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 American Geophysical Union
Résumé : International audience
The brittle to ductile transition (BDT) in rocks may strongly influence their transport properties (i.e., permeability, porosity topology ...) and the maximum depth and temperature where hydrothermal fluids may circulate. To examine this transition in the context of Icelandic crust, we conducted deformation experiments on a glassy basalt (GB) and a glass-free basalt (GFB) under oceanic crust conditions. Mechanical and micro-structural observations at a constant strain rate of 10(-5) s(-1) and at confining pressure of 100-300 MPa indicate that the rocks are brittle and dilatant up to 700-800 degrees C. At higher temperatures and effective pressures the deformation mode becomes macroscopically ductile, i.e., deformation is distributed throughout the sample and no localized shear rupture plane develops. The presence of glass is a key component reducing the sample strength and lowering the pressure of the BDT. In the brittle field, strength is consistent with a Mohr-Coulomb failure criterion with an internal coefficient of friction of 0.42 for both samples. In the ductile field, strength is strain rate-and temperature-dependent and both samples were characterized by the same stress exponent in the range 3 < n < 4.2 but by very different activation energy Q(GB) = 59 +/- 15 KJ/mol and Q(GFB) = 456 +/- 4 KJ/mol. Extrapolation of these results to the Iceland oceanic crust conditions predicts a BDT at similar to 100 degrees C for a glassy basalt, whereas the BDT might occur in non-glassy basalts at deeper conditions, i.e., temperatures higher than 550 +/- 100 degrees C, in agreement with the Icelandic seismogenic zone.
ISSN: 0148-0227

hal-00760905
https://hal.archives-ouvertes.fr/hal-00760905
DOI : 10.1029/2011JB008884

Éditeur(s) : HAL CCSD
Résumé : National audience
Objectives To define the different stages of spontaneous labour. To determine the indications, modalities of use and the effects of administering synthetic oxytocin. And to describe undesirable maternal and perinatal outcomes associated with the use of synthetic oxytocin. Method A systematic review was carried out by searching Medline database and websites of obstetrics learned societies until March 2016. Results The 1st stage of labor is divided in a latence phase and an active phase, which switch at 5 cm of cervical dilatation. Rate of cervical dilatation is considered as abnormal below 1 cm per 4 hour during the first part of the active phase, and blow 1 cm per 2 hours above 7 cm of dilatation. During the latent phase of the first stage of labor, i.e. before 5 cm of cervical dilatation, it is recommended that an amniotomy not be performed routinely and not to use oxytocin systematically. It is not recommended to expect the active phase of labor to start the epidural analgesia if patient requires it. If early epidural analgesia was performed, the administration of oxytocin must not be systematic. If dystocia during the active phase, an amniotomy is recommended in first-line treatment. In the absence of an improvement within an hour, oxytocin should be administrating. However, in the case of an extension of the second stage beyond 2 hours, it is recommended to administer oxytocin to correct a lack of progress of the presentation. If dynamic dystocia, it is recommended to start initial doses of oxytocin at 2 mUI/min, to respect at least 30 min intervals between increases in oxytocin doses delivered, and to increase oxytocin doses by 2 mUI/min intervals without surpassing a maximum IV flow rate of 20 mUI/min. The reported maternal adverse effects concern uterine hyper-stimulation, uterine rupture and postpartum haemorrhage, and those of neonatal adverse effects concern foetal heart rate anomalies associated with uterine hyper-stimulation, neonatal morbidity and mortality, neonatal jaundice, weak suck/poor breastfeeding latch and autism. Conclusion The widespread use of oxytocin during spontaneous labour must not be considered as simply another inoffensive prescription without any possible deleterious consequences for mother or foetus. Conditions for administering the oxytocin must therefore respect medical protocols. Indications and patient consent have to be report in the medical file. © 2016 Elsevier Masson SAS
Revue Sage - Femme

hal-01467543
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01467543
DOI : 10.1016/j.sagf.2016.11.006

