Influence of large-diameter shield tunneling on deformation of adjacent high-speed railway subgrade in soft soils and effectiveness of protective measures

• Combined simulation and experience optimize isolation pile parameters. • Utilising coupling beams to boost the effect of isolation piles. • Shield tunneling parameters significantly affect surrounding deformation. • Appropriate protective measures keep deformation within 2 mm. The excavation of large-diameter shield tunnels in soft soils inevitably impacts adjacent high-speed railway infrastructure. This study investigates the effects of constructing a 14.02 m large-diameter shield tunnel on the deformation of a nearby high-speed railway subgrade in soft soils of Shanghai, and evaluates the effectiveness of various protective measures. A numerical model was developed to simulate the horizontal deformations of railway subgrade piles, as well as the vertical and horizontal deformations of track slab resulting from shield excavation. Comprehensive real-time monitoring of track slab displacements in both vertical and horizontal directions, along with ground surface deformation, was conducted. The accuracy of the computational model and the effectiveness of the implemented protective measures were validated through field measurements. The results demonstrate that isolation piles with coupling beams proved to be the most effective method for protecting the railway subgrade. The maximum observed ground settlement above the tunnel reached −20.3 mm, while the peak heave was recorded at 3.7 mm. Notably, the additional vertical and horizontal deformations of the high-speed railway track were successfully constrained within the 2-mm threshold. These findings provide valuable insights for safety assessments and the implementation of protective measures in similar projects.