Swell–consolidation characteristics of biopolymer-treated expansive soil

This study investigates the stabilization effects of chitosan, guar gum, xanthan gum and sodium alginate (CS, GG, XG and SA, respectively) biopolymers (BPs) on the swelling and consolidation properties of a highly expansive soil. To this end, oedometer swell–consolidation tests (comprising stress-controlled constant-volume swelling, followed by consolidation under incremental loading–unloading) were performed on various BP-stabilized specimens after 1 d and 28 d of curing, and their performance was compared against baseline specimens treated with lime. BP stabilization resulted in notable reductions in the swelling pressure (and its temporal development rate), with extended curing providing additional improvements. While all BPs were effective in mitigating swelling, their long-term efficacy can be ordered as GG ≈ XG > CS ≈ SA. Similarly, all BP-treated specimens exhibited lower compression and swell indices relative to the untreated soil, with CS proving the most effective, followed by GG, XG and SA, which demonstrated similar performance. Moreover, all BPs produced lower consolidation coefficient and hydraulic conductivity values relative to the untreated soil, with further reductions achieved through extended curing. In terms of overall/mean performance, the four BPs exhibited comparable effects on the rate of consolidation and permeability. The BPs, at best, were able to replicate short-term lime treatment results obtained by the pH-deduced lime content demand (3% by mass) of the untreated soil. The study concludes with a comprehensive discussion of the underlying soil–BP interaction mechanisms, i.e. BP-induced clay flocculation and BP gelation-induced reinforcement, elucidating their individual and synergistic effects on the swell–consolidation behavior.