Modifying the strength and consolidation–creep of Shanghai Clay with various polysaccharides

Biopolymer-based soil amendments are increasingly studied in sustainable geotechnical engineering, yet comparative mechanical investigations of soils treated with different ionic polysaccharides, especially their consolidation–creep performance, remain insufficient and hinder engineering adoption. In this study, Shanghai Clay was stabilised using cationic chitosan (CS), anionic xanthan gum (XG) and non-ionic guar gum (GG). Unconfined compressive strength tests under wetting–drying cycles, one-dimensional consolidation–creep tests considering over-consolidation and scanning electron microscopy were performed. The XG-amended soil delivered the highest strength, modulus and durability against wetting-drying cycles, benefiting from its double-helical conformation and particle-binding cross-linking. However, the XG-treated clay showed larger primary consolidation and creep deformation owing to edge-to-edge flocculation and honeycomb-like fabric. Over-consolidation markedly reduced its creep settlement and narrowed performance gaps with the CS- and GG-treated soils. These findings advance understanding of ionic-type-dependent behaviour in biopolymer-stabilised soils and provide practical guidance for engineering applications, suggesting that anionic XG can be used to reinforce clayey soils for improved strength and wetting–drying resistance, with surcharge preloading effectively applied to control their long-term settlement.