Research on the Antifloating Performance of Grouts with Different Mix Proportions in Synchronous Grouting of Shield Tunnels: From Laboratory Tests to Theoretical Calculations

With the gradual increase in the number of shield tunnels, the construction risks caused by segment floating have become increasingly prominent. Although many construction measures have been proposed to control segment floating, there are still shortcomings, such as difficulty in popularization and unclear application mechanisms. In this paper, a framework is proposed based on laboratory tests and theoretical calculations, aiming to obtain mix proportions to effectively reduce the phenomenon of segment floating. The laboratory test results show that the mix proportions significantly influence the variation law of grout buoyancy. During the solidification process, the grout buoyancy shows a nonlinear reduction law that first decreases rapidly and then slowly, and the hyperbolic function can accurately fit this law. The theoretical calculation results show that the segment uplifting displacement decreases with increasing cement content and increases with increasing fly ash and bentonite contents. The recommended grout mix proportions are the cement–water ratio of 0.5, the fly ash–water ratio of 0.3, and the bentonite–water ratio of 0.15. In addition to meeting the basic construction requirements, grouts with this mix proportions can also reduce the construction risk caused by segment floating during tunneling. The research results can provide practical guidance for preparing antifloating grouts.