Optimisation of Simultaneous Grouting and Analysis of Lining Structural Response in Shield Tunnels Crossing Rivers Under Complex Geological Conditions

This study addresses erosion of synchronous grout and segment uplift in water‐rich river‐crossing shield tunnels. Taking the river‐crossing section of Chongqing Rail Transit Line 27 as a case study, laboratory tests, three‐dimensional structural finite element analysis and field monitoring were used to evaluate the performance of hydroxyethyl methylcellulose (HEMC)‐modified grout and the effects of grouting parameters on segment uplift. With 0.3% HEMC, the grout achieved an average mass retention rate of 80.7% at a flow velocity of 0.3 m/s and a 28‐day water‐to‐air compressive strength ratio of 0.88. Increasing grouting pressure or grout volume increased segment uplift, whereas increasing grout‐layer stiffness strengthened the restraint on the segments. The model reproduced the mean uplift response in the study section but underestimated local maxima. Following application of the optimised grout formulation, the maximum field‐measured segment uplift decreased from 60 to 52 mm. The findings provide practical guidance for synchronous grouting and segment‐uplift control in water‐rich shield tunnelling.