The rapid growth in industrial, commercial, mining, agricultural and domestic activities causes generation of huge quantities of solid and liquid wastes. When rain water percolates through these wastes, it is mixed with organic and inorganic chemicals generating ‘Leachate’. Depending upon the nature of chemicals present in the leachate, it will have different dielectric constants, electrolyte concentrations, cation valencies, pH and temperatures which may cause change in the thickness of diffuse double layer of fine-grained soils. The change in thickness of diffused double layer controls various geotechnical properties of the fine-grained soils. In this paper, the effects of change in thickness of diffused double layer due to change in pore fluid chemistry on various geotechnical properties of fine-grained soils, such as Consistency limits, Hydraulic conductivity, Compaction parameters, Swelling characteristics, Shear strength and Compressibility, are critically discussed.

Fine-grained soils, especially clays, carry negative charge on its surface. It attracts the positively charged ions towards it to reach an electrically balanced equilibrium. The negatively charged clay particle surface and the concentration of positive ion solution adjacent to the particle form diffused double layer. Most of the geotechnical properties depend on this thickness of diffused double layer.

The change in thickness of this diffused double layer is effected by the pore fluid chemistry, such as ionic valence, dielectric constant, electrolyte concentration, pH value and temperature (Mitchell, 1993). As indicated by Gouy-Chapman theory, thickness of diffused double layer is given by:

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