1501
Technical Committee 203 /
Comité technique 203
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 4 shows the
e
-log
p’
relationship observed in the
oedometer tests for these specimens from the shallow and deep
layers. It can be seen that the intact specimens from each layer
exhibited characteristics of high compression after application
of consolidation yield pressure (about 140 kPa) compared to
those of the reconstituted specimens. The compression index
ratio (defined as the ratio of the compression index of the intact
samples to that of the reconstituted samples) values for the
shallow and deep layers were 1.40 and 2.25, respectively.
According to Asaoka et al. (2000), clay obtained from deep
layers is characterized by a light structure. The layers in the
vicinity of the ground surface at the site appear to have been
over-consolidated, as the consolidation yield stress of samples
from both depths was about 140 kPa.
Figure 5 shows the relationship between deviator stress and
axial strain, and the effective stress paths of the static CU tri-
axial tests for the intact specimens sampled from both layers.
For the deep-layer samples with confining pressure values of 50
kPa and 100 kPa, the mean effective stress decreased with
greater excess pore water pressure (EPWP) and the mean
effective stress increased after the stress path reached the
critical state line (CSL), meaning that the volume of the soil
skeleton decreases after the deviator stress turned down. This
indicates that the samples exhibited compression-softening
behavior and were lightly structured. However, such behavior
was not observed in the samples with confining pressure values
of 150 kPa due to structural collapse during the isotropic
consolidation process up to more than consolidation yield stress
before shearing. Conversely, the samples from the shallow layer
showed typical behavior of over-consolidated soils, and the
deviator stress when the stress path reached the CSL was
slightly greater than that for the sample from the deep layer
subjected to the same conditions of confining pressure loading.
4 NUMERICAL SIMULATION
The Cyclic Mobility model developed by Zhang et al. (2007),
which incorporates the concepts of subloading and superloading
as described by Hashiguchi and Ueno (1977) and Asaoka et al.
(2002), was used as the constitutive model. A brief description
of its yielding surfaces and the evolution rule for the anisotropic
stress tensor, the degree of structure and overconsolidation is
given as:
( ,
∗
, ) + ln
∗
− ln −
= ln + ln
∗
+ ln
∗
− ln − = 0
(1)
̇
=
(
)
‖ ‖
=
√ (
)
(
∗
)
(2)
̇
∗
=
∗
(1 −
∗
)
=
∗
(
∗
)
∗
(
∗
)
(3)
̇
= −
(
)
(
)
ln ‖ ‖ + ⋅ ̇
=
∗
(
)
(
∗
)
(
)
(
)
+ ⋅ ̇
(4)
Figure 5 shows the performance of the element simulation
for the behavior of clay in undrained static compression tests.
The values of the material parameters and the initial conditions
used in the simulations are listed in Table 2. It can be seen from
this information that the simulation results exhibit close
correspondence to the experimental results except in the case of
high confining pressure. Soil was not sampled from this layer in
previous field investigations because no subsidence was
observed there. In this simulation, the values for typical silt such
as Fujinomori clay were used as parameters for the silt layer.
Figure 4.
e
-log
p’
relationship for intact and reconstituted
samples from the shallow and deep layers.
Figure 5(a). Static triaxial test simulation for intact samples
from the shallow layer
Figure 5(b). Static triaxial test simulation for intact samples
from the deep layer
Table 2. Soil parameters used in the simulation
The DBLEAVES soil-water coupling FE analysis code (Ye
et al., 2007) was used in the study’s simulation. The FE model
is simplified to a one-dimensional column of soil elements
measuring 1 m in width, length and height as shown in Figure 6.
Here it is assumed that the ground is level, and the effects of
terrain geometry are not taken into account in the simulation.
The boundary conditions are as follows: (a) The bottom of the
ground is fixed. (b) In dynamic analysis, an equal-displacement-
boundary condition is applied between nodes in two sides of the
ground; when the analysis is shifted to consolidation, the
boundary condition is changed to a fixed one. (c) The ground
surface is set with a drainage condition, while the other surfaces
are impermeable.
0.5
1.0
1.5
2.0
2.5
3.0
1
10
100 1000 10000
Intact (G.L. -16.7m ~ -19.0 m)
Reconstituted (G.L. -16.7m ~ -19.0m)
Intact (G.L. -9.0m ~ -11.7m)
Reconstituted (G.L. -9.0m ~ -11.7m)
Void ratio
e
Consolidation pressure (kPa)
Compression index ratio
c
c
/c
cr
= 2.25
Compression index ratio
c
c
/c
cr
= 1.40
0
50
100
150
200
250
0
5
10
15
50kPa (E)
100kPa (E)
150kPa (E)
50kPa (S)
100kPa (S)
150kPa (S)
Mean effective stress (kPa)
Deviator stress (kPa)
0
50
100
150
200
250
0 50 100 150 200 250
50kPa (E)
100kPa (E)
150kPa (E)
50kPa (S)
100kPa (S)
150kPa (S)
Mean effective stress (kPa)
Deviator stress (kPa)
0
50
100
150
200
250
0
5
10
15
50kPa (E)
100kPa (E)
150kPa (E)
50kPa (S)
100kPa (S)
150kPa (S)
Deviator stress (kPa)
Axial strain (%)
0
50
100
150
200
250
0 50 100 150 200 250
50kPa (E)
100kPa (E)
150kPa (E)
50kPa (S)
100kPa (S)
150kPa (S)
Mean effective stress (kPa)
Deviator stress (kPa)
Shallow layer
Deep layer
Silt
Compression index
l
0.264
0.214
0.104
Swelling index
k
0.080
0.031
0.010
Stress ratio at criticalstate
R
f
3.500
3.500
3.000
Void ratio (
p
'=98kPa on N.C.L)
N
1.610
1.540
0.920
Poisson's ratio
n
0.330
0.330
0.200
Degradation parameterofoverconsolidation state
m
5.000
15.000
2.200
Degradation parameterof structure
a
2.200
1.200
0.100
Evolution parameterofanisotropy
br
0.100
0.100
0.100
Initialmean effective stress [kPa]
p'
8~ 73
78~111
117~295
Initialdegree of structure
R
0
*
0.950
0.600
0.100
Initialdegree ofoverconsolidation
1/R
0
1.9~19
1.3~1.8
2.500
Initialanisotropy
z
0
0.000
0.000
0.000
Permiablity [m/sec]
k
1.00E-09
1.00E-09
1.00E-07
Saturated unit weight [kN/m
3
]
g
sat
15.36
15.66
17.00
Unit weight underwater [kN/m
3
]
g
'
5.36
5.66
7.00
