Biopolymer-Modified Bentonite Slurry with Gellan Gum for High Salt Resistance in Marine Geotechnical Engineering

The performance of bentonite slurry in submarine tunnel construction is significantly deteriorated by high-salinity seawater intrusion, increasing the risk of excavation face instability. This study investigates the incorporation of the biopolymer gellan gum (GG) into the bentonite slurry, as a high salt resistant and eco-friendly additive. The mechanisms underlying seawater-induced deterioration and GG-imparted salt resistance were analyzed. Results demonstrate that seawater increases the bleeding rate and API (American Petroleum Institute) fluid loss while reducing the apparent viscosity and yield stress of bentonite slurry, thereby compromising its shear-thinning properties. The addition of GG mitigates these negative effects and improves the colloidal stability, rheological properties, and filter cake quality of the slurry. With 1.2% GG, the 24-hour bleeding rate of slurry was reduced from 86.4% to 0%, and a low-permeability filter cake (5.6 × 10⁻⁹ m/s) was rapidly formed, as confirmed by sand infiltration tests. Scanning Electron Microscopy (SEM) analysis revealed that GG re-disperses seawater-induced bentonite platelet aggregates, while Fourier Transform Infrared Spectroscopy (FTIR) results highlight the synergistic effects of cation consumption and gel filling by GG. This study highlights the potential of GG as a sustainable additive for bentonite slurry in marine geotechnical engineering applications.