Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This article is devoted to the presentation of a multilevel method using finite differences that is well adapted for solving Stokes and Navier-Stokes problems in primitive variables. We use Uzawa type algorithms to solve the saddle point problems arising from spatial discretization by staggered grids and a semi-explicit temporal scheme. By means of a new change of basis operator, the two-dimensional velocity and pressure fields of an M.A.C mesh are gathered in a hierarchical order, into several grids preserving the M.A.C property on each of them. These new hierarchical unknowns, called Staggered Incremental Unknowns (SIU), allow us to develop techniques which reduce the cost of the resolution of either Stokes or generalized Stokes problems. An experimental estimation of the condition number of the inner matrix is given, and justifies the preconditioning effect of the staggered incremental unknowns.
ISSN: 0168-9274

hal-00770268
https://hal.univ-antilles.fr/hal-00770268
DOI : 10.1016/S0168-9274(99)00044-6

Éditeur(s) : HAL CCSD
Résumé : EGU2012-6377- Geophysical Research Abstracts vol. 14
The hot geothermal fluid produced by the wells of the Bouillante power station, in Guadeloupe, contains various dissolved species such as silica or some metals (Zn, Pb, etc). During the exploitation, the geothermal fluid is flashing and cooling (from 260 to 160°C for the high-pressure steam-liquid separation and down to 110°C for the low-pressure phase separation of a part of the separated liquid at 160°C). Consequently, the dissolved species can form scale deposits such as amorphous silica or poly-metallic sulphides, according to the exploitation conditions, and cause serious scaling problems on the production and the surface installations. These minerals could also precipitate during the partial underground re-injection of the production fluids which is being set up in the Bouillante power station. In this study, in order to predict and prevent the possible silica precipitation at temperature lower than 160°C, during the partial underground reinjection of the production fluids of Bouillante or their thermal valorization down to 110°C temperatures, we propose to investigate on site the kinetics of silica precipitation as a function of temperature and pH. The experiments presented here were carried out on site on samples of separated waters collected after the steam-water separator at 160°C, containing about 600 ppm of SiO2, at four cooling temperatures: 22, 50, 75 and 90°C, and for pH ranging from 4 to 9. These experiments showed that the silica deposition was always initiated by a polymerization mechanism characterized by an order 2 kinetic law and the formation of a white colloidal gel, which slowed down the silica precipitation under solid form. This latter was observed much later, after the polymerization stage, and only in particular conditions (long time of atmospheric exposure, water stagnation,. . . ). The results also confirmed that the silica precipitation kinetics is strongly dependent on pH. In acidic solution, a transition period is observed before the beginning to the silica polymerization. At neutral-basic pH, there is no transition period and the rate of polymerization is maximal for pH close to 8. The undergoing modeling of these experimental data and specific surface area measurements on the colloidal gel will allow us to determinate the kinetics parameters useful for the prediction and prevention of silica precipitation under the specific exploitation conditions of Bouillante power station. This work is financially supported by ADEME (French Agency for Energy and Environment), BRGM and UAG.
EGU General Assembly 2012
Vienne, Austria

