ; Y.-J. Cui ; A.M. Tang ; P. Delage ; P. Aimedieu ; F. Bernier ; M. Bornert
- TC106 Conferences in Unsaturated Soils - 7th International Conference on Unsaturated Soils 2018 (Hong Kong)
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- Récents développements de la technique osmotique de contrôle de succion
- P. Delage ; Y.J. Cui ; E.De Laure
- International Conference on Soil Mechanics and Geotechnical Engineering - 15th International Conference on Soil Mechanics and Foundation Engineering (Istanbul)
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- INFLUENCE DE LA SUCCION SUR LA COMPRESSIBILITE D’UN LIMON NON SATURE
- P. Delage ; G.P.R. DeSilva
- International Conference on Soil Mechanics and Geotechnical Engineering - 13th International Conference on Soil Mechanics and Foundation Engineering (New Delhi)
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- Sur la susceptibilité à l'effondrement des loess du Nord de la France
- Y.J. Cui ; P. Delage ; D. Marcial ; J.-M. Terpereau ; G. Marchadier
- International Conference on Soil Mechanics and Geotechnical Engineering - 16th International Conference on Soil Mechanics and Geotechnical Engineering (Osaka)
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- Soil Mechanics ; Laboratory Testing
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