849
Failure Modes for Geosynthetic Reinforced Column Supported (GRCS)
Embankments
Les modes de rupture de massifs renforcés par colonnes sol-ciment et géosynthétique (GRCS)
supportant des remblais
Yapage N.N.S., Liyanapathirana D.S., Leo C.J.
School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797,
Penrith, NSW 2751, Australia
ABSTRACT: Deep cement mixed columns are widely used to support highway embankments constructed on soft compressible
ground. Current design procedures for these embankments consider the sliding failure for external stability and the shear failure of
deep cement mixed (DCM) columns for internal stability. Other failure modes such as collapse failure, slip circle failure, punching
shear failure (overall or local) and bending failure of DCM columns are also significant for column supported embankments.
However, still there are uncertainties in identifying the critical failure modes for these embankments. Hence, this paper investigates
some failure modes for Geosynthetic reinforced column supported (GRCS) embankments using the finite element method. The
embankment and traffic loads are gradually increased to bring the embankment to the verge of failure. Bending failure of DCM
columns and subsequent shear failure for internal stability, local punching failure, overall punching failure and excessive total
settlement failure are identified from the finite element analysis results and discussed in detail.
RÉSUMÉ : Les colonnes profondes réalisées par mélange sol-ciment sont très utilisées pour soutenir des remblais de route construits
sur sol mou compressible . Les procédures actuelles de conception pour ces remblais considèrent la rupture par glissement pour la
stabilité externe et la rupture par cisaillement des colonnes (DCM) sol- ciment pour la stabilité interne. D'autres modes de rupture tels
que l'effondrement, le glissement circulaire, le poinçonnement de cisaillement (global ou local) et la flexion des colonnes de DCM
sont également significatifs pour les remblais soutenus par colonnes. Cependant, il reste des incertitudes en identifiant les modes de
rupture critiques pour ces remblais. Par conséquent, cette communication étudie quelques modes de rupture pour des remblais de
GRCS par la méthode des éléments finis. Le remblai et les charges de la circulation sont graduellement augmentés pour s’approcher
de la rupture.
KEYWORDS: deep cement mixed columns, embankment, finite element method, strain softening, progressive failure.
1. INTRODUCTION
Geosynthetic
reinforced
column
supported
(GRCS)
embankments are widely used in infrastructure development
projects in urban and metropolitan areas in most countries. The
design process should critically consider the behavior of single
columns as well as the global embankment system. A number of
possible failure mechanisms for these embankments are
discussed in the literature. Numerous research efforts have been
expended to understand the failure modes for GRCS
embankments using centrifuge modelling, numerical modelling
and case histories of field performance (Broms 1999, Kitazume
and Maruyama 2007) and thereby to develop analysis and
design procedures incorporating possible failure modes. Current
design procedures for these embankments only consider the
sliding failure for external stability and the shear failure of
DCM columns for internal stability (CDIT 2002, EuroSoilStab
2002). It is recently found that other failure modes such as
collapse failure, slip circle failure, punching shear failure
around column heads (overall or local), and bending failure of
DCM columns are also significant for GRCS embankments
(Kivelo 1998, Broms 2004, Kitazume and Mauyama 2007).
There are many case histories demonstrating that these
foundation systems are likely to have slope stability problems,
although they significantly improve the bearing capacity and
reduce the excessive settlements inherent in soft ground.
Progressive failure has been identified by Broms (2004) and
bending failure has been observed by Terashi (2003).
The main focus of this paper is to identify the critical failure
modes related to GRCS embankments. In this finite element
analysis, the bending failure of individual columns and
subsequent development of a slip surface shear failure are
investigated. These failure modes are critical for internal
stability of GRCS embankments. In addition, local and overall
punching failure modes relevant for the stability of fill layers
are investigated.
2 DESCRIPTION OF THE NUMERICAL MODEL AND
MODEL PARAMETERS
The geometry of the problem used in this study is shown in
Figure 1. The embankment is supported by DCM columns with
1 m diameter and 2.5 m center to center column spacing in each
direction. The model parameters used for the analysis are given
in Table 1. The embankment is constructed in stages expending
0.5 m fill layer followed by five 1 m thick layers. Each layer is
applied over a period of one month and the waiting period after
each fill layer is 0.5 months. Finally the traffic load is applied.
