1777
An elastic continuum model for interpretation of seismic behavior of buried pipes as
a soil-structure interaction
Un modèle de continuum élastique pour l'interprétation du comportement sismique des conduites
enterrés comme une interaction sol-structure
Tohda J.
Osaka City University
Yoshimura H.
Anan National College of Technology
Maruyoshi K.
Dainippon Plastic Co. Ltd.
ABSTRACT: An elastic 2-D continuum model to interpret the seismic behavior of buried pipes as a soil-structure interaction was
proposed. The model simulated a condition in which the ground under
K
0
-condition was subjected to simple shear due to earthquake.
The interface condition between pipe and soil was assumed to be perfectly smooth. A series of 1/30-scaled centrifuge model tests was
conducted to verify the proposed model, where normal and tangential earth pressures on, and bending moments of, two model pipes
with different flexibilities were precisely measured during 10 cyclic simple shear deformation of model grounds. The proposed model
generated results that were consistent with the measured ones, revealing that the proposed model gives a rational interpretation for the
seismic soil-pipe interaction, while current design using seismic deformation method based on spring models is misleading.
RÉSUMÉ : Un élastique 2-D modèle de continuum pour interpréter le comportement sismique des conduites enterrés comme une in-
teraction sol-structure a été proposée. Le modèle a simulation simulé une condition dans lequelle le sol sous condition K
0
a été soumis
à un cisaillement simple en raison de tremblement de terre. La condition d'interface entre le conduite et le sol était supposé être par-
faitement lisse.Une série d'essais sur modèle centrifugeuse enéchelle 1/30 a été effectuée afin de vérifier le modèle proposé, où la
pression des terres normales et tangentielles sur, les moments de flexion de deux conduites modèles avec différentes flexibilités ont
été précisément mesurée pendant 10 déformation de cisaillement cyclique simple des motifs du modèle. Les résultats du modèle pro-
posé qui étaient compatibles avec celles mesurées révélant que le modèle proposé donne une interprétation rationnelle de la sismique
interaction sol-conduites, tandis que la conception actuelle en utilisant la méthode déformation sismique basée sur des modèles de
printemps n'est pas raisonnable.
KEYWORDS: buried pipe, seismic soil-structure interaction, continuum model, earth pressure, centrifuge model test
1 INTRODUCTION
Two types of models, namely a continuum model and a spring
model, to interpret the mechanical behavior (earth pressure and
deformation) of buried pipes as a soil-structure interaction were
proposed hitherto. However, being their interpretation for the
phenomenon different, it often generates confusion in this re-
search field (e.g. Moore 1989). The authors investigated the
concentration of earth pressure on rigid pipes and its relaxation
on flexible pipes, as well as buckling of thin-walled buried
pipes through experimental and analytical researches (Tohda et
al. 1986, 1994, 1997 and Tohda 2001), revealing that the con-
tinuum model reasonably explains the actual behavior of buried
pipes, while the spring model is erroneous.
Current design standards for buried pipes in Japan (e.g.
JSWAS 2006) prescribe the application of seismic deformation
method based on the spring model to predict the stability of bur-
ied pipes against seismic loading. The authors pointed out again
that the current design standards prediction for the behavior of
buried pipes is different from those observed in dynamic centri-
fuge model tests (Tohda et al. 2010a). One of the critical differ-
ences between the measurements and prediction is the role of
tangential earth pressures (
) acting on the surfaces of buried
pipes.
in the measurement are always almost null, while in the
prediction
is assumed to govern the seismic behavior of buried
pipes.
In the present paper, the authors proposed a new elastic 2-D
(two-dimensional) continuum model to interpret reasonably the
seismic behavior of buried pipes as a soil-structure interaction.
Its validity was confirmed through comparison between the
analysis and measurement in centrifuge model tests that simu-
lated simple shear deformation of the ground produced by
earthquake.
2 PROPOSED MODEL AND ANALYTICAL RESULTS
2.1
Proposed seismic continuum model
Figure 1 shows the proposed 2-D continuum model. The model
simulates the condition in which the ground under
K
0
-condition
is subjected to simple shear due to earthquake. Soil and pipe are
assumed as linear elastic bodies. Relative stiffness between soil
and pipe (
=
E
s
/
S
p
) is varied from 0 (pipe as rigid body) to
(a
circular cavity exists in the ground). Where,
E
s
is the
Young’s modulus of soil;
S
p
=
E
p
t
3
/{12(1
p
2
)
R
3
}, the flexural
stiffness of the pipe;
E
p
and
p
are, respectively, the Young’s
modulus and Poisson’s ratio of the pipe;
t
is the wall thickness
of the pipe, and
R,
the neutral radius of the pipe. Poisson’s ra-
tios of soil (
s
) are also varied from 0.2 to 0.4.
x
=
x
xy
3
1
3
=
K
1
xy
xy
y
y
=
K
0
0
0
1
y
x
pipe
xy
=
K
h
0
Figure 1. Proposed 2-D seismic continuum model.
