Fleury-la-Vallée, France
Fleury-la-Vallée, France

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Yu L.,Belgian Nuclear Research Center | Weetjens E.,Belgian Nuclear Research Center | Sillen X.,Ondraf Niras | Vietor T.,National Cooperative for the Disposal of Radioactive Waste | And 4 more authors.
Rock Mechanics and Rock Engineering | Year: 2013

A proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the thermal transient on the evolution of the damaged zone (DZ) has been explored in the European Commission project TIMODAZ (thermal impact on the damaged zone around a radioactive waste disposal in clay host rocks, 2006-2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the thermo-hydro-mechanical behaviour of the clay host rocks. The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures nor of a significant permeability increase of the DZ. Instead, thermally induced plasticity, swelling and creep seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clayhost rock, which guarantee the effectiveness of the safety functions of the repository system, are expected to be maintained after the heating cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid, and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock.

Nguyen M.T.,French Institute of Petroleum | Bemer E.,French Institute of Petroleum | Dormieux L.,Ecole des Ponts Paris Technology
45th US Rock Mechanics / Geomechanics Symposium | Year: 2011

CO2 geological storage is considered as one of the effective solutions to prevent CO2 release into atmosphere and to reduce consecutive greenhouse effect. CO2 injection implies geochemical reactions between the reactive brine and in situ formations, leading to modifications of their petrophysical and geomechanical properties. Acidification effects have been studied at IFP Energies nouvelles using an experimental procedure of chemical alteration, which ensures a homogeneous dissolution pattern of rock samples and especially avoids any wormholing process that could lead to erroneous measurements at the core scale. Geomechanical characterization of altered carbonate samples shows a mechanical weakening of the carbonate formation. This paper presents a first attempt to estimate the evolution of carbonate mechanical properties induced by acid alteration through a micromechanical approach. © 2011 ARMA, American Rock Mechanics Association.

Doan D.H.,French Institute of Petroleum | Nauroy J.F.,French Institute of Petroleum | Delage P.,Ecole des Ponts Paris Technology | Tang A.M.,Ecole des Ponts Paris Technology | Mainguy M.,Total S.A.
45th US Rock Mechanics / Geomechanics Symposium | Year: 2011

Most thermal heavy oil recovery methods entails changes of pore fluid, pressure and temperature which in turn induce complex changes in the elastic properties of reservoirs that are in general unconsolidated or weakly consolidated porous rocks. In this paper, laboratory measurements of velocities and attenuations under different conditions of temperature and stress were performed on samples of a weakly consolidated reconstituted sandstone saturated with various fluids (air, water and glycerol). The sample investigated is representative of weakly cemented sandstone reservoirs with high porosity and permeability. The experimental results demonstrate the strong impact of the nature of the pore fluid on the compressional and shear wave velocities and attenuations. The influence of temperature and stress are discussed, together with the wave dispersion mechanisms. © 2011 ARMA, American Rock Mechanics Association.

Watanabe Y.,Kumamoto University | Otani J.,Kumamoto University | Lenoir N.,Ecole des Ponts Paris Technology | Hall S.A.,French National Center for Scientific Research
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering | Year: 2011

In geotechnical laboratory testing a detailed characterization of the strain field in soils under loading test is very important in order to well characterize deformation and failure, especially as strain localization is one of the key issues in soils. In fact strain localization can only really be studied through full-field measurement techniques. However, it is difficult to determine the displacement fields directly from such images. In a few published studies sparsely distributed natural or artificial markers in the soils have been traced between CT images, but this does not provide a detailed characterization of the soil behavior. An alternative approach to this problem is to use 3D-volumetric Digital Image Correlation (DIC) of X-ray CT images to determine displacements and strains. Based on the results of this combined X-ray CT/DIC analysis, the deformation process and the strain localization are quantitatively characterized in space and time under different triaxial compression conditions.

Fritsch A.,Vienna University of Technology | Hellmich C.,Vienna University of Technology | Dormieux L.,Ecole des Ponts Paris Technology
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2010

The successful design of ceramic bone biomaterials is challenged by two competing requirements: on the one hand, such materials need to be stiff and strong, which would suggest a low porosity (of pore sizes in the 10-100 mm range) to be targeted; on the other hand, bone biomaterials need to be bioactive (in particular vascularized), which suggests a high porosity of such materials. Conclusively, reliable information on how porosity drives the stiffness and strength properties of ceramic bone biomaterials (tissue engineering scaffolds) is of great interest. In this context, mathematical models are increasingly being introduced into the field. Recently, self-consistent continuum micromechanics formulations have turned out as expressedly efficient and reliable tools to predict hydroxyapatite biomaterials' stiffness and strength, as a function of the biomaterialspecific porosity, and of the 'universal' properties of the individual hydroxyapatite crystals: their stiffness, strength and shape. However, the precise crystal shape can be suitably approximated by specific ellipsoidal shapes: while it was shown earlier that spherical shapes do not lead to satisfactory results, and that acicular shapes are an appropriate choice, we here concentrate on disc-type crystal shape as, besides needles, plates are often reported in micrographs of hydroxyapatite biomaterials. Discbased model predictions of a substantial set of experimental data on stiffness and strength of hydroxyapatite biomaterials almost attain the quality of the very satisfactory needle-based models. This suggests that, as long as the crystal shape is clearly nonspherical, its precise shape is of secondary importance if stiffness and strength of hydroxyapatite biomaterials are predicted on the basis of continuum micromechanics, from their micromorphology and porosity. © 2010.

