321
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Experimental analysis of the mechanical properties of artificially cemented soils
and their evolution in time
Analyse expérimentale des propriétés mécaniques des sols cimentés artificiellement et leur
évolution dans les temps
Consoli N.C., Fonini A., Maghous S., Schnaid F.
Engineering School, Federal University of Rio Grande do Sul, Brazil
Viana da Fonseca A.
Faculty of Engineering, University of Porto, Portugal
ABSTRACT: In view of the new challenges in the field of foundation design induced by the necessity to resorting to reinforced soils,
the evaluation of behavior parameters of soils and soil-binder mixes by means of laboratory tests has become an important task. In
this context, experimental characterization of soil-cement mixtures in terms of elastic stiffness and its evolution in time has been
carried out. Both shear and oedometric moduli at infinitesimal strains have been measured through the technique of wave propagation
along cylindrical specimens of 70 mm and 140 mm in diameter. The analyzed specimens were molded with quartzitic sand and fast
curing cement using four relative densities of sand and five cement contents. Several loading times (i.e., times when the specimens are
subjected to wave propagation), ranging between the first and seventh curing day, were considered. The results have given evidence
of a significant increase in the magnitude of the stiffness properties as the curing process continues. When compared to uncemented
sand specimens with similar porosities, increases of about 360% to 6300% due to cement insertion are observed for the shear
modulus, and of 900% to 6700% for the oedometric modulus. In addition, the analysis showed that the higher is the amount of added
cement used in the mixture, the higher the ratio of initial modulus to final one.
RÉSUMÉ : Compte tenus des nouveaux défis induits, dans le domaine du dimensionnement de fondations, par la nécessité de recourir
à des sols renforcés, l'évaluation des paramètres définissent le comportement des sols ainsi que des mélanges sol-liant au moyen de
tests de laboratoire est devenue une tâche importante. Dans ce contexte, la caractérisation expérimentale des sols cimentés en termes
de rigidité élastique et son évolution dans le temps a été réalisée. Les deux modules de cisaillement et oedométrique sous
déformations infinitésimales ont été mesurées par la technique de propagation d’ondes le long d’échantillons cylindriques de 70 mm
et 140 mmde diamètre. Les échantillons analysés ont été moulés utilisant du sable et du ciment à prise rapide en considérant quatre
densités relatives de sable et cinq pourcentages de teneur en ciment. Plusieurs temps de chargement (c'est à dire, les instants où les
échantillons sont soumis à la propagation d’ondes), compris entre le premier jour et le septième jours en termes de temps de prise, ont
été considérés. Les résultats ont montré une augmentation significative de la rigidité au fur et à mesure que le processus de prise
continue. Selon la teneur en ciment, des augmentations allant de 360% à 6300% sont observées pour le module de cisaillement, et de
900% à 6700% pour le module oedométrique. En outre, l'analyse a montré que le rapport entre module initial et le module final est
d’autant plus élevé que la teneur en ciment du mélange est élevée.
KEYWORDS: ground improvement, artificially cemented soils, shear moduli, curing time period.
1 INTRODUCTION
Soil-cement is a geo-composite formed by highly compacted
mixture of soil, Portland cement, and water. As the cement
hydrates, the mixture gains strength, stiffness and improves the
engineering properties of the raw soil. The major variables that
control the properties and characteristics of soil-cement
mixtures are the type of soil, the proportion of cement in the
mix, the degree of compaction and curing time period. It is
possible, simply by varying the cement content and/or porosity
of mixture, to produce soil-cement that ranges from a basic
modification of the compacted soil to fully hardened soil-
cement that is strong, stiff and durable. The soil-cement
technique has been used successfully in pavement base layers,
slope protection for earth dams, as a base layer to shallow
foundations and to prevent sand liquefaction (Consoli
et al
.
2012a).
The unconfined compression test has been used as the most
convenient means to investigate the effect of different variables
on the soil-cement strength and to carry out dosage
methodologies. The first rational dosage methodology for sand-
cement was developed by Consoli
et al
. (2009) considering the
porosity/cement ratio (
/C
iv
), defined by the porosity of the
compacted mixture divided by the volumetric cement content
(volume of cement divided by total specimen volume), as an
appropriate parameter to evaluate the unconfined compressive
strength (q
u
) of the sand-cement mixture. Consoli
et al
. (2011),
has shown that compressive strength increases with curing time
period in artificially cemented soils and that there is a unique
function controlling strength with curing time period and that
such relation is a function of porosity and cement content.
However, nothing is known regarding stiffness behavior with
time. So, present study aims at fulfilling a breach of knowledge
at quantifying the influence of the curing time period, the
amount of cement and the porosity on the initial shear and
oedometric moduli of an artificially cemented sand, as well as
searching for a unique relationship linking both moduli (G
o
and
M
o
) with porosity/cement ratio (η/C
iv
) and curing period (t). The
main contribution of present work is showing the existence of a
direct relationship between G
o
, M
o
and η/C
iv
for all studied
curing time periods and only scalars differ regarding the effect
of curing time. So, for the sand-cement studied, unique
relationships were reached linking G
o
and M
o
with
, C
iv
and
curing time (
t
).
2 EXPERIMENTAL PROGRAM
The experimental program has been carried out in two parts.
First, the soil was characterized. Then a number of
