2556
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Table 1 correspond to effective normal stresses of 100 kPa and
300 kPa. Lime treatment of Brenna clay increased fully
softened friction angle by 5 to 10
at effective normal stress of
100 kPa, and by 3 to 5
at 300 kPa. Lime treatment increased
the residual friction angle by 3 to 6
at both 100 kPa and 300
kPa. These results suggest formation of stable clay aggregates
through the lime-clay chemical reactions. These increases in
frictional resistance were realized with lime contents in the
range of 3 to 8% and treatment periods of 2 to 8 weeks. The
detailed correlation between improvement in frictional
resistance of Brenna clay as well as other stiff clays and shales,
with lime content and with duration of treatment, is under
further investigation with additional index and direct shear tests,
including scanning electron observations of reaction products.
Table 1. Frictional resistance of lime-treated Brenna clay
Sample I
c
(%) Curing
(days) w
0
(%) [φ’
fs
]
s
100
[φ’
fs
]
s
300
[φ’
r
]
s
100
[φ’
r
]
s
300
1
0.0
0
67
15
14
9
7
2
a
0.0
0
111
24
-
9
6
3
b
3.0
7
74
-
-
-
7
4
3.0
11
98
17
-
11
9
5
a
3.0
28
30
-
-
11
8
6
b
3.0
54
74
-
-
-
9
7
c
4.0
1
74
11
-
8
5.0
11
109
20
-
11
11
9
a
5.0
7
111
29
-
15
10
10
a,d
5.0
120
111
34
-
13
-
11
5.0
40
274
-
17
-
12
12
5.0
56
274
-
-
12
12
13
6.6
3
75
20
18
13
13
14
6.6
8
97
18
-
15
-
15
6.6
14
75
-
-
13
13
16
6.6
26
64
20
-
11
-
17
6.6
26
77
-
21
-
11
18
6.6
-
105
-
18
-
16
19
c
8.0
0.4
74
-
-
16
-
20
a
10.0
180
111
36
-
-
-
Notes:
a- Lower Brenna was used for these specimens.
b- Lime was sprinkled on top and bottom of the sample to
investigate the treatment caused by lime diffusion.
c- Lime was sprinkled on the shear surface.
d- Lime-treated sample was stored for 120 days before being
placed in the shear box.
For the 27
th
Avenue slide in Grand Forks, North Dakota
(Mesri and Huvaj 2004), with entire slip surface in Brenna clay
at residual condition, 5% lime content treatment of fifty percent
of the slip surface increases computed factor of safety from 1.00
to the range of 1.26 to 1.37 (
φ’
r
= 7 to 8
increases to
φ’
r
= 12
).
This level of lime remediation effort is expected to have a
significant effect on rate of movement of the slide.
A combination of horizontal directional drilling (HDD),
mechanical deep mixing (MDM) with augers and paddles, and
dry jet mixing (DJM), together with signal receivers at the
ground surface, is being investigated for introducing lime into
clay along a pre-existing slip surface. The longest crossing of
HDD to date has been 2000 m and borehole diameter of up to
160 mm.
6 CONCLUSIONS
Remediation of the montmorillonitic Brenna clay from North
Dakota using lime contents of 3 to 8% and treatment periods of
2 to 8 weeks increased drained fully softened friction angle by 3
to 10
and drained residual friction angle by 3 to 6
, in the
effective normal stress range of 100 to 300 kPa. The increase in
drained frictional resistance suggests formation of stable clay
aggregates through lime-clay chemical reactions under the
highly alkaline pH 12.5 to 9.8 environment measured over a
period of 8 weeks. The measurements of liquid limit as an
indicator of changes in particle size and shape resulting from
lime treatment must be carried out on samples cured under an
effective stress condition rather than sealed but unconfined.
Unconfined lime treatment results in a significant increase in
liquid limit, thus underestimating the decrease in plasticity
index and associated increase in frictional resistance resulting
from lime remediation.
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