Characterization of xanthan gum biopolymer dehydration and rehydration influence on sandy soil by nuclear magnetic resonance

Although soil exhibits excellent mechanical performance, the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored. This study aims to explore xanthan gum soil microstructure and strength behavior under different dehydration and rehydration degrees using nuclear magnetic resonance (NMR) and unconfined compressive strength tests. The results showed that the proportion of large-volume biopolymer gel within the sample decreased from 91.91% to 38.28% during dehydration, but increased to 90.44% upon rehydration when sample moisture returned to its original level. The NMR images revealed that biopolymer gel evaporated from outside during the dehydration process, causing the dehydrated biopolymer to shrink and form a high-strength glass, which directly enhanced the soil's macroscopic mechanical properties. Upon rehydration, the biopolymer reabsorbed moisture and gradually expanded, leading to weakened connections between soil particles and a decrease in strength. Therefore, even when the moisture content of soil remained constant during the dehydration and rehydration processes, their unconfined compressive strength (UCS) and failure patterns exhibited significant differences. Both the UCS and NMR signal of biopolymer-treated soil decreased after the first dehydration and rehydration cycle, stabilizing gradually after subsequent cycles.