On the sensitivity of model parameters to tunnel deformations in soft soils

Abstract

In geotechnical engineering, various material models are available for numerical calculations, differing in formulation, applicability, and complexity. Selecting the right one is crucial for accurate results and high-quality predictions. Therefore, understanding the interactions between the material model's mathematical structure, input parameters, and the modelling process is essential. This paper investigates the impact and sensitivity of input parameters for the linear-elastic, ideal plastic Mohr-Coulomb Model, the elasto-plastic Hardening Soil Model, and the Soft Soil Model, focusing on tunnel cross-section deformations in challenging soft soils.Using the Finite Element Method Plaxis2D, a model accounting for relevant tunnelling boundary conditions is created. The three material models are calibrated based on simulated oedometric and triaxial tests to ensure comparable soil behaviour. The results demonstrate that the cross-sectional deformations determined from the two non-linear material models exhibit minimal discrepancy. For both, the heave of the invert, a consequence of tunnel excavation-induced unloading, represents the most significant deformation. The linear one proves to be inappropriate for modelling the given context due to an unrealistically large heave. The subsequent sensitivity analysis highlights the relevance of the soil unit weight γ, the stiffness $$ in the HSM and the swelling coefficient κ* and the Poisson's ratio ν_ur in the SSM.