Performance of chitosan and alginate for soil stabilization under saturated conditions

Chitosan and sodium alginate have been widely studied as sustainable agents for soil stabilisation. However, most existing studies focus on dry or compacted conditions, while the mechanical behaviour under fully saturated conditions remains poorly understood. In practice, soils in infrastructures such as embankments and road foundations may remain saturated for extended periods due to prolonged rainfall or flooding. Moreover, the effects of biopolymer treatments are mostly based on unconfined compression and direct shear tests, which do not allow control of saturation conditions or stress paths. This study, therefore, examines the performance of chitosan- and alginate-treated sands under fully saturated conditions. Cone penetration tests showed that chitosan-treated coarse and fine sands effectively retained their structural integrity for several months. In contrast, for alginate, merely using SA was insufficient; crosslinking with calcium chloride (CaCl2) was required to achieve greater mechanical stability. Consolidated drained triaxial tests further confirmed that both chitosan and Ca-crosslinked alginate significantly improved the shear strength of the sands, enhancing both cohesion and friction angle. Physicochemical and microstructural characteristics further explained the improved mechanical performance. These findings clarify the performance and applicability of biopolymer-treated soils under fully saturated conditions, demonstrating their potential for geotechnical applications where long-term saturation is unavoidable.