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Selected problems connected with the use of the jet grouting technique
Certains problèmes liés à l’application de la technologie d’injection de jet
Bzówka J., Juzwa A., Wanik L.
The Silesian University of Technology, Gliwice, Poland
ABSTRACT: The paper presents selected problems connected with the use of the jet grouting technique. It is one of the most popular
methods for subsoil strengthening, enhancement for existing foundation, vertical and horizontal waterproof cut-off walls. Columns
made using this method feature a high bearing capacity (very high friction on the shaft). The newest achievements of the numerical
explanation of the interaction between jet grouting columns and subsoil are presented in the paper. The created models will be used to
verify engineering methods of jet grouting columns dimensioning. Computational analyses are conducted using software based on the
finite element method (Z_Soil).
The computational model describes the interaction between a group of jet grouting columns and soil. The main element of this
analysis consists of selection and calibration of computational model of the "group of jet grouting columns – subsoil" interaction.
The model space is divided into three zones: columns, soil and the contact layer formed between the columns and the soil massif.
The computational model allows for a plastic character of deformation under load and especially for a non-linearity of contact zone.
The description of shape of a shaft surface of jet grouting columns is very difficult, so the fractal theory is used to describe this shape.
Fractal and box dimensions are used to estimate the irregular surface. This model allows a precise selection of formation parameters,
like the injection rod pull out velocity and number of rotations, injection pressure and the water/cement ratio, which define the
geometry of jet grouting columns.
RÉSUMÉ : Cet article présente quelques problèmes liés à l’utilisation de la technique d’amélioration des sols : le jet grouting. Cette
technique est une de méthodes les plus utilisées pour renforcer le sous-sol, les fondations déjà existantes et on s’en sert aussi comme
les parois verticales et horisontales étanches (imperméables à l’eau). Les colonnes réalisées par cette méthode se caractérisent par la
grande capacité portante (coefficient de frottement très élevé sur la surface latérale). Dans cet article, on présente les découvertes les
plus récentes liées aux modélisations numériques de l’interaction entre les colonnes de jet et du sol. Les modèles développés seront
utilisés pour vérifier les méthodes d’ingénierie et pour dimensionner les colonnes de jet grouting. Les analyses numériques sont
effectuées par les programmes basés sur la méthodes des éléments finis (Z_Soil).
Le modèle de calcul décrit l’interaction entre un groupe de colonnes de jet grouting et le sol. L’apport le plus important de cette
analyse réside dans le choix et le calage du modèle de calcul pour l’interaction « groupe de colonnes de jet grouting – sol". L’espace
du modèle est divisé en trois zones: colonnes, sol et couche de contact formée entre les colonnes et le massif du sol. Le modèle de
calcul permet d’avoir des déformations plastiques et en particulier de déformation non-linéaire de la zone de contact.
La description de la forme des surfaces latérales de ces colonnes est extrêmement difficile, alors on a introduit la théorie de fractales
pour la décrire. Les dimensions de type fractal et de boîte, sont utilisées pour estimer la surface latérale irrégulière des colonnes. Ce
modèle permet de choisir d’une manière précise des paramètres de formation des colonnes tels que: vitesses - de rotation et
d’avancement en descente de la tige de forage, le nombre de rotation, la pression de coulis injecté, rapport eau/ciment, qui définissent
la géométrie des colonnes de jet grouting.
KEYWORDS: jet grouting technique, interaction between columns and subsoil, shape and dimensions of jet grouting column.
1 JET GROUTIMG COLUMNS INTERACTION
WITH SUBSOIL
The jet grouting method is frequently used in the engineering
practice. It may be used for nearly all types of soils, both natural
and man-made. It does not work only for a subsoil built of
organic soils. The method consists in a high-pressure injection
into the subsoil of an injectant stream (most often being a
cement grout), which cuts and disintegrates the soil body,
forming – after binding with soil fractions – a petrified soil-
cement composite of any geometrical form, e.g. close to a
column cylinder shape. This solution – because of the speed of
performance and very good parameters of subsoil strengthening
– is frequently used to strengthen a weak subsoil under high
transport embankments or bridge abutments (Bzówka 2009;
Juzwa 2012b; Modoni and Bzówka 2012).
To explain the interaction between the jet grouting columns
and the strengthened subsoil it is suggested to apply numerical
methods and to build models reflecting the operation of a single
column and the interaction of jet grouting columns group in
transferring the load to deeper soil layers. A solution is sought,
which would allow optimising design solutions of jet grouting
columns, would ensure safety of a structure designed this way
and at the same time would contribute to the works costs
cutting. The authors emphasise especially as precise as possible
reflection of real conditions, existing on a site.
A single column and a group of columns are the subject of
numerical and in situ analysis. A single column is an idealised
form, seldom existing in practice. However, the analysis of its
behaviour is a starting point to make models more realistic and
built of a group of columns. For the needs of analysis of
interactions occurring between jet grouting columns
strengthening a weak subsoil and the soil body numerical
models were constructed, considering the environment division
into three material zones: the soil-cement material of jet
grouting columns – the contact layer – the subsoil (Bzówka
2009, 2010).
Because of a physical inhomogeneity and of a complicated
geometrical arrangement the finite element method was used to
