# Influence of Xanthan Gum-Based Soil Conditioners on the Geotechnical Properties of Soils
## 1 Introduction  
Biopolymers are polymeric, biodegradable materials derived from renewable sources [1, 2]. They play an increasingly important role in enhancing the geotechnical soil properties and providing the water retention ability of the soil in agriculture and other land management practices (e.g., forest management). Unlike other biomaterials, including proteins, which degrade within hours to days, biopolymers exhibit a prolonged degradation process, spanning years, with no reported adverse environmental effects [3]. Among widely used biopolymers, such as Xanthan gum, Gellan gum, Agar glue, and Guar gum, Xanthan gum stands out as one of the most commonly applied in geotechnical engineering [4, 5, 6, 7]. This stems from its soil property modification ability and its cost efficiency [8, 9]. The alteration of the soil properties induced by Xanthan gum (XG) resultsfrom two primary mechanisms: (i) the aggregation of the soil particles due to the deposition of the XG in the voids and (ii) the establishment of bonds between the XG and the soil particle surfaces, particularly if the soil particles are electrically charged, as is the case in clayey soils [10]. Several studies have demonstrated that the addition of XG affects the shear, the tensile strength, and the compressive strength of the soil [8; 11; 12; 13; 14; 15; 16; 17; 18], alters the compaction characteristics [14], reduces the swelling potential of high-plasticity soils [12; 14], decreases soil erosion [19], lowers the hydraulic conductivity of the soil [14; 16], and enhances the conditions for plant growth [1; 20; 21]. The effectiveness of the XG-based soil conditioners is highly dependent on the soil water content [5; 22; 23; 24; 25; 26]. Due to their hydrophilic nature, the XG-based soil conditioners form a low-viscosity hydrogel around the soil particles in a wet state. In a dry state, this hydrogel transforms into a high-strength network around the soil particles. As a result, the dried soil, previously treated with XG-based soil conditioners, has high strength. An equally treated soil in wet or submerged conditions has a significantly lower strength [5; 8; 18; 22; 25; 26]. Although the XG soil treatment offers advantages like high dry strength, cost-effectiveness, and improvement of soil water retention capacity, which reduce the soil vulnerability to drought, its widespread application in natural environments is limited due to its Efficacy as a soil-strengthening agent in wet conditions and associated durability concerns [5]. To improve the wet strength and durability of the XG-treated soil, numerous studies have focused on chemical modification of the XG physicochemical properties by adding Ba\({}^{2+}\), Ca\({}^{2+}\), Cr\({}^{3+}\), and Fe\({}^{3+}\) and observing their influences on the gelation process and the XG gel strength [5]. However, there is a shortage of data regarding other potential modifications of XG that could preserve its high retention capacity while maintaining or even improving the mechanical properties of the XG-treated soils in a wet or saturated state. The novelty of this research stems from the utilization of newly developed engineered bio-based soil conditioners (SCs) composed of Xanthan gum, oxide ash, and cellulose fillers of varying fiber lengths. Despite the potential synergies arising from the combination of Xanthan gum with cellulose fibers to create materials for soil conditioning and water retention, no study on this topic can be found in the open literature [2]. The primary objective of adding oxide ash and cellulose fillers of varying fiber lengths to the soil conditioners was to reduce their sensitivity to water. This prevents the decrease in strength of the treated soils in wet conditions, minimizes the volumetric changes during the wetting/drying cycles, and slows down the water release. The aim is to maintain the increased water retention capacity, which is a primary function of the developed SCs [1; 2].