The treatment of soils with cement is an attractive technique when a project requires improvement of the local soil for the construction of subgrades for rail tracks, for roads, as a support layer for shallow foundations, and to prevent sand liquefaction. This paper advances understanding of the key parameters for the control of strength and stiffness of cemented soils by testing two soils with different gradings and quantifying the influence of porosity/cement ratio on both initial shear modulus (G 0 ) and unconfined compressive strength (q u ). It is shown that the porosity/cement ratio is an appropriate parameter to assess both the initial stiffness and the unconfined compressive strength of the soil-cement mixtures studied. Each soil matrix has a unique relationship for G 0 /q u against adjusted porosity/cement ratio, linking initial stiffness and strength.KEYWORDS: compaction; ground improvement; laboratory tests; sands; soil stabilisation; stiffness Le traitement des sols au ciment est une technique attrayante pour les projets nécessitant un renforcement du sol pour la construction d'assiettes pour voies ferrées et chaussées, comme couche d'appui pour fondations peu profondes, et pour la prévention de la liquéfaction du sable. La présente communication renforce les connaissances sur les principaux paramètres pour la régulation de la résistance et de la rigidité des sols cimentés, en soumettant à des essais deux sols de différentes granulométries, et en quantifiant l'influence du ratio porosité / ciment à la fois sur le module de cisaillement initial (G 0 ) et sur la résistance à la compression simple (q u ). On y montre que le ratio porosité /ciment est un paramètre approprié pour évaluer à la fois la rigidité initiale et la résistance à la compression simple des mélanges solciment étudiés. Chaque matrice de sol présente un G 0 /q u unique en fonction du ratio porosité /ciment, mettant en rapport la rigidité initiale et la résistance. INTRODUCTIONIn highway and other shallow constructions, cement is often used to improve local soils, for example to make them suitable as subgrades, formations and foundation backfill (e.g. Rattley et al., 2008;Consoli et al., 2009). Previous studies of soil-cement (Moore et al., 1970;Clough et al., 1981;Consoli et al., 2010Consoli et al., , 2011 have shown that its behaviour is complex, and affected by many factors, such as the physical-chemical properties of the soil, the amount of cement, and the porosity and moisture content at the time of compaction. Consoli et al. (2007) were the first to establish a unique dosage methodology based on rational criteria where the porosity/cement ratio plays a fundamental role in assessment of the target unconfined compressive strength.This study shows the influence of the amount of cement and the porosity on the initial shear modulus (G 0 ) and unconfined compressive strength (q u ) of two different soils: uniform Osorio sand and very well-graded Porto silty sand. EXPERIMENTAL PROGRAMME MaterialsThe results of characterisation tests on t...

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