413
Technical Committee 101 - Session II /
Comité technique 101 - Session II
decomposition sequence of these minerals is also in agreement
with the stability order of minerals by Goldich (1938).
7 INTERFERENCE DRAWN FROM CORRELATION
The correlation between the engineering and geological
properties infers the conclusion that the pattern of the curves
obtained in the model (Fig 1) is apparently dominated by the
content of Feldspar and extent of decomposition of Feldspar in
relation to other constituent minerals.
The samples represented by the points along the curve A-B
show a continuous decomposition of Feldspar and alteration of
Biotite to Chlorite with the increase of the values of ½ (log
e
γ
d
+
3
√PI) and log
e
tanψ. Therefore it has been inferred that the initial
tangent modulus is apparently related to the content and extent
of decomposition of Feldspar and hence is expected as a major
influential factor in estimating the elastic behaviour of cohesive
soil.
The points along the curve C-D shows some exception to
the above inference and possibly suggests a reversal of the
above, whereby Ferromagnesian minerals are undergoing the
process of decomposition with increase in the values of log
e
tanψ and decrease in the values of ½ (log
e
γ
d
+
3
√PI). The point
number "O" is obviously an intermediate point for both the
curves of the model.
Correlation of engineering and geological properties based
on specific gravity analysis shows that the point no "O", that is,
the intersection point has the highest value of specific gravity
being 2.65, thereby suggesting presence of more or less an
intermediate composition of light and dark coloured minerals.
The bottom point of the curve A-B shows a specific gravity of
1.99 and the upper point of the curve A-B shows 2.19,
indicating enhancement of decomposition and alteration of both
light and dark coloured minerals with the increase in the values
of ½ (log
e
γ
d
+
3
√PI) and log
e
tanψ. The bottom and top points
of the curve C-D shows specific gravity values of 2.19 and 2.4
respectively, thereby indicating that Ferromagnesian minerals
have increased with the increase of log
e
tanψ and decrease of ½
(log
e
γ
d
+
3
√PI) values.
8 CONCLUSION
As the outcomes of the research, influence of a prime
constituent mineral has been identified and the extent of its
influence is derived. The constitutive modelling, an outcome of
the correlative study, is analysed based on its typical pattern.
The model thus derived, within the set scope of investigation,
has led to the conclusion that the pattern is unique for cohesive
soils and is under the possible domination of a common mineral
and extent of its weathering process. It leads to the indication of
the profound influence of mineral and its weathering state upon
elastic behaviour of cohesive soils. The model pointed out that
some of the engineering and geological properties are
interdependent. The model has been calibrated with other
available empirical correlations and its application in civil
engineering and limitations are derived. Outlines of subsequent
research areas are also indicated.
9 REFERENCES
Bowen N. L. 1915a.
The crystallisation-differentiation in silicate
liquids
, American Journal of Science, Series 4, 39, 175-191.
Bowen N. L. 1915b.
The crystallisation of haplobasaltic, haplodioritic,
and related magmas
, American Journal of Science, Series 4, 40,
161-185.
Goldich S. S. 1938. A study in rock weathering. Journal of Geology. 46,
17-58.
A carefully documented account of the chemical and
mineralogical changes produced by weathering on a granite gneiss,
two diabases, and an amphibolite.
Hussain M. 1996. A Correlative Study of Geological Nature and
Engineering Properties of Clay Samples to Interpret their Influence
upon elastic Behaviour of Cohesive Soil.
A dissertation submitted
for the Degree of Master of Science in Geology.
Gauhati
University, India.
Mason B. and Moore C. B. 1991.
Principles of Geochemistry.
Wiley
Eastern Limited. 4th Edition. P 155
10 NOTATIONS
γ
d
: Dry Density
PI: Plasticity Index
Tan ψ: Initial Tangent Modulus
ψ: Angle between initial tangent modulus and abscissa.
11 ACKNOWLEDGEMENTS
Author
1
wishes to thank Dr M. Chakravartty, Senior Lecturer,
Department of Geology, Cotton College, Guwahati, India for
agreeing to the area of research for joint supervision and for
scrutinising the geological aspects of the dissertation [Hussain
1996]. Further, Author
1
wishes to thank Ms Mehjebeen Hussain
nee Simi Deka, the Research Scholar for accomplishing the
R&D work as per the expectation. Furthermore, Author
1
wishes
to acknowledge the immense support he received from the
entire team of Road Research Laboratory, Guwahati, India,
where he worked as in-charge of the pavement laboratory. Last
but not the least, Author
1
wishes to record the contribution of
Author
2
in context to her contributions pertaining to this paper
in general literature review and from her international
publications on the correlation of partially saturated clays with
simple index properties. Besides general technical review she
specifically contributed to the translation aspects, being a
French literate.
