Éditeur(s) : HAL CCSD
Résumé : International audience
In most rock mechanical testing devices, the texture developed during deformation is only observed after the failure, and the detailed mapping of cracks and pore structure evolution, just before or after rupture, remains speculative. Computerized X-ray tomography (CT X-ray) offers a way to observe 'in vivo' some characteristics of a tested sample in the course of its deformation. Therefore we developed an X-ray transparent tri-axial cell that was included in a medical purpose X-ray scanner with a volumetric resolution of the order of 1 mm3. This technique is described and applied to a porous calcarenite, which is regularly scanned for porosity evolution during mechanical testing. The experiment is performed at low confining pressure (2-10 MPa). During testing, an axial load is applied until failure and is then progressively decreased. In these experiments, the peak stress is preceded by phase of diffuse dilatancy. After failure localization, the axial stress is unloaded until the stress reaches isotropy. During this unloading phase, the previous diffuse dilatancy is lost due to an elastic relaxation. Then, the stress is completely relaxed. At this moment the dilatancy increases again and the residual dilatancy is larger than that reached at the peak stress. When observed "post mortem" at microscopic scale, the dilatant structures are comprised of cataclastic deformation bands and cracks in some larger crystals.
International Journal of Rock Mechanics and Mining Science

hal-00767563
https://hal.archives-ouvertes.fr/hal-00767563
DOI : 10.1016/j.ijrmms.2012.07.020

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : Rock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' monument and the Abu Rawash monument. This study is based on geological and topographical observations, photomontages and field measurements. The results, which are correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a construction method under the Fourth Dynasty.
EISSN: 1777-5817

hal-00512644
https://hal.archives-ouvertes.fr/hal-00512644

Éditeur(s) : HAL CCSD
Résumé : We present an experimental study of relations between hydraulic properties of clayey rocks and their deformation at bulk and micro scale. The experimentation is based on triaxial deformation of kaolinitic core samples, on permeability measurements, and on several methods of analysis of the microstructure. To produce the samples, remoulded kaolinite material is consolidated by axial loading up to 20 MPa in an oedometric cell. Then, in a triaxial cell, an undrained stress path is applied in order to induce shearing damage in the sample. The permeability of the sample is measured by fluid flow across the sample. Before and after these hydro-mechanical tests, the evolution and the homogeneity of the pore space and moreover the texture of the material are analysed by X-ray tomography, environmental scanning electron microscopy and thermic neutron diffraction. Contrary to expectations, the permeability at the sample scale does not vary significantly, although quite large deformation is reached. The final deformation is heterogeneous, with well-developed shear bands. It appears that the development of compacting and dilating zones generates a heterogeneous permeability field, which results in a negligible variation of the bulk permeability at the sample scale.
International Journal of Rock Mechanics and Mining Science

hal-00496407
https://hal.archives-ouvertes.fr/hal-00496407
DOI : 10.1016/j.ijrmms.2010.04.007

Éditeur(s) : HAL CCSD American Association of Petroleum Geologists
Résumé : International audience
Determination of the membrane seal capacity of deformation bands is critical for managing geologic reservoirs in porous sandstones. In this study, we have analyzed a cataclastic shear-band network developed in uncemented porous sandstone in Provence, France. Geometrical analyses of the bands show significant differences between three types of bands (single strand, multistrand, and band cluster), sorted by their number of strands, their amount of shear displacement, and their thicknesses. At the microscopic scale, the image-analysis porosities and the grain-size distributions allow definition of three different types of microstructural deformation: damage zone, protocataclastic, and cataclastic. Whereas damage zone and protocataclastic deformations are observed in each type of band, cataclastic strands are observed in clusters and, sometimes, in multistrands. Cataclastic strands are characterized by a porosity reduction of 10 to 25% and a permeability reduction of three to five orders of magnitude compared to the host rock. Field observations of iron hydroxide precipitations around the bands suggest that cataclastic strands were membrane seals to water flow under vadose condition. This study therefore highlights the importance of the degree of cataclasis in shear bands as membrane seals to subsurface fluid flows in sandstone reservoirs.
ISSN: 0149-1423

hal-00766557
https://hal.archives-ouvertes.fr/hal-00766557
DOI : 10.1306/04051211097

