京 都 大 学 防 災 研 究 所 年 報 第 48 号 B 平成 17 年 4 月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 48 B, 2005

Effect of Permeability and Compressibility of Permeable Gravelly Sand Layers on
Long-term Settlement of Pleistocene Deposits

Wooyoung JANG and Mamoru MIMURA

Synopsis
A series of elasto-viscoplastic finite element analyses is carried out to investigate theeffect of the permeability and compressibility of the Pleistocene gravelly sand layers on the
stress-deformation characteristics of the Pleistocene deposits in Osaka Port. The relevant
procedure to evaluate the rigidity of the Pleistocene gravelly sand layers is also introduced.
It is found that the estimation of the elastic shear modulus, G0 as well as permeability of the
Pleistocene gravelly sand layers plays a significant role for the settlement prediction of thereclaimed islands in Osaka Port.
Keywords: quasi-overconsolidated Pleistocene clay, Pleistocene gravelly sand layer,
coefficient of permeability, excess pore water pressure, elastic shear modulus,
elasto-viscoplastic finite element analysis

1.

Introduction

Long-term settlement occurring at the reclaimed
Pleistocene deposits in Osaka Bay has been a serious
geotechnical issue which directly causes the obstacle
for superstructures on those reclaimed islands. Far
from the case for the Holocene clays, the Pleistocene
clays have so-called distinguished structure withrelatively high void ratio due to the effect ofdiagenesis even under the condition of high confining
stresses. This high void ratio of the Pleistocene clays
easily breaks down by the construction loading,which results in serious large and long-term
compression. The authors have reported the measured
achievement at the reclaimed islands in Osaka Bay(Mimura et al., 2003). On the basis of the in-situ
measured information, the new procedure has been
proposed in which a viscoplastic deformation isassumed to occur even in the region less than pc andthe proposed procedure has been found to provide
good description for the measured long-term

compression of each Pleistocene clay layers at
Sakishima, Maishima and Yumeshima Reclaimed
Islands in Osaka Bay (Mimura and Jang, 2004, 2005).
The thick Pleistocene deposits that consist ofalternating marine clay (Ma) and gravelly sand layers(Dg), are overlain by the Holocene clay layer (Ma13)
in Osaka Bay. And the horizontal continuity of thegravelly sand layers sandwiched by the Pleistocene
clay layers was definitely confirmed in Osaka Port(Research Committee on Ground in Osaka Bay,2002).
It is true that the modeling of compressibility for
quasi-overconsolidated Pleistocene clays is the main
factor to describe the long-term settlement of thereclaimed Pleistocene marine foundations, but a due
attention should also be paid to the fact that the
thickness and the coefficient of permeability, k of thegravelly sand layers are the influential factors tocontrol the process of generation and dissipation ofexcess pore water pressure in the Pleistocene deposits(Mimura and Sumikura, 2000). A rate ofconsolidation of the sandwiched Pleistocene clay

required for those layers are elastic shear modulus,

Measurement of settlement

Sheet Pile

Sand Replacement

Fill

SD

SCP

Ma12

Depth (m)

