968
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
20 40
0
100
60 80
4
2
0
6
8
Time
(sec)
large shear strain. Especially in Step C, volumetric strain tends
to expand with smaller shear strain compare to injection at
deeper depth (Step A and Step B). This derive from failure
mode at shallower depth tend to be uplift mode due to low
confining pressure, thus it can be said that a certain grout pile
diameter or injection volume is not largely contribute to
densification especially at shallower depth.
3.2 Centrifuge test
Figure 8 presents the changes in horizontal stress recorded
during shaking table test on centrifuge, expressed as K =
(horizontal effective stress, σ’
h
) / (initial vertical effective stress,
σ’
v0
). The results were fileted to remove the effect of variation
due to shaking. The K value before shaking starts (0 sec ~ 3 sec)
presents the value after grout injection. The influence of size of
shearing area by one grout pile or improvement ratio is clear,
with larger improvement ratio resulting in higher K value after
grout injection. The residual K value after shaking test in Cases
CPG18s and CPG30s keeps high K value even 250 m/s
2
of
acceleration was applied to the ground. This feature indicates
that the improved ground by CPG possibly to keep its
improvement effect in terms of residual K value. Figure 9
shows time histories of ratio of excess pore water pressure, Ru
= (excess pore water pressure ∆u) / (initial vertical effective
stressσ’
v0
). Liquefaction was observed in Case CPG30n,
without grout injection, from beginning of the dynamic loading.
In contrast, the remarkable increase of Ru cannot be observed in
the cases with grout injection even in the case CPG30s with
lower improvement ratio. This is indicating that the increase of
K value due to grout injection provides the increase of
liquefaction resistance even in lower improvement ratio.
4
CONCLUSIONS
Ground behavior due to compaction grouting was studied by x-
ray tomography and centrifuge tests, with particular interest in
the density change and the increase of liquefaction resistance.
Density change and ground response due to grout injection
were not only visualized by x-ray tomography but also
discussed quantitatively based on results of image analysis,
Volumetric Digital Image Correlation (V-DIC). The mechanism
of ground deformation caused by grout injection can be
considered as a cavity expansion for deep injection and cone
uplift for shallow injection. The densification of ground was
mainly observed in the area around the grout pile. However, it
can be also said that a certain grout pile diameter or injection
volume is not largely contribute to densification especially at
shallower depth because of lower confining pressure.
The influence of the improvement ratio appeared in the
residual K values after grout injection which was observed in
centrifuge tests. As the results of shaking table test, the increase
of K value due to grout injection provides the increase of
liquefaction resistance even in lower improvement ratio of
about 5 %.
5
REFERENCES
Boulanger R.W. and Hayden R.F. 1995. Aspects of compaction
grouting of liquefiable soil.
Journal of Geotechnical Engineering
,
ASCE
, 121 (12), 844-855.
Miller E.A. and Roycroft G.A. 2004. Compaction grouting test program
for liquefaction control,
Journal of Geotechnical and
Geoenvironmental Engineering, ASCE
, 130 (4), 355-361.
Nishimura S., Takehana K., Morikawa Y. and Takahashi H. 2012.
Experimental study of stress changes due to compaction grouting.
Soils and Foundations
, 51 (6), 1037-1049.
GL -3.3 m
GL -7.8 m
shaking
K
value
(σ
h
’ /σ
v0
’ )
20 40
0
100
60 80
Time
(sec)
GL -3.3 m
GL -7.8 m
shaking
K
value
(σ
h
’ /σ
v0
’ )
4
2
0
6
8
20 40
0
100
60 80
Time
(sec)
shaking
GL -3.3 m
GL -7.8 m
K
value
(σ
h
’ /σ
v0
’ )
4
2
0
6
8
(a) CPG18s
(c) CPG30n
(b) CPG30s
Figure 8. Time history of K values
20 40
0
100
60 80
0.6
0.4
0.0
0.8
0.2
1.0
Time
(sec)
R
u
GL -3.3 m
GL -7.8 m
shaking
20 40
0
100
60 80
0.6
0.4
0.0
0.8
0.2
1.0
20 40
0
100
60 80
0.6
0.4
0.0
0.8
0.2
1.0
GL -3.3 m
shaking
GL -3.3 m
shaking
Time
(sec)
R
u
GL -7.8 m
Time
(sec)
R
u
GL -7.8 m
(a) CPG18s
(c) CPG30n
(b) CPG30s
Figure 9. Time history of ratio of Ru
