2441
Column Supported Embankments for Transportation Infrastructures: Influence of
Column Stiffness, Consolidation Effects and Cyclic Loading
Remblais sur sols renforcés avec de colonnes ballastées pour les infrastructures de transport:
Influence de la rigidité des colonnes, des effets de consolidation et du chargement cyclique
Carvajal E., Vukotić G.
Kellerterra S.L., Madrid, Spain
Sagaseta C.
University of Cantabria, Santander, Spain
Wehr W.
Keller Holding GmbH, Offenbach, Germany
ABSTRACT: Ground improvement methods based on column-type elements are analyzed regarding the influence of the column
properties on serviceability and safety of the Column Supported Embankments (CSE). Particularly, treatments made by rigid
inclusions are analyzed and compared with stone columns. Stiffness of column-type elements determines the design and risks
involved. Rigid inclusions are analyzed according to the recent French national project ASIRI. In the case of these elements, a
considerable mobilization of negative skin friction and punching effects governs their behavior in the Ultimate Limit State, which
represents a non-ductile mechanism of failure. Whereas stone columns present a ductile behavior determined in the domain of
Serviceability Limit State (SLS). It is pointed out, that possible damages on CSE systems may extend settlement stabilization due to
the consolidation process, if no drainage elements are adopted. It is also noted that risks related to rigid columns in the SLS under
cyclic loading, may be decisive in the design of CSE composed by low-heights embankments. Briefly, it could be stated that rigid
inclusions present higher risks, increasingly when their diameters are smaller than 30 cm.
RÉSUMÉ : On analyse les méthodes d'amélioration des sols avec des colonnes pour la fondation des remblais sur sols mous. En
particulier, on analyse les inclusions rigides selon les recommandations du récent projet national français ASIRI, et on présente la
comparaison avec des colonnes ballastées. La rigidité de la colonne détermine la conception et les risques associés. Dans le cas des
inclusions rigides, une mobilisation considérable du frottement négatif et la portance résultante gouvernent leur comportement dans
l'état limite ultime, ce qui représente un mécanisme non-ductile de rupture. Au contraire, les colonnes ballastées présentent un
comportement ductile déterminée dans le domaine de l'état limite de service. Il a été observé que les risques de colonnes rigides dans
les ELS peut être retardés à moins que on installe quelques éléments de drainage. On a remarqué aussi que les risques associés aux
inclusions rigides soumises aux chargements cycliques peuvent être décisives pour remblais de faible hauteur. Ainsi, les inclusions
rigides présentent des risques plus élevés, de plus en plus lorsque leur diamètre est plus petit que 30 cm.
KEYWORDS: Load Transfer Platform, geosynthetic, embankment, rigid inclusion, stone columns, risk, stiffness, arching effect
1
INTRODUCTION
Column Supported Embankments (CSE) represent an
innovative solution for transport infrastructure over soft soils, in
order to reduce execution time and general earthworks. Hence,
the use of low-height embankments based on column-type
elements tends to be preferred, whenever possible, instead of
direct soil replacement or preloading with or without vertical
drains. Recently, the use of CSE is increasing, and consequently
growing interest in developing reliable and unified criteria for
their design and construction is observed.
However, due to the possibility of application of a wide
range of ground improvement techniques, further risk
assessment has to be done. Risks and reliability related to CSE
could be largely analyzed considering the influence of column
stiffness in Ultimate and Serviceability Limit States.
Furthermore, column stiffness also affects consolidation process
and the system behavior against cyclic or dynamic loading, very
often decisive for safety and serviceability.
2
COLUMNS SUPPORTED EMBANKMENT SYSTEMS
2.1 Type of columns
Typical elements of CSE systems are shown in Figure 1.
Initially, reinforced piles with concrete cap were applied, in
order to absorb the largest load of embankment as possible. In
order to optimize the solution, ground improvement methods
have been increasingly used in the last years.
Ground improvement methods should intent not to take the
entire action by the supporting elements, but only the difference
between the required and existing bearing capacity without
improvement (Wehr et al. 2012). This is applicable to stone and
sand columns, which take important part of the foundation load,
and make the most of soil confinement to ensure its own
capacity. These two types of columns accelerate the
consolidation process and do not need any embedment to
transfer the loads to stiffer soil layers; thereby they can be
considered as authentic ground improvements.
On the other side, the columns made by the addition of
bonding agents, mortar or concrete into the ground, do not
accelerate consolidation. The improvement introduced by such
columns mainly consists of the load transfer to the stiffer layers
in the same way as piles, thus, to ensure their correct application
the largest embedment is frequently desired.
Embankment
End Bearing
Columns
Soft Soil
Soilwith
intermediate
Stiffness
FirmSoil
Geosynthetics
LoadTransfer
Platform (LTP)
Plane with
S = 0
H
C
Floating Columns
Pile cap
Figure 1. Elements of Column Supported Embankment Systems