Tang C.-S.,Nanjing University | Tang C.-S.,China University of Mining and Technology | Shi B.,Nanjing University | Cui Y.-J.,Ecole des Ponts Paris Technology
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

The shrinkage characteristics of buffer-backfilling materials play an important role in the security and stability of the high-level radioactive waste geological disposal system. COx argillite is considered as a kind of potential buffer-backfilling materials in France. In this investigation, both the initially saturated compacted COx specimens and the paste-like COx specimens are prepared and subjected to different test methods to study their volumetric shrinkage behaviours. For the compacted specimens, it is found that the volumetric shrinkage deformation is significantly influenced by the initial dry density; the shrinkage limit, shrinkage efficiency and shrinkage strain decrease with the increasing dry density; in addition, it is observed that the shrinkage direction of specimens shows obvious anisotropism. For example, at low degree of compaction, the radial shrinkage strain is higher than axial shrinkage strain, and the shrinkage geometry factor is larger than 3; however, the contrary results are obtained at high degree of compaction. For the paste-like specimens, three shrinkage stages can be distinguished: normal shrinkage, residual shrinkage and zero shrinkage; most of the volume shrinkage deformation occurs before the air-entry point while the soil is still fully saturated. A group of four general shrinkage models are employed to fit the shrinkage curve of the paste-like specimens. The results show that the G & C model can get the highest performance for the present soil.

Tang C.-S.,Nanjing University | Cui Y.-J.,Ecole des Ponts Paris Technology | Tang A.-M.,Ecole des Ponts Paris Technology | Shi B.,Nanjing University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2010

The crushed Callovo-Oxfordian (COx) argillite powder is proposed as an alternative backfilling material in France, which will be used in the engineering barrier of high-level radioactive waste (HLW) repository. In this investigation, one-dimensional oedometer tests are carried out on highly compacted (dry density of 2.0 g/cm3) crushed COx argillite powder. The evolution of axial stress and the volumetric deformation characteristics of the samples are studied during saturation process. The effects of the initial axial stress level and the grain size distribution (GSD) on the hydro-mechanical behaviors are discussed. The results show that the volumetric deformation characteristics of samples greatly depend on the applied initial axial stress during saturation. Under the initial condition of higher axial stress, the monotone collapse behaviors are observed for the coarser powder samples. Whereas the finer powder samples present collapse-swelling-collapse behaviors, and the axial stress decreases firstly, then increases and finally decreases again. The initial lower axial stress causes obvious swelling behaviors for both the coarser and finer powder samples and the corresponding axial stress increases gradually. After saturation, the equilibrium axial stresses of finer powder samples are higher than those of coarser powder samples. The hydraulic conductivity is less than 10-11 m/s for all the studied samples after the dry density of 2.0 g/cm3 is reached.

Boussetta S.,Tunis el Manar University | Bouassida M.,Tunis el Manar University | Dinh A.Q.,Ecole des Ponts Paris Technology | Canou J.,Ecole des Ponts Paris Technology | Dupla J.C.,Ecole des Ponts Paris Technology
International Journal of Geotechnical Engineering | Year: 2012

An experimental study has been carried out at CERMES on 1 g physical model made up of reinforced soil by a rigid inclusion. Loading tests were conducted at a prescribed rate of displacement by using a rigid disk. The experimental work focused on the effect of thickness and grain size distribution of the mattress material on the load transfer between the rigid inclusion and compressible soil. The variation of cover ratio has been also analyzed and the composition of compressible soil as well. Obtained results indicate the increase of cover ratio from 2.22 % to 8.88 % leads to 100% increase of efficiency and the settlement reduction is 50%. The variation of mean diameter of mattress material from 2.5 mm to 12 mm clearly led to an increase of efficiency equal to 90% and settlement reduction of 25%. J. Ross Publishing, Inc. © 2012

Delage P.,Ecole des Ponts Paris Technology
Geomechanics from Micro to Macro - Proceedings of the TC105 ISSMGE International Symposium on Geomechanics from Micro to Macro, IS-Cambridge 2014 | Year: 2015

A series of oedometer compression tests and mercury intrusion porosimetry tests was carried out on 8 distinct samples of sensitive clays from eastern Canada. A good correspondence was observed between the compression index and the slope of the pore size distribution curves. This correspondence is explained based on the microstructure mechanism proposed by Delage & Lefebvre 1985 who showed that compression in such structured soils occurred, while increasing the compression stress, by the progressive and ordered collapse of pores from the largest ones to the smallest ones. The oedometer compression hence collapses, under a given stress increment, a well defined pore population, the total volume of which is given by the water expelled during the compression corresponding to this stress increment. © 2015 Taylor & Francis Group.

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