Mechanism of seawater intrusion on property degradation of slurry in slurry shield tunneling

Seawater intrusion into deteriorated slurry is a significant challenge faced by subsea slurry shield tunnels. Most existing studies simulate seawater intrusion (non-prehydrated) by adding seawater during slurry preparation; however, in practice, seawater intrusion occurs only during the slurry construction phase. To address this, the present study proposes a prehydrated seawater intrusion method that more accurately reflects real-world conditions (seawater added after freshwater slurry preparation). sing the response surface method, a regression model between slurry composition and properties was developed, predicting the optimal freshwater slurry ratio. The study then investigates the effects of different degrees of seawater intrusion on the properties and deterioration mechanisms of slurry with various additives, focusing on basic properties, rheological behavior and microscopic analysis. Results show that flaxseed gum performed better than the other three additives in terms of overall properties. At a 10% seawater intrusion degree, slurry rheological properties and particle size improved; Prehydrated seawater intrusion slurry outperformed non-prehydrated slurry. Previous studies have overestimated the impact of seawater on slurry in practice. The prehydrated seawater intrusion slurry only partially compresses the electric double layer structure of bentonite particles, retaining most of its integrity. These findings provide valuable insights for addressing seawater intrusion challenges in actual construction.