Etude des propriétés de transfert des sols injectés

A l'origine, procédé de traitement destiné à l'industrie pétrolière, l'injection des sols granulaires, et notamment l'injection au coulis de ciment, voit sa technologie se développer durant ces vingt dernières années. Ainsi pour optimiser cette technique, une bonne connaissance des conditions initiales du sol en place s'avère indispensable. L'amélioration consécutive à l'injection ainsi réalisée peut être évaluée par une série de tests. Des mesures de densité permettent de mieux suivre l'‘efficacité de l'injection et en particulier le phénomène de rétention de particules indissociable de ce procédé de traitement. Des expériences unidimensionnelles en laboratoire ont été conduites pour étudier l'injection de coulis de ciment ultrafin dans des colonnes de sable de Loire préalablement saturées à l'eau. Ces essais permettent de mettre en évidence l'effet de quelques facteurs clefs : le rapport ciment/eau, la densité initiale du squelette granulaire sur la filtration. La gammamétrie montre ainsi comment l'accumulation de particules de ciment s'opère au sein du massif de sable. Les résultats démontrent une dépendance spatiale de la rétention de particule du sable injecté

Micromechanical analysis of kinematic hardening in natural clay

This paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress-strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material

Cyclic behavior of an over-consolidated remoulded clay

International audienc

Equations of pressuremeter curve with an elastic strain-softening plastic model

International audienceWe propose analytical expressions of the pressuremeter curve that generalise previous equations found in the literature. We consider a linear elastic plastic model with strain-softening, assuming a Mohr-Coulomb yield surface. The softening behaviour affects either the cohesion or the friction angle. Three parameters are required to describe the softening behaviour. We finally show the effect of each of these three parameters on the pressuremeter curve

Dilating behavior of overconsolidated clay

International audienceThe object of this study was to understand and characterize dilatancy in clay in relation to the overconsolidation ratio. This phenomenon was investigated along a large range of loading paths, with strong emphasis placed on constant mean stress paths given that it was possible to measure the volumetric strain created by the sole deviatoric stress. Triaxial tests performed on remolded clay (Kaolinite P300) allowed us to determine three different types of behaviour for specimen submitted to a deviatoric stress: no volume change, dilatancy and contraction. In the (p', q) plane these domains are limited by the maximum strength envelope zeta, which coincides with the perfect plasticity line M for OCRs < 2. The experimental results were then compared to plastic flow theories used in the Cam Clay model and in Rowe's dilatancy theory. Finally, by measuring the plastic strain increment vectors along different stress paths in the (p', q) plane, we demonstrated that the uniqueness hypothesis of the plastic potential is not valid. The results could be explained by using two plastic strain mechanisms: a deviatoric one and an isotropic one

UN MODELE DE COMPORTEMENT POUR SOLS VIERGES ET INJECTES

The mechanical behaviors of both uncemented and grouted sands show somecommon features, in particular non linearity. A straightforward constitutive model with only sevenparameters allows to simulate this non linearity, as well as the contracting – dilating volumetricbehavior through an original plastic potential. Some computations are finally presented.Le comportement mécanique des sables vierges et injectés par du coulis montre descaractéristiques communes, en particulier un comportement non linéaire. Un modèle decomportement simple à sept paramètres permet de décrire cette non linéarité, ainsi que lecomportement volumique contractant – dilatant au travers d’une fonction potentiel plastiqueoriginale. Quelques calculs de validation sont finalement présentés