Ac

CL

Dg

174m

Ma11U
Dg

Ma11L

Dg

Ma10
Ma9

245m

355m

0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180

Ma13
Dg1
Ma12
Dg2
Ma11U
Dg3
Ma11L
Dg4

Ma10
Dg5
Ma9

Ma : Clay layer
Dg : Gravelly sand layer

Fig. 1 Model of the foundation ground for finite element analysis

layers is also controlled by the permeability of the
Pleistocene gravelly sand layers. The rigidity of the
Pleistocene gravelly sand layers is another key factor
to evaluate the deformability of the Pleistocene
deposits although the contribution to the total
settlement is not so large compared to the one taking
place in the Pleistocene clay layers. As theparameters controlling the compression of the hard
Pleistocene gravelly sand layers have been lessconcerned, the relevant information of them fordetailed numerical analysis is hardly found.
In this paper, behavior of excess pore waterpressure in the Pleistocene deposits with thepermeability of the gravelly sand layers isinvestigatedthrough
tow-dimensionalelasto-viscoplastic finite element analyses. Maishima
Reclaimed Island is selected for the representative of
the reclaimed islands in Osaka Port. Propagation ofexcess pore water pressure in the gravelly sand layers
is discussed. It is very important to know how far thegenerated excess pore water pressure will propagate
in the permeable gravelly sand layers because it
directly influences on the subsequent deformation as
well as the adjacent structure. The effect of thepermeability of the permeable Pleistocene gravelly
sand layers on the subsequent settlement process ofeach Pleistocene clay layer is also discussed.
Discussion is extended to the compressibility of the
Pleistocene gravelly sand layers. As it is assumed in
the present analysis that the Pleistocene gravelly sandbehaves as an elastic material, the main parameters

G0 and Poisson’s ratio Q'. A series of one-dimensionalelasto-viscoplastic finite element analyses is carriedout to investigate how the estimation of G0 for the
Pleistocene gravelly sand layer influences on thecalculated total settlement of the Pleistocene deposits.
In general, the values of G0 for sandy layers havebeen determined by an empirical relationship in termsof the NSPT value. In this research, two different
empirical equations related to NSPT values are
selected to determine G0 of Osaka Pleistocene
gravelly sand layers, and the calculated compressionof those layers with both procedures is compared.
Yumeshima Reclaimed Island where the total
settlement of the Pleistocene deposits has beenmeasured from the start of reclamation is selected as
the target area for discussion.
2.

Permeability of the Pleistocene Gravelly Sand
Deposits

2.1 Problems Set up and Parameters
A series of two-dimensional elasto-viscoplastic
finite element analyses is performed to investigate theeffect of permeability of the gravelly sand layers on
the stress-deformation characteristics for the
Pleistocene marine foundation. Maishima Reclaimed
Island is adopted as the model foundation shown in
Fig. 1. The bottom boundary and the sea sideboundaries of the gravelly sand layers are assumed to
be fully drained. The reclaimed side boundaries of alllayers are assumed to be fully undrained considering

the geometrical symmetry. The constitutive model
used for numerical analysis is the modified planestrain version (Sekiguchi et al., 1982) of theelasto-viscoplastic model (Sekiguchi, 1977). The
input parameters of the Pleistocene clay layers andloading sequence for Maishima Reclaimed Island
were already described in the reference (Mimura andJang, 2004). The Pleistocene gravelly sand layers,which are indicated by Dg, are assumed to be linear
elastic materials with finite permeability. The
comparative analyses with four different coefficientof permeability for gravelly sand layers are
performed. The adopted coefficient of permeability, kin the Pleistocene gravelly sand layers for each caseis summarized in Table 1. The sensitivity analyses are
performed by varying the coefficient of permeability,k. The one extreme condition is introduced with kequal to be infinite as a benchmark (Case 0). Valuesof k are varied with 10 times larger (Case 1) or
smaller (Case 3) from the actual one (Case 2) tocheck the effect of permeability of the Pleistocene
gravelly sand layers on the subsequent deformation.
Another extreme assumption is applied to Case 4
with k equal to 1/100 of the actual value that can beseen offshore far from river mouth. In the case thepermeable sandy layers are poor with such low
permeability, the effect of excess pore water pressure
propagation in those layers is remarkable and the rateof dissipation becomes very low. This kind ofproblem takes place at the offshore reclaimed islandof Kansai International Airport (Akai and Tanaka,
1999, Research Committee on Ground in Osaka Bay,2002).
Table 1 Adopted coefficient of permeability in the
Pleistocene gravelly sand layers for each caseCoefficient of permeability, k (m/day)
Case0