Éditeur(s) : HAL CCSD
Résumé : The present PhD thesis is devoted to the numerical simulation and analysis of shear on cohesive granular materials. In the framework of the Contact Dynamics method, we developed a model of cohesive bonding, which mimics cohesion by cementation. This model involves three contact strength parameters (a tensile strength, a coefficient of sliding friction, and a coefficient of rolling friction) as well as a local criterion, which controls the creation and the breaking of cohesive bonds. All contacts are cohesive at the beginning of the numerical simulations, and contact rupture leads to an irreversible loss of tensile strength (debonding). We varied systematically the three contact strength parameters and studied their influence on the shear strength, the dilatancy, and the microstructure of the granular media. Our results show that internal friction and macroscopic tensile strength have different origins at the contact scale. We also find that the microstructure of the granular media, when sheared at the steady state (also known as the `critical state"), is strongly affected by the local coefficients of sliding and rolling friction. In particular, the mechanical role of the weak network changes with these two contact parameters, which results from the formation of a new structure of force transmission. On the other hand, we also applied the same numerical simulation method to the simulation of landslides. We developed a methodology, which takes into account the initial morphology of the hillslope, the strength of geomaterials, and a triggering factor, integrating in the same model the initiation and propagation phases of the landslide. To illustrate this methodology, we applied it to the simulation of a hypothetical example of avalanche triggered by the progressive rise of a water table.
Ce travail de thèse porte sur la modélisation numérique et l'analyse du cisaillement dans les milieux granulaires cohésifs. Dans le cadre de la méthode de la Dynamique des Contacts, nous avons développé un modèle de cohésion qui cherche à imiter la cohésion par cimentation. Ce modèle fait intervenir trois paramètres de résistance au niveau des contacts (une résistance à la traction, un coefficient de frottement de glissement, et un coefficient de frottement de roulement) ainsi qu'un critère de création et de rupture des liens cohésifs. Les contacts sont cohésifs au début des simulations et leur rupture entraîne la perte irréversible de la résistance à la traction. Nous avons fait varier les trois paramètres microscopiques et nous avons étudié leur influence dans la résistance au cisaillement, la dilatance, et la microstructure du milieu. Nos résultats montrent que le frottement interne et l'adhésion macroscopiques ont des origines microscopiques différentes. Nous observons aussi que la microstructure du milieu cisaillé à l'état stationnaire (aussi connu comme ``l'état critique") est fortement affectée par l'angle de frottement et la résistance au roulement au niveau des contacts. En particulier, le rôle mécanique du réseau faible change avec ces deux paramètres microscopiques, ce qui résulte de la formation d'une nouvelle structure de transmission de forces. D'autre part, nous avons appliqué cette méthode de simulation numérique à l'étude d'un processus naturel : les glissements de terrain. Nous avons développé une méthodologie qui tient compte de la morphologie initiale du système, de la résistance des géomatériaux, et d'un mécanisme de déclanchement, ce qui permet d'intégrer dans le même modèle les phases d'initiation et de propagation du glissement. Pour illustrer cette méthodologie, nous l'avons appliquée à la modélisation d'un exemple hypothétique d'avalanche déclenchée par la montée progressive du niveau d'une nappe d'eau.
https://tel.archives-ouvertes.fr/tel-00311303

tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303/document
https://tel.archives-ouvertes.fr/tel-00311303/file/these_estrada.pdf

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Fractures or discontinuities perpendicular to the least stress σ3 were generated in a synthetic rock analogue (granular, frictional, cohesive, and dilatant) material in axisymmetric extension tests. These fractures are of two types defined by the mean stress σ. When σ is very small, the fractures form through the mode I cracking at tensile σ3 equal to the material tensile strength. The fracture walls have smooth surfaces. At higher σ, these surfaces become rougher, with the topography features forming faint or delicate plumose patterns. The amplitude of the plumose topography increases with σ. The axial stress σ3 at fracturing reduces in magnitude and changes in sign with the σ increase. Thus σ3 orthogonal discontinuities can form at compressive σ3. SEM observations show that these discontinuities are deformation localization bands where the material is characterized by the heterogeneous decohesion and volume and porosity increase due to dilatancy. The band thickness is several grain sizes. At formation, the bands are not opened, so they are not mode I fractures. They become fractures with plumose fractography after the separation of the sample parts along the band. The formation mechanism of these discontinuities or fractures is not completely clear, but it is suggested that it represents a running constitutive instability in the form of dilatancy banding (with further σ increase the bands become inclined to σ1, i.e., shear). The similarity between the experimentally generated plumose surface fractures and natural joints is discussed, and it is suggested that they can be formed as propagating constitutive instabilities.
ISSN: 0148-0227

hal-00585846
https://hal.archives-ouvertes.fr/hal-00585846
DOI : 10.1029/2010JB008104

