425
Technical Committee 101 - Session II /
Comité technique 101 - Session II
series of recent tests in connection to a ground investigation at
Esbjerg Habour (EB) highlights the strength properties of Mica
clay – a Miocene marine clay of high plasticity.
The additional old test data covers glacial clay till, a few
glacial/late glacial meltwater and late glacial marine clays and
furthermore a wide range of Tertiary (Palaeogene) marine clays
of late Miocene age to Palaeocen age: Mica clay, Septarian clay,
Søvind marl, Lillebælt clay, Røsnes clay, Ølst clay, Tarras clay
and Holmehus clay.
The majority of the very high plasticity Palaeogene clays
from the listed test series are found to be fissured in nature.
Figure 4 shows the outline of the index properties of the
tested clays in Casagrandes classification chart. The
classification parameters have generally been determined in
accordance with BS 1377:Part 2:1990 using the Casagrande
method to determine the liquid limit. The data points for the
different soils generally fall close around straight lines and
above the A-line corresponding to clays of very low
(4%<I
P
<7%) to extremely high plasticity (I
P
>100%).
Figure 4. Outline of index properties of the tested clays shown in
Casagrandes classification chart I
P
vs. w
L
The classification parameters incl. clay-size fraction (CF) and
natural water content w
n
for the tested clays are also listed in
Table 1 alongside test types and number of tests (n). For the
consistent test series (GB, FB and EB) the mean values of the
classification parameters are listed and the standard deviations
are shown in brackets. A more detailed description of the
Palaeogene clays incl. mineralogy is given by Fehmarnbelt
(Fixed Link) 2011.
2.2
Test procedures
The recent triaxial compression tests have generally been
performed on nominally undisturbed specimens with a diameter
of approximately 70mm and a height to diameter ratio of 1.
Smooth end platens have been used. Samples have been
extracted by means of a push-in Shelby-tube sampler (called A-
tube in Denmark) with an inner diameter of 70mm.
Samples are saturated using backpressure and typically
preloaded to reduce the effects of possible sample disturbance
and bedding effects. The preloading are in most cases
performed under anisotropic K
0
conditions. After the preloading
and unloading of the sample, the specimen is sheared in either
drained or undrained compression to failure. Multiple tests are
carried out, consisting of preloading, unloading to a new and
higher stress level followed by a drained or undrained
compression test (these steps are repeated 2 or more times).
The applied rate of straining during shearing is chosen
according to the soil type to ensure slow enough rates to achieve
full equalization of pore water pressures in the specimen. For
the high plasticity clays this means that the applied strain rate is
around 0.02-0.05%/hr, while a strain rate of approximately 0.1-
0.7%/hr has been used for specimens of clay till.
For specimens of very high plasticity clay care is generally
taken during all test stages to avoid that the effective stress
reduces below the in-situ stresses to prevent swelling, which
may lead to destructuration of the micro-structure (Leroueil and
Vaughan 1990).
Older triaxial compression tests have in contrast typically
been performed with a height to diameter ratio of 2:1 and a
diameter of approximately 36 mm. Samples were usually
extracted using a 42mm inner diameter sampler. Preloading was
in some cases carried out under isotropic conditions and in some
cases omitted. Saturation was in most cases carried out without
the application of backpressure and compression was performed
with the pore water pressure kept equal to zero. Hence,
undrained compression was achieved by adjusting the cell
pressure during testing to obtain constant volume displacement.
The applied rate of straining during the compression stage
was generally higher than what would be recommended today
to ensure full equalization of pore water pressures within the
samples of especially high plasticity clays. Hence, the actual
effective stresses at the failure state are somewhat uncertain
because the pore water pressure is unknown. Nevertheless, the
old triaxial tests constitute a very comprehensive database of
strength parameters for low to high plasticity clays, which can
be compared to the recent and presumably more reliable tests
results.
Table 1. Overview of classification parameters and larger series of
triaxial compression tests on undisturbed overconsolidated clays
performed by GEO.
Project
Soil
type
w
n
#
[%]
w
L
#
[%]
I
P
#
[%]
CF
#
[%]
Test types
n
GB
(1992)
Clay till
11
(2)
16
(2)
6
(2)
-
MCAU
u=0
and CAU
45
FB
(2011)
Upper till
9
(-)
19
(1)
7
(1)
26
(9)
CAU and
CAD
5
Chalk till
9
(-)
20
(1)
6
(0)
23
(-)
CAU and
CAD
5
Lower till
13
(5)
28
(4)
16
(3)
24
(3)
CAU and
CAD
8
Røsnes
35
(4)
147
(28)
117
(27)
70
(7)
CAU and
CAD
48
Ølst
45
(11)
140
(25)
106
(23)
51
(15)
CAU and
CAD
5
Holmehus
42
(6)
133
(23)
98
(25)
61
(7)
CAU and
CAD
5
Palaeogene
clays
37
(6)
145
(27)
114
(27)
67
(9)
CAU and
CAD
58
EB
(2012)
Mica clays
28
(3)
58
(9)
36
(8)
-
MCAU,
MCAD,
MCIU
10
Other
recent
test
Tertiary
clays
-
-
19-
85
-
MCAD
CAU
CU
8
GEO old
test
(> 30
yrs)
(Late)
Glacial &
Tertiary
clays
-
-
5-
151
-
CAU
u=0
CAD
u=0
CU
u=0
CD
u=0
108
#
mean values with the standard deviation shown in brackets
An overview of the number of tests (n) and test types are given
in Table 1. The following abbreviations are used:
CAU/CAD Anisotropically (K
0
) Consolidated.
Undrained/Drained compression.
MCAU/MCAD Anisotropically (K
0
) Consolidated.
Undrained/Drained compression. Multiple test on the
sample.
CU/CD Isotropically Consolidated Undrained
/Drained compression.
u=0 denominates older test procedures with no
backpressure and pore water pressure kept at zero
kPa.
0
50
100
150
200
250
0
50
100 150 200 250 300
I
P
(%)
w
L
(%)
A-line
I
P
=0.73·(w
L
-20)
Palaeogene
clays (FB)
v.high plasticity
tertiary clays
(oldtest)
Lowto high plasticity
lateglacial,glacialand
tertiary clays (old test)
Claytills(GB)
Glacial
deposits (FB)
