Numerical Assessment of Deformation and Lining Forces in a Cross-Passage Tunnel Using Hardening Soil and HSS Models with PLAXIS 3D

Cross passage tunnels are essential components of underground transportation systems, facilitating emergency access and operational connectivity between main tunnels. Their construction in soft soil conditions poses significant geotechnical challenges due to complex soil-structure interactions. This study presents a three-dimensional numerical analysis of a cross-passage tunnel using PLAXIS 3D, employing two advanced constitutive models: the Hardening Soil (HS) model and the Hardening Soil model with Small-Strain Stiffness (HSS). The analysis simulates the staged excavation of twin tunnels followed by the cross passage, incorporating tunnel lining and construction sequences. The results show that excavation of the cross passage induces significant localized deformation, particularly at the junctions with the main tunnels. Displacement patterns and stress redistribution were captured in detail for both constitutive models. Comparison of the numerical outcomes indicates that the HS model produces higher displacement values than the HSS model. This difference is attributed to the HSS model’s ability to incorporate small-strain stiffness, which results in reduced deformation under similar loading and boundary conditions. The findings demonstrate how the choice of constitutive model affects the assessment of ground deformation and structural response. This study provides valuable insights for geotechnical engineers involved in the design and analysis of cross-passage tunnels in soft ground environments.