Fully drained

Case1

2.16×10Case2

2.16×101

Case3

2.16×10Case4

2.16×10-1

20

2.2 Distribution of Excess Pore Water Pressure
Figure 2 shows the calculated contours of excess
pore water pressure ratio ('u/'p) for each case at thecompletion of reclamation and after 20 years form thecompletion of reclamation. The applied load, 'p isdifferent between at the inside of reclaimed islandand the revetment. In this paper, to compare the
distribution mode of the excess pore water pressure
for each case, 224 kPa is adopted as 'p, which is theapplied load at the inside of reclaimed island. So, thepresented values of 'u/'p around the revetment in
Fig. 2 are a little less than the actual calculated ones.
As shown in Fig. 2, the distribution of excess porewater pressure for the three cases, Case1, Case2 andCase3 are almost the same with the one for Case0 inwhich the gravelly sand layers are assumed to be
fully drained. Although in the untreated Holocene
layer (12m to 27m in depth), a large amount ofexcess pore water pressure remains at the completionof reclamation, the excess pore water pressure in the
Pleistocene gravelly sand layers has already beendissipated at the completion of reclamation. It canalso be seen that the excess pore water pressure in the
Pleistocene clay layers is almost dissipated after 20
years in those cases. On the other hand, for Case4 inwhich k of the gravelly sand layer is assumed to be
2.16×10-1 m/day, the distribution of excess porewater pressure is quite different form other cases. As
shown in Fig. 2, a large amount of excess pore waterpressure in the upper layer (10m to 82m in depth)
remains at the completion of reclamation. In
particular, the excess pore water pressure of thegravelly sand layer (Dg1) overlying the Pleistocene
clay layer Ma12 is significant. Because of the poor
permeability of the gravelly sand layer, relatively
larger excess pore water pressure is distributed in the
Pleistocene clay deposits than those of the other threecases. It is noteworthy that a remarkable excess porewater pressure remains not only in the upper
Pleistocene clay layer such as Ma12 and Ma11 but
also in the gravelly sand layer (Dg1) even after 20
years from the completion of reclamation.
It is also very interesting to know the mode ofpropagation of excess pore water pressure in thegravelly sand layers due to reclamation. Mimura andSumikura (2000) explained the mechanism of excess
pore water pressure propagation in the poorly
permeable sandy layers that can be seen at the
Pleistocene deposits, southern Osaka. As it is shownin Fig. 2, a significant propagation of excess porewater pressure does not occur in the gravelly sandlayers toward the sea side for Case1, Case2 andCase3, not to mention for Case0. On the contrary, forCase4, the excess pore water pressure generated in
Dg1 and Dg2 propagates toward the sea side

significantly. It is found that the poor permeablegravelly sand layers provides a serious propagation of

60

20

0.1

0.1

0.2

40

0.3

Depth (m)Depth (m)

40

0.6

Case0
Completion of reclamation

0.1

20

the excess pore water pressure in them even if they
have sufficient thickness.

0.1
0.1

80

0.2

100
120

60
80

0.05

100
120

0.1

0.05

140

140

160

0.1

160
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

-50

Distance form center (m)

0.6

Case1
Completion of reclamation

20

0.1

0.1

0.2

40

0.3

60

Depth (m)Depth (m)

40

0.1

80

0.1

0.2

100
120

60

after 20 years

80

0.05

100
0.05

140
0.1

160
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

160

-50

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

Distance form center (m)

60

0.6

0.1

Case2
Completion of reclamation

20

0.1
0.1

0.2

40

0.3
0.1

80

0.1

0.2

100
120

60
80

0.05

100
0.05

140
0.1

160
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

160
-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

-50

Distance form center (m)

60

0.6

0.1

Case3

0.1

0.1
0.2

20

0.1
0.3

0.2

0.1

40

0.3
0.4

0.3

Completion of reclamation

80
100

0.1

140

0.1

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

60
80

0.05

100
0.05

160

-50

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100

Distance form center (m)

0.4

0.2

0.3

60

0.7
0.5 0.6
0.5
0.3

0.2

80

0.3

0.1

100
140
160

0.3

0.1

Case4
Completion of reclamation

0.2
0.1

-550 -500 -450 -400 -350 -300 -250 -200 -150 -100
Distance form center (m)

