## 4 Concluding Remarks  
The effects of a variety of materials using the chemical stabilisation technique on the improvement of geomechanical properties of clayey soil were investigated and compared, considering conventional materials (lime and cement), waste materials (fly ash and rock flour), as well as alternative materials--chloride-based compounds (ferric chloride, calcium chloride, and potassium chloride), along with the determination of the optimal content of a single additive in the soil mixture and the durability of the effects of the implemented soil chemical stabilisation. The most important conclusions are as follows:  
* All the considered stabilisers contributed to the improvement of the uniaxial compressive strength of the clayey soil, among which conventional stabilisers proved to be the most effective. * The results of the change in pH value revealed that conventional stabilisers are the most successful in reducing soil acidity, a slight increase in the pH value was registered with the addition of waste materials, whereas with the use of chloride the pH value of the natural soil decreased. * It was determined that the optimal content of stabiliser for the treated clayey soil in the case of applying chlorides attains 2%, in the case of lime is 5%, for rock flour is 10%, with the addition of flying ash is 15%, whereas for cement is found to be higher than the considered 15%, which on the other hand raises the question of the economic justification of the procedure with this binder. * None of the examined stabilisers contributed to a significant change in the LL value, whereas each of them contributed to an increase in the PL value, which ultimately led to a reduction in the plasticity index of the treated clayey soil. * The best results in terms of increasing the value of the compressibility modulus were achieved with the addition of conventional stabilisers, although the other considered stabilisers also contributed to the reduced compressibility of the treated soil compared to the natural soil material. Figure 10: Change in the soil swelling over time given the optimal content of the considered conventional, waste, and alternative materials as stabilisers. * In the case of all the considered stabilisers, CBR values are higher than 3%, which is of great benefit when it comes to road construction, whereby the greatest improvement was achieved in the case of stabilisation with conventional stabilisers. * Each of the considered stabilisers contributed to the reduction of soil swelling, whereby the greatest reduction was achieved by the addition of conventional stabilisers. After conducting extensive laboratory tests, the obtained results presented in this paper confirmed that the improvement of the geomechanical properties of the clayey soil can be successfully achieved with the use of traditional stabilisers, but also with the use of waste materials and chloride-based compounds. Each of the considered stabilisers, added to the natural clayey soil, would enable its application for various practical purposes in the field of construction. Lastly, it should be emphasised that the results presented in this paper refer to local clayey soil. Therefore, there is a need for more comprehensive further research, which will analyse soil samples from a wider area, as a larger number of tests on a greater variety of clayey soils will result in more reliable findings. All authors have contributed to all major parts of the presented research (conceptualisation, methodology, investigation, resources, data curation, formal analysis, writing--original draft preparation, writing--review and editing, visualisation, and supervision); project administration, E.Z. and Z.B. ; funding acquisition, E.Z. All authors have read and agreed to the published version of the manuscript.