559
Long-term Deformation of the Reclaimed Pleistocene Foundation of the Offshore
Twin Airport
Déformations à long terme d’une fondation de remblai pléistocène récupéré sur mer pour un projet
d’aéroport jumelé
Jeon B.G.
Samsung C&T Corporation
Mimura M.
Graduate School of Engineering, Kyoto University
ABSTRACT: A series of elasto-viscoplastic finite element analyses is performed to assess the long-term deformation including the
interactive behavior of the reclaimed Pleistocene foundation due to the adjacent construction of the offshore twin airport. Attention is
paid to the modeling of permeability for the Pleistocene sand gravel layers considering the sedimentation environment. The concept of
“mass permeability” is introduced to model the actual process of
dissipation of excess pore water pressure in the field. It is regarded
as the macroscopic capability of permeability for the individual Pleistocene sand gravel layers by evaluating the permeability not of
each element but of the whole layer in one body. The mechanism for the propagation of excess pore water pressure due to
construction of the adjacent reclamation is discussed through the numerical procedure using the concepts of “mass permeability”. The
concept of “mass permeability” for the individual Plei
stocene sand gravel layers is found to well function to assess the long-term
deformation including the interactive behavior in the reclaimed Pleistocene foundation.
RÉSUMÉ :
Les déformations à long terme d’un remblai pléistocène en mer sont évaluées a partir d’une série d’analyses élasto
-
viscoplastiques par éléments finis. Les interactions dues aux travaux d’aménagement d’aéroport jumelé sont aussi prises en compte.
On vise plus particulièrement à modéliser la perméabilité du sable/gravier pléistocène en considérant la sédimention du milieu. La
dissipation des surpressions interstitielles in-
situ est calculée à partir d’une perméabilité massique de l’ensemble des couches
sable/gravier. Les mécanismes de propagation de surpressions interstitielles induites par le remblai voisin sont déterminés par
modélisation numérique faisant appel au concept de perméabilité massique. L’application de ce concept semble être commode pour
évaluer les déformations à long terme des couches sable/gravier pléistocène en interacti
on avec d’autres ouvrages voisins.
KEYWORDS: elasto-viscoplastic finite element analysis, mass permeability, standard hydraulic gradient
1 INTRODUCTION
The development of coastal areas accomplished in Japan has
been outstanding. Kansai International Airport (KIX) was
constructed in Osaka Bay as two man-made reclaimed islands to
minimize noise and pollution in residential areas as well as to
meet the increasing demand for air transportation. Such a large-
scale offshore reclamation in Osaka Bay is accompanied with
large and rapid settlement of deep Pleistocene clay deposits
(Mimura et al., 2003). Long-term settlement of the Pleistocene
marine foundations due to huge reclamation load has been of
great concern in this project. The seabed deposits of Osaka Bay
have been formed due to the soil supply from the rivers and the
alternating deposits of KIX have been formed due to
sedimentation of clayey soils during transgression and of sandy
to gravelly soils during regression on the sinking base of Osaka
Bay. The Pleistocene clay deposited in Osaka Bay exhibits the
behavior of the quasi-overconsolidated clay without definite
mechanical overconsolidation history. Itoh et al. (2001)
summarized on the basis of the data from elastic wave
exploration and in-situ boring logs that the Pleistocene sand
gravel deposits are not always distributed uniformly in
thickness, consistently and that the amount of fine contents
included in them is significant. The most serious problem
originating from these sand gravel deposits is the
“
permeability
”
that controls the rate of consolidation of sandwiched Pleistocene
clays. In the sense, the modeling for the quasi-overconsolidated
Pleistocene clay and the evaluation of permeability for the
Pleistocene sand gravel deposits are the significant factors to
assess the long-term behavior of the reclaimed Pleistocene
foundation due to the reclamation of the offshore twin airport.
Mimura and Jang (2004) proposed a concept of compression in
which viscoplastic behavior is assumed to occur even in the
quasi-overconsolidated region less than
p
c
for the Pleistocene
clays in Osaka Bay. The procedure has been found to be
versatile and allows for the long-term settlement monitored in
the reclaimed islands in Osaka Port to be described (Mimura
and Jang, 2005a). In the present paper, the numerical procedure
to assess the long-term behavior of the Pleistocene deposits at
KIX in terms of elasto-viscoplasitc FEM is proposed by
introducing the concept of
“
mass permeability
”
and
“
standard
hydraulic gradient
”
for the Pleistocene sand gravel layers. The
validity of the procedure is carefully discussed by comparing
the performed results with in-situ measurements.
2 CONCEPTS OF
“
MASS PERMEABILITY
”
AND
“
STANDARD HYDRAULIC GRADIENT
”
Mimura and Jang (2005a) reported when the permeability of
sand gravel layers is considered perfectly drained, one-
dimensional analysis only considering the characteristic of
clayey soil can be adopted for the consolidation problem
without considering the effect of permeability loss in the those
sand gravel layers. However, the sand gravel layers sandwiched
by the Pleistocene clay layers at KIX were recognized not to
function as perfect drainage layers through the in-situ
measurement of excess pore water pressure. Therefore, the two
or three-dimensional analysis that considers the permeability of
the Pleistocene sand gravel layers is required to assess the long-
term behavior of the reclaimed Pleistocene foundation. The
influential factors to evaluate the permeability of sand gravel
layers are the thickness, the horizontal continuity and the fine
contents of them. The permeability of them is different with
places even if they are categorized as the identical ones. But, it
is impossible to evaluate the permeability of sand gravel layers
at every point. It is also very difficult to confirm how the sand
gravel layers under the Pleistocene marine foundation are
