## 2 Materials and Methods Considered in the Research
### Materials Considered in the Research
#### 2.1.2 Chemical Stabilisers  
The stabilisers analysed in this research are grouped into three categories: conventional stabilisers--cement and lime, waste materials--fly ash and rock flour, and alternative chloride-based stabilisers--ferric chloride, calcium chloride, and potassium chloride. When it comes to conventional stabilisers that have been used in civil engineering and geotechnics for a long time, adding the optimal content of stabiliser contributes to a significant increase in the strength, stability, and load-bearing capacity of the soil, while on the other hand, it reduces soil plasticity, water permeability, and swelling [11; 12]. In addition, conventional stabilisers contribute to improving soil resistance to adverse climatic and hydrological factors [13]. On the other hand, waste materials have a huge potential for reuse and are successfully applied in other civil engineering fields. They can be used independently but also in combination with conventional stabilisers, which, in the literature, is referred to as a complex stabilised mixture--CSM [14]. Research on chemical stabilisation of expansive soils shows that lime can be replaced by reagents based on chloride compounds due to their easy solubility in water, their more efficient mixing with the soil, and the fact that they provide sufficient amounts of cations for cation exchange [15]. Taking all this into account, the primary goal of this research was to examine the potential of each of the abovementioned reagents alone (without combining them mutually) in terms of improving the geomechanical properties of clayey soils using the chemical stabilisation technique. * Conventional stabilisers  
Among conventional stabilisers, **lime** stands out as a versatile and economical solution for chemical soil stabilisation, primarily due to its ability to neutralise acidity (by increasing the soil pH value) and improve the engineering properties of natural soil. In engineering practice, lime is most often used to stabilise fractions of clayey soils of medium to high plasticity [16]. Lime is also successfully applied to coarse-grained soils with a sufficient content of clay fractions. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property of Soil** & **Symbol (Unit)** & **Value** \\ \hline Particle Density & Gs (-) & 2.705 \\ \hline  & Gravel (\%) & 1.2 \\ Grain Size Distribution & Sand (\%) & 4.9 \\  & Silt (\%) & 40.6 \\  & Clay (\%) & 53.3 \\ \hline Coefficient of Uniformity & Cu (-) & 8.0 \\ Coefficient of Curvature & Cc (-) & 2.0 \\ USCS Soil Classification & Symbol (-) & CL \\ Maximum Dry Density & MDD (g/cm\({}^{3}\)) & 1.903 \\ Optimal Moisture Content & OMC (\%) & 18.5 \\ Uniaxial Compressive Strength & UCS (kPa) & 205 \\ Liquid Limit & LL (\%) & 49 \\ Plastic Limit & PL (\%) & 23 \\ Plasticity Index & PI (\%) & 26 \\ pH Value & pH (\(\cdot\)) & 9.5 \\ Modulus of Compressibility & Mv (MPa) & 12.945 \\ California Bearing Ratio & CBR (\%) & 2.71 \\ Swelling & s (\%) & 2.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of the clayey soil used in the present research. Within the stabilisation process, a reaction between lime (calcium hydroxide Ca(OH)2) and clay minerals takes place, the intensity of which depends on the mineralological composition of the clayey soil (silica SiO2, alumina Al2O3). As illustrated in Figure 1, in the soil, calcium hydroxide (lime) is partially separated into Ca2+ ions and 2 OH- ions, whereby a cationic exchange is enhanced during which the positively charged ions (cations) of the clayey soil particles (H+, Na+, or K+) as weaker bonded ions are replaced with the positively charged ions from the solution phase (calcium from lime (Ca2+)). Increasing the pH value of the soil contributes to the weakening of the bonds within the crystal lattice of soil particles, which facilitates exchange of cations and thus contributes to the better solubility of silica and alumina contained in clay.