Abstract: To explore the ground deformation mechanism after prereinforcement induced by overlargediameter shield tunneling, a case study is conducted on a shield tunneling in Jihua west road extension line crossing underneath a dam. Threedimensional numerical simulation is conducted to examine the ground settlement control effect by various ground reinforcement schemes. Findings are as follows: (1) The soil deformation is effectively controlled by prereinforcing the soil above the shield tunnel, and the maximum surface settlement decreases by approximately 50% after the ground reinforcement. (2) The optimal reinforcement depth is reinforcing to the bottom of the tunnel by jet grouting piles. However, the three different reinforcement depths to the arch, the arch waist, and the arch bottom have similar control effects on the ground deformation, which can be rationally selected based on the principle of economy and efficiency. (3) The different reinforcement lengths along the shield advancing direction affect the deformation of reinforced area, thus, the reinforcement area can only be determined according to the crossing length.

Key words: overlargediameter shield tunnel, fine silty sand, dam protection, surface settlement, ground reinforcement