Settlement prediction of undercrossing semicircular tunnel-pile set up in soft clay soil.

Soil-structure interactions commonly induce displacements, with settlements in weak soils becoming increasingly significant under growing urbanization, making it important to minimize them to prevent structural defects. This study investigated the influence of tunnel-pile configurations on ground settlement during tunnel construction at Zhongshan Road with an undercrossing, using numerical simulation. Prediction functions describing settlement behavior within the model were developed and proposed. The Mohr-Coulomb (MC) model in MIDAS GTS NX was employed to simulate settlement levels of a semicircular tunnel lining and surrounding soil under various pile setups, in order to identify the most effective configuration for ground improvement. Results showed substantial variations in vertical settlement. The designed 5 × 4 m pile setup produced the highest crown settlement, increasing it by 32-47% longitudinally along the tunnel compared to the case without piles, while reducing lining uplift by only 138-165%. In contrast, the 4 × 4 m pile arrangement performed best overall, reducing uplift by 184-194% and limiting settlement fluctuations to - 12% to - 47%, maintaining values within 5-10 mm along the 80 m tunnel length. The 4 × 4 m pile setup was therefore more reliable and less variable in both settlement and uplift. Uniform pile arrangements provided smoother settlement troughs than non-uniform setups. Furthermore, prediction formulas based on Gaussian functions, using parameters n and k, reliably estimated settlement for greenfield conditions and projected behavior for tunnel undercrossings. The greenfield prediction function was validated against 12 existing projects, with n values within [Formula: see text] prediction and back-calculated settlements closely matching observed settlements.