International audienceA comparison of the behavior of uncemented and grouted sands is presented. Four sands Fontainebleau sand and three types of alluvial deposits of the Seine River were tested. Specimens of grouted sands were prepared in the laboratory by injection of very fine cement or mineral grouts. An initial series of unconfined uniaxial compression tests and tensile tests was performed to highlight the effect of some key factors mainly the cement-to-water ratio of the grout and the relative density of the granular skeleton on the strength of the grouted sands. Subsequent triaxial tests showed that when a soil is impregnated by either a very fine cement grout or a mineral grout, both stiffness secant stiffness or small-strain stiffness and strength of the soil improve. Similar trends were observed for the behavior of both uncemented and grouted sands. The behavior of grouted sands can be roughly reproduced by applying a linear elastic, perfectly plastic model with a nonassociated Mohr–Coulomb yield criterion whose parameters can be easily determined. Finally, preliminary recommendations are proposed relative to improvements ratios of the parameters of this simple constitutive model that is still commonly used in geotechnical engineering

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L'amélioration des propriétés mécaniques d'un sol par injection d'un coulis de nouvelle génération peut être quantifiée soit par des essais de laboratoire, soit par des essais in situ. Il a été déduit des essais de laboratoire qu'un modèle de comportement élastique linéaire avec un critère de plasticité non associé de Mohr-Coulomb permet de donner une approximation du comportement mécanique des sols injectés. On propose d'identifier les paramètres de ce modèle par analyse inverse d'essais pressiométriques. La procédure est basée sur l'expression analytique de la courbe pressiométrique donnée par (Yu et Houlsby, 1991) et un algorithme d'optimisation de Newton-Gauss. Les résultats sont comparés avec les paramètres déduits des essais triaxiaux en laboratoire. ABSTRACT. The improvement of the mechanical properties of a soil by injection of a new generation grout can be assessed either by laboratory tests or by field tests. It has been deduced from laboratory tests that a linear elastic -perfectly plastic model with a non associated Mohr-Coulomb failure criterion enables to roughly reproduce the mechanical behaviour of grouted sands. We propose in this paper to identify the parameters of this model by inverse analysis of pressuremeter tests. The procedure is based on the analytical expression of the pressuremeter curve given by (Yu and Houlsby, 1991) and a Newton-Gauss optimization algorithm. The results are then compared with the values of the parameters determined in the laboratory. MOTS-CLÉS : analyse inverse, essais pressiométriques, sols injectés.