40

0.10
0.05

80

0.10
0.05

0.05

100
120
160

-50

0.15

0.05

60

140
0.1

0.20

0.15
0.10

20
Depth (m)Depth (m)

0.2
0.1

-50

Distance form center (m)

0.1

120

0.05

140

160

40

0.10

0.05

Case3
after 20 years

120

120

20

-50

Distance form center (m)Depth (m)Depth (m)

40

0.10

0.05

Case2
after 20 years

120

0.1

140

20

-50

Distance form center (m)Depth (m)Depth (m)

40

0.10

0.05

Case1

120

0.1

140

20

-50

Distance form center (m)

0.1

20

0.05

0.05

Case0
after 20 years

Case4
after 20 years

0.05-550 -500 -450 -400 -350 -300 -250 -200 -150 -100
Distance form center (m)-50

Fig. 2 Contour of Calculated excess pore water pressure ratio

Ground improvement
00'u/'p (%)
20

40

'u/'p (%)
60

80

100

0

Ma13

10

20

13

20

13

30

Dg1

30

Dg1

40
12

60

Dg2

70

11U
Dg3

70

11U
Dg3

80

11L

Depth (m)Depth (m)

Dg2

11L

90

Dg4

120
10

130
Completion of reclamation

Dg4

140

Case0
Case1
Case2
Case3
Case4

150
160

9

170
180

10

after 5 years
Dg4

160

9

170
180
190

Ground improvement
00'u/'p (%)
20

40

'u/'p (%)
60

80

100

0

0
10

20

13

20

13

30

Dg1

30

Dg1

40

12

60

Dg2

70

11U
Dg3

70

11U
Dg3

80

11L

80

11L

Depth (m)

Dg2

90

120
10

180
190

130
after 10 years

Dg4

150
170

Dg4

110

120

160

80

90
100

Dg4

110

140

60

12

60

130

40

50

50

100

20

Ma13

Ma13

40

Case0
Case1
Case2
Case3
Case4

150

190

10

100

110

120
140

80

90
100

Dg4

110
130

60

12

60

100

40

50

50

80

20

Ma13

10

40

Depth (m)

0

9

Case0
Case1
Case2
Case3
Case4

140

10

after 20 years
Dg4

150
160

9

170
180
190

Fig. 3 Profiles of excess pore water pressure ratio with depth

Case0
Case1
Case2
Case3
Case4

100

2.3 Comparison of Long-term Settlement in the
Pleistocene Clay Deposits
The calculated time-settlement relations at thecenterline for each Pleistocene clay layer withdifferent permeability of the gravelly sand layers arecompared in Fig. 4. First, let us discuss about Ma10
and Ma9 layers whose final stresses remain less thanpc. The generated excess pore water pressure ratio of
those layers is less than 20% at the completion ofreclamation (see in Fig. 3). As the calculated
settlement for those Pleistocene clay layers isdeveloped by the decrease in void ratio not due todissipation of excess pore water pressure but mainly
strain rate dependent behavior without dissipation ofexcess pore water pressure, it is natural that thesettlement process of all cases for Ma10 and Ma9 isalmost the same irrespective of the permeability of
the gravelly sand layers. On the other hand, thecalculated settlement for the upper Pleistocene clay
layers such as Ma12, Ma11U and Ma11L in Case4 issmaller than that of other three cases. This differenceis caused by the dissipation process of excess porewater pressure influenced by the permeability of thegravelly sand layers. For example, as it is known in
Fig. 3, 40% of the maximum excess pore waterpressure can be seen in Ma12 even after 10 years
form the completion of reclamation for Case4,
whereas only 20% of the maximum excess pore waterpressure remains for other four cases. Consequently,
this difference in effective stress due to dissipation ofexcess pore water pressure induces the difference insettlement between case4 and other four cases. It
should be emphasized that the calculated settlementof the upper Pleistocene clay layers (Ma12 andMa11) for Case1, Case2 and Case3 is almost thesame with the one for Case 0. In other words, thesettlement inside the reclaimed island is not affected
0
50

