Abstract: This study aims to investigate the problem that segment of shield tail is easy to float up in surrounding rock formation. Based on the self-developed gravity testing system of grouting, the nonlinear variation law of grouting buoyancy is obtained, and based on the equivalent continuous beam theory, a refined longitudinal uplift model of shield tail segment is established. The model can comprehensively consider the time-varying of grouting, the nonlinear distribution characteristics of grouting buoyancy and the cumulative effect of construction steps. The reliability of the model is verified by using the actual floating test results of shield construction in an underground pipe gallery in Guangzhou. The results show that with the increase of the pressure difference of the grouting and the permeability of the strata, the dissipation speed of the grouting buoyancy presents an increasing trend, and the uplift values of shield tail segment exhibits a decreasing trend. When the shield tunnels are in strongly weathered pebbly sandstone formation, the uplift characteristic curve follows the law of first increasing and then decreasing, and finally floating stably. Under an action of 20 kPa differential pressure, the maximum uplift value of segment is 151.74 mm, the value of which is 39.2 m away from the shield tail, and finally floating stably near 70 m away from the shield tail. At this time, the uplift value is 145.2 mm. The longitudinal model of segment upward movement further reveals the influence mechanism of grouting consolidation law on its uplift characteristics. The model has good reliability compared with the measured results. The results can be used to predict the uplift deformation of segment induced by grouting buoyancy and provide a theoretical basis for similar projects.

Key words: shield tunnel, segment uplift, elastic foundation beam, synchronous grouting, foundation coefficient