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Hybrid Application of Deep Mixing Columns Combined with Walls as a Soft Ground
Improvement Method Under Embankments
Application hybride de la méthode de « Deep Mixing » sur des colonnes combinées à des murs en
tant que méthode d’amélioration des sols mous sous remblais
Matsui H., Ishii H., Horikoshi K.
Technology Center, Taisei Corporation, Yokohama, JAPAN
ABSTRACT: In this paper, we introduce theconcepts and general functions of a hybrid application of deep mixing columns combined
with walls. This newmethod for improving the soft ground under embankments helps control ground deformation. We brieflydescribe
a case in which the method was applied under an embankment 7m in height. The method effectively restricted the induced
deformation of the ground surface to a target level, not only under the embankment but also adjacent to the embankment toes. Two-
dimensional finite element analysis was adopted to the case and foundeffective for simulating the performance. Also proposed is a
design flow for the new methodto efficiently determine the best arrangement of deep mixing columns and walls. Numerical
parametric studies were carried out to compare the new method with conventional methods.
RÉSUMÉ : Dans cet article, nous présentons les concepts et les fonctions générales de l’application hybride de méthode de « Deep
Mixing » sur des colonnes combinées à des murs. Cette nouvelle méthode d’amélioration de sols mous sous remblais aide à contrôler
la déformation du terrain. Nous décrivons brièvement un cas dans lequel la méthode a été appliquée sous un remblai d’une hauteur de
7 m. La méthode a permis de limiter efficacement la déformation induite de la surface du sol à un niveau cible, non seulement sous le
remblai, mais aussi dans les zones adjacentes aux pieds de talus. Une analyse par éléments finis en deux dimensions a été appliquée à
ce cas et s’est avérée efficace pour simuler les performances. Une méthode d’optimisation est également proposée en vue de
déterminer de manière efficiente la meilleure disposition des colonnes et des murs. Des études paramétriques numériques ont été
menées pour comparer la nouvelle méthode avec les méthodes classiques.
KEYWORDS:soft ground improvement method, finite element analysis, deep mixing method
1 INTRODUCTION
Deep mixing methods have been widely used in Japan for the
foundation systems of embankments constructed on soft clayey
ground, and various low improvement ratio arrangements have
been proposed (Miki and Nozu 2004, Ishikura et al. 2009, Miki
et al. 2011). Typical of recent applications is to achieve limited
soil improvement— around 10-20%—through an arrangement
of soil improvement columns. This reduces the volume of soil
that must be improved and limits the ground settlement under
the embankments. Moreover, embankment construction in
urban areas requires strict control of ground deformation,
especially in the areas adjacent to the embankment toes.
The authors propose a new hybrid application of deep
mixing columns combined with walls (Tsutsumi et al. 2009) as
a method of improving the soft ground under embankments to
control ground deformation. In this paper, the concepts and
general functions of the method are introduced. The paper then
describes a case in which the method was applied under a tall
embankment 7 m in height. Two-dimensional finite element
analysis was adopted to simulate the performance. Also
proposed is a design flow for the new method that efficiently
determines the best arrangement of deep mixing columns and
walls. Finally, numerical parametric studies were carried out to
compare the new method with conventional methods.
2 CONCEPTS AND GENERAL FUNCTIONS OF A
HYBRID APPLICATION OF DEEP MIXING COLUMNS
COMBINED WITH WALLS
The basic concept of this method is to place deep mixing walls
in the ground directly under the embankment slopes, which
Ac1- 2
As2
Ac2- 2
Dvc
Ac2- 3
12.0m
7.0m
37.2m
1:1.8
6.7m
10.0m
36.2m
1.9m
4.5m
Dvs
9.8m
5.2m
21.2m
39.2m
Inside piles
Outside piles
Walls
Section view
37.2m
2.5m 2.5m
1.76m 2.6m
2.6m 1.76m
2.81@8=22.48m
16.48m
3.0m 3.0m
3.0m 3.0m
Plain view
Figure 1.Geological profile and arrangement of the deep mixing
columns and walls at theconstruction site where the method was applied.
