Research on Time-Dependent Buoyancy Characteristics of Shield Tail Grouting Slurry

During the construction of large-diameter shield tunnels, tunnel lining segments frequently experience uplift after exiting the shield tail, inducing structural defects such as dislocation, cracking, and water leakage. This issue threatens both construction safety and the long-term sustainable operation of large-diameter shield tunnels. Shield tail grouting slurry buoyancy is the primary cause of segment uplift. However, existing studies mainly rely on atmospheric pressure tests and simplified models, failing to capture the dynamic evolution of grout buoyancy under real confining pressures. This study optimized grout mix proportions through laboratory tests and developed a novel buoyancy testing apparatus. Systematic time-dependent buoyancy tests were conducted. Results show that cement-based grouts exhibit a distinct three-stage buoyancy dissipation pattern, which is strongly influenced by confining pressure, stratum conditions, and mix design, whereas inert grouts follow a single-stage exponential decay. The optimized mix YH1 reduced the complete buoyancy dissipation time by 20–35% compared with conventional cement-based grout S9. Based on field monitoring at the Yangcheng West Lake Third Channel project, approximately 90% of segment uplift deformation occurred during the grout buoyancy persistence stage. These findings provide reliable theoretical support for optimizing anti-floating grout design and contribute to the resilience and sustainability of urban underground infrastructure.