Éditeur(s) : HAL CCSD Elsevier
Résumé : Different types of fractures and fault rocks occur within the major normal fault zones bordering the NW of the Neogene Penedes basin (NE Spain). In the southwest part of the basin, the main fault is the Baix Penedes fault that places the Upper Jurassic-Lower Cretaceous dolomicrites of the footwall in contact with the Miocene siliciclastic sediments of the hangingwall. Within the footwall damage zone, different fracture systems and their respective associated breccias and cements have been recognized. Using a combination of structural, petrologic and geochemical analyses, we show that these fracture systems evolved from mainly tectonic to mainly karstic features during the progressive development and upward propagation of the fault. The earlier fractures and associated breccias represent the initial stages of the fault propagation, when the process zone formed around the fault tip was dominated by dilatant fracturing (fractures 1 and dilatant breccias B1). The fluid involved in this early deformation precipitated the dolomite cement Cl, in equilibrium with the host-rock in a closed hydrogeological system. Localization of frictional processes generated cataclasites and ultracataclasites along distinct second-order faults (fractures 2). In these fractures, the dolomite cement C2 precipitated in relation to the incipient opening of the hydrological system to percolating meteoric waters. The later fractures and associated breccias represent the late stages of the fault propagation. These structures (fractures 3, fractures 4 and the dilatant breccias B2) were formed when the extensional deformation reached the surface, resulting in an increasingly open hydrogeological system. At these stages, deposition of the dolomitic sediment DS and precipitation of the calcite cements C3, C4 and C5 show the circulation of freshwaters in a vadose meteoric environment, i.e. in karstic conditions.
ISSN: 0375-6742

hal-00512690
https://hal.archives-ouvertes.fr/hal-00512690
DOI : 10.1016/j.gexplo.2009.11.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Both oedometric and plane-strain tests were performed with parallelepipedic samples made of synthetic granular, cohesive, frictional and dilatant rock analogue material GRAM2. For the first time parallel sets of fractures that have all the characteristics of natural joints were reproduced in the laboratory. The fractures are regularly spaced, normal to σ3, and have plumose morphology very similar to that of natural joints. These fractures can form at tensile stress σ3 much smaller in magnitude than the tensile strength of material and even at slightly compressive σ3. When mean stress σ exceeds a certain value, the fractures become oblique to σ1 (the obliquity increases with σ), forming networks of conjugate shear bands/fractures. These results of plane-strain experiments are in good agreement with those of better controlled conventional axisymmetric tests on a similar material in Chemenda et al. (2011b) and are closer to real geological situations. Both types of experiments are complementary. Their results lead to the conclusion that at least certain categories of natural fractures (including joints, and conjugate shear fractures/bands) were initiated as deformation localization bands. The band orientation is defined by the constitutive properties/parameters (notably the dilatancy factor) that are sensitive to σ.
ISSN: 0040-1951

hal-00795555
https://hal.archives-ouvertes.fr/hal-00795555
DOI : 10.1016/j.tecto.2011.11.021

Éditeur(s) : HAL CCSD Publisher : Paris : Baillière [1980-. Latest Publisher : Paris : Elsevier
Résumé : National audience
Introduction L’atteinte œsophagienne est fréquente chez les patients présentant une sclérodermie systémique. Le diagnostic est confirmé par la manométrie œsophagienne. La sensibilité et la spécificité de la manométrie œsophagienne ont été améliorées par l’avènement de la manométrie de haute résolution. L’objectif principal de cette étude observationnelle est de caractériser les troubles moteurs œsophagiens par manométrie de haute résolution, à la lumière de la troisième version de la classification de Chicago, chez des patients présentant une sclérodermie systémique selon les critères de l’EULAR/ACR 2013. Patients et méthodes Trente-six patients répondant au diagnostic de sclérodermie systémique selon les critères EULAR/ACR 2013 et ayant bénéficié d’une manométrie de haute résolution dans un centre de compétence français ont été inclus de manière consécutive. Les résultats de la manométrie de haute résolution ont été interprétés selon la troisième version de la classification de Chicago. Les caractéristiques cliniques, biologiques et les atteintes viscérales des patients ont également été relevées et confrontées aux données manométriques. L’atteinte pulmonaire était évaluée selon la méthode de Goh et al. en aveugle des données manométriques. Résultats L’âge moyen à l’inclusion était de 58,4 ans (SD = 14,2 ans) ; 83,3 % des patients étaient de sexe féminin. 22,2 % des patients avaient une sclérodermie systémique avec atteinte cutanée diffuse selon la classification de LeRoy ; 67 % des patients avaient un pyrosis, 30,6 % une dysphagie, 33,3 % une dyspepsie. 11 % des patients avaient des épisodes de fausses routes. D’après les résultats de la manométrie de haute résolution, 55,6 % des patients avaient un apéristaltisme, 33,3 % une hypotonie du sphincter inférieur de l’œsophage et 19,4 % une hypotonie du sphincter supérieur de l’œsophage. En analyse univariée, il n’était pas retrouvé d’association significative entre la présence d’une hypotonie du sphincter inférieur de l’œsophage et les caractéristiques cliniques ou biologiques quelles qu’elles soient. La présence d’un apéristaltisme était associée avec une symptomatologie de pyrosis (p = 0,004). L’apéristaltisme était associé de manière significative avec la présence de télangiectasies (p = 0,007) et d’anticorps anti-centromères (p = 0,038). La présence de calcinose ou d’une sclérodactylie n’était pas spécifiquement associée à une atteinte sphinctérienne ou motrice œsophagienne. Vingt-neuf patients (80,6 %) avaient bénéficié d’une TDM thoracique dans l’année de la réalisation de la manométrie de haute résolution. Parmi eux, 7 patients étaient atteints d’une pneumopathie interstitielle diffuse sévère (atteinte interstitielle de plus de 20 % du parenchyme pulmonaire évaluée sur 5 coupes standardisées). Il existait une association significative entre la présence d’un apéristaltisme et la présence d’une dilatation œsophagienne en TDM (p = 0,002) et la présence d’une atteinte pulmonaire sévère (p = 0,005, OR = 6,85 IC95 % (1,12–41,82)). Discussion L’association retrouvée entre apéristaltisme en manométrie de haute résolution et sévérité de la PID est confirmée par ce travail. Néanmoins un lien de causalité n’est pas certain. Une étude prospective évaluant la mise en évidence d’une atteinte œsophagienne par manométrie de haute résolution au moment du diagnostic de sclérodermie systémique et l’atteinte pulmonaire par TDM à distance serait nécessaire. L’entité nosologique représentée par le syndrome CREST n’est pas retrouvée dans cette cohorte de patients atteints de sclérodermie systémique selon les critères EULAR/ACR 2013, où 2 des critères diagnostiques (présence de calcinose et sclérodactylie) ne sont pas associés de manière significative à l’atteinte œsophagienne d’après les résultats de la manométrie de haute résolution. Conclusions Dans cette série, chez plus de la moitié des patients atteints de sclérodermie systémique la manométrie de haute résolution permet de détecter un apéristaltisme. La présence de troubles moteurs œsophagiens est associée à une atteinte pulmonaire plus sévère en TDM
ISSN: 0248-8663

