Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Previous work has demonstrated that geoelectrical measurements, acquired either along the Earth’s surface or in boreholes, can be sensitive to the presence of fractures. However, a lack of numerical approaches that are well suited to modelling electric current flow in fractured media prevents us from systematically exploring the links between geoelectrical measurements and fractured rock properties. To address this issue, we present a highly computationally efficient methodology for the numerical simulation of geoelectrical data in 2.5-D in complex fractured domains. Our approach is based upon a discrete-dual-porosity formulation, whereby the fractures and rock matrix are treated separately and coupled through the exchange of electric current between them. We first validate our methodology against standard analytical and finite-element solutions. Subsequent use of the approach to simulate geoelectrical data for a variety of different fracture configurations demonstrates the sensitivity of these data to important parameters such as the fracture density, depth, and orientation.
ISSN: 0956-540X

hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151/document
https://hal.archives-ouvertes.fr/hal-01622151/file/sanzGJI2017.pdf
DOI : 10.1093/gji/ggx080

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The full numerical simulation of turbulent flows in the context of industrial applications remains a very challenging problem. One of the difficulties is the presence of a large number of interacting scales of different orders of magnitude, ranging from the macroscopic scale to the Kolmogorov dissipation scale. In order to better understand and simulate these interactions, new algorithms of incremental type have recently been introduced, stemming from the theory of infinite-dimensional dynamical systems (see, e.g., the algorithms of Foias, Jolly et al. (1988), Foias, Manley and Temam (1988), Laminie et al. (1993, 1994), Marion and Temam (1989, 1990), and Temam (1990)). These algorithms are based on decompositions of the unknown functions into a large- and a small-scale component, one of the underlying ideas being to approximate the corresponding attractor. In the context of finite element methods, the decomposition of a solution into small- and large-scale components appears when we consider hierarchical bases (Yserentant, 1986; Zienkiewicz et al., 1982). In the present article we derive several estimates of the size of the structures for the linear and nonlinear terms which correspond to interactions of different hierarchical components of the velocity field, and also their time variation. The one-step time variation of these terms can be smaller than the expected accuracy of the computation. Using this remark, we implement an adaptive spatial and temporal multilevel algorithm which treats differently the small- and large-scale components of the flow. We derive several a priori estimates in order to study the perturbation introduced into the approximated equations. All the interaction terms between small- and large-scale structures are frozen during several time steps. Finally, we implement the multilevel method in order to simulate a bidimensional flow described by the Burgers equations. We perform a parametric study of the procedure and its efficiency. The gain in CPU time is significant and the trajectories computed by our multi-scale method remain close to the trajectories obtained with the classical Galerkin method.
ISSN: 0168-9274

hal-00730710
https://hal.archives-ouvertes.fr/hal-00730710

Éditeur(s) : HAL CCSD
Résumé : To understand the effect of inherited lithospheric structures on the continental plates deformation process, we have developed a multi scale model that explicitly takes into account an anisotropic viscosity due to the Crystal Preferred Orientation (CPO) of olivine in the mantle by coupling a viscoplastic self-consistent simulation of the deformation at the polycrystalline aggregate to a 3D Finite Element code. Using this tool, we calculate the mechanical behavior of a continental lithosphere submitted to extension for various initial structures. The first set of experiments investigates the deformation of a plate with a homogeneous initial olivine CPO. Results show that the macroscopic anisotropy is strongly dependent on the initial orientation of the olivine CPO relative to the solicitation and to its evolution. The second set of experiments aims to analyze the deformation of a continental plate containing pre-existing lithospheric scale shear zones. These multi-domain models show that the olivine mechanical anisotropy may induce the reactivation of pre-existing lithospheric scale shear zones in a plate submitted to rifting. In both cases, the results shows that the macroscopic mechanic anisotropy induced by the evolution of olivine CPO in the upper mantle is a key parameter to understand the deformation of the continental plates and to explain the observed reactivation of inherited structure from past tectonics events
Afin de comprendre l'effet des structures préexistantes sur la déformation des plaques continentales, nous avons développé une méthode de modélisation mécanique multi-échelle utilisant une viscosité anisotrope induite par les Orientations Préférentielles du Réseau (OPR) des cristaux d'olivine présents dans le manteau. Cette méthode en couple le calcul viscoplastique autocohérent de la déformation d'un agrégat d'olivine à un code éléments finis 3D. Elle a été utilisée pour le calcul du comportement mécanique d'une plaque continentale soumise à une extension. Une première série d'expériences numériques sur l'extension de plaque lithosphérique présentant des OPR initiales d'olivine homogènes a permis de montrer que l'anisotropie mécanique macroscopique est fortement dépendante de l'orientation initiale de l'OPR. La seconde série de simulations analyse l'extension d'une plaque continentale présentant une zone présentant des OPR d'olivine héritées d'un événement tectonique précédant. Les résultats de ces calculs multi-domaines que l'anisotropie mécanique de l'olivine peut expliquer la réactivation des zones de cisaillement héritées lors du rifting. Les résultats obtenus dans les deux séries de modèles montrent que l'anisotropie mécanique macroscopique induite par l'évolution des OPR d'olivine dans le manteau supérieur est un paramètre clé pour la compréhension de la déformation des plaques continentales et pour expliquer la réactivation observée de structures tectoniques, tels que les grands décrochements, lors des épisodes tectoniques ultérieurs.
https://tel.archives-ouvertes.fr/tel-00369463

