## 1 Introduction
A polymer stabilizer covers soil particles, and the bonding effect is created when the water is evaporated from the emulsion, leaving a solidified soil-polymer structure. Therefore, the increase in soil strength depend mainly on how well are soil particles covered in emulsion. A similar mechanism is observed in natural polymer (lignosulfonates or natural resins) stabilization. Laboratory experiments [4; 5; 7] confirm a clearly physical mechanism of solidification. For fine-grained soils the stabilization effect is less pronounced as the coverage of the smallest particles insufficient. Stabilization with polymer emulsions is more appropriate for coarse-grained soils, also because of the larger specific surface area that allows for more efficient mixing. Synthetic polymers have a very high tension and bending strength, and create strong physical bonding in the soil-polymer composites. Depending on the specific chemical composition of the stabilizer, an ionic exchange between polymer and soil minerals can also occur and affect the stabilizing effect. The polymer stabilization mechanisms are comprehensively described in literature (see [8]). Due to rapid global climate changes, a strong emphasis is placed on carbon neutral material production processes. The material research is more and more focused on environmentally neutral materials and possible applications of waste materials that can be used as alternatives for traditional solutions (e.g., eggshell-derived lime as an alternative pozzolanic material for sandy soil stabilization [9] or clayey soil stabilization [10]). In addition, biopolymers (synthetically or naturally obtained) are getting more and more attention. In recent years many review articles concerning the use of biopolymers for soil stabilization were published [11; 12; 13; 14; 15; 16]. Biopolymers are typically produced from gum trees, shrimp shell, milk, fermentation of glucose, algae, fungi or bacteria that consist of polysaccharides [17]. [PERSON] et al. [18] presented a broad analysis of applications and potential benefits of using various biopolymers in geotechnical engineering. The review is focused on the results of the latest studies on biopolymers like agar gum, guar gum, gellan gum, dextran, \(\beta\)-glucan, xanthan gum, chitosan, starch and casein. The main benefits of using those materials are increase in soil strength, modification of consistency through increase of water absorption, erosion reduction, etc. (see Table 1). All of these ground improvement effects are obtained in accordance with the principles of sustainable development, as the biopolymers are mostly microbial hydrocarbons with low CO\({}_{2}\) footprints compared to conventional soil binders and promote seed germination and the growth of vegetation in soils [18]. Another aspect of sustainable development is effective and safe waste management and reuse of waste materials [19]. Most of the published studies that concern mechanisms and effects of biopolymer soil stabilization focus mainly on the composite's strength parameters, like internal friction angle, cohesion and compression strength [17; 20; 21; 22; 23; 24]. There are few studies that focus on deformation characteristics, stiffness or damping. Chitosan is a waste product of the sea food processing industry. This cationic polymer is obtained by deacetylation of chitin, found abundantly in crustacean, insect, arthropod exoskeletons, and molluscs [25]. Despite its numerous applications in water treatment [26],