923
Dynamic centrifugal model test for unsaturated embankments considering seepage
flow and the numerical analysis
Expérimentation en centrifugeuse et modélisation numérique de la réponse aux
séismes de remblais non saturés en prenant en compte l’écoulement
Higo Y., Oka F., Kimoto S., Kinugawa T.
Department of Civil and Earth Resources Engineering, Kyoto University, Japan
Lee C.-W., Doi T.
Former graduate student of Department of Civil and Earth Resources Engineering, Kyoto University, Japan
ABSTRACT: Earthquake-induced failure of unsaturated road embankments has taken place during the past earthquakes. It has been
pointed out that water flow or higher water content of road embankments was a possible reason of the damage. In this study, dynamic
resistance of unsaturated embankments with and without the seepage flow has been studied through the centrifugal model tests of
unsaturated embankment and their numerical simulations by a multi-phase coupled finite element method with an elasto-plastic
constitutive model. During the tests, displacement, pore pressures, and acceleration of embankments have been fully monitored. The
dynamic behavior of unsaturated embankments with infiltration of pore water has been discussed on the basis of comparison between
the experimental and the numerical results. From the present study, we have found that the seepage flow and the high water content
extensively affect the dynamic stability of unsaturated road embankments.
RÉSUMÉ: Les remblais routiers non saturés peuvent s’écrouler lors d’un séisme, la cause de cet écroulement étant sans doute à
rechercher dans l’écoulement d’eau ou dans des grandes valeurs de teneur en eau au sein du remblai. Dans cet article, la résistance
dynamique d’un remblai non saturé est étudiée, avec ou sans écoulement, par des essais en centrifugeuse et par leur modélisation
numérique aux Eléments Finis, en utilisant une approche hydromécanique couplée et un modèle constitutif élasto-plastique pour le
sol. Les déplacements, les pressions interstitielles et les accélérations ont été mesurés tout au long des essais. Les résultats
expérimentaux et les résultats numériques ont été comparés. Les résultats de cette étude confirment que l’écoulement et la forte teneur
en eau ont effectivement un rôle majeur pour la stabilité dynamique des remblais routiers non saturés.
KEYWORDS: unsaturated soil, embankment, earthquake, failure, dynamic centrifugal model test, numerical simulation.
1 INTRODUCTION
It is well known that the road embankment is still vulnerable
against earthquakes. Earthquakes damaged road embankments
during the extensive earthquakes such as the 2011 off the
Pacific Coast of Tohoku Earthquake (M9.0). In particular, road
embankments constructed on mountain/hill sides were severely
damaged by the 2009 Suruga Bay Earthquake, the 2007 Noto
Hanto Earthquake and the 2004 Niigata-ken Chuetsu
Earthquake etc.
In the cases of the Noto Hanto Earthquake and the Niigata-
ken Chuetsu Earthquake, seepage water flow or higher water
content in the embankments was a possible reason of the
damage of the road embankments. Increase in the water
contents causes loss of the inter-particle force caused by suction
and decrease in the skeleton stress. This suggests that the effect
of the seepage water flow and the high water content in the
embankments on the dynamic failure of road embankment has
to be studied in detail. However, to the authors’ knowledge,
there are a limited number of physical model studies on
unsaturated embankments considering seepage water as well as
numerical ones (e.g., Hayashi et al. 2002, Doi et al. 2010).
In this study, seismic resistance of unsaturated embankments
with and without the seepage water has been studied through the
centrifugal model tests and their numerical simulations by a
multi-phase coupled finite element method with an elasto-
plastic constitutive model (Oka et al. 2008, Oka et al. 2011).
The dynamic behavior of unsaturated embankments with
infiltration of the pore water has been discussed on the basis of
comparison between the experimental and numerical results.
2 DYNAMIC CENTRIFUGAL MODEL TESTS
2.1
Soil used in the test
The soil used in the model tests is Yodogawa-levee sand, which
has been used to fix the embankment of Yodo River in Kansai
area. The physical properties of Yodogawa-levee sand are listed
in Table 1.
2.2
Testing procedure
The model configuration and the sensor locations are illustrated
in Fig. 1. Prior to preparing the specimen, test samples were
mixed with water to set up the initial water contents of 15%.
Then, model embankments were prepared by compacting
method in eight layers; the base ground and the embankment
were separated into three layers (thickness: 30mm, 15mm,
15mm), and five layers (as same thickness: 20mm),
respectively. During the model construction, the accelerometers
and the pore pressure transducers were embedded at the
prescribed locations. The degree of compaction of all the cases
Table 1. Physical properties of Yodogawa-levee sand
Parameter
Value
Sand content (%)
73.2
Silt content (%)
14.7
Clay content (%)
12.1
D
max
(mm)
*
2.0
D
50
(mm)
0.29
ρ
s
(g/cm
3
)
2.661
w
opt
(%)
13.7
ρ
dmax
(g/cm
3
)
1.861
k(m/sec)
**
4.79
×
10
-6
*Maximum diameter of sieved particle
**Permeability when degree of compaction is 90%
