Dispersivity of clay soils is one of the most important issues that should be considered
in civil engineering projects. Dispersive soils are clay soils that are easily washed
in water with low concentrations of salt; these clay soils usually contain high levels
of sodium ions in their adsorption cation sites. Kaolin, sepiolite (fibrous clay),
and bentonite soils are among the most important and useful industrial materials.
Therefore, in this study, these three clay soils were selected to investigate dispersivity
potential by adding 4% of dispersive materials (Sodium hexametaphosphate) and performing
shear strength, crumb, double hydrometer, pinhole tests, and chemical experiments.
Results indicated a change in the Sodium Adsorption Ratio (SAR) in the following order:
kaolin > sepiolite > bentonite. Stabilization practices using chemical methods were
done after performing soil divergence with sodium hexametaphosphate. CaCl2, CaSO4,
AlCl3, and Al2 (SO4)3 were used for chemical stabilization to assess the effect of
ion valence on soil improvement parameters. Results obtained for chemical properties
showed that, stabilization potential was in the following order: kaolin > sepiolite
> bentonite; meaning that clay soils with lower cation exchange capacity have more
remediation potential and are more susceptible to dispersion. The role of calcium
and aluminum cations was prominent in improving mechanical and dispersivity properties,
respectively. In general, further dispersion potential of clays in the same Na+ concentration
was found to be related to a decrease in the cation exchange capacity, specific surface
area, and plastic index. Soil dispersion was directly associated with diffuse double
layer and electrostatic forces while; soil strength parameters were mainly dependent
on cementation and connection of soil particles to each other. Consequently, it was
observed that, clay soils with suitable engineering properties (higher strength and
compaction or lower Atterberg limits) are more sensitive to dispersion compared to
other types of clay with higher CEC and plasticity values.