hal-00697627
https://hal-brgm.archives-ouvertes.fr/hal-00697627

Résumé : L’objet de cette thèse est l’étude des comportements mécanique et à la corrosion d’un nouveau système de fondation, dit pieux SPIRMEC, adapté aux structures légères. Le travail s’est focalisé sur deux grands aspects. Le premier aspect concerne l’analyse du comportement sous chargement axiale des pieux SPIRMEC sur la base de l’expérimentation et de la modélisation numérique dans un sol mou non cohésif. Quant au deuxième aspect, il traite du problème de la corrosion de l’acier constituant le pieu dans un environnement tropical humide. Le comportement des pieux SPIRMEC sous une charge axiale de traction, dans un sol fin non cohésif, a montré le développement d’une surface cylindrique de rupture. Celle-ci ne dépend pas de la configuration géométrique des pieux tel que : l’espacement S, le diamètre d’hélice Dh et le diamètre du tube d. En adoptant ce critère de rupture et à l’aide d’une analyse statistique des données, nous avons proposé quatre méthodes analytiques de prédiction de la capacité portante des pieux SPIRMEC à partir des essais in-situ et au laboratoire qui sont: •Méthode CPT basée sur la résistance de pointe pénétromètrique (essai CPT), •Méthode MPT basée sur la pression limite pressiomètrique (essai MPT), •Méthode du couple d’installation, •Méthode analytique basée sur les paramètres de cisaillement de sol notamment l’angle de frottement interne (essais triaxial et boîte de cisaillement). Ces méthodes tiennent compte de la géométrie du pieu, du procédé de mise en oeuvre et de la compacité du sol. L’analyse de performance des méthodes proposées a montré que les méthodes analytique et CPT représentent mieux le comportement des pieux testés. La modélisation numérique du comportement des pieux SPIRMEC sous charge axiale de traction a été également étudiée à l’aide du code de calcul Plaxis 2D. Un modèle axisymétrique a été adopté pour modéliser la géométrie de la structure. Le modèle de comportement hardening soil a été retenu pour modéliser le comportement élastoplastiq des couches de sol. Un modèle élastique linéaire a été retenu pour le pieu. Quant au comportement de l’interface sol-structure, il a été pris en compte par un modèle élastoplastique basé sur les critères de Mohr-Coulomb. L’expansion du sol résultant de l’installation des pieux a été approchée par une cavité cylindrique. Cette dernière a été modélisée par des déformations volumiques anisotropes. Nous avons constaté, qu’appliquer une déformation volumique de l’ordre de 40% permet une bonne concordance entre les résultats numériques et expérimentaux. L’étude paramétrique nous a également permis de constater l’existence d’une variation linéaire entre la capacité portante et l’espacement S. Le comportement de l’acier galvanisé dans le sol a été également étudié au moyen de trois approches: électrochimique, visuelles grâce au microscope électronique et gravimétrique. Les tests électrochimiques de corrosion du zinc ont été réalisés dans la solution de sol artificielle pour deux périodes bien distinctes : saison des pluies et après 8 mois de contact sol-pieu. Une forte dépendance est constatée de la vitesse de corrosion de zinc au pH et à la conductivité de la solution. La vitesse de corrosion est plus importante en saison des pluies qu’après 8 mois de contact de pieu avec le sol. Les fortes concentrations en sulfates semblent augmenter la vitesse de corrosion. Les analyses menées au MEB montrent que la zone de fluctuation de nappe et en surface externe (sol/air) sont les zones les plus corrodées. La comparaison entre les différentes techniques d’évaluation de la vitesse de corrosion a montré que l’eau de nappe peut être utilisée comme un milieu représentatif du profil chimique d’un sol non cohésif et légèrement granulaire.
The purpose of this thesis is to study the both behaviors mechanical and of the corrosion of a new foundation system, called spirec piles, for lightweight structures. The work was based on two main aspects. The first aspect concerns the analysis of behavior of the spirmec piles under axial loading on the basis of experimental and numerical modeling in a non-cohesive soft soil. On the second aspect, it addresses the problem of corrosion of steel forming the pile in a humid tropical environment. The behavior of the tested piles under axial traction load, in a non-cohesive soil, showed the development of a cylindrical surface of failure. This does not depend on the geometrical configuration of the tested piles such that: the spacing s, the helix diameter dh and the diameter of the shaft. By adopting this failure criterion and using statistical data analysis, we proposed four analytical methods for predicting the bearing capacity of the piles from in-situ and laboratory tests, which are: cpt method based on tip resistance penetrometer (cpt test), mpt method based on pressuremeter limit pressure (test mpt), method of installation torque and analytical method based on the shear parameters of soil (triaxial tests and shear box). These methods take into account the geometry of the pile, the method and implementation of soil compaction. Performance analysis of the proposed methods showed that the analytical methods and cpt represent better the behavior of piles tested. An axisymmetric condition was assumed to model this geometry in two-dimensional space. In this study, we proposed to model the pipe screw pile with plates elements available in plaxis 2d. The helixes were modeled as circular disks. Interface elements were incorporated along the pile to simulate the soil-pile interaction. Hardening soil model was chosen to describe the soil with drained behavior was assigned for all layers. Linear elastic for pile and elastic plastic model based on the mohr-coulomb criterion was used to describe the interface behavior. The lateral expansion generated by the pile shaft was modeled by anisotropic volumetric strains (ɛxx=ɛzz, ɛyy=0). The pile behavior under tensile loading at different volumetric strains, it is clear that the best fit was obtained at volumetric strain of 40%. The parametric study also allowed us to establish the existence of a linear variation between the bearing capacity and spacings. The behavior of the galvanized steel in the ground has also been studied using three approaches such as: electrochemical, microscopic imaging and gravimetrically. Electrochemical tests of the corrosion of the zinc have been made in artificial soil solution into two periods, the rainy season and after eight months of contact soil-pile. Is a strong dependence of the observed corrosion rate of the zinc at the ph and conductivity of the solution. The corrosion rate is higher in the rainy season compared to eight months of contact of the pile with soil. High sulfate concentrations increase the rate of corrosion. The meb analysis shows that the fluctuation zone of the water table is the most corroded area. Comparison between the different methods of evaluating the corrosion rate showed that the ground water may be used as a representative profile of the chemical environment of a non-cohesive soil and slightly granular.

