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Laboratory tests and numerical modeling for embankment foundation on soft chalky
silt using deep-mixing
Essais au laboratoire et modélisation numérique de la fondation d’un remblai sur un limon crayeux
mou des sols améliorés par malaxage en profondeur
Koch E., Szepesházi R.
Széchenyi István University, Győr, Hungary
ABSTRACT: The deep-mixing is nowadays world-wide accepted method as a ground treatment technology to improve the
permeability, strength and deformation properties of soils. Binders, such as lime or cement are mixed in-situ with the soil by rotating
mixing tools. The method is undergoing rapid development, particularly with regard to its range of applicability, cost effectiveness
and environmental advantages. The paper describes the results of laboratory tests on chalky silt samples mixed with cement of
different content. The influence of the different mixing parameters on the unconfined compression strength and deformation modulus
is shown and evaluated. Typical results of the laboratory tests were used in numerical modeling with PLAXIS 3D as input parameters
to study the behavior of a 4 m high embankment constructed on this soil improved by deep mixed columns with different spacing and
diameters. The parameters of the soil improvement technique were analyzed to study their influence on the settlement and the stability
of the embankment. The trends of the calculation outputs are shown and evaluated.
RÉSUMÉ : Pour l’amélioration de la pérméabilité, de la résistance et des caractéristiques de déformation des sols mous la malaxage
est considéré comme une technique courante, préconisée partout. La procédure consiste á malaxer, par rotation, les liants: la chaux
ou/et le ciment et le sol in-situ à l’aide de l’outil de malaxage par rotation. Grace á la diversité technique et aux possibilités
d’application de l’appareillage, ainsi que ses avantages économiques, tout en respectant les intéréts de l’environnement, cette
technologie approuve un développement continu même dans nos jours. L’étude a pour but de faire connaitre las résultats des essais au
laboratoire réalisés sur des éprauvettes prélevées du sol traité avec les liants: la chaux et le ciment, dont la teneur par éprouvettes était
variable. L’analyse des résultats de ces essais a mis à l’évidence l’influence des divers paramétres de malaxage sur la résistance à la
compression simple et sur le modul de déformation du sol traité. Ces résultats nous ont rendu possible d’appliquer le programme
d’éléments finis PLAXIS 3D, en vue d’étudiar une digue de 4m de hauteur, reposant sur des colonnes de sol traité, ayant une
disposition variable et des diamétres différents. Le but de cette étude était de fournir un moyen de calcul qui permat le suivi des
tassements et la stabilité de la digue, en fonction de la variation des paramétres de malaxage.
KEYWORDS: deep mixing, laboratory test, numerical modeling
1 INTRODUCTION
Road and railway embankments have often been constructed on
soft, saturated, organic subsoil. In the future this type of
construction is suspected to increase, due to environmental and
land management considerations.
The low strength and the high
compressibility together with the low permeability and the high
creep potential result in stability problems, extremely large
settlements with prolonged consolidation times, and long term
secondary compression. One of the solutions to avoid these
problems is deep-mixing stabilization of the subsoil.
The development of deep-mixing was started in Sweden and
Japan in the late 1960’s with the application of a single mixing
tool to produce column-type elements (Figure 1.). Since then,
new technologies using different mixing tools or binder types
have been introduced. Lately, another technology; mass
stabilization, based on Finnish research is gaining acceptance,
where the whole soil mass is treated normally to a depths of 2 to
4 m (Figure 2.).
The goal of deep-mixing is to improve the soil
characteristics, e.g. increase the shear strength and/or reduce the
compressibility, by mixing the soil with some type of chemical
additives that react with the soil. The improvement occurs due
to ion exchange at the clay surface, bonding of soil particles
and/or filling of voids by chemical reaction products.
Mass stabilization is preferred if the subsoil is very poor e.g.
peat, organic clay or soft clay deposits, and the thickness of the
mass to treat is less than 5 m, the height of the embankment is
low, and the main purpose of the treatment is to increase
stability (Allu Stabilisation System). If the main purpose is to
reduce settlements and the weak soil is thicker than 5 m;
approximately 60 cm diameter single columns are used. With
this technology the treated depths can be increased up to 40 m
(Moseley and Kirsch, 2004, Logar, 2012).
Recently, the use of deep-mixing technology has been
planned on several Hungarian railway projects. The „Sárrét”
railway line rehabilitation is one of these projects; the railroad
crosses an area where the subsoil is soft chalky silt. Both deep-
mixing technologies could be applied on this site. This paper
describes the preparation of their use at this project. Firstly, the
mechanical properties of the improved soil were investigated in
the laboratory, then, the effectiveness of the technology as
embankment foundation was evaluated with the PLAXIS 3D
finite element program using the laboratory test results.
Figure 1.
Column-type deep-mixing
Figure 2.
Mass stabilization