Ma12

100
150
0
20

Ma11U

40

Settlement (cm)Figure 3 shows the profiles of excess pore waterpressure ratio with depth at the centerline of theground model. It is natural that the profile of excess
pore water pressure for Case0 exhibits the jagged
shape with a value of zero in the gravelly sand layers,
because the gravelly sand layers are assumed to be
fully drained for Case 0. Although the gravelly sandlayers are assumed as partially drained with finite
permeability for Case 1 and Case 2 as shown in Table
1, it can be seen that the calculated profiles of excess
pore water pressure ratio are almost the same withthat of Case 0. It is true the excess pore waterpressure ratio is slightly larger at the completion ofreclamation for Case 3 than those for Case1 andCase2 in the upper layer (10m to 82m in depth), butthat is almost the same with Case1 and Case2 in thelower layer (below 82m). After 5 years form thecompletion of reclamation, the excess pore waterpressure ratio for Case3 becomes the same with
Case1 and Case2. As it is excess pore water pressure
contour in Fig. 2, much larger excess pore waterpressure ratio is derived for Case4 at the Pleistocene
clay layers as well as at the gravelly sand layers due
to poor permeability of the gravelly sand layers.
Attention should be paid to the fact in Case4 that theprocess of excess pore water pressure of the gravelly
sand layers such as Dg1, Dg2 and Dg3 is very similar
for the Pleistocene clay layers overlain by eachgravelly sand layers. This mode of excess pore waterpressure distribution can be seen in the marine
deposits at Kansai International Airport (Akai andTanaka, 1999), where they have the thinner, lesscontinuous, poorly permeable Pleistocene gravelly
sand deposits in the Pleistocene alternating layers.
Based on the discussion, it is confirmed that thedissipation of excess pore water pressure could
prolong when the quality of permeable layers is poor
even if they have sufficient thickness.

Case0
Case1
Case2
Case3
Case4

60
0
20
40
60
80
0

Ma11L

20

Ma10

40
60
0
20

Ma9

40
60
0

2000 4000 6000 8000 10000 12000 14000 16000

Elapsed Time (days)

Fig. 4 Comparison of calculated settlement for each
Pleistocene clay layer with permeability of thegravelly sand layer

3.

Compressibility of the Pleistocene Gravelly
Sand Deposits

3.1 Problems Set up and Parameters
It is self-evident that the compression of the
Pleistocene deposits is dominated mainly by thecompressibility of the Pleistocene clays, but the
instantaneous compression of the intermediate
Pleistocene sand layers also contributes to the total
settlement even if it is not so significant. Particularly,
non-negligible compression can take place in the
Pleistocene gravelly sand layers encountered in
Osaka Bay because of their large thickness. As they
have
littleconstruction
achievementwithmeasurement related to the Pleistocene gravelly sanddeposits, it is very difficult to get the reliable
information for evaluating the physical properties of
the Pleistocene gravelly sands that are very hard withvalues of NSPT almost equal to 50 to 60. Undisturbed
sampling of those hard Pleistocene gravelly sands isnormally associated with disturbance, which resultsin the serious underestimation of their rigidity
derived from laboratory tests. Yoshinaka (1968)
suggested the correlation between NSPT and elastic
modulus obtained from a borehole lateral load test for
the Holocene sand layer as well as clay layer.
Sekiguchi et al. (1988) introduced the way
determining the elastic shear modulus, G0 for theintermediate
Pleistocene
sandsof
KansaiInternational Airport foundation ground by using theprocedure proposed by Yoshinaka (1968). In thepresent research, the authors have introduced theprocedure on the basis of the field measurement by
Okura
et
al.
(1996).
Characteristics
ofcompression/swelling for gravelly sand layers
including the upper Pleistocene layers with avariation of groundwater level were observed at
Osaka Plain (Okura et al., 1996). The value of G0 for
the site was obtained from the relation between theeffective stress and occurring volumetric strain due tothe variation of groundwater level. The superiority ofthe procedure by Okura et al. (1996) consists in thefact that the strain was measured in-situ with thechange in effective stresses due to changing the
ground water level. As the derived rigidity is freefrom any disturbance associated with sampling,digging holes etc, the values of them are consideredmuch more precise.
A series of one-dimensional elasto-viscoplastic
finite element analyses is carried out to investigate
the effect of estimation of the rigidity for the
Pleistocene gravelly sand layers on the total
settlement prediction of the Pleistocene deposits.
Yumeshima Reclaimed Island is selected as a target
for discussion, because the in-situ total settlement of
the Pleistocene deposit including the compression of
the Pleistocene gravelly sand layers has beenmeasured there from the start of reclamation. The
adopted one-dimensional finite element mesh isshown in Fig. 5 together with the boundary
Yumeshima

