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The mechanical behavior of frozen soils is strongly affected by the amount of ice. The amount of ice depends on the temperature and the applied mechanical stresses. The influence of ice content and temperature on the mechanical behavior and the coupling effects on the reverse direction can be mentioned as the main difference between frozen and unfrozen soils. In the light of this difference, an elastoplastic constitutive model for describing the stress-strain behavior of saturated frozen soils is proposed. By dividing the total stress into fluid pressure and solid phase stress, in addition to consideration of the cryogenic suction, the model is formulated within the framework of two-stress state variables. The proposed model is able to represent many of the fundamental features of the behavior of frozen soils, such as ice segregation phenomenon and strength weakening due to pressure melting. In the unfrozen state the model becomes a conventional critical state model. Typical predictions of the model for simulating the characteristic trends of the frozen soil behavior is described qualitatively. Model predictions are also compared with the available test results and reasonable agreement is achieved. Key words: frozen soil, elastoplastic model, cryogenic suction, solid-phase stress. Le comportement mecanique des sols geles est fortement affecte par la quantite de glace. La quantite de glace depend de la temperature et des contraintes mecaniques appliquees. L'influence de la teneur en glace et de la temperature sur le comportement mecanique et les effets de couplage sur le sens inverse peut etre mentionnee comme la principale difference entre les sols geles et non geles. A la lumiere de cette difference, un modele constitutif elastoplastique est propose pour decrire le comportement de contrainte-deformation des sols geles satures est propose. En divisant la contrainte totale en pression du fluide et en contrainte de phase solide, en plus de l'examen de la succion cryogenique, le modele est elabore dans le cadre des variables d'etat de deux contraintes. Le modele propose est en mesure de representer beaucoup de caracteristiques fondamentales du comportement des sols geles comme le phenomene de segregation de glace et l'affaiblissement de la force du fi la pression de fusion. En etat non gele, le modele devient un modele conventionnel de l'etat critique. Les predictions typiques du modele pour simuler l'evolution caracteristique du comportement de sol gele est decrit qualitativement. Les predictions du modele sont egalement comparees avec les resultats des tests disponibles et un accord raisonnable est atteint. [Traduit par la Redaction] Mots-cles : sol gele, modele elastoplastique, succion cryogenique, contrainte de la phase solide., Introduction The constitutive modeling of frozen soils has been closely linked with identifying the relevant stress measurements describing the stress-strain behavior. Total stress-based models have been widely used in the [...]

During conventional cone penetration testing in silt, the soil will normally be partially drained. If the penetration rate varies, time for drainage is altered and therefore the measured cone resistance and pore pressure will change. This paper studies the change in soil microstructure around the probe during cone penetration carried out at different penetration rates to investigate the failure mechanism and the processes controlling drainage in silt. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration were used. Making use of advanced image-processing techniques, the statistical distribution of particle orientations and the local porosity were investigated for zones around the cone tip and shaft. The spatial distribution of the measured microscale parameters in the region near the probe indicates that the soil deformation during a piezometric cone penetration test (CPTU) in silt leads to the formation of both contractive and dilative zones. The macro response of the material, presented by the pore pressure and cone penetration resistance measured during the test, results from the competition between these zones during penetration, which is shown to be dependent on the penetration rate. Key words: silts, site investigation, fabric-structure of soils, microscopy, cone penetration test. Durant un essai au penetrometre statique dans du limon, le sol est en principe partiellement draine. Si la vitesse de penetration varie, le temps de drainage et donc la resistance du cone et la pression interstitielle varient egalement. Le present article s'interesse aux variations de la microstructure du sol autour de la sonde durant la penetration du cone dans le sol pour differentes vitesses de penetration, avec l'objectif d'etudier le mecanisme de rupture et les processus qui influent sur le drainage de l'eau dans le limon. Dans le cadre de la presente etude, on a utilise des images, obtenues a l'aide d'un microanalyseur a faisceau electronique, de fines sections d'echantillons de limon congeles preparees apres penetration du cone. A l'aide de techniques avancees de traitement d'image, la distribution statistique de l'orientation des particules et la porosite locale dans les zones avoisinant la pointe du cone et la tige du penetrometre ont ete analysees. La distribution spatiale des parametres mesures a l'echelle microscopique a proximite de la sonde montre que la deformation du sol durant l'essai au penetrometre statique (CPTU) realise sur le limon entraine la formation de zones de contraction et de dilatation. La reponse macroscopique du materiau, representee par la pression interstitielle et par la resistance a la penetration du cone, toutes deux mesurees durant les essais, est causee par la competition entre ces zones lors de la penetration, competition qui semble dependre de la vitesse de penetration. [Traduit par la Redaction] Mots-cles: limon, etude sur le terrain, structure et microstructure des sols, microscopie, essai au penetrometre statique., Introduction A cone penetration test (CPT) consists of pushing a cone tip at the end of a cylindrical probe of 35.7 mm diameter (standard size) into the ground at a [...]

The circumferential failure surface of a shear vane in strain softening soft sensitive clay is studied. A set of shear vane experiments are performed in situ, where the sheared region is retrieved from the ground using an over-coring technique. By producing thin sections, the circumferential failure zone is revealed when viewed under a polarised light microscope. The failure zone is found to first evolve after reaching the peak global resistance. Its shape is not a full cylinder, but rather a rounded square. The structure of the shear zone is non-smooth and characterised by complex shear patterns of micrometre size. [ABSTRACT FROM AUTHOR]