Modelling the Destructuring in Xanthan gum biopolymer-treated soils: Insights from the Untreated Compression Line

Xanthan gum (XG)-treated soils commonly exhibit improved strength, increased yield stress, and pronounced post-yield compression. However, despite these characteristics typical of structured geomaterials, their compression behaviour is still largely interpreted empirically, and a physically consistent framework for compression-induced destructuring in chemically stabilized compacted soils (CSCS) is lacking. This study investigates the compressibility and destructuring behaviour of XG-treated sand-bentonite mixture (SBM) with XG contents ranging from 1-3% and curing periods of 1-90 days. A framework based on the Untreated Compression Line (UCL) is proposed, using the untreated virgin compression line as a mechanically consistent reference to interpret destructuring. Results indicate that increasing XG content induces a structured response, characterized by higher swelling void ratios, larger recompression indices, elevated yield stresses, and progressive post-yield destructuring. In contrast, extended curing promotes hydrogel densification and reduces susceptibility to destructuring. Scanning electron microscopy observations reveal the collapse of polymer bridges during loading, supporting a swelling-destructuring mechanism. Strong correlations between unconfined compressive strength (q_u) and key destructuring parameters enable the development of a simplified predictive framework. This approach extends classical destructuring concepts to CSCS and provides a practical basis for predicting their compression behaviour.