Parameters controlling stiffness and strength of artificially cemented soils

Abstract

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...

Influence of grain size and mineralogy on the porosity/cement ratio

“…The results of unconfined compression strength and maximum shear modulus presented in this paper showed that the best exponent to the fine sand fraction is 0?10, while for Osorio sand it is 1?0 (Consoli et al, 2012a), despite their close grain size distribution curves. Again, this can be explained by their different mineralogies, which result in different particle shapes.…”

“…According to Consoli et al (2012a), mineralogical analysis of this soil showed that the sand particles are predominantly quartz.…”

“…For this reason, it is simpler to use an index property that includes well-known parameters and which can represent a certain mixture. In fact, this ratio has proved to be very useful to predict the mechanical behaviour of artificially cemented soils, as has been demonstrated in terms of compression strength and stiffness (Consoli et al, 2012a), tensile strength (Consoli et al, 2011), stress-dilatancy (Consoli et al, 2012b), isotropic compression behaviour at high pressures (Rios et al, 2012), shearing behaviour (Rios et al, 2013) and fatigue tests (Viana da Fonseca et al, 2012a).…”

Heat-Induced Bonding of Sands

“…Natural cementing agents include calcium carbonate and precipitated salts (Mitchell and Soga 2005), whereas artificial cementation with Portland cement has been used for soil stabilization (PCA 2003). Numerous studies describe the role of cementation on small-strain dynamic properties (e.g., Baig et al 1997) and strength behavior (e.g., Clough et al 1981;Lade and Overton 1989;Consoli et al 2012) of sands. In general, the role of mineral-based cementation on strength and stiffness is stress-dependent.…”

“…The most common additive is Portland cement, and is typically incorporated in the soil by mixing (e.g., Consoli et al 2012). Recent work on bio-cementation relies on calcium carbonate deposited in the soil via bacterial action (DeJong et al 2010).…”