Analyse microscopique des mecanismes de dessiccation et de gonflement des sols argileux

National audienceL'article présente quelques analyses menées sur une argile : la montmo-rillonite grecque. Elles ont été réalisées à l'aide d'un Microscope Electronique à Ba-layage Environnemental (MEBE). Dans ce dernier, on a imposé un cycle d'humidification-séchage et parallèlement un séchage à l'air libre sur une galette d'argile. Les premières observations semblent montrer une certaine réversibilité du gonflement. Toutefois une " pseudo-précipitation " de petits grains s'est initiée. Les formes géométriques des galettes d'argile ne semblent pas présenter d'influence sur le comportement au séchage à l'air libre de l'argile

Analyse à l'échelle micro et macroscopique des mécanismes de retrait et de gonflement des sols argileux

International audienceThis paper presents some experimental analyses performed, within an ESEM, of the shrinkage and swelling of a clay.Cette communication présente l'analyse expérimentale, menée au MEBE, du retrait et du gonflement d'une argile

Stifness and influence of non-saturation in granitic materials

Neste artigo, apresentam-se as características de deformabilidade para dois materiais com a mesma origem geológica: um agregado granítico (0/12.5; D50=0.52mm) e uma areia siltosa designada de areia de Perafita (0/6.35; D50=0.36mm). A rigidez, dos materiais compactados, no domínio das pequenas deformações (<10-5) é estudada através de ensaios triaxiais de precisão. A influência da não saturação na deformabilidade dos materiais é estudada através de ensaios triaxiais com medição das pressões intersticiais. Tais medidas permitiram a análise do comportamento mecânico dos materiais não saturados em termos de tensões efectivas, que foram calculadas através das aproximações de Terzaghi e Bishop. Os resultados obtidos mostram para cada material uma relação única entre o módulo de deformabilidade e a tensão efectiva (para e=0.5), independentemente do grau de saturação das amostras ensaiadas.In this paper, the stiffness of two materials with the same geological origin is presented, a granite aggregate (0/12.5, D50=0.52mm) and a silty sand, called Perafita sand (0/6.35; D50=0.36mm). The stiffness in very small strains (<10-5) of the compacted materials is studied by means of precision triaxial tests. The influence of non-saturation on the stiffness is also studied through triaxial tests with measurement of negative pore water pressures. Such measurements allow the analysis of the mechanical behaviour of the unsaturated material in terms of effective stresses. For this purpose two approaches were used: the Terzaghi’s and Bishop’s approaches. The results obtained show, for each material, a unique relationship between vertical stiffness and vertical effective stress (constant void ratio=0.5), independently of the saturation degree of the studied samples.Universidade de Coimbra. Faculdade de Ciências e Tecnologia (FCT-UC)GRICES/CNRS – “Security of road and railway infrastructures versus climatic changes

Influencia de la no saturación y granulometría en la rigidez de materiales de naturaleza granítica

In this paper, the stiffness of two materials with the same geological origin is presented, a silty sand, called Perafita sand (D50=0.36mm) and a granite aggregate (0/12.5, D50=0.52mm). The stiffness in very small strains ( <10-5) of the compacted materials is studied by means of precision triaxial tests (with local strain measurements). The influence of non-saturation on the stiffness is also studied through triaxial tests with measurement of negative pore water pressures. Such measurements allow the analysis of the mechanical behaviour of the unsaturated material in terms of effective stresses. For this purpose two approaches were used: the Terzaghi’s and Bishop’s approaches. The results obtained show, for each material, a unique relationship between vertical stiffness and vertical effective stress (constant void ratio = 0.5), independently of the saturation degree of the studied samples.En este artículo se presenta la rigidez de dos materiales con el mismo origen geológico, una arena con limo, llamada arena Perafita (D50=0.36mm) y un agregado granítico (0/12.5, D50=0.52mm). La rigidez para deformaciones muy pequeñas ( <10-5) de los materiales compactados es estudiada mediante ensayos triaxiales de precisión (con medidas locales de deformación). La influencia de la no-saturación en la rigidez se ha estudiado también mediante ensayos triaxiales con medición de la presión negativa del agua en los poros. Estas medidas permiten el análisis del comportamiento mecánico de materiales no saturados por lo que se refiere a tensiones efectivas. Con este propósito fueron usados dos procedimientos: el de Terzaghi y el de Bishop. Los resultados obtenidos revelan, para cada material, una relación única entre la rigidez vertical y la tensión efectiva vertical (ratio de vacíos constante = 0.5), independientemente del grado de saturación de las muestras estudiadas

