ABSTRACT
The use of continuum models for FEM-analyses of tunnels with low overburden in soft soil has its draw-backs: Usually the shape of the calculated settlement trough is smoother and extending over a larger area with less pronounced inclinations than observed in reality. A constitutive model originally proposed for concrete is applied for the analysis of a tunnel excavation according to NATM-principles. This model is based on the ideas of Mohr and realized in the framework of anisotropic softening plasticity including a transition from mode I failure under tensile loading into mixed mode sliding under complex loading conditions.
Observed settlements are compared with analysis results from a classic isotropic Mohr-Coulomb model. The effect of the anisotropic failure process of the new model is discussed in terms of the onset of failure localization and the overall deformation pattern.
