Numerical Simulation of Visualized Grout Diffusion in Backfill-grouting of Shield Tunnel

Synchronous grouting in shield tunnel construction plays a critical role in enhancing tunnel impermeability, ensuring precise alignment of segment rings, and mitigating surface settlement. Despite its importance, limited research has been conducted on the visualization of numerical simulations for grouting behind the shield tunnel wall. This study addresses this gap by simulating the grouting diffusion process during shield tunnel post-grouting using CFDEM software. The simulation results reveal that grout injected from the upper opening of the tunnel initially diffuses in a hemispherical pattern centered at the injection point and subsequently migrates downward along the outer diameter of the segment under the influence of gravity. Conversely, grout from the lower outlet rapidly fills the annular gap and transitions to a permeation diffusion phase. At a grouting volume of 100%, the slurry coverage area reaches 62.5%, with a slurry waste of 37.4%. When the grouting volume increases to 200%, the coverage area marginally improves to 73.1%. Balancing grouting effectiveness with construction costs, the optimal grouting effect is achieved at a grouting volume of 100%, as excessive grouting will not be greatly improved and leads to substantial material waste. To achieve complete grout coverage, particularly in unfilled regions at the tunnel head and sides, secondary grouting is recommended instead of further increasing the initial grouting volume. This approach minimizes material waste while maintaining construction efficiency.