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Synchronous grouting technology is a crucial aspect of shield tunnel construction. However, understanding the mechanism of slurry diffusion during this process is challenging due to its complexity and invisibility. Existing theoretical models often oversimplify the grouting process and do not account for multi‐stage diffusion mechanisms. By considering the radial penetration of slurry and viewing the diffusion process as the formation of annular pancakes through circumferential filling, a 3D diffusion numerical model is established using the volume of fluid (VOF)‐multiphase flow model in Fluent software. The model's validity is confirmed through calculations based on theoretical formulas and monitoring data from engineering examples. This study uncovers the patterns of slurry diffusion and examines how factors like porosity, grouting pressure, and slurry density impact diffusion radius and segment stress. The findings of this research provide a crucial theoretical foundation for shield synchronous grouting construction. [ABSTRACT FROM AUTHOR]

A large number of shield tunnel construction practices have shown that the assembled tunnel segments just detached from the tail of the shield machine are prone to various defects such as ring displacement, crack propagation, and local damage. The reason for these defects is that the tunnel segments tend to float locally or as a whole during the construction process between the connecting rings. To investigate the reasons for the floating of tunnel segments during the construction period, a combination of theoretical derivation, numerical simulation, and on-site monitoring were used to roughly divide the floating force into two parts: "static floating force" and "dynamic floating force" for different strata and stages. The study focused on the theoretical derivation and analysis of the dynamic floating force magnitude and distribution during the grouting process at different stages. With the support of numerical simulation and on-site monitoring of the tunnel segment floating condition in the shield tunnel section from Sanyuanqiao station to Taiping Temple station of Chengdu metro line 9, the correctness of the formula and distribution pattern of the dynamic floating force calculation were verified for the poorly permeable and weathered mudstone stratum. [ABSTRACT FROM AUTHOR]

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