B1

Depth (m)
0

Ma13
Dg1
Ma12
Dg2

26
35
49

65
Ma11U 72
Dg3
78
Ma11L
90
Dg4
120
Ma10
137
Dg5
151

174 m

by the permeability of the gravelly sand layers, as far
as the coefficient of permeability of those layers has
more than 100 m/day such as the Pleistocene deposits
in Osaka Port. It is noteworthy to find that thecalculated settlement of the Pleistocene deposits in
Osaka Port is not influenced by the difference inpermeability of the sandwiched Pleistocene gravelly
sand layers if the value of the coefficient of
permeability, k exceeds 100 m/day. It means that the
propagating effect of excess pore water pressure in
the Pleistocene gravelly sand layers can be ruled out
for stress-deformation analysis for the reclaimed
Pleistocene deposits in Osaka Port. These facts
guarantee that the present procedure in terms ofelasto-viscoplastic finite element analysis certainly
provides the consistent calculated settlement even if
the values of k for the Pleistocene gravelly sandlayers are set to be infinite.

Ma9
174

B1
Element of 'Ma' : B2

B2

Element of 'Dg' : B1

B1

B1 : Drainage boundary
B2 : Impermeable boundary

Fig. 5 One-dimensional finite element mesh for
Yumeshima Reclaimed Island

Strain (%)

Table 2 Determination of elastic shear modulus
0

Yoshinaka (1968)
2

G0 (kgf/cm ) =72(1+Q')

2

3

4

Strain (%)
5

6 0

1

2

3

4

5

6

Okura et al. (1996)
N2

G0 (kgf/cm ) =D
N
2(1+Q')

D = (31- 52)
G0 = 15790 kPa

1

G0 = 103000 kPa

conditions determined on the basis of the
Geo-database (Research Committee on Ground in
Osaka Bay, 2002). The bottom boundary is set to be
perfect drained because Ma9 is underlain by the thickgravelly sand layer. The side boundaries of thegravelly sand layers are assumed to be also perfectdrained on the basis of the findings that thepermeability of the sandwiched Pleistocene gravelly
sand layers does not affect the settlement of the
Pleistocene deposits as far as the coefficient of
permeability, k of the Pleistocene gravelly sand layers
exceed 100 m/day. The side boundaries of the clay
layers are set to be fully undrained as shown in Fig. 5.
The adopted soil parameters for the Pleistocene clay
deposits and loading sequence of Yumeshima
Reclaimed Island were already described by Mimura
and Jang (2004). It is assumed that an elastic
settlement occurs in the gravelly sand layers, which
can be calculated by the elastic shear modulus, G0
and Poisson’s ratio, Q'. In this research, the value of
G0 is determined by the above-mentioned two typicalempirical procedures with NSPT values. The used
empirical equations and determined G0 arecomparatively shown in Table 2. Here, the values of
NSPT and Q' of Osaka Pleistocene gravelly sand layers
are assumed to be 60 and 0.33 respectively (ResearchCommittee on Ground in Osaka Bay, 2002). The
value of D is assumed to be 40 in the empiricalequation suggested by Okura et al. (1996). It can beseen that the determined G0 is quite different between
two empirical equations as shown in Table 2. Whenthe target sand layers are relatively thick encounteredin Osaka Port, the total compression gained by the
Pleistocene gravelly sand layers can possibly not be
ruled out even if the strain level due to elastic
deformation is not so large.
3.2 Comparison of Compression for the Gravelly
Sand Layers
Vertical strain of the gravelly sand layers
calculated by using G0 that obtained from both
empirical equations for Yumeshima Reclaimed Island

