Investigation of water migration behavior in biopolymer- modified sand: A multiscale analysis

Intensified rainfall events driven by climate change have increasingly compromised soil stability, leading to erosion, land degradation, and a range of geoenvironmental and geological challenges. Polymer treatments have been widely adopted as effective measures to mitigate soil erosion. In this study, a series of physical and numerical experiments, including permeability tests, water migration tests, computed tomography (CT) scanning, and pore-scale flow simulations—were conducted to evaluate the effects of microbial extracellular heteropolysaccharides (MHP) biopolymer on the multiscale dynamics of soil water migration. The results show that MHP significantly enhances soil resistance to water infiltration and improves sealing capacity. At biopolymer contents of ≥3 %, the permeability coefficient decreased by more than two orders of magnitude. Water flux in treated sand was reduced by 84.9 %, and evaporation rates declined by 73.5 %. MHP modification also altered soil microstructure by reducing porosity, fractal dimension, and pore connectivity, while shifting the pore and throat size distribution toward smaller radii and increasing the fraction of isolated pores. These structural changes reshape pore geometry and topology, limit preferential flow paths, increase flow resistance, and enhance selectivity within the porous medium. These findings provide valuable insights for advancing biopolymer-based strategies in soil erosion control.