## 1 Introduction  
It is a very common situation that during the construction of large infrastructure facilities, it is necessary to use local soil material, which, in its natural conditions, does not meet the criteria required for construction purposes. Accordingly, there is a need to apply some soil stabilisation techniques. One of the oldest, but also the most commonly used, techniques is chemical soil stabilisation, which involves the mechanical mixing of a single stabiliser (or a combination of stabilisers) with the soil. In addition to conventional chemical stabilisers, waste products such as fly ash, limestone powder waste, rice husks, polypropylene fibres, recycled textile fibres, lignin fibres from the paper industry, and alike can be used as stabilisers [1; 2; 3; 4]. More recently, many researchers are looking for alternative materials that would be suitable in both economic and environmental aspects, such as chlorides or silica-based additives [5; 6; 7; 8]. The success of applying chemical stabilisation is reflected, first of all, through improvements in the physical and mechanical properties of the soil. In addition, added stabiliser(s) make(s) the soil more resistant to water. The presence of water can induce apparent cohesion in sandy soils, whereas in clayey soils, it increases their tendency to swell and shear [8; 9; 10]. By comprehensively reviewing the available literature, it can be concluded that the research so far has mostly concentrated on the effects of a specific stabiliser or on the effects of a combination of two stabilisers of different types. What is observed is the lack of a comprehensive comparative analysis that would include a wider range of stabilisers of different types and their individual effects on a broad range of geomechanical soil properties. Lime and cement have been successfully used for decades, and many authors classify them as \"conventional stabilisers\". However, their production involves the consumption of a large amount of natural raw materials and fossil fuels. Therefore, any reduction in the consumption of cement and lime contributes to a reduction in the consumption of these resources (natural raw materials and fossil fuels), thereby reducing CO\({}_{2}\) emission. Since for a long time there has been a trend of reusing industrial waste as a secondary raw material in construction engineering, fly ash and rock flour are a separate group of stabilisers used in this study and called \"waste materials\". The third group includes chemical reagents that do not yet have a commercial use in geotechnics, and studies on their effects on soil properties are current worldwide. The application of new chemical stabilisers has opened up new possibilities for solving the challenges posed by clayey soils, offering more sustainable, cost-effective, and environment-friendly solutions for construction industry projects. Thus, in a separate third group, chloride-based compounds called \"alternative stabilisers\" have been studied, such as ferric chloride, calcium chloride, and potassium chloride. Taking all aforementioned into consideration, this paper presents extensive research on the chemical stabilisation of clayey soil by considering a variety of materials as stabilisers: conventional stabilisers (lime, cement), waste materials (fly ash, rock flour), as well as alternative chloride-based reagents (ferric chloride, calcium chloride, potassium chloride), with an aim of identifying and comparing the individual effects of each on a variety of very important geomechanical properties of the soil. To achieve the abovementioned goal, in the first part of the conducted research, for each of the mentioned reagents, soil samples were treated with three different percentages of reagents with respect to the dry weight of the soil sample, after which the change in uniaxial compressive strength (UCS) and the change in pH value were monitored at time intervals of 3, 7, and 28 days after the treatment.