Éditeur(s) : HAL CCSD
Résumé : 22 pages; 20 figures
Rock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' mastaba and the Abu Rawash pyramid. This study is based on geological and geomorphological observations, visual observation, and photomontages. Results, correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a characteristic of the construction methods under the Fourth Dynasty.
Le substratum rocheux des pyramides de Kheops et Khephren est étudié en comparaison avec celui d'autres monuments de la quatrième dynastie de l'ancienne Egypte : le Sphinx, le mastaba de la reine Kentkawes et la pyramide d'Abu Rawash. Cette étude est basée sur des observations géologiques et géomorphologiques, l'observation visuelle et des photomontages, ainsi que des mesures réalisées sur le terrain. Les résultats, corrélés avec ceux d'études antérieures, démontrent l'existence de collines naturelles utilisées comme assises pour la construction des deux grandes pyramides. Le volume minimum de ces collines peut être estimé par rapport au volume total à 12% pour Khephren et 23% pour Kheops. L'utilisation de collines rocheuses pour asseoir la construction d'un monument apparaît être caractéristique des méthodes de construction utilisées sous la quatrième dynastie.
https://hal.archives-ouvertes.fr/hal-00319586

hal-00319586
https://hal.archives-ouvertes.fr/hal-00319586
https://hal.archives-ouvertes.fr/hal-00319586/document
https://hal.archives-ouvertes.fr/hal-00319586/file/PyramidsSR.pdf

Éditeur(s) : HAL CCSD Pergamon
Résumé : This paper presents an experimental study of the deformation of Beaucaire marl subjected to drained triaxial tests under a wide range of confining pressure. Several methods of observation have been used: X-ray computed tomography, scanning electronic microscopy, quantitative image analysis of thin sections and mercury porosimetry. The analysis at the grain scale shows the existence of various deformation modes depending on the mean stress level. These modes are classified with reference to the brittle and ductile regimes. In specimens deformed under low confining pressure, macro-cracks are localised in a band more contracting than the rest of the specimen. In specimens deformed under moderate confining pressure, a series of micro-scale shear bands characterised by a grain re-orientation towards the direction of macro-shear is detected in the zones of localised deformation. The material in between the micro-scale shear bands is contracting more than the rest of the specimen in some cases; in other cases, a schistosity is detected also in the rest of the specimen outside the localisation zones. In the specimen deformed under high confining pressure, no localisation occurs, and a schistosity is observable throughout the specimen.
ISSN: 1365-1609

hal-00411208
https://hal.archives-ouvertes.fr/hal-00411208
DOI : 10.1016/j.ijrmms.2007.08.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The brittle structures of a Hercynian granite (La Borne, French Massif Central) observed at several scales, from regional to microscopic, are presented and interpreted on mechanical terms. Emphasis is placed on strike slip faults, joints, and cracks related to incipient shear fracturing during horizontal compression. Three compressive tectonic phases have been identified according to their brittle structures and characterised by the burial depth at the time of their generation.The two first phases (H1, H2) are Hercynian and occurred while the granite was deeply buried (∼5 to 3 km depth) whereas the last phase (P) is Pyrenean and occurred at very low depth. The geometric organizations of cracks, joints and faults are clearly similar at various scales from about 10 μm to several m.These field observations are strong arguments for the occurrence of shear structures at microscopic to macroscopic scales during tectonic events. Following this inference, it is proposed that, at least in the case of Hercynian phases, cracks, joints and macroscopic strike slip faults have been generated by the same mechanical process under high overburden weight. Therefore, incipient fractures seem to be generated as shearing structures and to evolve by coalescence with neighbouring ones with the same direction.
ISSN: 0191-8141

hal-01115718
https://hal.archives-ouvertes.fr/hal-01115718
DOI : 10.1016/j.jsg.2014.05.002