hal-01321854
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01321854
DOI : 10.1016/j.revmed.2016.04.267

Éditeur(s) : HAL CCSD
Résumé : National audience
Since the 1950s, Friedman's curves served as reference to guide obstetrical practice around the world. However, recent studies have suggested guidelines based on Freidman's results were too stringent and induce inappropriate and excessive interventionism. The committee aimed to redefine the structure and the normal duration of the labor, as well as the criterion to be fulfilled to consider a labor as abnormal. Several recommendations have been produced based on a systematic literature review. Labor dystocia should not be diagnosed during the latency phase. The beginning of the active phase of the 1st stage of labor has been established between 5 and 6 cm of cervical dilatation, which is later than previously suggested. Rate of cervical dilatation is considered as abnormal below 1 cm per 4 hour during the first part of the active phase, and blow 1 cm per 2 hour above 7 cm of dilatation. A maximum duration for the 2nd stage of labor cannot be defined in the French context, based on the literature. However, exceeding 3 hours, the risk-benefit balance becomes less beneficial. These new guidelines would help to reduce the use of oxytocin and caesarian delivery for labor dystocia. © 2016 Elsevier Masson SAS
Revue Sage - Femme

hal-01467546
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01467546
PUBMED : 28483643
DOI : 10.1016/j.sagf.2016.10.006

