608
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
①
Pump
②
Mud screen
③
Mixer for mud water
④
Boring machine
⑤
Tank for clean water
⑥
Tank for sludge
⑦
Suction tank
⑧
Tank for mud water
⑨
Winch
⑩
Casing pipe
(
Φ
=10”,8”,6”)
Sea level
Sea bottom
Boring rod
(
Φ
=135mm)
Outer tube
Rigid sampler or
Denison sampler
Wire rope
(
Φ
=9mm)
Water pressure
Thin-walled tube sampler
with fixed piston
Sample
Sampling tube
Figure 1. System of Koken wire line method.
Bit
Guide ring
Outer cube
Inner cube
Sampling tube
Drain hole
Ball cone clamp
Shoulder ring
Wire
Piston
Piston rod
Valve for air extraction
Denison sampler
Cutting wedge
Outer tube
Sampling tube
Ball check
Shoulder ring
Latch
Wing
Bit
Inner tube
Spring
Thrust bearing
Thin-walled tube sampler with fixed piston
Rigid sampler
Metal crown
Outer tube
Inner tube
Sampling tube
Shoulder ring
Latch assembly
Spring
Bit
Guide ring
Ball check
Figure 2. Samplers for Koken wire line method.
3 ESTIMATION OF SAMPLESQUALITY OBTAINED
FROM GREAT DEPTH
The samples obtained from great depth which is up to 400m
in depth are influenced not only mechanical disturbance but
also stress release. As mechanical disturbance can avoid
improving sampling technic, stress release cannot avoid even
what kind of method. Therefore, the estimation of sample
quality has to be examined quantitatively to interpret the
results of constant strain rate consolidation test (CRS test).
The volumetric strain which is consolidated to
the in-situ effective stress,
ε
v0
, can be used as
an indication of sample quality. The relationship between
change of
ε
v0
and quality of samples having various degree of
sample disturbance is shown in Table 2 (Andersen A. and
Kolstad P. 1979). The relationship between
Δe/e
0
and sample
quality, where
Δe
is change in void ratio in recompressing a
sample to in-situ effective stress and
e
0
is initial void ratio, is
shown in Table 3 (Lunne T., et al. 1997). According to this
figure, when the range of
Δe/e
0
is within 0.07, the sample can
regard good quality.
The change of
ε
v0
and
Δe/e
0
profile of Pleistocene clay
samples with recompression to the corresponding in-situ
effective vertical stress is shown in Figure 3. With few
exceptions, the range of
ε
v0
varies within 2% to 4%. It is
apparent that the majority of samples of Pleistocene clay are
good quality. The values of
Δe/e
0
vary in a narrow band of
0.04 to 0.07, and are not sensitive with depth. It may be
recalled that if
Δe/e
0
is within 0.07, the soil samples can be
considered to be good quality.
The relation between
ε
v0
and OCR, Δ
e
/
e
0
and OCR of
Pleistocene clay samples is shown in Figure 4. It is obvious
that OCR is almost constant with depth, and is independent of
ε
v0
and Δ
e
/
e
0
. As the consequence, it is clear that the samples
obtained from great depth in the Osaka bay have good and
uniform quality.
Table 2. Relationship between volumetric strain (
ε
v0
) and sample
uality.
q
ε
v0
(%)
Sample quality
＜
1
Very good
1
～
2
Good
2
～
4
Fair
4
～
10
Poor
＞
10
Very poor
Table 3. Relationship between changing rate of void ratio (Δ
e
/
e
0
) and
ample quality.
s
Δ
e
/
e
0
Overconsolidation
Ratio
Very good
to excellent
Good
to fair
Poor
Very
poor
1-2
＜
0.04
0.04-0.07
0.07-0.14
＞
0.14
2-4
＜
0.03
0.03-0.05
0.05-0.10
＞
0.10
For particular clay multiply Δ
e
/
e
0
by
e
0
/(l+
e
0
) to get the criteria in terms of
ε
V0
Table 1. Specification of samplers.
Sampler
Sampling tube
Applicated
soil property
Sampler Name
Outer
diameter
(mm)
Length
(mm)
Remarks
Material
Inner
diameter
(mm)
Thickness
(mm)
Angle of
edge
(°)
Ratio of
inside
diameter
(%)
Length
(mm)
Remarks
Soft clay
Thin-walled tube sampler
with fixed piston
108
4358
Hydraulic type
sampler
Stainless steel
(SUS-304)
90
2
6
0
1250
-
Stiff clay
Thick-walled tube sampler
with fixed piston
108
4358
Hydraulic type
sampler
Same as the
above
81.1
4
6
0
1170
Exchange of
edge blade is
possible
Stiff clay
Denison sampler
108
2850
Projection length
of edge blade
(20-50mm)
Same as the
above
81.1
4
6
0.5
1000
Exchange of
edge blade is
possible
Stiff sand and
gravel
Rigid sampler
108
2875
-
Same as the
above
90
2
-
-
1000
-