Influence of Compaction and Loading Conditions of the Dynamic Properties of a Silty Sand

Elastic properties of a compacted silty sand were measured in a precision triaxial cell at the École Centrale de Paris in the range of very small strains (between 10-6 and 10-4), using improved Hall effect-based local strain gauges and data acquisition system. The dynamic properties of the soil were also derived from resonant column tests at the IST, in Lisbon, as functions of shear strain, compaction water content and confining pressure. Elastic limits as low as 5.10-6 were found in both devices, with Poisson’s ratio from triaxial tests ranging from 0.05 at very strains (\u3c 10-4) to 0.37 at larger strains. Comparison between quasi-static and dynamic values were found to be in good agreement, with a reasonable value of Poisson’s ratio, despite the complex properties of this soil such as viscosity, ageing effects and anisotropy

Influence of suction on the properties of two granular road materials

The results of an experimental work on two road granular materials are presented, including small strains precision triaxial tests under cyclic loading, large strains triaxial tests with measurement of the negative pore water pressure (suction) and wetting tests. The influence of different initial conditions of density, water content and fines content was studied. The two materials differ by their fine contents (7 % for MHC and 10% for HFC). The specimens are compacted at different water content and at a density corresponding to 97% of the Modified Proctor maximum density. The interpretation of the results, in the quasi-elastic domain, is based on an effective stress analysis that allows to take into account both the effects of total stresses and negative pressure, in the perspective of a more rational design of pavement layers

A Hybrid Tissue-Level Model of the Left Ventricle: Application to the Analysis of the Regional Cardiac Function in Heart Failure

International audienceThis work contributes to the systemic interpretation of clinical data for the analysis of the regional cardiac function in the context of heart failure. A two-step patient-specific approach, combining a realistic geometry and a hybrid, tissue-level electromechanical model of the left ventricle is proposed. For the first step, a fast framework to extract a realistic geometry of the left ventricle from MSCT data is proposed. This geometry is then applied to a tissue-level model of the left ventricle, coupling a discrete electrical model, a mechanical model integrating a visco-elastic law, solved by a finite element method and a hydraulic model. A set of simulations carried out with the model are shown and preliminary results of the parameter identification approach, based on real patient data, are presented and discussed

Uma abordagem à modelação de solos não saturados

Os geomateriais das camadas dos pavimentos e das vias-férreas, bem como os das respectivas fundações, encontram- se no estado não saturado nas boas condições de serviço destas infra-estruturas. Torna-se por isso necessário considerar o aspecto não saturado destes materiais na modelação e no dimensionamento destas infra-estruturas. O presente artigo propõe a generalização do conceito de tensão efectiva para solos não saturados. De modo a descrever o comportamento exibido pelos solos não saturados, nomeadamente os fenómenos de colapso durante a humidificação, é proposto um modelo elastoplástico. Este modelo, descrito em termos de tensões efectivas, é calibrado para o caso de uma areia siltosa com base em resultados de ensaios triaxiais clássicos e de precisão com medição da pressão intersticial negativa

Turning Tangent Empirical Mode Decomposition: A Framework for Mono- and Multivariate Signals.

International audienceA novel Empirical Mode Decomposition (EMD) algorithm, called 2T-EMD, for both mono- and multivariate signals is proposed in this paper. It differs from the other approaches by its computational lightness and its algorithmic simplicity. The method is essentially based on a redefinition of the signal mean envelope, computed thanks to new characteristic points, which offers the possibility to decompose multivariate signals without any projection. The scope of application of the novel algorithm is specified, and a comparison of the 2T-EMD technique with classical methods is performed on various simulated mono- and multivariate signals. The monovariate behaviour of the proposed method on noisy signals is then validated by decomposing a fractional Gaussian noise and an application to real life EEG data is finally presented