Mechanical responses and probabilistic sensitivity analysis of shield tunnel segment in water-rich soft strata

Lining segments of shield tunnels in water-rich soft strata face severe mechanical challenges from groundwater fluctuations and fluid-solid coupling. Taking the Liuyang River-crossing shield tunnel of Changsha Metro Line 3, this study establishes a 2D hydro-mechanical coupling finite element model using ANSYS to analyze segment mechanical responses (pore water pressure, stress, displacement) under four groundwater levels. Based on ANSYS/PDS, the Monte Carlo method is adopted for probabilistic sensitivity analysis involving nine random variables of surrounding rock and segment parameters, with 10,000 cyclic samplings. Probabilistic sensitivity analysis identifies key factors affecting segment internal forces. Results show that groundwater level dominates segment behavior. Peak pore water pressure, stress, and horizontal convergence of lining segment positively correlate with groundwater level, while vertical deformation negatively correlates. The outer ring is prone to tensile failure, with crown and haunches as key control positions. Increasing segment stiffness elevates internal forces, whereas higher surrounding rock elastic modulus reduces segment forces. Higher surrounding rock density and permeability coefficient increase segment loads. Probabilistic sensitivity analysis reveals that surrounding rock density dominates axial force, and lining thickness dominates bending moment. Surrounding rock cohesion and friction angle have limited effects. This study clarifies segment mechanical responses under variable groundwater levels and identifies key sensitive parameters, providing references for shield tunnel lining design in similar water-rich soft strata.