Experimental and mechanistic investigation of synergistic effects of particle size distribution and xanthan gum on rheological and infiltration properties of bentonite slurries

The properties of slurry are crucial for pressure conversion efficiency and excavation face stability in slurry shield tunneling. It is essential to investigate the impact of additives and material properties on the performance of bentonite slurry. This study systematically explores the multifactorial interactions governing slurry performance through an experimental approach. A Box–Behnken experimental design incorporating three key factors—particle size distribution, bentonite content, and xanthan gum content—each evaluated at three distinct levels, was implemented within the framework of response surface methodology. The experimental approach enabled a quantitative assessment of their synergistic effects on two critical engineering parameters: rheological yield stress and infiltration distance. The microstructure of four slurries was examined using a scanning electron microscope to reveal the modification mechanism of xanthan gum in bentonite slurry. The analytical results showed that the rheological and infiltration properties of the slurry are influenced by the interacting effects of multiple factors. The addition of xanthan gum significantly improved the rheological performance of the bentonite slurry. When the xanthan gum content was increased from 0 to 4 g/l, the yield stress of the slurry increased by over 200%. Concurrently, under the same ratio, the use of bentonite with different particle gradations reduced the penetration distance from 25 cm to as low as 5 cm. The developed regression models demonstrated exceptional predictive capability (R2 > 0.97). These results establish a quantitative method providing actionable insights for the evaluation of rheological and infiltration performance in slurry shield tunneling.