tel-00369463
https://tel.archives-ouvertes.fr/tel-00369463
https://tel.archives-ouvertes.fr/tel-00369463/document
https://tel.archives-ouvertes.fr/tel-00369463/file/KnollThese09.pdf

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The association of experimental data showing that the plastic deformation of olivine, the main constituent of the upper mantle, is highly anisotropic and the ubiquitous seismic anisotropy in the upper mantle, which indicates that olivine crystals show coherent orientations over scales of tens to hundreds of kilometers, implies that the long-term deformation in the upper mantle is anisotropic. We propose a multiscale approach, based on a combination of finite element and homogenization techniques, to model the deformation of a lithospheric plate while fully considering the mechanical anisotropy stemming from a strain-induced orientation of olivine crystals in the mantle. This multiscale model explicitly takes into account the evolution of crystal preferred orientations (CPO) of olivine and of the mechanical anisotropy during the deformation. We performed a series of numerical experiments simulating the uniaxial extension of a homogeneous (100% olivine) but anisotropic plate to test the role of the olivine CPO on the plate mechanical behavior and the link between CPO and mechanical anisotropy evolution. Even for this simple solicitation, different orientations and intensity of the initial olivine CPO result in variable plate strengths and deformation regimes. A plate with an initial CPO where the olivine [100] and [010] axes are concentrated at 45 degrees to the extension direction has high resolved shear stresses on the easy (010)[100] and (001)[100] slip systems of olivine. This results in low strength and in deformation by transtension. Plates with an initial CPO where the maximum of [100] axes is parallel or normal to the extension direction show a high initial strength. Isotropic plates have an intermediate behavior. The progressive rotation of olivine [100] axes toward the imposed stretching direction results in hardening in all models, except in those characterized by an initial concentration of olivine [100] axes normal to the imposed extension, in which softening is followed by hardening.
ISSN: 1525-2027

hal-00420063
https://hal.archives-ouvertes.fr/hal-00420063
DOI : 10.1029/2009GC002423

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
Thermoelastic behavior of different marble types was analyzed using computational modeling and experimental measurements. Eight marble samples with different composition, grain size, grain boundary geometry, and texture were investigated. Calcitic and dolomitic marbles were considered. The average grain size varies from 75 μm to 1.75 mm; grain boundary geometry differs from nearly equigranular straight grain boundaries to inequigranular-interlobate grain boundaries. Four typical marble texture types were observed by EBSD measurements: weak texture; strong texture; girdle texture and high-temperature texture. These crystallographic orientations were used in conjunction with microstructure-based finite element analysis to compute the thermoelastic responses of marble upon heating. Microstructural response maps highlight regions and conditions in the marble fabric that are susceptible to degradation phenomena. This behavior was compared to the measured thermal expansion behavior, which shows increasing residual strains upon repetitive heating-cooling cycles. The thermal expansion behavior as a function of temperature changes can be classified into four categories: (a) isotropic thermal expansion with small or no residual strain; (b) anisotropic thermal expansion with small or no residual strain; (c) isotropic thermal expansion with a residual strain; and (d) anisotropic thermal expansion with residual strain. Thermal expansion coefficients were calculated for both simulated and experimental data and also modeled from the texture using the MTEX software. Fabric parameters control the amount and directional dependence of the thermal expansion. Marbles with strong texture show higher directional dependence of the thermal expansion coefficients and have smaller microstructural values of the maximum principal stress and strain energy density, the main precursors of microcracking throughout the marble fabric. In contrast, marbles with weak texture show isotropic thermal expansion behavior, have a higher propensity to microcracking, and exhibit higher values of maximum principal stress and strain energy density. Good agreement between the experimental and computational results is observed, demonstrating that microstructure-based finite-element simulations are an excellent tool for elucidating influences of rock fabric on thermoelastic behavior.
ISSN: 1866-6280