Éditeur(s) : HAL CCSD
Résumé : Fault zones are major discontinuities in sedimentary basins. Understanding their role on fluid migrations is an essential issue to (i) characterize the mechanisms and kinematics of deformation and (ii) to determine the parameters which control the distribution of energetic or mineral resources. This work applies to faulting under a temperature range of 200-250°C, corresponding to that of deeply buried reservoirs as well as potentially seismogenic fault zones. The studied faults are normal faults affecting the “Grès d’Annot” Formation, a Priabonian-Rupelian siliclastic turbidite succession of the Alpine foreland basin. They are located in two distinct areas: the Moutière-Restefond area in the eastern part of the basin and the Estrop area in the western part. Vitrinite reflectance outside fault zones indicates maximal temperatures of 240-260°C at Moutière-Restefond and 170-200°C at Estrop, i.e. burial depths around 8 km and 6 km, respectively, assuming a mean geothermal gradient of 30°C/km. Burial was due to underthrusting below the Embrunais-Ubaye Alpine nappes, the difference in burial between the two areas traducing the westward taper of the nappe front.The studied faults affect alternating arkosic sandstone beds and pelite layers with offsets from centimeters to decameters. Two types of core zones are recognized: (1) the foliated core zones of the Moutière-Restefond area, where deformation dominated by pressure solution and synkinematic phyllosilicate neoformation resulted in a foliated fabric, and (2) the core zones of the Estrop area, characterized by dilatant quartz-mineralized veins and breccia. Fault and host rock petrophysical properties were measured on drill plugs, using the water porosity technique and nitrogen permeability technique under 2 Mpa of confining pressure. In the Moutière-Restefond fault zones, plug axes were oriented in three orthogonal directions corresponding to the main deformation axes (X, Y, Z) of the foliated arkose to characterize the effect of structural anisotropy. In the Estrop fault zones, where deformation does not show equivalent anisotropy, the plug axes were oriented according to the main fault plane orientation (i.e., parallel to azimuth, parallel to dip and normal). In each fault zone, the porosity of fault rocks is equivalent to that of host rocks. In the Moutière-Restefond fault zones, the plugs parallel to the X and Z axes of deformation have a permeability similar to that of the host rocks, whereas permeability parallel to the Y axis (i.e. parallel to the foliation and the main fault plane) is one order of magnitude higher. By contrast, the permeability values in the Estrop fault zones are isotropic and equivalent to the host rock values. This study highlights the importance of various types of deformation mechanisms and related fluid-rock interactions in determining different fault rock types within a similar protolith, ultimately controlling distinct petrophysical properties of fault zones.
Les zones de failles constituent des discontinuités majeures dans la croûte supérieure. Ce mémoire s’intéresse aux failles actives à des profondeurs de 5-8 km, i.e. dans des conditions pouvant jouer un rôle important (i) sur le comportement mécanique de de la croûte, en particulier sur son potentiel sismogénique et (ii) sur la compartimentation des réservoirs géologiques profondément enfouis.Les failles étudiées sont des failles normales (rejet jusqu’à 50 mètres) affectant des alternances de bancs de grès arkosiques et de pélites dans les Grès d’Annot, une formation turbiditique d’âge priabonien-rupélien du bassin d’avant-chaine alpin. Les Grès d’Annot ont été enfouis sous les nappes de l’Embrunais-Ubaye peu de temps après leur dépôt et exhumés au Miocène moyen-supérieur. L’étude a été réalisée dans deux secteurs des Alpes de Haute-Provence, (1) le secteur de l’Estrop (chaine des Trois Evéchés, dans la partie occidentale du bassin) et (2) le secteur de Point Vert-Restefond (alentours du col de la Bonette, dans la partie orientale du bassin). La réflectance de la vitrinite dans les Grès d’Annot indique des températures maximales de 160-190°C dans le secteur (1) et de 240-260 °C dans le secteur (2) , soit des profondeurs d’enfouissement de 5-6 km et 8-10 km, respectivement, dans l’hypothèse d’un gradient géothermique moyen de 25-30°C/km. A partir des observations microstructurales, de données d’inclusions de fluides, de modélisations thermodynamiques sur chlorites syncinématiques et des indices de cristallinité de l’illite, on a établi que les failles du secteur (1) ont fonctionné à une température d’environ 200°C pour une pression de 0.6Kbar et celles du secteur (2) dans une gamme de température de 200-220°C et de pression comprise entre 0.6 et 1.1 Kba. L’activité de la faille de Point-Vert a été datée par la méthode 40Ar/39Ar au Miocène inférieur (21 Ma). Ces failles sont interprétées comme associées aux premiers stades du soulèvement résultant de l’activité des chevauchements dans le socle sous-jacent.Deux types principaux de roches de failles caractérisent les failles étudiées. Les brèches dilatantes sont majoritaires dans les zones de failles du secteur (1) alors que les arkoses foliées sont majoritaires dans les zones de failles du secteur (2). Les brèches dilatantes témoignent de mécanismes de déformation dominés par la fracturation transgranulaire et la pression-solution des silicates. Ce dernier mécanisme se manifeste principalement par d’abondantes précipitations cycliques de quartz, les stylolites restant peu développés. Les géométries structurales sont associées à l’activation de plans T de Riedel déterminant l’ouverture de relais extensifs et un régime localement dilatant. Nous associons ce type de roche de faille à une faible pression effective au cours de la déformation.La déformation cisaillante exprimée dans les arkoses foliées témoigne de mécanismes de déformation dominés par (i) la fracturation intragranulaire et transgranulaire, (ii) la pressionsolution/ précipitation des silicates, principalement le quartz, (iii) la néoformation de micas blancs liée à l’altération des feldspaths et (iv) la précipitation de chlorite. Ce travail montre également que les transformations minéralogiques liées aux interactions fluide-roche dans la zone de faille (forte augmentation de la proportion des phyllosilicates au dépend des feldspaths) changent radicalementla composition minéralogique de la roche. Nous associons ce type de roche de faille à une forte pression effective au cours de la déformation.La pétrophysique montre que les brèches de failles (secteur 1) ont une perméabilité isotrope et équivalente à celle du protolithe (10-3mD sous 2 MPa de confinement) tandis que les roches foliées (secteur 2) montrent une augmentation de perméabilité (10-2mD) selon l’axe Y de la déformation, d’un ordre de grandeur supérieure aux perméabilités suivant les axes X et Z et dans la roche hôte (10-3mD). Ce drain préférentiel potentiel est associé à l’orientation des phyllosilicates dans la foliation.
https://hal.archives-ouvertes.fr/tel-01310382

