## 1 Introduction  
Geotechnical engineering is a branch of civil engineering that focuses on the behavior of soil and rock materials near the surface of the earth [1]. It is unquestionable that civil engineering has a significant impact on the natural environment as it rapidly consumes natural resources and usually interferes with the local ecosystem functioning. Therefore, it is of vital importance to promote sustainable development in this branch of industry. Development of geotechnical engineering is stimulated, in a large part, by advancement of technology and new material solutions that enable realization of construction projects in difficult geotechnical conditions. One of the main aspects of sustainable geotechnical engineering is safe and effective use of soil stabilizers. Soil stabilization is a process of enhancing mechanical properties of soil. It can alter soil physical and chemical characteristics like strength, compressibility and permeability. It can also include actions aimed at limiting soil surface erosion or preventing air pollution by fine-dispersed dust [2]. Ground improvement methods include deep or surface soil stabilization. Surface soil stabilization usually consists of applying an admixture to the surface layer of soil and compacting the resulting mixture. It can be used not only for increasing performance of in situ subsoils but also for, e.g., soils used in road embankments. Soil can be stabilized mechanically, chemically, thermally or electrically. Mechanical methods (compacting) are used most often as they do not alter the soil composition. For chemical stabilization the following materials can be used  
* cement,
* calcium-based stabilizers,
* fly ash,
* bitumen,
* non-standard stabilizers. Desired performance characteristics and economic aspects often call for using (and studying) non-traditional additives. Due to ecological reasons, non-standard soil additives are becoming more and more popular. Especially for forest road construction, bike lanes, pedestrian ways on protected sites, weak soil protection from excessive water absorption or working platform construction on weak ground. Traditional soil stabilizers have been thoroughly studied and their properties and stabilizing mechanisms are mostly identified. Various non-traditional soil additives are currently intensively developed and there is still a great need for research in this subject. Most non-traditional additives can be classified as ionic, enzymes, lignosulfonates, salts, petroleum resins, polymers or tree resins. Many products contain additional substances, e.g., surfactants. However, due to commercial confidentiality the exact composition of a given product is not available to the public. In [3; 4; 5] non-traditional additives were tested. Series of laboratory tests were performer on stabilized coarse- and fine-grained soils and the increase in soil strength was evaluated. The stabilization mechanisms were broadly divided into two types, mechanical and chemical bonding. However, the experiments were mainly focused on stabilization effect evaluation and not on the underlying mechanisms. [PERSON] et al. [6] conducted research that was specifically aimed at identifying the chemical and physical bonding mechanisms of non-traditional additives. Series of laboratory experiments included macroscopic analysis, physical characterization and chemical analysis of mineral, soil, stabilizer and soil-stabilizer composites. The research suggests that stabilization mechanisms that occur in soil-stabilizer mixtures cannot be considered separately. The final effect results from a complex interplay of many different factors. Many chemical stabilizers (ionic, lignosulfonates, salts and enzymes) can react with soil mineral particles, so the stabilization effect depends on a particular soil's mineral composition. Synthetic stabilizers are mostly vinyl acetates and acrylic copolymers [6].