SCHOOL OF GRADUATE STUDIES FACULTY OF TECHNOLOGY ...

2. Literature Review
2.1 General
Plastic clays exhibiting volume changes when subjected to moisture variations due to
seasonal climatic conditions or artificial causes are termed expansive soil. These soils are
commonly known as black clays. The fact that they are found favorable in some regions
for growing cotton in India has also given them the name black cotton soil [1]. Expansive
soil in most cases has adverse effect on any engineering structure built on it.
Deformations occurring in the soil, affects the structure negatively and the consequence
causes tremendous loss on the economy of a country. For example some studies showed
that the annual average loss in the United States in 1981 due to failure of structures built
on expansive soil was about $ 9 billion [14].
2.2 Factors Responsible for Shrink-Swell Phenomena Occurring in
Expansive Soil
Shrink and Swell in expansive soil can be induced by different factors. Generally, these
factors are categorized into three groups namely the soil characteristics, the
environmental factors and the state of stress.
2.2.1 The Soil Characteristics
The soil characteristics influence the basic nature of the internal force field between
particles. The following properties are categorized in this group.
Clay mineralogy
A clay mineral has two fundamental units which forms its structure. These
fundamental units are a tetrahedral unit which silicon atom is in the center and four
oxygen ions arranged tetrahedrally and Octahedral unit which has an aluminum atom
in the center and six Oxygen or hydroxyl ions arranged octahedrally around the
aluminum .
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