454
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
100 km
55ºN
105ºE
107ºE
109ºE
53ºN
Novosibirsk
Kukuy
53ºN
55ºN
Figure 1. Survey and sampling sites in the Lake Baikal.
3 ON-BOARD TEST RESULTS
Figure 2 shows the on-board tests results (vane share strength,
v
, and cone penetration resistance,
q
c
), together with the
profiles of water content,
w
, with depth. In the samples retrieved
from Novosibirsk site, the water contents in the upper strata of
samples that were able to collect GH in lower part of the core
(with GH) are lower than those of the samples that were not
able to collect GH (without GH), and the strengths of samples
with GH are higher than those of samples without GH, as
shown in Figure 2(a). On the other hand, in the samples
retrieved from Kukuy site, although the water contents of
samples with GH are lower than those of samples without GH
as same as Novosibirsk samples, the strengths are similar, as
shown in Figure 2(b). Thus, the relations between the strength
and the water content are different from the sampling site. The
reason seems to be that the difference of degree of sample
disturbance due to the exsolution of dissolved gas in the pore
water caused by the decrease of pressure during the pulling up
of core, because the concentrations of methane gas dissolving in
pore water may be different from site. Then, the concentrations
of methane gas dissolving in the pore water of sediments were
measured, and the effects of the concentrations of gas on the
strength of samples were examined.
Figure 3 shows the relations between the depth and the
concentrations of dissolved methane gas, CH
4
, per sediment of
one liter (Hachikubo et al. 2010). In the case of Novosibirsk
samples, the gas concentrations are high from surface layer,
irrespective of with/without GH. On the other hand, in the case
of Kukuy samples, although the gas concentrations of samples
with GH are high from surface layer, those of samples without
GH are low at surface layer and increase suddenly from a
certain depth.
Figure 4 shows the relations between the vane shear strength,
v
, and the water content,
w
. It is found that the difference of
strengths in Novosibirsk samples is not recognized irrespective
of with/without GH, as shown in Figure 4(a). It would seem that
the degree of sample disturbance due to the exsolution of
dissolved gas in the pore water are similar, because the gas
concentrations are high from surface layer irrespective of cores,
as shown in Figure 3(a). On the other hand, in Kukuy samples,
the strengths of samples with GH are lower than those without
GH. It would seem that this is because the gas concentrations of
samples with GH are high from surface layer as shown in
Figure 3(b), so that the sample disturbance due to the exsolution
of dissolved gas became large, and the strength became low.
Thus, the correlation between the strength and the water content
is recognized, considering the sample disturbance due to the
difference of the gas concentration. The similar test results were
obtained on the sea-bottom sediments retrieved from offshore
Sakhalin Island, Sea of Okhotsk (Yamashita et al. 2011).
400
350
300
250
200
150
100
50
0
0 100 200 300 0 10 20 30 40 50 0 100 200 300 400
w
(%)
Depth (cm)
v
(kN/m
2
)
q
c
(kN/m
2
)
:without GH
:with GH
Novosibirsk
(a)
400
350
300
250
200
150
100
50
0
0 100 200 300 0 10 20 30 40 50 0 100 200 300 400
w
(%)
Depth (cm)
v
(kN/m
2
)
q
c
(kN/m
2
)
:without GH
:with GH
Kukuy
(b)
Figure 2. On-board test results; (a) Novosibirsk site, (b) Kukuy site.
400
350
300
250
200
150
100
50
0
0 50 100 150 0 50 100 150 200
CH
4
(mL/L)
Depth(cm)
:without GH
:with GH
Novosibirsk
CH
4
(mL/L)
Kukuy
(a)
(b)
Figure 3. Concentration of methane gas with depth; (a) Novosibirsk site,
(b) Kukuy site.
0
100
200
0
10
20
30
40
0
100
200
300
v
(kN/m
2
)
w
(%)
:without GH
:with GH
Novosibirsk
w
(%)
Kukuy
(a)
(b)
Figure 4. Relations of vane shear strength and water content;
(a) Novosibirsk site, (b) Kukuy site.
