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Influence of Minerals on the Elastic Behaviour of Cohesive Soil
Influence des minéraux sur le comportement élastique des sols cohésifs
Sarma D., Sarma M.D
M-AGS, M-ISSMGE, Independent Consultant (Southern Africa)
ABSTRACT: The trend of predicting the design parameters of soil from the index properties is continuing since decades, however,
those correlations do not focus much on the prediction of elastic behaviour of cohesive soils. Moreover, the influence of mineral(s) for
the validation of such correlations is either ignored or presumed to be covered by the Atterberg's limits. As the outcomes of the
research, pertaining to the title of the paper, 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 the investigation has led to the conclusion that the pattern is unique for cohesive soils and is under the
possible domination of the existence of a common mineral and extent of its weathering process. It leads to the indication of the
profound influence of the 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 civil engineering applications and limitations are derived. Outlines of subsequent research areas are also indicated.
RÉSUMÉ : La tendance de prédire les paramètres de conception du sol des propriétés de l'index se poursuit depuis des décennies,
cependant, ces corrélations ne se concentrent pas autant sur la prédiction du comportement élastique des sols cohésifs. En outre,
l’influence de minéraux (s) pour la validation de ces corrélations est soit ignorée, soit présumée être couverte par des limites
d’Atterberg . Comme les résultats de la recherche, portant sur le titre du document, l’influence d’un minéral constituant principal a été
identifiée et l’étendue de son influence en découle. La modélisation constitutive, le résultat de l’étude corrélative sont analysés en
fonction de son modèle typique. Le modèle ainsi obtenu dans le cadre d’ensemble de l’enquête a conduit à la conclusion que le
modèle qui est unique pour les sols cohésifs et est sous la domination possible de l’existence d’un minéral commun et l’étendue de
son processus de vieillissement. Elle conduit à l’indication de l’influence profonde de la matière minérale et de son état intempéries
sur le comportement élastique des sols cohésifs. Le modèle a fait remarquer que certaines des propriétés techniques et géologiques
sont interdépendants. Le modèle a été calibré avec d’autres corrélations empiriques disponibles et ses applications en génie civil et les
limites sont dérivées. Les contours des domaines de recherche sont également indiqués.
KEYWORDS: Index properties, elastic behaviour, influence of minerals, cohesive soil, constitutive modelling, weathering process.
1 INTRODUCTION
The trend for prediction of design parameters of soil from the
index properties is continuing since decades for avoiding
complex, time-consuming, and relatively costly tests. Many
empirical correlations are already published and some are being
used in practice. Preliminary literature survey indicates that
those correlations do not focus much on the prediction of elastic
behaviour of cohesive soil. Moreover, the influence of
mineral(s) for the validation of such correlations is either
ignored or presumed to be covered by the Atterberg's limits. In
a postgraduate research of engineering geology, formulated by
the Author
1
, it was intended to establish the empirical
correlation for the prediction of elastic behaviour of cohesive
soil from the index properties and any influence of mineral(s).
Subsequent development was to use the correlation for fast-
track design of road and airport pavements, foundation of
structure, and for slope stability analysis within restricted
deformation based on known geological formations.
In this research, a detailed literature study and its inference
was drawn for the prevailing empirical correlations with
particular emphasis on the coverage of elastic property, directly
or indirectly. Further, this research included brief
methodologies of samplings collected from various locations to
the extent necessary for common civil engineering structures,
schedule of laboratory investigations on index properties, stress-
strain responses of shear tests, and relevant geological studies.
Laboratory investigations for civil engineering properties and
geological studies were carried out at state Road Research
Laboratory and Geological Science Laboratory of the state
Public Works Department and University respectively. Based
on the outcomes of these studies the inference of all such
investigations has been drawn. Furthermore, constitutive
modelling for the empirical correlation and influence of
minerals has been investigated.
2 INFERENCES
This research was carried out with an objective of correlating
geological nature of soil and engineering properties, with
particular emphasis on the prediction of elastic behaviour of
cohesive soils vis-à-vis the elastic settlement of structures.
Significant outcome of the research is the constitutive model
(Ref Figure-1), which is based on some sensitive parameters,
namely, dry density (γ
d
), Plasticity Index (PI), and initial
tangent modulus (tan ψ), where ψ is the angle between initial
tangent modulus and abscissa and presented in graphical form.
The graphical model has been obtained by plotting two factors,
as shown in the abscissa and ordinates, based on the results
from about 8 sites in northeast India, which is famous for
highest rainfall, flood, earthquake, and complex geological
formations. The result yields two curves that intersect at nearly
90 degree depicting two classified characteristics of the model.
Hence, it was found necessary to verify whether the graphical
