The unconfined compressive strength and shear strength represent the basic mechanical properties of clayey soil. If the soil in its natural state does not have sufficiently good mechanical properties, in engineering practice, it can be improved by chemical stabilisation of the soil. The stabilisation procedure involves adding reagent(s) to the soil with the aim of permanent improvement in the mechanical properties of the soil. In this study, the individual effects of seven different chemical stabilisers (traditional and alternative) on the mechanical properties of clayey soil were analysed. In the first stage of the research, comprehensive analyses were conducted on the effect of each of the selected stabilisers on the compressive strength of the soil. Each of the selected stabilisers was considered with three different content percentages in the soil mixture, with the aim of determining the optimal stabiliser content. Unconfined compressive tests were conducted to determine the unconfined compressive strength (UCS) of the soil. In the second stage of the research, extensive analyses of the effects of each of the selected stabilisers alone on the improvement in soil shear strength parameters (cohesion and internal friction angle), were carried out with the optimal content of each of the stabilisers. The shear strength parameters were determined by direct shear tests. Both stages of the research were conducted at three different time intervals after the chemical stabilisation (3, 14, and 28 days) in order to determine the long-term efficiency of the chemical treatment of clayey soil. Based on detailed comparative analyses, it was determined that all the selected stabilisers contributed to a lesser or greater extent to a significant improvement in the analysed mechanical properties of clayey soil. A statistical analysis of the obtained results was also conducted using the method of analysis of variance (ANOVA), on the basis of which the individual effect of each selected stabiliser on improving the mechanical properties of clayey soil was validated and quantified.

This paper presents an extensive comparative analysis of the experimental results of chemical stabilisation of clayey soil in laboratory conditions by comparing the effects of adding conventional stabilisers (lime, cement binder), stabilisers that can be considered as waste material (fly ash, rock flour), as well as alternative chloride-based materials (ferric chloride, calcium chloride, potassium chloride) on the geomechanical properties of the soil. With the aim of determining the stabiliser optimal content in the mixture with the soil, in the first part of the research, the effects of stabilisation of clayey soil of medium plasticity using the considered stabilisers with different percentage share on the change in uniaxial compressive strength (UCS) and pH value of the soil at different time intervals after the treatment were analysed. In the second part of the research, additional tests were conducted on soil samples with optimal content for each of the considered stabilisers by monitoring changes in the physical and mechanical properties of the soil. These include Atterberg's limits (liquid limit and plasticity limit), modulus of compressibility in the oedometer, California bearing ratio (CBR), and swelling potential at different time intervals after the chemical treatment to determine the durability of stabilisation effects. The results of the conducted research reveal that each of the conventional, waste, and alternative materials considered as chemical stabilisers contributes to the improvement of the geomechanical properties of the clayey soil, primarily in terms of increasing the bearing capacity and reducing the swelling of the treated soil.