• Physique/Physique/Physique Numérique
  
• Sciences de l'ingénieur/Mécanique/Mécanique des solides
  
• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Génie civil/Géotechnique
  
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• Sciences de l'ingénieur
  
• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Mécanique/Génie mécanique
  
• Sciences de l'ingénieur/Mécanique/Mécanique des structures
  
• Sciences de l'ingénieur/Génie civil/Construction hydraulique
  
• Sciences de l'ingénieur/Génie civil/Matériaux composites et construction
  
• Sciences de l'ingénieur/Mécanique
  
• Physique/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Mécanique/Matériaux et structures en mécanique
  
• Sciences de l'ingénieur/Génie civil/Structures
  
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The behavior of a natural soil is known to change substantially in presence of water under unsaturated conditions, due to additional capillary forces. Water can be absorbed by hygroscopic soil particles (such as clay), or remains at the surface of solid grains (sand, silt) and forms either a discontinuous (pendular regime) or a continuous phase (funicular regime), depending on the water content of the soil. Capillary bridges exist solely between pairs of grains at small water contents, giving rise to simple capillary force expressions and straightforward subsequent modeling. For larger water contents, these generic capillary bridges progressively merge into more complex coalesced bridges involving several grains (i.e. at least three) and whose description remains little known. In the present study, a numerical approach based on surface energy minimization isproposed to compute capillary forces for assemblies of two or three grains. The methodology is frst validated for a standard capillary bridge between two grains by comparison both with previous experiments and with other alternative theoretical and numerical approaches. The method is next extended to a triplet of grains within a wide range of water content (or equivalently reduced water volume) during imbibition, to switch from uncoalesced to coalesced bridges. Eventually, the infuence of contact angle, surface tension and gravity on the capillary force, the volume of coalescence and the morphology of the bridge as well is investigated. The present study paves the way for the implementation of capillary efects in micromechanical models relying on mesostructures composed of a few grains.

The main objective of this study is to compare the mechanical behavior of two sands (Hostun or Dune sands) mixed with crushed rubber obtained from used tires. However, it is essential to ensure that his geotechnical application do not result in long-term negative impacts on the environment. The chemical properties of these two sands are given by energy dispersive analysis X-ray fluorescence spectrometry. The mineral composition of these two sands is performed by X-ray diffractometry. The morphological characteristics of the sand grains are given by the analysis of the images of the two sands given by the scanning electron microscope. This study is based on 120 direct shear tests performed on sand-rubber aggregate mixtures. The results show that the rubber content of the aggregates has a significant effect on the shear strength of sand-rubber mixtures in both cases of sand. In fact, the shear strength of the sand-rubber mixture increases with increasing crushed rubber up to 20% for different normal stresses. The analysis of the test results also shows the effect of the angular shape of the sand grains on the interparticle friction. The contribution of the structure effect in the mobilized friction is analyzed by comparing the shear test results of Hostun and dune sand mixtures.

Delayed Ettringite Formation (DEF), is one of the different Internal Sulfate Attack (ISA), is a slow chemical reaction that can be responsible for the degradation of cementitious materials, through the swelling of the material followed by crack diffusion in the structure. The objective of this study is the experimental characterization at the local scale (10 x 10 x 30 mm 3 samples) of the concrete reached by DEF. The composite samples, consist of a 15 mm thick cement paste placed in contact with a siliceous aggregate. The shape of these samples makes it possible to study the mechanical behavior of the interface between the cement paste and the aggregate. This zone is identified as a privileged zone of the development of DEF. Given the slowness of this pathology, the experimental setting in the laboratory is accelerated by choosing conditions favoring the appearance of DEF. The tests are exploited at the local scale by measuring expansions by image correlation of the degraded samples and by scanning electron microscope observations. The results showed a higher expansion at the cement paste-aggregate interface compared to the cement paste. A tensile test performed at local scale allowed to characterize the impact of DEF on mechanical properties of the cement paste-aggregate interface. A drop in strength was observed with heterogeneous formation and localization of ettringite inside the interface.

Une approche par éléments finis cohésifs-volumétriques, tenant compte des propriétés mécaniques de la zone de transition interfaciale (ITZ), est utilisée pour étudier le comportement mécanique du béton lors d'un essai de compression uniaxiale. Dans ce travail, un modèle géométrique bidimensionnel à l'échelle mésoscopique du béton numérique a été considéré. Les échantillons obtenus sont maillés à l'aide du logiciel GMSH avec une méthode de Delaunay.Les résultats des simulations à l’aide du Modèle de Zones Cohésives Frottantes (MZCF) permettent, à travers une étude de criblage de type Hadamard, d’apporter des éléments de réponses concernant les facteurs les plus influents et leur contribution à la résistance maximale du béton en compression uniaxiale.

Tensegrity systems are a class of reticulated space structures composed of compressed bars maintained in equilibrium by a network of tensioned cables. Their stiffness depends both on elements’ mechanical properties and their internal self-stress state. Taking advantage of their structural properties, we respond to the challenge of accessibility for everybody to the sea with a new concept of modular lightweight and deployable platforms. Variable configurations are developed to fit ecologically into the marine environment thanks to the transparency of double layer tensegrity structures. Moreover, allowing practical assembly and disassembly is considered in the design to respect the coastal law. Through a numerical study, we demonstrate in this paper the capability of this solution under various representative load cases and support conditions.After the structural and design optimization of elements constrained by weight and stiffness, we detail the design of the nodes, which are the key components ensuring geometry and foldability of the structure. Finally, on-site setting and interfacing with ground supports is experimented in marine conditions to proof the feasibility of this concept.