1192
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
reflects the attempt to correlate the degradation magnitude of
constructions founded on such soils, with the intensity of the
swell potential (Figure 1 and Figure 2) (Das 1995).
Table 1. The physical properties of the representative investigated clays.
Soil
Liquid
limit
(%)
Plasticity
index (%)
Colloidal
fraction
(%)
Reference
Bahlui clay-
Romania
83÷98 57÷67
51÷87
Boti, 1974
London
clay-U.K.
60÷71 36÷43
42÷60 Gasparre , 2005
Hubballi
clay- India
51÷71 32÷53
51÷56
Hakari, 2010
Ankara clay
-Turkey
64÷75 29÷34
39÷55
Hakari, 2010
Figure 1. The classification of the swell potential, after Van Der Merwe,
1964.
It was noticed though, both from the published data and from
the results in Table 2 that these two approaches (Van Der
Merwe and Casagrande) using only two indices (I
P
, w
L
),
indicate different magnitudes of the swell potential for the same
soil.
By consequence, the Romanian Norms (STAS 1913/12-88
and Code N.E. 0001-96) propose
the use of the “soil chart” to
identify and characterize the expansive soils. This
representation, considered unique (Andrei 1980) and specific
for each soil, is obtained by joining the points I; II; III; IV and
V on a composite diagram by assembling on the same graph, the
Casagrande-Chleborad diagram, the Skempton-Van Der Merwe
diagram and the granulometric curve (Figure 3). The size of the
figure area (I, II, III, IV and V), (
A
) constitutes a first criterion
to characterize the soil swell potential (Andrei 1997). The
reference circle that intersects the 50% w
L
, I
P
, X
d
points and the
1mm diameter as the point of interest on the diameter axis is
introduced to scale the graph on the four axes. The normalized
surface is calculated (
0
n
A
) using the reference circle area (
A
circle
)
with the formula:
0
/
n
circle
A A A
(1)
It is defined an activity coefficient (
C
A
), constructed
similarly as the consistency index (I
C
), to evaluate the
magnitude of the swell potential (Stanciu et al. 2011), fixing as
the variation limits, the chart minimum and maximum areas for
two soils with extreme behaviour: with maximum content of
kaolinit, as with the lowest potential, and of sodium
montmorillonite as for soils with maximum volume variations.
Figure 2. The classification of the swell potential based on the
Casagrande’s plasticity chart
.
Table 2. The swell potential of the investigated clays.
The classification of the swell potential after
Soil
Van Der Merwe
Casagrande
Bahlui clay-Romania
Very high
Very high
London clay-U.K.
Very high
High
Hubballi clay- India
Very high
High
Ankara clay -Turkey
High
High
By consequence, the activity coefficient
C
A
for the
normalized area of the soil chart
n
O
A
is given by the relation:
(
) / (
)
n
n
n
n
A
O C
M C
C A A A A
(2)
where:
C
A
–
the activity coefficient;
n
O
A
- the normalized area of
the chart referring to the investigated soil;
n
C
A
- the normalized
area of the kaolin chart;
n
M
A
- the normalized area of the sodium
montmorillonite chart.
The clay swell potential can be classified based on the value
of the activity coefficient as presented in Table 3.
Table 3. The classification of the soil swell potential based on the
activity coefficient, after Stanciu 2011
Activity coefficient
C
A
Swell potential
0 ÷ 0.24
low
0.25 ÷ 0.49
medium
0.50 ÷ 0.74
high
0.75 ÷ 1.00
very high
The example of this new evaluation procedure for the clay
swell potential is presented in Figure 3, where the average
charts have been plot for four representative clays: from
London, Hubbali, Ankara and Bahlui-Romania, together with
the corresponding Romanian kaolinitic and montmorillonitic
clays. The values of the normalized area
n
A
and respectively
the values of the activity coefficient
C
A
have been calculated for
each soil, based on the plotted charts from Figure 3 (Table 4).
The resulted swell potential from the classification based on
the activity coefficient
C
A
, referring to the diagrams of
