Abstract: To address the ineffective performance of conventional grouting techniques in rectifying uneven settlement of metro shield tunnels, an experiment is conducted to evaluate the effectiveness of the bag grouting method for tunnel lifting. Grout is first injected into pre-positioned bags beneath the tunnel bottom; subsequently, the additional earth pressure around the lifted shield tunnel and the tunnel deformation are measured. The findings are as follows: (1) The novel bag grouting method used for uplifting the tunnel bottom prevents grout diffusion. When confined by the bags, the grout is uniformly distributed with a controllable geometry, effectively avoiding grout leakage. This method significantly enhances the lifting effect and results in more stable deformation. (2) Compared with single-point grouting, multi-point bag grouting induces larger variations in additional earth pressure around the tunnel, while producing a more uniform pressure distribution. (3) Under the action of additional earth pressure generated by bag grouting, the vertical diameter of the model shield tunnel decreases, whereas the horizontal diameter increases, resulting in pronounced transverse elliptical deformation. When the average grout amount per bag is smaller, the deformation of the shield tunnel becomes more evident and remains moderate when multi-point simultaneous grouting is adopted. (4) Compared with single-point grouting, multi-point grouting produces greater tunnel uplift and reduces the risks of segment misalignment and local stress concentration. Therefore, multi-point bag grouting is recommended for application in practical engineering.

Key words: shield tunnel, bag grouting method, grouting uplift, model experiment, additional earth pressure