Dg1

0.06 %

0.42 %

Ma12
Dg2
Ma11U
Dg3
Ma11L
Dg4
Ma10
Dg5
Ma9

Yoshinaka (1968)

Okura et al. (1996)

Fig. 6 Calculated vertical strain of the Pleistocene
gravelly sand layers
Table 3 Comparison of settlement for thegravelly sand layers
Layer

Settlement of gravelly sand layers (cm)
Yoshinaka (1968)

Okura et al. (1996)

Dg1

3.75

0.58

Dg2

6.66

1.02

Dg3

2.50

0.38

Dg4

12.49

1.91

Dg5

5.83

0.89

Total

31.23

4.78

is compared in Fig. 6 together with the vertical strainof the Pleistocene clay layers. As the same NSPT value
is assumed for all gravelly sand layers, the verticalstrain of those layers is the same irrespective of depth.
It is natural that the calculated vertical strain by G0
Yoshinaka for the gravelly sand layers is quite larger thanthat by G0 Okura et al. in Fig. 6, because G0 Okura et al. ismuch larger than G0 Yoshinaka. The vertical strain of
0.42 % and 0.06 % are obtained by G0 Yoshinaka and G0
Okura et al. in the gravelly sand layers respectively. The
calculated settlement of the gravelly sand layers at
Yumeshima Reclaimed Island is compared in Table 3.
It is noteworthy that the calculated settlement ofsandy layer is strongly affected by G0 values,
particularly when the target sandy layers are
relatively thick such as the ones encountered in
Osaka Port. Introduction of more sophisticatedconstitutive models for sands has to be considered todescribe realistic deformation including non-elastic
one in the Pleistocene sand layers. In the present
study, the linear elastic deformation is assumed

'P (kPa)

300
0
5
10

200
100
0

20
0

200

400

600

800

1000

Settlement (cm)

15
50
100
G0 Yoshinaka
G0 Okura et al.
Measured

150
200
0

1000

2000

3000

4000

5000

Elapsed time (days)

Fig. 7 Comparison of calculated settlement with in-situ settlement for Yumeshima Reclaimed Island
because we only have the information of NSPT values.
The sophisticated constitutive models require various
soil parameters derived form relevant laboratory tests.
Without those reliable values for soil parameters, thecalculated results by the sophisticated models cannot
guarantee the validity. The use of the sophisticatedmodels should be associated with the relevant subsoil
investigations that can provide reliable soil
parameters for the models. As the authors consider
that the simplified linear elastic behavior isappropriate for the condition that only values of NSPT
are available, the linear elastic model with G0 and Q'
is introduced in the present study.
The calculated settlement of the Pleistocene
deposits for Yumeshima Reclaimed Island iscompared with the in-situ settlement in Fig. 7. The
long-term settlement of the Pleistocene clay deposits
was already discussed (Mimura and Jang 2005). The
instant settlement occurring in the gravelly sandlayers is highlighted in Fig. 7. It can be seen in Fig. 7that the slight settlement took place at the starting
stage of reclamation. Scattering of measured data do
not merit discussion because of the resolution of
measurement. It is noteworthy to point out that thecalculated settlement with G0 Yoshinaka overestimatesthe measured settlement while that with G0 Okura et al.
can well describe the field data. From those results, it
is confirmed that the evaluation of G0 for the
Pleistocene gravelly sand deposits play a significant
role for the settlement prediction especially at earlyreclamation stage, and the values of G0 for the hard
Pleistocene gravelly sand layers should bedetermined by the procedure by Okura et al (1996).

4.