Failure Mode for Geosynthetic Reinforced Column Supported (GRCS)
Embankments
Les modes rupture de massifs renforcés par colonnes sol-ciment et géosynthétique (GRCS)
supportant des remblais
N.N.S. Yapage, D.S. Liyanapathirana and C.J. Leo
School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797,
Penrith, NSW 2751, Australia
ABSTRACT: De p cement mixed colum s are wide y used to support highway embankments constructed on soft com ressible
ground. C rent design procedures for these embankments consider the sliding failure or external stability and th shear failur of
deep cemen mix d (DCM) columns for internal stability. Other failure modes such as coll pse failure, slip circle f ilure, punching
hear
(overall r local) and bending failure of DCM columns are also significant for column supported e bankments.
However, still there are uncertainties in ident fying the critical failur odes for these mbankments. H nce, th s paper investigates
s me failure mod s for Geosynthetic reinforc d column supp rted (GRCS) embankments using the fin te lement m thod. The
embankment and t affic loads a e gradually increased to br ng the embankment to the verge of failure. Bending failure of DCM
columns and subsequent shear failure for internal stability, local punching failure, overall punching failure and excessive total
settlement failure are identified from the finite element analysis results and discussed in detail.
RÉSUMÉ : Les colonnes p ofonde realisées par méla g sol-ciment sont très utilisées pour soutenir des remblais route construit
s r sol mou compressib e . Les procédures actuelles de conception pour ces remblais c nsidèrent la rupture par glissem nt pour la
tabilité exter e et la rup ure par cisaille ent des colonnes (DCM) sol- ciment pour la abilité interne. D'autres modes de ruptur tels
q e l'effondrement, le gliss ent circulaire, le poinçonn ment de c s illement (globa o local) t la flexion des colonnes de DCM
sont également significatifs pour les remblais soutenus par olonnes. Cependant, il reste des incertitudes en ide tifiant le modes de
ruptu e critiques pour ces remblais. Par conséquent, cette communication étudie quelques modes de rupture pour des remblais de
GRCS par la méthode des éléments finis. Le remblai et les charges de la circulation sont graduellement augmentés pour s’approcher
de la rupture.
KEYWORDS: deep cement mixed columns, embankment, finite element method, strain softening, progressive failure.
1 INTRODUCTION
Geosynthetic
reinforced
column
supported
(GRCS)
embankments are widely used in infrastructure development
projects in urban and metropolitan areas in most countries. The
design process should critically consider the behavior of single
columns as well as the global embankment system. A number of
possible failure mechanisms for these embankments are
discussed in the literature. Numerous research efforts have been
expended to understand the failure modes for GRCS
embankments using centrifuge modelling, numerical modelling
and case histories of field performance (Broms 1999, Kitazume
and Maruyama 2007) and thereby to develop analysis and
design procedures incorporating possible failure modes. Current
design procedures for these embankments only consider the
sliding failure for external stability and the shear failure of
DCM columns for internal stability (CDIT 2002, EuroSoilStab
2002). It is recently found that other failure modes such as
collapse failure, slip circle failure, punching shear failure
around column heads (overall or local), and bending failure of
DCM columns are also significant for GRCS embankments
(Kivelo 1998, Broms 2004, Kitazume and Mauyama 2007).
There are many case histories demonstrating that these
foundation systems are likely to have slope stability problems,
although they significantly improve the bearing capacity and
reduce the excessive settlements inherent in soft ground.
Progressive failure has been identified by Broms (2004) and
bending failure has been observed by Terashi (2003).
The main focus of this paper is to identify the critical failure
modes related to GRCS embankments. In this finite element
analysis, the bending failure of individual columns and
s bsequent dev lopm nt of a slip surface shear failure are
investigated. These failure modes are critical for internal
stability of GRCS embankments. In addition, local and overall
punching failure modes relevant for the stability of fill layers
are investigated.
2 DESCRIPTION OF THE NUMERICAL MODEL AND
MODEL PARAMETERS
Th geometry of the roblem used in this study is shown i
Figure 1. The embankment is supported by DCM columns with
1 m diameter and 2.5 m center to center olumn pacing in each
direction. The model parameters used for the nalysis are given
in Table 1. The embankment is constructed in st ges ex ending
0.5 m fill layer followed by five 1 m thick layers. Each layer is
applied over a period of one month and the waiting period after
each fill layer is 0.5 months. Finally the traffic load is applied.
