Study on Floating of Shield Tail Segment Controlled by Synchronous Two-Component Grout in Weathered Rock Strata

Aiming at the problem of excessive floating of segments when shield tunneling in full section weathered surrounding rock strata firstly, the initial setting time of the slurry was tested by the inverted cup method under different additive dosage (strengthening dry powder (Material A), liquid activator (Material B)), and the synchronous two-component grout with controllable initial setting time and satisfactory pumping performance was prepared. Secondly, the finite element model of segment floating was established, considering the nonlinearity of axial tension and circumferential shear stiffness of the ring joints. The model can be used to consider the gradual accumulation effect of floating displacement during shield tunneling, and the influence of synchronous two-component grout on the floating of shield tail segment in stable surrounding rock stratum was obtained. Finally, the developed synchronous two-component grout was applied to a shield tunnel project in Guangzhou, and the effect of controlling segment floating is verified, which greatly reduces the leakage of segment joint with excellent segment assembly quality. The results show that: (1) 1% Material A and 1.5% Material B are mixed evenly with the single grout mortar in the shield tail grouting pipe and injected into the shield tail gap, which can effectively reduce the floating displacement of the segment up to 79%. (2) The floating displacement gradually increases with the increase of the distance from the shield tail and tends to be stable. The stable position is about 10.5 m (7 rings) from the shield tail. The maximum floating displacement is about 23 mm. (3) The use of the new synchronous two-component grout also effectively reduces the number of leakage points of the segments. The reduction is up to 59%, which greatly reduces the construction cost of plugging grouting due to leakage and has good economic benefits.