tel-01310382
https://hal.archives-ouvertes.fr/tel-01310382
https://hal.archives-ouvertes.fr/tel-01310382/document
https://hal.archives-ouvertes.fr/tel-01310382/file/Th%C3%A8seCAVAILHES2012.pdf

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : This study describes normal fault zones formed in foreland arkosic turbidites (the Grès d'Annot Formation, SW French Alps) under deep diagenesis conditions (~200 °C) and highlights the occurrence of two markedly different fault-rock types: (1) the foliated fault rocks of the Moutière-Restefond area; and (2) the dilatant fault rocks of the Estrop area. The deformation of (1) is dominated by intra- and transgranular fracturing, pressure solution of quartz and feldspar grains and syn-kinematic phyllosilicate precipitation resulting from feldspar alteration. The combination of these mechanisms results in a strongly anisotropic strain with intense shortening normal to the foliation (pressure solution) and extension parallel to the foliation (quartz- and calcite-sealed extension veins). This deformation implies local mass transfer that may be achieved without (or with limited) volume change. The deformation of (2) is expressed as dilatant quartz-sealed veins and breccia textures in which the main mechanisms are transgranular fracturing and quartz precipitation. Type (2) implies fault volume increase, isotropy of deformation and mass transfer at distances larger than in type (1). This study discusses the origins of (1) and (2) and shows that the permeability of (1) is anisotropic, with higher values than the host rocks parallel to the Y main deformation axis (i.e. perpendicular to the slip vector), whereas the permeability of (2) is isotropic and equivalent to that of the host rocks.
ISSN: 0954-4879

hal-01115177
https://hal.archives-ouvertes.fr/hal-01115177
DOI : 10.1111/ter.12100

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Displacement-length data from dilatant fractures (joints, veins, igneous dikes) and several varieties of deformation bands were analyzed statistically to investigate the applicability of mechanical models proposed for their formation. All 17 datasets are generally consistent with equilibrium or long-term power-law slopes on the displacement-length diagram of either 1.0 or 0.5. Similar to many faults, disaggregation deformation bands are consistent with a power-law scaling relation having a slope of approximately c = 1, implying a linear dependence of maximum displacement and discontinuity length (Dmax = γL). In contrast, dilatant fractures, cataclastic deformation bands, and shear-enhanced compaction bands are consistent with a power-law scaling relation with a slope of approximately c = 0.5, implying a dependence of maximum displacement on the square root of length (Dmax = αL1/2). The scaling relations represent an average, or long-term equilibrium outcome of deformation for conditions such as length-scale, time-scale, temperature, chemistry, and an effectively homogeneous far-field stress field, allowing for variations such as rapid and/or localized behaviors. The displacement-length scaling of these geologic structures follows systematic relationships that provide information on host-rock properties and the physics of fracture and deformation-band propagation.
ISSN: 0191-8141

hal-00818130
https://hal.archives-ouvertes.fr/hal-00818130
DOI : 10.1016/j.jsg.2012.12.005

Éditeur(s) : HAL CCSD American Geophysical Union (AGU) American Geophysical Union
Résumé : International audience
The brittle to ductile transition may strongly influence hydraulic properties of rocks at the depth and temperature ranges that hydrothermal fluids circulate. To examine this transition in the context of the oceanic crust, we conducted a series of deformation experiments on a natural basalt sample at in situ oceanic crust conditions. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Mechanical and microstructural observations at experimental constant strain rate of 10−5 s−1 indicated that the basalt was brittle and dilatant up to 800°C. At higher temperature, the deformation mode became macroscopically ductile and samples compacted. These observations have important implications on heat transfer and fluid migration in oceanic crust.
ISSN: 0094-8276

hal-01172352
https://hal.archives-ouvertes.fr/hal-01172352
DOI : 10.1002/2015GL063437

