Abstract: The control of ground settlement during shield-driven excavation has long been a critical technical challenge in tunnel engineering. This paper examines the Shanghai Rail Transit City Line Airport Liaison Line project as a case study. It focuses on the complexities associated with constructing an ultra-large-diameter shield tunnel in soft soil conditions, particularly where the alignment runs parallel to an operating high-speed railway with a very small clear distance and crosses beneath a river—conditions that impose stringent safety requirements. Two construction scenarios—unreinforced excavation and grouting-reinforced excavation—are evaluated. A refined three-dimensional numerical model is developed using the commercial finite-element platform MIDAS, and the simulation results are integrated with on-site monitoring data. This combined approach enables a systematic assessment of the deformation behavior of existing structures and the surrounding ground under the influence of the super-large-diameter shield excavation in soft strata. The findings indicate that rapid grouting and fast-setting slurry techniques effectively limit vertical deformation in the soil surrounding the shield tunnel. Additionally, the use of long-distance, large-area isolation piles significantly reduces soil disturbance within the pile zone, thereby controlling both differential and overall settlement of the high-speed railway bridge foundations. The specialized construction strategy—featuring tailored slurry properties, rapid grouting, and extensive isolation piling demonstrated to be both safe and appropriate for the project’s demanding conditions.

Key words: Shielded Excavation, Small Parallel Clearances, High Speed Rail Bridges, Numerical Analysis, Reinforcement Measures