hal-00858095
https://hal.archives-ouvertes.fr/hal-00858095
DOI : 10.1007/s12665-013-2406-z

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The outstanding exposure of deformation bands in a multilayer sequence of the Orange quarry, Provence, France, motivates a study investigating the development and controls of deformation band geometries by field mapping combined with finite element modeling. Field mapping yields new insights into angular relations between, and evolution of, the deformation bands as well as provides input parameters for the setup and boundary conditions of the numerical simulations using ADELI 2D. In particular, reverse-sense deformation bands are found to have developed within three of the four exposed layers of the multilayer stack with similar orientations to bedding, indicating layer-parallel contraction. Numerical simulations, carried out as a parametric study to investigate the influence on deformation band development and geometry, successfully reproduce the sequential development of deformation bands in the three layers as seen in the field as well as recreate the observed angular geometries of similar to 39 degrees to the maximum compression. This angular relationship is put into context with observations from other field studies and theoretical values to explore controls of deformation band orientations. Furthermore, band localization is impeded in the model by increased layer cohesive strength, demonstrating the importance of host-rock property variations on where localization of bands within the multilayer sequence. Results from both field investigation and numerical simulations are consistent with regional tectonics, where the strata underwent gentle folding due to thrust faulting at depth, and bring further insight into the development and geometry of deformation bands in both extensional and contractional tectonic regimes.
ISSN: 0148-0227

hal-00639452
https://hal.archives-ouvertes.fr/hal-00639452
DOI : 10.1029/2011JB008365

Éditeur(s) : HAL CCSD Institute for Scientific Computing and Information
Résumé : International audience
The production of oil in soft highly compacted reservoirs produces a significant reduction in the pore space which in turn causes the surface to subside. The authors couple two simulators to model the mechanical deformations in the presence of a Darcy flow, both one- and two-phase. The simulators solve for flow in a porous medium using a finite volume method, and solve for the mechanical deformation of the porous media using a finite element method. The flow equations and the deformation equations are coupled using Biot's law. The authors use two different methods for the coupling: the first uses a staggered algorithm; the second is based on a preconditioned conjugate method. The authors use a multiscale method in both approaches. The authors show that the inf-sup condition is not satisfied, because of the mixed discretization which is done by using two separate simulators. The authors give convergence comparisons for the two methods for several examples. Two of the examples are for the linear problem (one-phase) where they know the exact solution and one is for the nonlinear problem (two-phase). In all cases, the preconditioned conjugate algorithm is faster and more robust, in particular when the inf-sup condition is not satisfied. In the nonlinear problem the authors state that the results agree with physical predictions but do not give actual empirical data. Finally, they show the effects of grid orientation on the nonlinear problem.
ISSN: 1705-5105

hal-00730673
https://hal.archives-ouvertes.fr/hal-00730673

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : International audience
The interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts. Here we investigate the modalities of deformation in Central Nepal on a c. 100 ka time scale in response to tectonic and external forcings, through the use of a finite-element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding. We study the complex coupling existing between tectonics and erosion, with special emphasis on the influences of rock strength and rainfall distributions. Our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography. We show that the location of the Main Frontal Thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the Siwaliks Hills. As previously suspected (Burbank et al. 2003), our simulations demonstrate that the pattern of uplift in Nepal is mainly dependent on both erodability and fault geometry, rather than on rainfall distribution.
ISSN: 2041-4927

hal-01543331
https://hal-amu.archives-ouvertes.fr/hal-01543331
DOI : 10.1144/GSL.SP.2006.253.01.18

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