Analysis of the influence of bottom bag grouting lifting on the mechanical response of shield tunnels

This paper investigates the slurry diffusion patterns, variations in additional soil pressure within the strata, and their impacts on the mechanical response and deformation characteristics of shield tunnels during the bag grouting method lifting process. The study was conducted through unit tests of bag grouting in different strata and model tests of tunnel lifting via bag grouting at the bottom of shield tunnels. The results indicate that under the same grouting parameters, when bag grouting is performed in different strata, lower soil compressibility leads to greater additional soil pressure generated by injecting the same volume of slurry. Under the constraint of the bag, high-water-content slurry primarily undergoes compaction diffusion, resulting in a limited slurry diffusion range and concentrated grouting pressure. When bag grouting is performed at 45° positions on both sides of the tunnel bottom, the inner diameter of the tunnel bottom changes minimally, no significant "horizontal elliptical deformation" occurs during the lifting process, and the deflection deformation of the inner wall at the tunnel top is significantly reduced, demonstrating effective lifting. The study reveals the load transfer mechanism of "Grouting Pressure → Bag Volume Expansion Force → Stratum Additional Earth Pressure → Tunnel Additional Loads" during the bag grouting process, providing a theoretical basis for the engineering practice of shield tunnel lifting using the bag grouting method.