Influence of bamboo biochar on the hydro-mechanical behavior of xanthan gum stabilized clayey soil

Xanthan gum (XG) significantly enhances the compressive strength of clayey soils through hydrogel-induced interparticle bonding. However, its hydrophilic nature leads to pronounced shrinkage and desiccation-induced deformation. This study explores a sustainable hybrid stabilization approach that combines XG and bamboo-derived biochar (BC) to improve the mechanical and volumetric performance of clayey soil. Soil specimens were treated with varying dosages of XG (0.5%, 1%, 2%, and 4% by dry weight) and BC (1%, 2%, 5%, and 10% by dry weight) and cured for up to 56 days. A comprehensive experimental program, including compaction, unconfined compressive strength (UCS), wetting–drying (W-D) durability, hydraulic conductivity, shrinkage behavior, and microstructural analysis (SEM), was conducted. XG treatment significantly enhanced strength, with an optimal dosage of 2% yielding a UCS of 7.1 MPa after 56 days. However, it induced pronounced desiccation-driven curling and loss of durability under cyclic W-D conditions. The incorporation of BC into XG-treated soil produced a synergistic response, with the 5% BC-2% XG mixture achieving the highest UCS of 8.5 MPa and sustaining up to 11 W-D cycles. All treated soils maintained hydraulic conductivity on the order of 10 -9 cm/s, meeting landfill liner requirements. The BC-induced XG matrix effectively mitigated shrinkage and curling by regulating moisture redistribution and serving as a rigid skeletal reinforcement within the polymeric network. The results demonstrate that BC-XG composites can mitigate several limitations associated with individual stabilizers and show potential as low-carbon construction materials for landfill liners, cover systems, and pavement subgrades under laboratory conditions.