http://www.theses.fr/2014AGUY0790/document

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : Combined petrographic study and apatite fission track analysis (apatite FTA) across the Gres d'Annot basin document maximum temperatures reached by this turbiditic sandstone formation, from around 60 degrees C at the SW basin margin up to around 200 degrees C below the Penninic frontal thrust, in relation to burial below the front of Alpine nappes. Increasing diagenetic grade across the basin is primarily expressed by the development of silica transfer by pressure solution and correlated porosity loss. We infer the nappe thickness profile, from the nappe front in the SW up to around 8-10 km in the NE. Apatite FTA dates exhumation of the Gres d'Annot during the Late Miocene, in relation to thrusting of the underlying Argentera and Barrot Palaeozoic massifs. This study illustrates the influence of thrust front propagation on foreland basin diagenesis and exhumation, and highlights potential implications for the evolution of sediment reservoir properties in this context.
ISSN: 0954-4879

hal-00411860
https://hal.archives-ouvertes.fr/hal-00411860
DOI : 10.1111/j.1365-3121.2008.00793.x

Éditeur(s) : HAL CCSD Global Science Press
Résumé : International audience
In this paper, the authors present two different time-discretization schemes combined with a finite-volume space discretization for the incompressible Navier-Stokes equations. They show that the collocated space discretization, usually used with a projection method, can also be extended to other time discretizations over previous projection methods, like the splitting methods. The main advantage of this splitting method is that the pressure approximation is truly of second order. In the first and second parts of this article, two different time-discretization schemes are considered with a collocated space discretization and it is explained how the unknown can be correctly coupled. Numerical simulations are presented in the last part. Tests of spatial and time accuracies are made. The numerical results when the Navier-Stokes problem is solved are shown, in the model problem of the driven cavity.
ISSN: 1815-2406

hal-00730191
https://hal.archives-ouvertes.fr/hal-00730191

Éditeur(s) : HAL CCSD De Gruyter
Résumé : International audience
Wallaba (Eperua falcata) is a tropical wood which is known to have naturally low swelling characteristics. Samples of wallaba heartwood were subjected to differential solvent extraction. Wood pieces that were extracted with methanol experienced significantly higher swelling after rehydration from oven dry to 96% relative humidity in comparison to non-extracted samples and samples extracted with other solvents. Methanol soluble wallaba heartwood extract was purified by high pressure liquid chromatography and the compounds present were characterised by nuclear magnetic resonance spectroscopy. Methanol extract was found to contain a very high relative proportion of polar compounds which are proposed to bind to the polymeric cell wall by multiple hydrogen bonds restricting the association of water and therefore acting as natural anti-swelling agents.
ISSN: 0018-3830

hal-00856942
https://hal.archives-ouvertes.fr/hal-00856942
https://hal.archives-ouvertes.fr/hal-00856942/document
https://hal.archives-ouvertes.fr/hal-00856942/file/Chemical_extractives_tropical_wood_Royer_al.pdf

Résumé : La gestion du foncier martiniquais est un sujet complexe, sensible et à forte densité politique. La superficie de la Martinique est de 1 100km2, soit l’une des plus petites régions françaises, avec la plus forte densité de population, soumise à de multirisques (cyclonique, sismique, volcanique, technologique, inondation, pollution de l’air, des sols et de l’eau, tsunami…).La triangulation urbanistique composée d’une multiplicité d’acteurs, de textes et de réglementations et d’un millefeuille institutionnel (6 niveaux d’administration : commune, intercommunalité, département, région, Etat, Europe) annihile toute responsabilité et obère un développement endogène de ce micro territoire.Un juste équilibre entre développement économique, social, culturel et environnemental doit être trouvé en conciliant les objectifs économiques et sociaux liés au développement insulaire.La remarquable biodiversité de la Martinique constitue un atout touristique indéniable, menacé par de fortes pressions anthropiques foncières.Cette recherche démontre la pertinence de la réglementation applicable au foncier à la Martinique et l’influence du développement durable sur cette réglementation. La thèse propose des solutions pérennes à mettre en œuvre pour pallier les incohérences juridiques révélées par l’étude.
Management of land in Martinique is a complex, sensitive and highly political topic.The total area of the island is 1 100 km2 (square meters), e.g, one of the smallest French areas, with the highest concentration of population, submitted to multirisk desasters (cyclonic, seismic, volcanic, technological, flood, air, ground and water pollutions, tsunami…).The urban triangulation made up of a multiplicity of actors, texts and regulations, as well as a multi-level institutional cream cake (6 levels of administration: the city, the intercity, the Department, the Regional Council, the State and Europe), destroys all kind of responsibility and obstruct an endogenous development of this micro territory.A fair balance between economic, social, cultural and environmental development is necessary, by reconciling with the economic and social goals related to the insular development.The astonishing biodiversity of the island of Martinique represents an obvious tourist asset, threatened by strong land anthropic pressures.This research study highlights the relevance of the regulation applicable to the land in Martinique as well as the influence of sustainable development on this regulation. This thesis suggests perennial solutions to implement, in order to mitigate the legal inconsistencies pointed out by the study.