Conclusion Remarks
Sandwiched gravelly sand layers in the
Pleistocene deposit function as the permeableboundaries for compressible Pleistocene clay layers.
How the capacity of permeability of the Pleistocene
gravelly sand layers influences the compression of
the Pleistocene deposits is interpreted through theelasto-viscoplastic finite element analyses for
Maishima Reclaimed Island in Osaka Port. Becauseof the large thickness, well horizontal continuity andgravel-based formation, the Pleistocene gravelly sandlayers in Osaka Port have high permeability with thecoefficient of permeability of 2.16 x 101 m/day. On
the basis of the calculated performance, it isconcluded that the effect of the permeability can beruled out for the reclaimed islands in Osaka Port as
far as the values of the coefficient of permeability, kexceed 100 m/day. No serious propagation of excess
pore water pressure occurs in the Pleistocene gravelly
sand layers during reclamation. The mode ofsettlement of the Pleistocene deposit in Osaka Port is
scarcely affected by the permeability of the
sandwiched Pleistocene gravelly sand layers. In thesense, one-dimensional consolidation is permitted to
introduce for evaluation of the long-term settlementof the Pleistocene deposits inside the reclaimed
islands in Osaka Port.
Compression of the hard Pleistocene gravelly
sand layers is less influential than that of the
Pleistocene clay layers. As is often the case, thecontribution of those gravelly sand layers to thesettlement is not taken into consideration. However,the contribution of the Pleistocene gravelly sandlayers to the total settlement of the Pleistocene
deposits in Osaka Port merits a discussion because of
their large thickness. The procedure to evaluate therigidity of the hard Pleistocene gravelly sand layers is
introduced. The superiority of the present procedure
consists in the fact that the compression and swellingassociated with the change in effective stress due tolowering and recovering of the underground water
during excavation project were directly monitored in
the field. The in-situ derived values of the rigidity arecompletely free from disturbance by sampling, stressrelease and trimming. The calculated performancewith the rigidity of the Pleistocene gravelly sandlayers derived by the newly introduced procedure forYumeshima Reclaimed Island shows a good
agreement with the measured total settlement of the
Pleistocene deposit.
Acknowledgements
The authors express their sincere gratitude to thestaffs of Port and Harbor Bureau, City of Osaka for
their cooperation to provide the significant data.
Modeling of the subsoil condition and determinationof the required parameters are rationally conductedon the basis of the existing information from theGeo-database. Thanks are also extended to Mr. K.
Yamamoto and Mr. J. Nagaya, Geo-research Institutefor giving useful suggestion to utilize theGeo-database
References
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Mimura, M. and Jang, W.Y. (2004): Description oftime-dependent behavior of quasi-overconsolidated
Osaka Pleistocene clays using elasto-viscoplastic
finite element analyses, Soils and Foundations,Vol. 44, No. 4, pp. 41-52.

Mimura, M. and Jang, W.Y. (2005): Verification of
the elasto-viscoplastic approach assessing thelong-term
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and Jang, W.Y. (2003): Long-term settlement of
the reclaimed quasi-overcosolidated Pleistocene
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(1996): Change of underground water level andground deformation monitored during theconstruction of JR Katafuku Line, Proc. Symp. on
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Sekiguchi, H., Shibata, T., Mimura, M. andSumikura, K. (1988): Behaviour of the seawall andbridge abutment at the edge of an offshore airport
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海上埋立による更新統地盤の長期沈下に対する硬質砂礫層の寄与について
張

祐榮・三村

衛

要旨
大阪港では更新統砂礫層が厚く、十分な透水性を有しており、k=10-3cm/s 以上の透水係数であれば、その透水性は更新統粘土地盤の沈下性状にほとんど影響しないことがわかった。埋立初期からの更新統全層の沈下実測結果との比較から，更新統砂礫層の剛性はかなり大きく，地下水位低下に伴う有効応力変化によって生じる更新統
砂礫層の圧縮量から算定する大倉らの手法で求めた値がパラメータとして妥当であることがわかった。
キ−ワ−ド：擬似過圧密更新統粘土，更新統砂礫層，透水係数，過剰間隙水圧，せん断弾性係数，弾粘塑性 FEM