1624
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
0 1 2 3 4 5 6 7 8 9 10 11 12 13
-300
-200
-100
0
100
200
300
Time (sec)
Acceleration (Gal)
2d d
d
2d
X
Y
2d
2d
Compacted sand (Non-liquefied layer)
D
r
= 75 %
150 350
Loose sand (Liquefied layer)
D
r
= 40%
(mm)
600
Improved area
2650
390
Accelerometer
Pore water pressure transducer
Inclinometer
Colored sand for measuring of displacement
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11 A12A13
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
Gradient=10%
3 METHOD OF SHAKING TABLE TESTS
The shaking model tests were conducted at the University of
Tokyo by using a soil container that measured 2,650 mm in
length, 390 mm in width, and 600 mm in depth. The scale of
modeling was supposed to be 1/20.
3.1 Tests in a rigid box on sloping ground model
Figure 2 shows the schematic view of a sloping ground model.
The model ground consisted of a base unliquefiable layer of 150
mm in thickness, and a sloping and liquefiable sandy layer at
the top. The surface gradient was set equal to 10%. The entire
ground was made of Toyoura sand (
G
s
=2.684,
e
min
=0.605,
e
max
=0.974,
D
50
=0.21mm) and was submerged in water.
The base layer was prepared by air pluviation of dry Toyoura
sand, followed by compaction to the relative density of 75 %.
This dry layer was then saturated by one-hour slow percolation
of water. The upper liquefiable layer was prepared by water
pluviation to attain 40% relative density. This low relative
density was employed to cancel the effects of low effective
stress level on dilatancy and liquefaction resistance of sand
(Towhata, 2008). The height of fall was maintained constant,
irrespective of the ongoing height of sand surface, while the
water depth was also controlled to be 20 cm that was expected
to remove pore air from the falling sand and help achieve high
degree of saturation. During shaking, the water surface was set
at the same elevation as the top of the slope (Fig. 2).
The embedded columns were modeled by acryl pipes that
measured 26 mm in the outer diameter and 20 mm in the inner
diameter, respectively, implying the equivalent diameter of 520
mm in the prototype. The bottoms of the pipes were fixed, as
stated above, by screwing into a PVC (polyvinyl chloride) plate
of 20 mm thickness. On the other hand, the top of the pipes
were connected with another PVC plate of 5 mm thickness by
two O-rings. Thus, rotation was possible to occur at the top.
During shaking, acceleration, excess pore water pressure,
and lateral displacement of liquefied soil were recorded (Fig. 2).
The lateral deformation was recorded by photographs and
motion pictures of colored sand in the cross section (Fig. 3) and
on the surface. As Fig. 2 illustrates, the central part of the slope
model had vertical columns and the time history of lateral soil
displacement was recorded at both upstream and downstream
sides of the columns by using embedded inclinometers.
Moreover, some of the columns (acryl pipes) were equipped
Figure 2. Schematic view of sloping ground model
(a) Irregular configuration
Figure 3. Schematic view of sloping ground model
(c) Triangular configuration
(b) Square configuration
Figure 1. Geometry of column installation
Figure 4. Base input motion
Table 1. Details of sloping ground model
Test case
CASE1 CASE2 CASE3 CASE4 CASE5
Configuration
of columns
-
Irregular
Regularly
triangular
Improvement
ratio (%)
0
25
35
25
35
Maximum
acceleration
(Gal)
200
with strain gages to record bending strain therein.
Horizontal shaking took place in the longitudinal direction of
the slope with 10Hz and 200 Gal at the maximum, while the
duration time was 6 seconds (Fig.4). More details of tests are
summarized in Table 1 where configuration of columns and
improvement ratio are varied from tests to tests.
Table 2 summarizes the law of similitude concerning the
present study.
3.2 Tests in a rigid box on quay wall model
The second series of shaking tests were performed on sheet-pile
quay wall models with liquefiable backfill sand. The columnar
soil improvement was intended to reduce the distortion of the
quay wall and the backfill sand.
As illustrated in Fig. 5, a limited part of the backfill was
improved by columns. The sheet-pile quay wall was supported
by an anchorage plate (Fig.6) that was further supported by the
improved part of backfill sand.
The model ground consists of 100 mm compacted sand at the
bottom (relative density = 85%) and the upper 400 mm of
liquefiable sand (relative density = 40%).
The columns were modeled by PVC pipes whose outer
diameter was 26 mm, thickness 3 mm, and length 500 mm.
Pipes were filled with sand for equilibrium of weight and
buoyancy. Both top and bottom of the pipes were fixed to avoid