http://www.theses.fr/2011AGUY0503/document

Éditeur(s) : HAL CCSD
Résumé : International audience
Semantic web standards, tools, ontologies and related technologies have considerably matured in the recent years. Nowadays, accessing a wide catalogue of biological, social, environmental, and ecological data sources helps stakeholders working on biodiversity to answer their complex questions. Will the real time access to web resources effectively support the definition of strategies to conserve and manage biodiversity? How might semantic web technologies help us to handle the complex and heterogeneous big data related to biodiversity? The workshop aims to identify the key challenges faced by the bioinformatics community, discuss potential solutions and identify the opportunities emerging from the trans-disciplinary interactions between Plant Science and Informatics experts. Therefore, we expect the bioinformatics experts to explain how they apply semantic web standards and tools to their scientific topic, from biology, agriculture, agro-ecology, genomics, environmental studies, to social sciences, citizen sciences. Research papers presenting various aspects of semantic web technologies applied to biodiversity data, ranging from position papers to implemented systems descriptions and their evaluation, will be selected. We are particularly interested in the use of the semantic technologies to design and develop systems that supports research on agricultural and wild biodiversity conservation and management for food security. Examples may include strategies for resilience to climate change pressures, sustainability of productive ecosystems, ecosystems services monitoring or territories management, rather than systems supporting only research on climate patterns or soil erosion.
http://hal-lirmm.ccsd.cnrs.fr/lirmm-00831757

lirmm-00831757
http://hal-lirmm.ccsd.cnrs.fr/lirmm-00831757
http://hal-lirmm.ccsd.cnrs.fr/lirmm-00831757/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In fold-and-thrust belts, shortening is mainly accommodated by thrust faults which are preferential zones for recrystallisation and mass transfer. This study focuses on a detachment fault related to the emplacement of the Monte Perdido thrust unit in the southern Pyrenees. The studied fault zone consists of a 10 m thick intensively foliated phyllonite developed within the Millaris marls, of Eocene age. The lithological homogeneity of the hanging wall and footwall allows us to compare the Millaris marls outside the fault zone with the highly deformed marls located in the fault zone and to quantify the chemical, mineralogical and volumetric changes related to deformation processes along the fault. The Millaris marls are composed of detrital quartz, illite, chlorite, minor albite and pyrite, in a micritic calcite matrix. In the fault zone, the cleavage planes are marked by clay minerals and calcite ± chlorite veins attest to fluid-mineral interactions during deformation. The mineral proportions in all samples from both the fault zone and Millaris marls have been quantified by two methods: (1) X-ray diffraction and Rietveld refinement, and (2) bulk chemical analyses as well as microprobe analyses to calculate modal composition. The excellent agreement between the results of these two methods allows us to estimate mineralogical variations using a modification of the Gresens' equation. During fault activation, up to 45 wt% of calcite was lost while the amounts of quartz and chlorite remained unchanged. Illite content remained constant to slightly enriched. The mineralogical variations were coupled with a significant volume loss (up to 45%) mostly due to the dissolution of micritic calcite grains. Deformation was accompanied by pressure solution and phyllosilicates recrystallisation. These processes accommodated slip along the fault. They required fluids as catalyst, but they did not necessitate major chemical transfers.
ISSN: 0264-8172

hal-00976361
https://hal.archives-ouvertes.fr/hal-00976361
DOI : 10.1016/j.marpetgeo.2013.12.016

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation
ISSN: 0191-8141

hal-01172423
https://hal.archives-ouvertes.fr/hal-01172423
DOI : 10.1016/j.jsg.2015.03.012