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
During compressive events, deformation in sedimentary basins is mainly accommodated by thrust faulting and related fold growth. Thrust faults are generally rooted in the basement and may act as conduits or barriers for crustal fluid flow. Most of recent studies suggest that fluid flow through such discontinuities is not apparent and depends on the structural levels of the thrust within the fold-and-thrust belt. In order to constrain the paleofluid flow through the Jaca thrust-sheet-top basin (Paleogene southwest-Pyrenean fold-and-thrust belt) this study compares on different thrust faults located at different structural levels. The microstructures in the different fault zones studied are similar and consist of pervasive cleavage, calcite shear veins (SV1), extension veins (EV1) and late dilatation veins (EV3). In order to constrain the nature and the source of fluids involved in fluid-rock interactions within fault zones, a geochemical approach, based on oxygen and carbon stable isotope and trace element compositions of calcite from different vein generations and host rocks was adopted. The results suggest a high complexity in the paleohydrological behaviors of thrust faults providing evidence for a fluid-flow compartmentalization within the basin. Previous studies in the southern part of the Axial Zone (North of the Jaca basin) indicates a circulation of deep metamorphic water, probably derived from the Paleozoic basement, along fault zones related to the major basement Gavarnie thrust. In contrast, in northern part of the Jaca basin, the Monte Perdido thrust fault is affected by a closed hydrological fluid system involving formation water during its activity. The Jaca and Cotiella thrust faults, in turn, both located more to the south in the basin, are characterized by a composite fluid flow system. Indeed, stable isotope and trace element compositions of the first generations of calcite veins suggest a relatively closed paleohydrological system, whereas the late calcite vein generations, which are probably associated with the late tectonic activity of the basin, support a contribution of both meteoric and marine waters. Based on these results, a schematic fluid-flow model is presented. This model allows visualization of three main fluid flow compartments along a N-S transect.
ISSN: 0264-8172

hal-00963606
https://hal.archives-ouvertes.fr/hal-00963606
DOI : 10.1016/j.marpetgeo.2013.09.005

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : Extension fractures of two types defined by the mean stress σ were generated in a synthetic rock analogue material. When σ is very small, the fractures are mode I cracks with smooth surfaces. At higher σ, these surfaces have plumose topography, with the amplitude increasing with σ. Both SEM observations and mechanical measurements show that fractures/discontinuities in the latter case are initiated as dilatancy localization bands. They form under tensile or slightly compressive normal stress and can be seen as running constitutive instabilities. The similarity between the plumose fractography of the experimental fractures and natural joints suggests similarity in the formation mechanism.
ISSN: 1631-0721

hal-00585886
https://hal.archives-ouvertes.fr/hal-00585886
DOI : 10.1016/j.crme.2011.01.002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Networks of localized conjugate compactive shear bands with large dihedral angles (corresponding to so-called shear-enhanced compaction bands) were generated in 3-layer plane strain finite-difference models. The central layer has elastic–plastic properties with a small positive internal friction coefficient, negative dilatancy factor, and the hardening modulus reducing during the deformation. The two other layers are elastic. The spatial organization of the networks in the central layer, resulting from the elastic–plastic instability of the 3-layer system, was shown to be dependent on the contrast of the elastic stiffness of the layers and on the friction between them. When the stiffness E of the elastic layers and/or the friction are small, the networks are rather symmetric (the bands of both orientation families are distributed homogeneously within the layer). An increase in E at high friction, results in the clustering of the bands of one orientation along a layer segment which is followed by another segment filled with the bands of the other orientation. Different network types are characterized by different band spacing which is smaller in the clustered networks. The intensity of inelastic deformation and hence of porosity reduction within the bands are also smaller in this case. The obtained band networks are very similar to those in nature where the same variability of the network organization is observed. Available geological and mechanical data confirm the conclusions from the modeling about the origin of this variability.
ISSN: 0040-1951

hal-01116201
https://hal.archives-ouvertes.fr/hal-01116201
DOI : 10.1016/j.tecto.2014.01.021

Éditeur(s) : HAL CCSD American Institute of Physics
Résumé : International audience
In order to be able to provide valuable data in multiparameter measurement field operations, tiltmeters need to have a noise level better or equal than 10-9 rad for a period range from a few minutes to a few years and a long term stability ranging from 10-7 to 10-8 rad/yr. Tiltmeter measurements should also be as much as possible insensitive to thermal disturbances, by taking great care of the horizontality of the base line tube first. Secondly, thermal responses have been assessed. We also took great care of the coupling of our tiltmeters with the bedrock. We've designed a long base tiltmeter with sensors in silica which has a low dilatation coefficient. The linear variable displacement transducer is based on coil coupling (powered by an alternative voltage). Finally we show the results of two 100 m silica water tube tiltmeters which were installed in a mine in the French Vosges massif in the framework of a hydrology research project. These instruments show a remarkably good stability (6.5×10-9 rad/month) and a low noise level (of the order of 10-11 rad). Toroidal and spheroidal free modes of the Earth were observed after the two last major earthquakes on Sumatra.
ISSN: 0034-6748

hal-00708013
https://hal.archives-ouvertes.fr/hal-00708013
https://hal.archives-ouvertes.fr/hal-00708013/document
https://hal.archives-ouvertes.fr/hal-00708013/file/2008_RSI.pdf
BIBCODE : 2008RScI...79c4502B

