- 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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- Effects of lime treatment on the microstructure and hydraulic conductivity of Héricourt clay
- T.D. Tran ; Y.J. Cui ; A.M. Tang ; M. Audiguier ; R. Cojean
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2014 , Volume: 6
- Rock Mechanics
- Keywords: lime hydration ; hydraulic conductivity ; microstructure
- Description
- This study aims at evidencing the effects of lime treatment on the microstructure and hydraulic conductivity of a compacted expansive clay, with emphasis put on the effect of lime hydration and modification. For this purpose, evolutions of hydraulic conductivity were investigated for both lime-treated and untreated soil specimens over 7 d after full saturation of the specimens and their microstructures were observed at the end. Note that for the treated specimen, dry clay powder was mixed with quicklime prior to compaction in order to study the effect of lime hydration. It is observed that lime hydration and modification did not affect the intra-aggregate pores but increased the inter-aggregates pores size. This increase gave rise to an increase of hydraulic conductivity. More precisely, the hydraulic conductivity of lime-treated specimen increased progressively during the first 3 d of modification phase and stabilised during the next 4 d which correspond to a short period prior to the stabilisation phase. The microstructure observation showed that stabilisation reactions took place after 7 d. Under the effect of stabilisation, a decreasing hydraulic conductivity can be expected in longer time due to the formation of cementitious compounds.
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- Instability assessment of Loess using a CPT-based evaluation method
- J.P. Karam ; Y.J. Cui ; C. Yang ; J.M. Terpereau
- 2nd International Symposium on Cone Penetration Testing, Huntington Beach, CA, USA. Volume 2&3: Technical Papers, Session 3: Applications, Paper No. 3-45
- Year: 2010
- Site Characterization & In-situ Testing (General)
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- Effects of mineralogy on thermo-hydro-mechanical parameters of MX80 bentonite
- A.M. Tang ; Y.J. Cui
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2010 , Volume: 2
- Rock Mechanics
- Keywords: compacted bentonite ; thermal conductivity ; water retention property ; swelling potential ; mineralogical effects
- Abstract
Thermal conductivity, water retention curve and swelling behavior of two MX80 bentonite samples were studied in the present work. The difference obtained from these two MX80 bentonite samples was then analyzed in terms of mineralogical effects (effects of the proportion of quartz and montmorillonite). It was concluded that the mineralogical effect was significant on the thermal conductivity and the swelling capacity; on the contrary, it was negligible on the water retention property. 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 |
- Experimental study on hydro-mechanical coupling behaviours of highly compacted expansive clay
- A.M. Tang ; Y.J. Cui
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2010 , Volume: 2
- Rock Mechanics
- Keywords: expansive clay ; suction ; compressibility ; yield pressure ; engineered barrier ; radioactive waste disposal
- Abstract
Highly compacted expansive clays have been usually considered as a possible material for sealing and backfill in deep geological disposal of radioactive waste. In this condition, the material is simultaneously subjected to water infiltration from the geological barrier and stresses generated by the swelling of engineered barriers in confined conditions. Its behaviour under hydro-mechanical loading is essential to the safe design of the whole storage system. In the present work, MX80 bentonite, a kind of expansive clay from Wyoming, USA, was studied. After compaction, its dry density was 1.8Mg/m3 and its initial suction was 110MPa. Firstly, the soil was humidified under controlled suction and free-swelling conditions. Significant swelling was observed. Secondly, four values of suction of 110, 39, 9 and 0MPa were employed to perform isotropic compressive tests at constant suction conditions. That allowed studying the effect of suction on the yield pressure, elastic and plastic compressibility parameters. The results show that the elastic and plastic compressibility parameters increase when the suction decreases. The relationship between these parameters and the logarithm of suction can be linearly correlated. The yield stress drastically decreases upon wetting under free-swelling conditions, from 12 – 18MPa (at an initial suction of 110MPa) to 0.2MPa at saturated state. 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 |
- 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
- Railway Geotechnics
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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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- Laboratory Testing ; Soil Mechanics
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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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- Influence des mécanismes de rétention des polluants sur la résistance au cisaillement d’un sol compacté
- Y.J. Cui ; P. Alzoghbi ; L. Lei ; P. Delage
- International Conference on Soil Mechanics and Geotechnical Engineering - 15th International Conference on Soil Mechanics and Foundation Engineering (Istanbul)
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