1191
Soil chart, new evaluation method of the swelling-shrinkage potential, applied to the
Bahlui’s clay stabilized with cement
.
L’empreinte du sol, une nouvelle méthode d’évaluation du potentiel de gonflement, appliqué
e à
l’argile de Bahlui stabilisée avec
du ciment.
Stanciu A., Aniculaesi M., Lungu I.
The
“Gheorghe Asachi”
Technical University
from Iaşi, România
ABSTRACT: Clays, in both their remoulded and natural state, can present a certain swelling-shrinkage potential. A specific
behaviour characterized by extreme swelling and shrinkage values is exhibited by the colloidal clays such as L
ondon’s, Swellhaven’s,
Cambridge’s clay. Bahlui’s clay from Romania fits the same domain, based on the authors’ proper tests. The indirect evaluation of the
Bahlui’s clay swelling potential, besides using the classical methods has been performed also based
its own
“
chart
”
. By consequence,
the variation of the swelling potential was analyzed in this paper, based on the indirect methods (Seed 1962, Van der Merwe 1964)
and as novelty, also based on the activity coefficient (C
A
) (Stanciu et al. 2011) for the Ba
hlui’s clay both
in its natural state and mixed
with Portland cement and respectively with ecologic cement. The laboratory test results indicated the decrease of the swell-shrinkage
potential presenting reduced values of C
A
= 0.58 ÷ 0.18.
RÉSUMÉ: Les argiles, à la fois naturelles et restructurés, disposent d'un certain potentiel de retrait-gonflement. Un comportement
spécifique des argiles colloïdales telles que celles de Londres, de Swellhaven, de Cambridge, etc. est caractérisé par des valeurs
extrêmes du gonflement et du retrait. Dans la même catégorie, basée sur des mesures propres, on peut aussi encadrer l'argile de
Bahlui, de Roumanie.
L’évaluation indirecte
du potentiel de
gonflement de l’argile de Bahlui
, avec des méthodes traditionnelles, a été
effectuée sur la base de
son “empreinte”
. Dans cet article, basé sur des méthodes indirectes (Seed 1962, Van der Merwe 1964) et
comme nouveauté, basé sur l'empreinte des sols (Stanciu et al. 2011), nous avonsanalysé la variation du potentiel de gonflement de
l'argile de Bahlui, à la fois naturelle et mélangée avec de ciment de Portland et avec du ciment écologique. Les résultats ont indiqué
une diminution du potentiel de retrait-gonflement mis en évidence par une diminution des valeurs C
A
= 0.58 ÷ 0.18.
KEYWORDS: expansive clay, swell potential, soil chart, activity coefficient, stabilization with ecologic cement
1 INTRODUCTION
The swell potential evaluation for a certain soil has a very
significant importance in the mitigation and limitation of
potential structural damages of future constructions founded on
active soils.
Among soils with special behaviour, the expansive ones take
an important place due to their volume variations determined by
moisture variations. These volume variations are reflected in
soil differential swells/shrinkages due to soil uneven drying or
wetting processes developed both beneath foundations and near
them. Various solutions such as chemical stabilization
techniques have been developed with more or less satisfactory
results to limit the potential degradations of constructions on
these soils (Gueddouda et al. 2011). The objective of the
expansive soils stabilization is to reduce the swell potential
within acceptable limits. The expansive soils stabilization with
Portland cement reduces the swell potential as well as increases
their mechanical strength. The substitution of the Portland
cement in soil stabilization with 50% eco-cement has lead to
promising results. The substitution solution of the Portland
cement with eco-cement has the purpose of reducing the
negative environmental impact, especially due to the
manufacturing process of the Portland cement. The direct
determination of the physical parameters that characterize the
expansive soil behaviour such as the swell pressure, free
swelling, volumetric shrinkage and of other properties takes a
long time and is costly, due to the rather complex laboratory
works. By consequence, it is necessary to develop and use
simple and fast estimation methods for the swell potential.
There is an important number of empirical methods to estimate
the swell potential available in publications. It is generally
considered that the swell potential is directly correlated with:
the Atterberg limits (w
P
, w
L
), he colloidal clay fraction (A
2µ
),
the shrinkage limit (w
s
), the dry density (
d
), etc. These
correlations are currently semi-empirical and based on statistics
(Yilmaz 2006).
2 EVALUATION METHODS OF THE SWELL
POTENTIAL
There are many methods to determine the parameters that
characterize the swell-shrinkage of clays. The most utilized
parameter to estimate the swell-shrinkage potential is the
plasticity index (I
P
). It is well known that the swell-shrinkage
potential is dependent on the granulometric composition of the
investigated clay (A
2µ
) as well as on the specific available
surface for the interface phenomena display (Stanciu 2006).
Numerous attempts have been made to find an acceptable
system to evaluate the swell potential. The most utilized
systems for the indirect evaluation and classification of the
swell potential are based on the graphical correlation between
two or more geotechnical indices (Van Der Merwe
–
Figure
1and respectively Casagrande
–
Figure 2).
The principal physical properties of the representative clays
investigated in this research are presented in Table 1.
The swell potential has been estimated based on these
properties reflected by the indices (A
2µ
/w
L
/I
P
) and their
representation on the diagrams in Figures 1 and 2. The swell
potential of the investigated clays, established using the Van
Der Merwe
’s and
respectively Casagrande
’s diagrams is
presented in Table 2. The domains of the swell potential, from
very high to low, within these two diagrams, have generally a
conventional representation on a (0-1) or (0-100) scale. This