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In orogenic systems, thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins (metamorphic, diagenetic, meteoric). This study focuses on the Monte Perdido thrust unit emplaced in the Paleogene Jaca thrust-sheet-top basin, in the SW-central Pyrenees. We aim to decipher the mechanisms and P-T conditions of deformation in fault zones and characterize the related fluid involvement, through combined microstructural, geochemical and microthermometry analyses. Two thrust faults cutting platform limestones, marls and siliciclastic turbidites of the lower part of the basin-fill (Paleocene-lower Eocene) have been studied. The fault zones are characterized by metre-thick shear zones with highly deformed, foliated clay-rich sediments. Foliation is underlined by preferentially oriented phyllosilicates. Several generations of shear and extension calcite, quartz and chlorite-bearing veins attest to fluid-rock interactions during a multi-stage deformation. Microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins, with mineralizing fluids in equilibrium with the host sediments. Our results suggest an essentially closed hydrologic system, and imply the absence of significant fluid flow along the studied fault zones. Microthermometric study on fluid inclusions present in calcite and quartz veins, and calcite-quartz oxygen isotopic fractionation determined for the first generation shear veins, allow a geothermal gradient of 34 degrees C/km to be estimated. Analytical results demonstrate an evolution of the fault zones in three stages. The first stage was related to the emplacement of the Monte Perdido thrust unit during the middle Eocene at a temperature of similar to 208 degrees C and a burial depth of similar to 5.7 km. The second stage corresponds to a fault reactivation at a temperature of similar to 240 degrees C and a burial depth of similar to 6.5 km. The latter deformation may have been related to folding of the Monte Perdido thrust unit during the emplacement of the underlying Gavarnie thrust unit during the late Eocene-early Oligocene, with deeper burial resulting from aggradation of the thrust-sheet-top basin-fill. The last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif.
ISSN: 0191-8141

hal-00644828
https://hal.archives-ouvertes.fr/hal-00644828
DOI : 10.1016/j.jsg.2011.06.006

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : International audience
High-resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow-slip events, and to estimate slow transients related to earthquake swarms. However, they are also sensitive to other numerous influences, internal or external. Furthermore, the quality of their coupling to the rock through cementation, and the mechanical properties of the rock mass around them, have a critical influence on their records. Many of the existing strainmeters present such problems, and the correction for these effects often remains a challenge. In this paper, we present the analysis of the records of a high-resolution borehole dilatometer (Sacks–Evertson), located in the seismically active rift of Corinth (Greece) (station TRZ in the Trizonia island). We show that the instrument suffers from an only partial-solid coupling, and that the nearby sea tides have a direct (through elastic response) and indirect (through pore-pressure diffusion) effect on the dilatation signal, which adds up to the solid tidal strain source. We propose a methodology that allows, in a first step, to better separate the internal (solid tide) from the external (air pressure, sea level) influences, by calculating a frequency-dependent transfer function outside the range of the tidal periods. We then extrapolate this function, in particular at the tidal periods. In a second step, the resulting variation with frequency of the coupling coefficients with sea level led us to estimate the proportion of instrument not solidly cemented to rock (thus in contact with water pore pressure), which is about 90 % of the total height. Despite the small proportion of solid coupling, the sensor resolution remains very good up to a few tens of hours of a time period, thanks to the confining effects of the rocks on the local pore pressure. These results allow us to correct for the external effects, and reduce the associated variance by 80–90 % (in the period range of minutes to days). The empirical correction of the sea level effect could be explained using a simple Boussinesq’s approximation and 1D pore-pressure diffusion model, which contributed to better constraint of some of the poro-elastic parameters in the vicinity of the instrument. After correction, the solid tidal signal at the 24-h period is almost anti-correlated with those of the theoretical solid tide. This surprising result is consistent with a similar anti-correlation observed for the longest period surface waves (200 s) comparing the TRZ dilatometer signals to the strain measured by a nearby borehole strainmeter (MOK, 15 km). This could be related to the presence of a shallow fault close to the instrument, which would creep in response to seismic wave-related stress.
ISSN: 0033-4533

hal-01122853
https://hal.archives-ouvertes.fr/hal-01122853
DOI : 10.1007/s00024-013-0742-2

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure (lambda(fract)) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of lambda(fract), are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetiy) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks. (C) 2011 Elsevier B.V. All rights reserved.
ISSN: 0012-821X

hal-00745640
https://hal.archives-ouvertes.fr/hal-00745640
DOI : 10.1016/j.epsl.2011.10.029