Multi-Scale Study of Sodium Bentonite Slurry for Shield Muck Improvement

Aiming to address the problems of shield chamber blockage and poor muck discharge faced by earth pressure balance shields during tunneling in sandy strata, bentonite slurry is used for muck improvement. Using a multi-scale approach combining macro-scale experiments, micro-scale analysis, and molecular dynamics simulations, this study systematically investigates the interface interactions between particles of sandy soil in shield tunneling and the improvement mechanism of sodium-based bentonite slurry additives. Through the macroscopic experiment, the sodium bentonite slurry soil–water ratio of 1:7 and injection ratio of 25% showed the best improvement effect. After improvement, the permeability coefficient decreased by 99.72%; the cohesion of the excavated soil increased from 3.055 kPa to 11.458 kPa, representing a 275.06% increase; and the angle of internal friction decreased from 42.318° to 36.985°, a decrease of 12.60%. The improvement was significant. Through SEM, XRD, and FTIR microanalysis, it is found that bentonite slurry forms a flexible film on the surface of sandy soil. By coating sand particles, filling voids in the soil, and enhancing interparticle cohesion, it improves the properties of the soil. On the nanoscale, a Na-MMT/SiO2 system model is established based on molecular dynamics simulations to elucidate the interactions between bentonite slurry and sand particle interfaces. The results indicate the presence of van der Waals forces and hydrogen bonds between Na-MMT and SiO2. Interlayer water molecules form a hydrogen bond network that strengthens interfacial bonding, enabling bentonite slurry to tightly adhere to soil particle surfaces. This improves the microstructure of the soil, thereby enhancing its macroscopic properties.